explanation blue bibcodes open ADS page with paths to full text
Author name code: fletcher
ADS astronomy entries on 2022-09-14
author:"Fletcher, Lyndsay"
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Title: Flare Kernels May be Smaller than You Think: Modelling the
Radiative Response of Chromospheric Plasma Adjacent to a Solar Flare
Authors: Osborne, Christopher M. J.; Fletcher, Lyndsay
2022arXiv220903238O Altcode:
Numerical models of solar flares typically focus on the behaviour
of directly-heated flare models, adopting magnetic field- aligned,
plane-parallel methodologies. With high spatial- and spectral-resolution
ground-based optical observations of flares, it is essential also
to understand the response of the plasma surrounding these strongly
heated volumes. We investigate the effects of the extreme radiation
field produced by a heated column of flare plasma on an adjacent slab
of chromospheric plasma, using a two-dimensional radiative transfer
model and considering the time-dependent solution to the atomic level
populations and electron density throughout this model. The outgoing
spectra of H$\alpha$ and Ca II 854.2 nm synthesised from our slab show
significant spatial-, time-, and wavelength-dependent variations (both
enhancements and reductions) in the line cores, extending on order 1 Mm
into the non-flaring slab due to the incident transverse radiation field
from the flaring boundary. This may lead to significant overestimates of
the sizes of directly-heated flare kernels, if line-core observations
are used. However, the radiation field alone is insufficient to drive
any significant changes in continuum intensity, due to the typical
photospheric depths at which they forms, so continuum sources will not
have an apparent increase in size. We show that the line formation
regions near the flaring boundary can be driven upwards in altitude
by over 1 Mm despite the primary thermodynamic parameters (other than
electron density) being held horizontally uniform. This work shows
that in simple models these effects are significant and should be
considered further in future flare modelling and interpretation.
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Title: Fast prograde coronal flows in solar active regions
Authors: Hudson, Hugh S.; Mulay, Sargam M.; Fletcher, Lyndsay;
Docherty, Jennifer; Fitzpatrick, Jimmy; Pike, Eleanor; Strong, Morven;
Chamberlin, Phillip C.; Woods, Thomas N.
2022MNRAS.515L..84H Altcode: 2022MNRAS.tmpL..75H; 2022arXiv220713461H
We report the discovery and characterization of high-speed (>100 km
s<SUP>-1</SUP>) horizontal flows in solar active regions, making use
of the Sun-as-a-star spectroscopy in the range 5-105 nm provided by
the EVE (Extreme Ultraviolet Variability Experiment) spectrometers on
the Solar Dynamics Observatory. These apparent flows are persistent on
time-scales of days, and are well observed in lines of Mg X, Si XII,
and Fe XVI for example. They are prograde, as evidenced directly
by blueshifts/redshifts peaking at the east/west limb passages of
isolated active regions. The high-speed flow behaviour does not depend
upon active-region latitude or solar cycle, with similar behaviour in
Cycles 24 and 25.
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Title: Development of Integral Field Spectrographs to Revolutionize
Spectroscopic Observations of Solar Flares and other Energetic
Solar Eruptions
Authors: Lin, Haosheng; Anan, Tetsu; Cauzzi, Gianna; Fletcher, Lyndsay;
Huang, Pei; Kowalski, Adam; Kramar, Maxim; Qiu, Jiong; Samra, Jenna;
Spittler, Constance; Sukegawa, Takashi; Wirth, Gregory
2022arXiv220900788L Altcode:
The Sun's proximity offers us a unique opportunity to study in detail
the physical processes on a star's surface; however, the highly dynamic
nature of the stellar surface -- in particular, energetic eruptions
such as flares and coronal mass ejections -- presents tremendous
observational challenges. Spectroscopy probes the physical state of
the solar atmosphere, but conventional scanning spectrographs and
spectrometers are unable to capture the full evolutionary history of
these dynamic events with a sufficiently wide field of view and high
spatial, spectral, and temporal resolution. Resolving the physics of the
dynamic sun requires gathering simultaneous spectra across a contiguous
area over the full duration of these events, a goal now tantalizingly
close to achievable with continued investment in developing powerful
new Integral Field Spectrographs to serve as the foundation of both
future ground- and space-based missions. This technology promises to
revolutionize our ability to study solar flares and CMEs, addressing
NASA's strategic objective to "understand the Sun, solar system, and
universe." Since such events generate electromagnetic radiation and
high-energy particles that disrupt terrestrial electric infrastructure,
this investment not only advances humanity's scientific endeavors
but also enhances our space weather forecasting capability to protect
against threats to our technology-reliant civilization.
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Title: Ice Giant Atmospheric Structures from Spitzer and How the
James Webb Space Telescope will Advance Our Understanding
Authors: Rowe-Gurney, N.; Fletcher, L. N.; Orton, G. S.; Roman, M. T.;
Sinclair, J. A.; Moses, J. I.; Irwin, P. G. J.; Milam, S. N.; Hammel,
H. B.
2022LPICo2686.4045R Altcode:
NASA's IRS acquired mid-infrared disc-averaged spectra of Uranus &
Neptune 2004-2007. We analyze the differences in temperature &
composition between the separate hemispheres to shed light on the
variability of stratospheres and upper tropospheres.
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Title: Hazy Blue Worlds: A Holistic Aerosol Model for Uranus and
Neptune, Including Dark Spots
Authors: Irwin, P. G. J.; Teanby, N. A.; Fletcher, L. N.; Toledo,
D.; Orton, G. S.; Wong, M. H.; Roman, M. T.; Pérez-Hoyos, S.; James,
A.; Dobinson, J.
2022JGRE..12707189I Altcode: 2022arXiv220104516I
We present a reanalysis (using the Minnaert limb-darkening
approximation) of visible/near-infrared (0.3-2.5 μm) observations of
Uranus and Neptune made by several instruments. We find a common model
of the vertical aerosol distribution i.e., consistent with the observed
reflectivity spectra of both planets, consisting of: (a) a deep aerosol
layer with a base pressure >5-7 bar, assumed to be composed of a
mixture of H<SUB>2</SUB>S ice and photochemical haze; (b) a layer of
photochemical haze/ice, coincident with a layer of high static stability
at the methane condensation level at 1-2 bar; and (c) an extended layer
of photochemical haze, likely mostly of the same composition as the
1-2-bar layer, extending from this level up through to the stratosphere,
where the photochemical haze particles are thought to be produced. For
Neptune, we find that we also need to add a thin layer of micron-sized
methane ice particles at ∼0.2 bar to explain the enhanced reflection
at longer methane-absorbing wavelengths. We suggest that methane
condensing onto the haze particles at the base of the 1-2-bar aerosol
layer forms ice/haze particles that grow very quickly to large size
and immediately "snow out" (as predicted by Carlson et al. (1988), <A
href="https://doi.org/10.1175/1520-0469(1988)045%3C2066:CMOTGP%3E2.0.CO2">https://doi.org/10.1175/1520-0469(1988)045<2066:CMOTGP>2.0.CO2</A>),
re-evaporating at deeper levels to release their core haze particles
to act as condensation nuclei for H<SUB>2</SUB>S ice formation. In
addition, we find that the spectral characteristics of "dark spots",
such as the Voyager-2/ISS Great Dark Spot and the HST/WFC3 NDS-2018,
are well modelled by a darkening or possibly clearing of the deep
aerosol layer only.
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Title: First high resolution interferometric observation of a solar
prominence with ALMA
Authors: Labrosse, Nicolas; Rodger, Andrew S.; Radziszewski, Krzysztof;
Rudawy, Paweł; Antolin, Patrick; Fletcher, Lyndsay; Levens, Peter J.;
Peat, Aaron W.; Schmieder, Brigitte; Simões, Paulo J. A.
2022MNRAS.513L..30L Altcode: 2022arXiv220212434L; 2022MNRAS.tmpL..22L
We present the first observation of a solar prominence at 84 - 116 GHz
using the high resolution interferometric imaging of ALMA. Simultaneous
observations in Hα from Białkaw Observatory and with SDO/AIA reveal
similar prominence morphology to the ALMA observation. The contribution
functions of 3 mm and Hα emission are shown to have significant
overlap across a range of gas pressures. We estimate the maximum
millimetre-continuum optical thickness to be τ<SUB>3mm</SUB> ≍ 2,
and the brightness temperature from the observed Hα intensity. The
brightness temperature measured by ALMA is ~6000 - 7000 K in the
prominence spine, which correlates well with the estimated brightness
temperature for a kinetic temperature of 8000 K.
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Title: Compositional Mapping of Ganymede with VLT/SPHERE Using Markov
Chain Monte Carlo Spectral Analysis
Authors: King, O. R. T.; Fletcher, L. N.
2022LPICo2678.1461K Altcode:
Infrared spectral observations of Ganymede from VLT/SPHERE have been
analysed using a Monte Carlo model to calculate compositional abundances
and uncertainties.
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Title: Probing the Physics of the Solar Atmosphere with the Multi-slit
Solar Explorer (MUSE). II. Flares and Eruptions
Authors: Cheung, Mark C. M.; Martínez-Sykora, Juan; Testa, Paola;
De Pontieu, Bart; Chintzoglou, Georgios; Rempel, Matthias; Polito,
Vanessa; Kerr, Graham S.; Reeves, Katharine K.; Fletcher, Lyndsay; Jin,
Meng; Nóbrega-Siverio, Daniel; Danilovic, Sanja; Antolin, Patrick;
Allred, Joel; Hansteen, Viggo; Ugarte-Urra, Ignacio; DeLuca, Edward;
Longcope, Dana; Takasao, Shinsuke; DeRosa, Marc L.; Boerner, Paul;
Jaeggli, Sarah; Nitta, Nariaki V.; Daw, Adrian; Carlsson, Mats; Golub,
Leon; The
2022ApJ...926...53C Altcode: 2021arXiv210615591C
Current state-of-the-art spectrographs cannot resolve the fundamental
spatial (subarcseconds) and temporal (less than a few tens of
seconds) scales of the coronal dynamics of solar flares and eruptive
phenomena. The highest-resolution coronal data to date are based on
imaging, which is blind to many of the processes that drive coronal
energetics and dynamics. As shown by the Interface Region Imaging
Spectrograph for the low solar atmosphere, we need high-resolution
spectroscopic measurements with simultaneous imaging to understand the
dominant processes. In this paper: (1) we introduce the Multi-slit Solar
Explorer (MUSE), a spaceborne observatory to fill this observational
gap by providing high-cadence (<20 s), subarcsecond-resolution
spectroscopic rasters over an active region size of the solar transition
region and corona; (2) using advanced numerical models, we demonstrate
the unique diagnostic capabilities of MUSE for exploring solar coronal
dynamics and for constraining and discriminating models of solar flares
and eruptions; (3) we discuss the key contributions MUSE would make
in addressing the science objectives of the Next Generation Solar
Physics Mission (NGSPM), and how MUSE, the high-throughput Extreme
Ultraviolet Solar Telescope, and the Daniel K Inouye Solar Telescope
(and other ground-based observatories) can operate as a distributed
implementation of the NGSPM. This is a companion paper to De Pontieu
et al., which focuses on investigating coronal heating with MUSE.
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Title: Probing the Physics of the Solar Atmosphere with the Multi-slit
Solar Explorer (MUSE): II. Flares and Eruptions
Authors: Cheung, Chun Ming Mark; Martinez-Sykora, Juan; Testa, Paola;
De Pontieu, Bart; Chintzoglou, Georgios; Rempel, Matthias; Polito,
Vanessa; Kerr, Graham; Reeves, Katharine; Fletcher, Lyndsay; Jin,
Meng; Nobrega, Daniel; Danilovic, Sanja; Antolin, Patrick; Allred,
Joel; Hansteen, Viggo; Ugarte-Urra, Ignacio; DeLuca, Edward; Longcope,
Dana; Takasao, Shinsuke; DeRosa, Marc; Boerner, Paul; Jaeggli, Sarah;
Nitta, Nariaki; Daw, Adrian; Carlsson, Mats; Golub, Leon
2021AGUFMSH51A..08C Altcode:
Current state-of-the-art spectrographs cannot resolve the fundamental
spatial (sub-arcseconds) and temporal scales (less than a few tens
of seconds) of the coronal dynamics of solar flares and eruptive
phenomena. The highest resolution coronal data to date are based on
imaging, which is blind to many of the processes that drive coronal
energetics and dynamics. As shown by IRIS for the low solar atmosphere,
we need high-resolution spectroscopic measurements with simultaneous
imaging to understand the dominant processes. In this paper: (1)
we introduce the Multi-slit Solar Explorer (MUSE), a spaceborne
observatory to fill this observational gap by providing high-cadence
(<20 s), sub-arcsecond resolution spectroscopic rasters over an
active region size of the solar transition region and corona; (2)
using advanced numerical models, we demonstrate the unique diagnostic
capabilities of MUSE for exploring solar coronal dynamics, and for
constraining and discriminating models of solar flares and eruptions;
(3) we discuss the key contributions MUSE would make in addressing the
science objectives of the Next Generation Solar Physics Mission (NGSPM),
and how MUSE, the high-throughput EUV Solar Telescope (EUVST) and the
Daniel K Inouye Solar Telescope (and other ground-based observatories)
can operate as a distributed implementation of the NGSPM. This is a
companion paper to De Pontieu et al. (2021, also submitted to SH-17),
which focuses on investigating coronal heating with MUSE.
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Title: Hot onsets of solar flares
Authors: Hudson, Hugh; Fletcher, Lyndsay; Hannah, Iain; Hayes, Laura;
Simoes, Paulo
2021AGUFMSH22B..02H Altcode:
The GOES/XRS data show low-level soft X-ray emissions prior to
a flare in a "hot onset" precursor of the main flare development
(2021MNRAS.501.1273H). This phenomenon provides clear evidence for
energy release not identifiable with the impulsive phase, and apparently
not mediated by non-thermal particles. The hot onset phase may last for
tens of seconds to minutes, characterized by gradual and roughly linear
growth of emission measure at characteristic isothermal temperatures
of 10-15 MK and no clear pattern of temperature increase in the sense
of dT/dt > 0. The figure shows an example of this behavior, from
SOL2004-02-26 (X1.1). The newer GOES-R data also show this effect,
providing higher time resolution (1 s) and better noise properties,
although with higher background levels. Hot onsets occur in most if
not all flares, but their properties do not appear to provide any
guidance towards the magnitude of the flare that follows.
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Title: Microwave observations reveal the deep extent and structure
of Jupiter’s atmospheric vortices
Authors: Bolton, S. J.; Levin, S. M.; Guillot, T.; Li, C.; Kaspi, Y.;
Orton, G.; Wong, M. H.; Oyafuso, F.; Allison, M.; Arballo, J.; Atreya,
S.; Becker, H. N.; Bloxham, J.; Brown, S. T.; Fletcher, L. N.; Galanti,
E.; Gulkis, S.; Janssen, M.; Ingersoll, A.; Lunine, J. L.; Misra,
S.; Steffes, P.; Stevenson, D.; Waite, J. H.; Yadav, R. K.; Zhang, Z.
2021Sci...374..968B Altcode:
Jupiter’s atmosphere has a system of zones and belts punctuated by
small and large vortices, the largest being the Great Red Spot. How
these features change with depth is unknown, with theories of their
structure ranging from shallow meteorological features to surface
expressions of deep-seated convection. We present observations
of atmospheric vortices using the Juno spacecraft’s Microwave
Radiometer. We found vortex roots that extend deeper than the altitude
at which water is expected to condense, and we identified density
inversion layers. Our results constrain the three-dimensional structure
of Jupiter’s vortices and their extension below the clouds.
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Title: The high-energy Sun - probing the origins of particle
acceleration on our nearest star
Authors: Matthews, S. A.; Reid, H. A. S.; Baker, D.; Bloomfield, D. S.;
Browning, P. K.; Calcines, A.; Del Zanna, G.; Erdelyi, R.; Fletcher,
L.; Hannah, I. G.; Jeffrey, N.; Klein, L.; Krucker, S.; Kontar, E.;
Long, D. M.; MacKinnon, A.; Mann, G.; Mathioudakis, M.; Milligan,
R.; Nakariakov, V. M.; Pesce-Rollins, M.; Shih, A. Y.; Smith, D.;
Veronig, A.; Vilmer, N.
2021ExA...tmp..135M Altcode:
As a frequent and energetic particle accelerator, our Sun provides
us with an excellent astrophysical laboratory for understanding
the fundamental process of particle acceleration. The exploitation
of radiative diagnostics from electrons has shown that acceleration
operates on sub-second time scales in a complex magnetic environment,
where direct electric fields, wave turbulence, and shock waves all
must contribute, although precise details are severely lacking. Ions
were assumed to be accelerated in a similar manner to electrons, but
γ-ray imaging confirmed that emission sources are spatially separated
from X-ray sources, suggesting distinctly different acceleration
mechanisms. Current X-ray and γ-ray spectroscopy provides only a basic
understanding of accelerated particle spectra and the total energy
budgets are therefore poorly constrained. Additionally, the recent
detection of relativistic ion signatures lasting many hours, without
an electron counterpart, is an enigma. We propose a single platform
to directly measure the physical conditions present in the energy
release sites and the environment in which the particles propagate and
deposit their energy. To address this fundamental issue, we set out
a suite of dedicated instruments that will probe both electrons and
ions simultaneously to observe; high (seconds) temporal resolution
photon spectra (4 keV - 150 MeV) with simultaneous imaging (1 keV -
30 MeV), polarization measurements (5-1000 keV) and high spatial and
temporal resolution imaging spectroscopy in the UV/EUV/SXR (soft X-ray)
regimes. These instruments will observe the broad range of radiative
signatures produced in the solar atmosphere by accelerated particles.
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Title: On the importance of Ca II photoionization by the hydrogen
lyman transitions in solar flare models
Authors: Osborne, C. M. J.; Heinzel, P.; Kašparová, J.; Fletcher, L.
2021MNRAS.507.1972O Altcode: 2021MNRAS.tmp.1947O; 2021arXiv210711145O
The forward fitting of solar flare observations with
radiation-hydrodynamic simulations is a common technique for learning
about energy deposition and atmospheric evolution during these explosive
events. A frequent spectral line choice for this process is Ca II
854.2 nm due to its formation in the chromosphere and substantial
variability. It is important to ensure that this line is accurately
modelled to obtain the correct interpretation of observations. Here,
we investigate the importance of photoionization of Ca II to Ca III by
the hydrogen Lyman transitions, whilst the Lyman continuum is typically
considered in this context in simulations, the associated bound-bound
transitions are not. This investigation uses two RADYN flare simulations
and reprocesses the radiative transfer using the Lightweaver framework
which accounts for the overlapping of all active transitions. The
Ca II 854.2 nm line profiles are found to vary significantly due to
photoionization by the Lyman lines, showing notably different shapes
and even reversed asymmetries. Finally, we investigate to what extent
these effects modify the energy balance of the simulation and the
implications on future radiation-hydrodynamic simulations. There
is found to be a 10-15 per cent change in detailed optically thick
radiative losses from considering these photoionization effects on
the calcium lines in the two simulations presented, demonstrating the
importance of considering these effects in a self-consistent way.
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Title: Jupiter's Temperate Belt/Zone Contrasts Revealed at Depth by
Juno Microwave Observations
Authors: Fletcher, L. N.; Oyafuso, F. A.; Allison, M.; Ingersoll, A.;
Li, L.; Kaspi, Y.; Galanti, E.; Wong, M. H.; Orton, G. S.; Duer, K.;
Zhang, Z.; Li, C.; Guillot, T.; Levin, S. M.; Bolton, S.
2021JGRE..12606858F Altcode: 2021arXiv211014620F
Juno microwave radiometer (MWR) observations of Jupiter's midlatitudes
reveal a strong correlation between brightness temperature contrasts and
zonal winds, confirming that the banded structure extends throughout the
troposphere. However, the microwave brightness gradient is observed to
change sign with depth: the belts are microwave-bright in the p<5 bar
range and microwave-dark in the p>10 bar range. The transition level
(which we call the "jovicline") is evident in the MWR 11.5 cm channel,
which samples the 5-14 bar range when using the limb-darkening at
all emission angles. The transition is located between 4 and 10 bars,
and implies that belts change with depth from being NH3-depleted to
NH3-enriched, or from physically warm to physically cool, or more
likely a combination of both. The change in character occurs near
the statically stable layer associated with water condensation. The
implications of the transition are discussed in terms of ammonia
redistribution via meridional circulation cells with opposing flows
above and below the water condensation layer, and in terms of the
"mushball" precipitation model, which predicts steeper vertical ammonia
gradients in the belts versus the zones. We show via the moist thermal
wind equation that both the temperature and ammonia interpretations can
lead to vertical shear on the zonal winds, but the shear is ∼50×
weaker if only NH3 gradients are considered. Conversely, if MWR
observations are associated with kinetic temperature gradients then
it would produce zonal winds that increase in strength down to the
"jovicline", consistent with Galileo probe measurements; then decay
slowly at higher pressures.
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Title: Demonstration of an x-ray Raman spectroscopy setup to study
warm dense carbon at the high energy density instrument of European
XFEL
Authors: Voigt, K.; Zhang, M.; Ramakrishna, K.; Amouretti, A.; Appel,
K.; Brambrink, E.; Cerantola, V.; Chekrygina, D.; Döppner, T.;
Falcone, R. W.; Falk, K.; Fletcher, L. B.; Gericke, D. O.; Göde,
S.; Harmand, M.; Hartley, N. J.; Hau-Riege, S. P.; Huang, L. G.;
Humphries, O. S.; Lokamani, M.; Makita, M.; Pelka, A.; Prescher, C.;
Schuster, A. K.; Šmíd, M.; Toncian, T.; Vorberger, J.; Zastrau,
U.; Preston, T. R.; Kraus, D.
2021PhPl...28h2701V Altcode:
We present a proof-of-principle study demonstrating x-ray Raman
Spectroscopy (XRS) from carbon samples at ambient conditions in
conjunction with other common diagnostics to study warm dense
matter, performed at the high energy density scientific instrument
of the European x-ray Free Electron Laser (European XFEL). We obtain
sufficient spectral resolution to identify the local structure and
chemical bonding of diamond and graphite samples, using highly annealed
pyrolytic graphite spectrometers. Due to the high crystal reflectivity
and XFEL brightness, we obtain signal strengths that will enable
accurate XRS measurements in upcoming pump-probe experiments with a
high repetition-rate, where the samples will be pumped with high-power
lasers. Molecular dynamics simulations based on density functional
theory together with XRS simulations demonstrate the potential of this
technique and show predictions for high-energy-density conditions. Our
setup allows simultaneous implementation of several different diagnostic
methods to reduce ambiguities in the analysis of the experimental
results, which, for warm dense matter, often relies on simplifying
model assumptions. The promising capabilities demonstrated here provide
unprecedented insights into chemical and structural dynamics in warm
dense matter states of light elements, including conditions similar
to the interiors of planets, low-mass stars, and other celestial bodies.
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Title: VizieR Online Data Catalog: TEXES spectra of Saturn from
February 03 2013 (Blake+, 2021)
Authors: Blake, J. S. D.; Fletcher, L. N.; Greathouse, T. K.; Orton,
G. S.; Melin, H.; Roman, M. T.; Antunano, A.; Donnelly, P. T.;
Rowe-Gurney, N.; King, O.
2021yCat..36530066B Altcode:
We observed Saturn in the N-band 8.6 m region for one night in February
2013, using the high spectral resolution of the TEXES instrument and
the 3-meter diameter mirror of NASA's IRTF. <P />TEXES spectra of
Saturn from February 03 2013. <P />(2 data files).
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Title: In Situ exploration of the giant planets
Authors: Mousis, O.; Atkinson, D. H.; Ambrosi, R.; Atreya, S.;
Banfield, D.; Barabash, S.; Blanc, M.; Cavalié, T.; Coustenis,
A.; Deleuil, M.; Durry, G.; Ferri, F.; Fletcher, L. N.; Fouchet, T.;
Guillot, T.; Hartogh, P.; Hueso, R.; Hofstadter, M.; Lebreton, J. -P.;
Mandt, K. E.; Rauer, H.; Rannou, P.; Renard, J. -B.; Sánchez-Lavega,
A.; Sayanagi, K. M.; Simon, A. A.; Spilker, T.; Venkatapathy, E.;
Waite, J. H.; Wurz, P.
2021ExA...tmp...96M Altcode:
Remote sensing observations suffer significant limitations when used
to study the bulk atmospheric composition of the giant planets of our
Solar System. This impacts our knowledge of the formation of these
planets and the physics of their atmospheres. A remarkable example of
the superiority of in situ probe measurements was illustrated by the
exploration of Jupiter, where key measurements such as the determination
of the noble gases' abundances and the precise measurement of the helium
mixing ratio were only made available through in situ measurements
by the Galileo probe. Here we describe the main scientific goals to
be addressed by the future in situ exploration of Saturn, Uranus, and
Neptune, placing the Galileo probe exploration of Jupiter in a broader
context. An atmospheric entry probe targeting the 10-bar level would
yield insight into two broad themes: i) the formation history of the
giant planets and that of the Solar System, and ii) the processes at
play in planetary atmospheres. The probe would descend under parachute
to measure composition, structure, and dynamics, with data returned
to Earth using a Carrier Relay Spacecraft as a relay station. An
atmospheric probe could represent a significant ESA contribution to
a future NASA New Frontiers or flagship mission to be launched toward
Saturn, Uranus, and/or Neptune.
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Title: Characterizing a "Solar FRB"
Authors: Hudson, H.; Briggs, M.; Chitta, L.; Fletcher, L.; Gary, D.;
Monstein, C.; Nimmo, K.; Saint-Hilaire, P.; White, S.
2021AAS...23812716H Altcode:
A remarkable solar microwave (1.4 GHz) burst,
SOL2019-05-06T17:47:35.385, has been reported by the STARE2 fast cosmic
transient survey (Bochenek et al., 2020). Its behavior resembles
that of the Fast Radio Burst (FRB) extragalactic events in having a
relatively broad spectral bandwidth and brief (19-msec) duration. It
also had no measureable dispersion. The associated flare, GOES class
C1, had a relatively hard X-ray spectrum as observed by Fermi/GBM,
but no temporal association at the msec time scale suggested by the
microwaves. Although msec variability in the microwave domain has
been known to solar radio astronomy since the 1970s, the brightness
and isolation of this event (both spatial and temporal) suggests
novelty. Accordingly we survey the available correlative data from
many sources and discuss possible interpretations in terms of type
III-like behavior, electron cyclotron masering, and gyrosynchrotron
emission. We note that the radio data (e-Callisto and EOVSA) revealed
abundant type III activity in the vicinity, and the related flares
as observed by GOES had exceptionally short time scales, suggesting
burst origins in the lower solar atmosphere.
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Title: Evidence of chromospheric molecular hydrogen emission in a
solar flare observed by the IRIS satellite
Authors: Mulay, Sargam M.; Fletcher, Lyndsay
2021MNRAS.504.2842M Altcode: 2021arXiv210203329M; 2021MNRAS.tmp..434M
We have carried out the first comprehensive investigation of enhanced
line emission from molecular hydrogen, H<SUB>2</SUB> at 1333.79 Å,
observed at flare ribbons in SOL2014-04-18T13:03. The cool H<SUB>2</SUB>
emission is known to be fluorescently excited by Si IV 1402.77 Å
UV radiation and provides a unique view of the temperature minimum
region (TMR). Strong H<SUB>2</SUB> emission was observed when the Si
IV 1402.77 Å emission was bright during the flare impulsive phase and
gradual decay phase, but it dimmed during the GOES peak. H<SUB>2</SUB>
line broadening showed non-thermal speeds in the range 7-18 $\rm
{km\,s}^{-1}$, possibly corresponding to turbulent plasma flows. Small
red (blue) shifts, up to 1.8 (4.9) $\rm {km\,s}^{-1}$ were measured. The
intensity ratio of Si IV 1393.76 Å and Si IV 1402.77 Å confirmed that
plasma was optically thin to Si IV (where the ratio = 2) during the
impulsive phase of the flare in locations where strong H<SUB>2</SUB>
emission was observed. In contrast, the ratio differs from optically
thin value of 2 in parts of ribbons, indicating a role for opacity
effects. A strong spatial and temporal correlation between H<SUB>2</SUB>
and Si IV emission was evident supporting the notion that fluorescent
excitation is responsible.
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Title: The science enabled by a dedicated solar system space telescope
Authors: Young, Cindy; Wong, M. H.; Sayanagi, K. M.; Curry, S.;
Jessup, K. L.; Becker, T.; Hendrix, A.; Chanover, N.; Milam, S.;
Holler, B. J.; Holsclaw, G.; Peralta, J.; Clarke, J.; Spencer, J.;
Kelley, M. S. P.; Luhmann, J.; MacDonnell, D.; Vervack, R. J., Jr.;
Rutherford, K.; Fletcher, L. N.; de Pater, I.; Vilas, F.; Feaga,
L.; Siegmund, O.; Bell, J.; Delory, G.; Pitman, J.; Greathouse, T.;
Wishnow, E.; Schneider, N.; Lillis, R.; Colwell, J.; Bowman, L.; Lopes,
R. M. C.; McGrath, M.; Marchis, F.; Cartwright, R.; Poston, M. J.
2021BAAS...53d.232Y Altcode: 2021psad.rept..232Y
We advocate for a large/medium-class space telescope dedicated to
planetary science to transform our understanding of time-dependent
phenomena & enable a comprehensive survey & spectral
characterization of minor bodies across the solar system. The key
science questions & themes presented here cannot fully be addressed
using astrophysical assets.
---------------------------------------------------------
Title: On the clouds and ammonia in Jupiter's upper troposphere from
Juno JIRAM reflectivity observations
Authors: Grassi, Davide; Mura, A.; Sindoni, G.; Adriani, A.; Atreya,
S. K.; Filacchione, G.; Fletcher, L. N.; Lunine, J. I.; Moriconi,
M. L.; Noschese, R.; Orton, G. S.; Plainaki, C.; Sordini, R.; Tosi, F.;
Turrini, D.; Olivieri, A.; Eichstädt, G.; Hansen, C. J.; Melin, H.;
Altieri, F.; Cicchetti, A.; Dinelli, B. M.; Migliorini, A.; Piccioni,
G.; Stefani, S.; Bolton, S. J.
2021MNRAS.503.4892G Altcode: 2021MNRAS.tmp..746G
We analyse spectra measured by the Jovian Infrared Auroral Mapper
(JIRAM, a payload element of the NASA Juno mission) in the 3150-4910
cm<SUP>-1</SUP> (2.0-3.2 μm) range during the perijiove passage of 2016
August. Despite modelling uncertainties, the quality and the relative
uniformity of the data set allow us to determine several parameters
characterizing the Jupiter's upper troposphere in the latitude range
of 35°S-30°N. Ammonia relative humidity at 500 millibars varies
between 5 per cent to supersaturation beyond 100 per cent for about
3 per cent of the processed spectra. Ammonia appears depleted over
belts and relatively enhanced over zones. Local variations of ammonia,
arguably associated with local dynamics, are found to occur in several
locations on the planet (Oval BA, South Equatorial Belt). Cloud
altitude, defined as the level where aerosol opacity reaches unit
value at 3650 cm<SUP>-1</SUP> (2.74 μm), is maximum over the Great
Red Spot (>20 km above the 1 bar level) and the zones (15 km),
while it decreases over the belts and towards higher latitudes. The
aerosol opacity scale height suggests more compact clouds over zones
and more diffuse clouds over belts. The integrated opacity of clouds
above the 1.3-bar pressure level is found to be minimum in regions
where thermal emission of the deeper atmosphere is maximum. The
opacity of tropospheric haze above the 200-mbar level also increases
over zones. Our results are consistent with a Hadley-type circulation
scheme previously proposed in literature for belts and zones, with
clear hemisphere asymmetries in cloud and haze.
---------------------------------------------------------
Title: The effect of a solar flare on chromospheric oscillations
Authors: Millar, David C. L.; Fletcher, Lyndsay; Milligan, Ryan O.
2021MNRAS.503.2444M Altcode: 2021MNRAS.tmp..652M; 2020arXiv200710301M
Oscillations in the solar atmosphere have long been observed both in
quiet conditions and during solar flares. The chromosphere is known
for its 3-min signals, which are strong over sunspot umbrae, and have
periods determined by the chromosphere's acoustic cut-off frequency. A
small number of observations have shown the chromospheric signals to
be affected by energetic events such as solar flares, however the link
between flare activity and these oscillations remains unclear. In this
work, we present evidence of changes to the oscillatory structure of
the chromosphere over a sunspot which occurs during the impulsive
phase of an M1 flare. Using imaging data from the CRISP instrument
across the H α and Ca II 8542 Å spectral lines, we employed a method
of fitting models to power spectra to produce maps of where there is
evidence of oscillatory signals above a red-noise background. Comparing
results taken before and after the impulsive phase of the flare, we
found that the oscillatory signals taken after the start of the flare
differ in two ways: the locations of oscillatory signals had changed
and the typical periods of the oscillations had tended to increase
(in some cases increasing from <100 s to ∼200 s). Both of these
results can be explained by a restructuring of the magnetic field in
the chromosphere during the flare activity, which is backed up by images
of coronal loops showing clear changes to magnetic connectivity. These
results represent one of the many ways that active regions can be
affected by solar flares.
---------------------------------------------------------
Title: Critical Science Plan for the Daniel K. Inouye Solar Telescope
(DKIST)
Authors: Rast, Mark P.; Bello González, Nazaret; Bellot Rubio,
Luis; Cao, Wenda; Cauzzi, Gianna; Deluca, Edward; de Pontieu, Bart;
Fletcher, Lyndsay; Gibson, Sarah E.; Judge, Philip G.; Katsukawa,
Yukio; Kazachenko, Maria D.; Khomenko, Elena; Landi, Enrico; Martínez
Pillet, Valentín; Petrie, Gordon J. D.; Qiu, Jiong; Rachmeler,
Laurel A.; Rempel, Matthias; Schmidt, Wolfgang; Scullion, Eamon; Sun,
Xudong; Welsch, Brian T.; Andretta, Vincenzo; Antolin, Patrick; Ayres,
Thomas R.; Balasubramaniam, K. S.; Ballai, Istvan; Berger, Thomas E.;
Bradshaw, Stephen J.; Campbell, Ryan J.; Carlsson, Mats; Casini,
Roberto; Centeno, Rebecca; Cranmer, Steven R.; Criscuoli, Serena;
Deforest, Craig; Deng, Yuanyong; Erdélyi, Robertus; Fedun, Viktor;
Fischer, Catherine E.; González Manrique, Sergio J.; Hahn, Michael;
Harra, Louise; Henriques, Vasco M. J.; Hurlburt, Neal E.; Jaeggli,
Sarah; Jafarzadeh, Shahin; Jain, Rekha; Jefferies, Stuart M.; Keys,
Peter H.; Kowalski, Adam F.; Kuckein, Christoph; Kuhn, Jeffrey R.;
Kuridze, David; Liu, Jiajia; Liu, Wei; Longcope, Dana; Mathioudakis,
Mihalis; McAteer, R. T. James; McIntosh, Scott W.; McKenzie, David
E.; Miralles, Mari Paz; Morton, Richard J.; Muglach, Karin; Nelson,
Chris J.; Panesar, Navdeep K.; Parenti, Susanna; Parnell, Clare E.;
Poduval, Bala; Reardon, Kevin P.; Reep, Jeffrey W.; Schad, Thomas A.;
Schmit, Donald; Sharma, Rahul; Socas-Navarro, Hector; Srivastava,
Abhishek K.; Sterling, Alphonse C.; Suematsu, Yoshinori; Tarr, Lucas
A.; Tiwari, Sanjiv; Tritschler, Alexandra; Verth, Gary; Vourlidas,
Angelos; Wang, Haimin; Wang, Yi-Ming; NSO and DKIST Project; DKIST
Instrument Scientists; DKIST Science Working Group; DKIST Critical
Science Plan Community
2021SoPh..296...70R Altcode: 2020arXiv200808203R
The National Science Foundation's Daniel K. Inouye Solar Telescope
(DKIST) will revolutionize our ability to measure, understand,
and model the basic physical processes that control the structure
and dynamics of the Sun and its atmosphere. The first-light DKIST
images, released publicly on 29 January 2020, only hint at the
extraordinary capabilities that will accompany full commissioning of
the five facility instruments. With this Critical Science Plan (CSP)
we attempt to anticipate some of what those capabilities will enable,
providing a snapshot of some of the scientific pursuits that the DKIST
hopes to engage as start-of-operations nears. The work builds on the
combined contributions of the DKIST Science Working Group (SWG) and
CSP Community members, who generously shared their experiences, plans,
knowledge, and dreams. Discussion is primarily focused on those issues
to which DKIST will uniquely contribute.
---------------------------------------------------------
Title: Carrington's lost photograph
Authors: Cliver, E. W.; Fletcher, Lyndsay; Hudson, H. S.
2021A&G....62.2.40C Altcode:
Ed Cliver, Lyndsay Fletcher and Hugh Hudson are looking for a photograph
of Richard Carrington. Can you help?
---------------------------------------------------------
Title: Compositional Mapping of Europa and Ganymede with VLT/SPHERE
and Galileo/NIMS Using Markov Chain Monte Carlo Fitting
Authors: King, O. R. T.; Fletcher, L. N.
2021LPI....52.1060K Altcode:
Infrared spectral observations of Europa and Ganymede from VLT/SPHERE
and Galileo/NIMS have been fit using a Monte Carlo model to calculate
compositional abundances and uncertainties.
---------------------------------------------------------
Title: A machine-learning approach to correcting atmospheric seeing
in solar flare observations
Authors: Armstrong, John A.; Fletcher, Lyndsay
2021MNRAS.501.2647A Altcode: 2020arXiv201112814A; 2020MNRAS.tmp.3530A
Current post-processing techniques for the correction of atmospheric
seeing in solar observations - such as Speckle interferometry and
Phase Diversity methods - have limitations when it comes to their
reconstructive capabilities of solar flare observations. This,
combined with the sporadic nature of flares meaning observers cannot
wait until seeing conditions are optimal before taking measurements,
means that many ground-based solar flare observations are marred with
bad seeing. To combat this, we propose a method for dedicated flare
seeing correction based on training a deep neural network to learn
to correct artificial seeing from flare observations taken during
good seeing conditions. This model uses transfer learning, a novel
technique in solar physics, to help learn these corrections. Transfer
learning is when another network already trained on similar data
is used to influence the learning of the new network. Once trained,
the model has been applied to two flare data sets: one from AR12157 on
2014 September 6 and one from AR12673 on 2017 September 6. The results
show good corrections to images with bad seeing with a relative error
assigned to the estimate based on the performance of the model. Further
discussion takes place of improvements to the robustness of the error
on these estimates.
---------------------------------------------------------
Title: Hot X-ray onsets of solar flares
Authors: Hudson, Hugh S.; Simões, Paulo J. A.; Fletcher, Lyndsay;
Hayes, Laura A.; Hannah, Iain G.
2021MNRAS.501.1273H Altcode: 2020MNRAS.tmp.3462H; 2020arXiv200705310H
The study of the localized plasma conditions before the impulsive phase
of a solar flare can help us understand the physical processes that
occur leading up to the main flare energy release. Here, we present
evidence of a hot X-ray 'onset' interval of enhanced isothermal plasma
temperatures in the range of 10-15 MK over a period of time prior to
the flare's impulsive phase. This 'hot onset' interval occurs during
the initial soft X-ray increase and definitely before any detectable
hard X-ray emission. The isothermal temperatures, estimated by the
Geostationary Operational Environmental Satellite X-ray sensor,
and confirmed with data from the Reuven Ramaty High Energy Solar
Spectroscopic Imager, show no signs of gradual increase, and the
'hot onset' phenomenon occurs regardless of flare classification or
configuration. In a small sample of four representative flare events, we
tentatively identify this early hot onset soft X-ray emission to occur
within footpoint and low-lying loop regions, rather than in coronal
structures, based on images from the Atmospheric Imaging Assembly. We
confirm this via limb occultation of a flaring region. These hot
X-ray onsets appear before there is evidence of collisional heating
by non-thermal electrons, and hence challenge the standard modelling
techniques.
---------------------------------------------------------
Title: Measuring the structure and equation of state of polyethylene
terephthalate at megabar pressures
Authors: Lütgert, J.; Vorberger, J.; Hartley, N. J.; Voigt, K.;
Rödel, M.; Schuster, A. K.; Benuzzi-Mounaix, A.; Brown, S.; Cowan,
T. E.; Cunningham, E.; Döppner, T.; Falcone, R. W.; Fletcher, L. B.;
Galtier, E.; Glenzer, S. H.; Laso Garcia, A.; Gericke, D. O.; Heimann,
P. A.; Lee, H. J.; McBride, E. E.; Pelka, A.; Prencipe, I.; Saunders,
A. M.; Schölmerich, M.; Schörner, M.; Sun, P.; Vinci, T.; Ravasio,
A.; Kraus, D.
2021NatSR..1112883L Altcode:
We present structure and equation of state (EOS) measurements
of biaxially orientated polyethylene terephthalate (PET,
(<SUB>C1<SUB>0</SUB>H<SUB>8</SUB>O<SUB>4</SUB>) n</SUB>?, also called
mylar) shock-compressed to (155 ±20 ?) GPa and (6000 ±1000 ?) K
using in situ X-ray diffraction, Doppler velocimetry, and optical
pyrometry. Comparing to density functional theory molecular dynamics
(DFT-MD) simulations, we find a highly correlated liquid at conditions
differing from predictions by some equations of state tables,
which underlines the influence of complex chemical interactions
in this regime. EOS calculations from ab initio DFT-MD simulations
and shock Hugoniot measurements of density, pressure and temperature
confirm the discrepancy to these tables and present an experimentally
benchmarked correction to the description of PET as an exemplary
material to represent the mixture of light elements at planetary
interior conditions.
---------------------------------------------------------
Title: Constraints on the height of the CH<SUB>4</SUB> homopause
from an analysis of IRTF-TEXES spectra
Authors: Sinclair, J. A.; Greathouse, T. K.; Giles, R.; Antuñano,
A.; Moses, J. I.; Fouchet, T.; Bezard, B.; Clark, G. B.; Tao, C.;
Grodent, D. C.; Orton, G.; Hue, V.; Fletcher, L. N.; Irwin, P. G.
2020AGUFMA076...03S Altcode:
We present an analysis of high-resolution spectra of Jupiter's
CH<SUB>3</SUB> (methyl radical) and CH<SUB>4</SUB> emission measured at
mid-to-high latitudes with the goal of determining spatial and temporal
variations in the altitude of the CH<SUB>4</SUB> homopause. IRTF-TEXES
(Texas Echelon Cross Echelle Spectrograph, Lacy et al., 2002, PASP
114, 153-168) spectra were measured on April 16<SUP>th</SUP> and
August 20<SUP>th</SUP> 2019 and were inverted as follows. A family of
photochemical models, based on Moses & Poppe (2017, Icarus 297,
33-58), was computed by varying the eddy diffusion coefficient in
the upper stratosphere and thereby increasing the altitude of the
CH<SUB>4</SUB> homopause. Adopting each photochemical model in turn,
the emission features of CH<SUB>3</SUB> and CH<SUB>4</SUB> were modeled
simultaneously by allowing the vertical temperature profile to vary,
and the quality of fit to the observations was used to discriminate
between models. In preliminary results of August 20<SUP>th</SUP>
2019 spectra, we find that a CH<SUB>4</SUB> homopause altitude below
~350 km (with respect to 1 bar) is required to fit the observations
equatorward of the main oval. At 68°N, 180°W (planetocentric, System
III), the center of the northern auroral region, a homopause altitude
of ~450 km optimized the fit to the spectra. At 68°N, but sampling
longitudes outside the main oval, a homopause altitude between ~336
km and ~400 km was required to fit the spectra. Our results confirm
the hypothesis presented in previous work (e.g. Clark et al., 2018,
JGR 123, 7554-7567) that the CH<SUB>4</SUB> homopause altitude is
higher in Jupiter's auroral regions compared to elsewhere on the
planet. This suggests deposition of energy from the magnetosphere
drives turbulence and vertical winds, which advects CH<SUB>4</SUB>
and its photochemical by-products to higher altitudes. We will repeat
this analysis for IRTF/TEXES and SOFIA/EXES observations scheduled
near-contemporaneously with Juno's 29<SUP>th</SUP> perijove (September
16th 2020) and search for temporal variations between measurements.
---------------------------------------------------------
Title: Modelling Optically Thick Radiation from Solar Flares with
the Lightweaver Framework
Authors: Osborne, C.; Fletcher, L.
2020AGUFMSH0500002O Altcode:
Most spectral lines formed in the chromosphere present complex profiles
due to their formation in optically thick regions and this is further
exacerbated by the rapid variations of this layer during a flare. Whilst
these lines carry a wealth of information regarding their formation
conditions, this information is difficult to extract. The Lightweaver
framework is flexible new software package for synthesising radiation
from both plane-parallel and multi-dimensional atmospheres where the
atomic populations can be out of local thermodynamic equilibrium. In
addition to the more commonly solved statistical equilibrium equations,
Lightweaver also provides tools to facilitate solving the problem of
time-dependent level populations. This framework is an open source
project designed to be used through Python and easily reconfigured
to solve new problems. We have applied tools built on Lightweaver to
reprocess simulations produced by the RADYN code, allowing further
investigation into the effects of partial frequency redistribution, and
calculation of response functions in this time dependent context. We
expect that these new methods should provide additional diagnostic
potential coinciding with observations from next generation telescopes
such as DKIST. Lightweaver is also being used to investigate the effect
of the radiation emitted from compact flare kernels on surrounding
plasma, by extending this reprocessing to multi-dimensional radiative
transfer. We will present the Lightweaver framework and discuss how
it can easily be adapted to investigate these different phenomena as
well as the initial results from these investigations.
---------------------------------------------------------
Title: SOFIA FORCAST observations of Jupiter in the JWST-era
Authors: De Pater, I.; Reach, W. T.; Fletcher, L. N.; Goullaud, C.;
Wong, M. H.
2020AGUFMP056.0005D Altcode:
Jupiter, the most accessible example for the study of atmospheric
circulation on a giant planet, serves as a template for our
understanding of the atmospheric dynamics and chemistry of the
ever-growing number of extrasolar planets. The atmospheres of
giant planets are extremely active, varying on timescales ranging
from decades (seasonally evolving chemistry and clouds), to months
(variability of storms and banded structures) and even minutes (e.g.,
asteroidal/cometary impacts and localized storm systems). These
evolving atmospheres serve as natural planetary-scale laboratories
for studying the fundamental meteorology, chemistry and evolutionary
mechanisms that shape the worlds around us. SOFIA's remote sensing
in the far-IR penetrates thick upper-tropospheric hazes to explore
the complex, turbulent dynamics of Jupiter's weather layer. <P />In
2014 we observed Jupiter with FORCAST at 17-37 micron to constrain the
shape of its continuum emission (Fletcher et al., 2017, Ic. 286, 223),
which can only be achieved if obscuration by telluric water vapor is
minimized, i.e., from SOFIA or from space. The SOFIA data confirmed
the Voyager findings in detecting an equator to pole increase in the
para-H<SUB>2</SUB> fraction (f<SUB>p</SUB>), with low f<SUB>p</SUB>
and sub-equilibrium conditions at the equator and high f<SUB>p</SUB>
and super-equilibrium conditions polewards of 60°latitude. The
para-H<SUB>2</SUB> fraction traces mean vertical mixing on timescales of
years to decades, depending on the poorly-known hydrogen equilibration
time in Jupiter's atmosphere. Equilibrium f<SUB>p</SUB> thus implies
weak vertical mixing, while sub- or super-equilibrium fractions
correspond to mean upwelling or subsidence, respectively (in the
upper troposphere where f<SUB>p</SUB> is measured). Interestingly,
both Voyager and SOFIA measured higher f<SUB>p</SUB> values at high
northern latitudes than at high southern latitudes, suggesting an
asymmetry between the two hemispheres where none is expected on the
basis of seasonal variability. We discuss the advantages of a similar
experiment simultaneously with JWST/ERS observations planned to be
carried out after launch.
---------------------------------------------------------
Title: Hot Onsets of Solar Flares
Authors: Hudson, H. S.; Simoes, P. J. D. A.; Fletcher, L.; Hayes,
L.; Hannah, I. G.
2020AGUFMSH0500003H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Atmospheric chemistry on Uranus and Neptune
Authors: Moses, J. I.; Cavalié, T.; Fletcher, L. N.; Roman, M. T.
2020RSPTA.37890477M Altcode: 2020arXiv200611367M; 2020RSPTA.37800477M
Comparatively little is known about atmospheric chemistry on Uranus and
Neptune, because remote spectral observations of these cold, distant
`Ice Giants' are challenging, and each planet has only been visited by
a single spacecraft during brief flybys in the 1980s. Thermochemical
equilibrium is expected to control the composition in the deeper, hotter
regions of the atmosphere on both planets, but disequilibrium chemical
processes such as transport-induced quenching and photochemistry alter
the composition in the upper atmospheric regions that can be probed
remotely. Surprising disparities in the abundance of disequilibrium
chemical products between the two planets point to significant
differences in atmospheric transport. The atmospheric composition of
Uranus and Neptune can provide critical clues for unravelling details
of planet formation and evolution, but only if it is fully understood
how and why atmospheric constituents vary in a three-dimensional sense
and how material coming in from outside the planet affects observed
abundances. Future mission planning should take into account the key
outstanding questions that remain unanswered about atmospheric chemistry
on Uranus and Neptune, particularly those questions that pertain to
planet formation and evolution, and those that address the complex,
coupled atmospheric processes that operate on Ice Giants within our
solar system and beyond. <P />This article is part of a discussion
meeting issue `Future exploration of ice giant systems'.
---------------------------------------------------------
Title: The internal structure of Jupiter's Great Red Spot
Authors: Li, C.; Fletcher, L. N.; Wong, M. H.; Allison, M. D.; Atreya,
S. K.; Bjoraker, G. L.; Bolton, S. J.; Guillot, T.; Ingersoll, A. P.;
Janssen, M. A.; Levin, S.; Li, L.; Orton, G.; Oyafuso, F. A.; Steffes,
P. G.; Zhang, Z.
2020AGUFMA076...15L Altcode:
Contrasts in thermal emission within and surrounding Jupiter's
Great Red Spot (GRS) were mapped at six frequencies by the Juno
Microwave Radiometer (MWR) during its 7<SUP>th</SUP> flyby (PJ7)
over Jupiter. Compared to the average thermal emission at the other
longitudes, the GRS appears brighter by about 22 K in the 0.6-GHz
(50-cm) channel, which senses thermal emission from hundreds of bars in
pressure. The brightness-temperature anomaly decreases with increasing
altitude and almost vanishes at the 2.6-GHz (11.5-cm) channel, probing
approximately the 10-bar pressure level. At levels shallower than 10
bars, the GRS exhibits a brightness-temperature asymmetry in latitude,
with thermal emission from the northern part of the GRS being fainter
and the southern part being brighter by up to 10 K compared to the
average. A novel way of exploring the degenerate space of temperature
and opacity is developed by progressively increasing the constraint
on the temperature profile. The result suggests that the GRS has
an extended upwelling branch in the north between 20<SUP>o</SUP>S ~
16<SUP>o</SUP>S originating at depths > 100 bars (230 km down from
the 1-bar level) and a narrow subsiding branch in the south near
23.5<SUP>o</SUP>S penetrating to about 30 bars. We did not see the
bottom of the GRS in our longest wavelength channel, which means that
the bottom of the GRS must be deeper than 100 bars.
---------------------------------------------------------
Title: Thermal Measurements of the Ring System of Uranus
Authors: Molter, E. M.; De Pater, I.; Roman, M. T.; Fletcher, L. N.
2020AGUFMP017...03M Altcode:
The narrow main rings of Uranus are composed of primarily centimeter-
to meter-sized particles, with a very small or nonexistent dust
component. This property presents a challenge to visible and
near-infrared instruments observing the rings, which are largely
unable to differentiate large particles from dust; thus, the thickness,
mass, filling factor, and detailed particle size distribution of these
rings remain poorly constrained. In this work we observed the thermal
component of the Uranian ring system for the first time, making use of
millimeter (1.3-3.1 mm) imaging from the Atacama Large (sub-)Millimeter
Array and mid-infrared imaging from the Very Large Telescope VISIR
instrument. The ε ring was readily seen by eye in the images; the
other main ring groups were visible in a radial (azimuthally-averaged)
profile at millimeter wavelengths. A simple thermal model similar to the
Near-Earth Asteroid Thermal Model (NEATM) of near-Earth asteroids was
leveraged to determine a ring particle temperature of 77.3 ± 1.8 K for
the ε ring. This temperature is higher than expected for fast-rotating
ring particles viewed at our observing geometry, meaning that the data
favor a model in which the thermal inertia of the ring particles is
low and/or their rotation rate is slow. The ε ring displayed a factor
of 2-3 brightness difference between periapsis and apoapsis, and an
average fractional visible area (the two-dimensional projection of the
filling factor) of 49.1% ± 2.2%. These observations are consistent with
optical and near-infrared reflected light observations, confirming the
hypothesis that micron-sized dust is not present in Uranus's main rings.
---------------------------------------------------------
Title: Long-term Cycles of Variability of Jupiter's Atmosphere from
Ground-based Infrared Observations
Authors: Antuñano, A.; Fletcher, L. N.; Orton, G.; Sinclair, J. A.;
Kasaba, Y.
2020AGUFMA076...06A Altcode:
Jupiter's atmosphere displays some of the most dramatic weather of
any planet in our Solar System, with cycles of activity changing the
upper tropospheric and stratospheric temperatures, aerosols, and
cloud structures through physical processes that are not yet well
understood. Here we use almost 40 years (more than 3 jovian years)
of ground-based infrared observations captured at NASA's Infrared
Telescope Facility (IRTF), the Very Large Telescope (VLT) and Subaru
between 1980 and 2019 in a number of filters spanning from 7.9 to
24.5 µm (sampling upper tropospheric and stratospheric temperatures
and aerosols via collision-induced hydrogen and helium absorption, and
emission from stratospheric hydrocarbons), to (i) understand the impact
of the tropospheric activity on the periodicity of the stratospheric
temperature oscillations, (ii) characterize the long-term variability of
Jupiter's atmosphere at different altitudes in the upper troposphere
and stratosphere, and (iii) investigate the long-term thermal,
chemical and aerosol changes in Jupiter's troposphere. In particular,
we generate Lomb-Scargle periodograms and apply a Wavelet Transform
analysis to our dataset to look for potential periodicities on the
brightness temperature variability in different filters and compare
them to previously reported cyclic activity at visible wavelengths
(sensing the ammonia cloud top at ~500 mbar) and 5 µm (sensing the
1-4 bar pressure level). Finally, a Principal Component Analyses
(PCA) is also performed to analyse the correlation of the brightness
temperature variations at different belts and zones.
---------------------------------------------------------
Title: Saturn's Seasonal Atmosphere at Northern Summer Solstice
Authors: Fletcher, L. N.; Sromovsky, L.; Hue, V.; Moses, J. I.;
Guerlet, S.; West, R. A.; Koskinen, T.
2020arXiv201209288F Altcode:
The incredible longevity of Cassini's orbital mission at Saturn has
provided the most comprehensive exploration of a seasonal giant planet
to date. This review explores Saturn's changing global temperatures,
composition, and aerosol properties between northern spring and
summer solstice (2015-2017), extending our previous review of
Cassini's remote sensing investigations (2004-14, Fletcher et al.,
2018) to the grand finale. The result is an unprecedented record
of Saturn's climate that spans almost half a Saturnian year, which
can be used to test the seasonal predictions of radiative climate
models, neutral and ion photochemistry models, and atmospheric
circulation models. Hemispheric asymmetries in tropospheric and
stratospheric temperatures were observed to reverse from northern
winter to northern summer; spatial distributions of hydrocarbons
and para-hydrogen shifted in response to atmospheric dynamics
(e.g., seasonally-reversing Hadley cells, polar stratospheric vortex
formation, equatorial stratospheric oscillations, and inter-hemispheric
transport); and upper tropospheric and stratospheric aerosols exhibited
changes in optical thickness that modulated Saturn's visible colours
(from blue hues to a golden appearance in the north near solstice),
reflectivity, and near-infrared emission. Numerical simulations of
radiative balance and photochemistry do a good job in reproducing the
observed seasonal change and phase lags, but discrepancies between
models and observations still persist, indicating a crucial role for
atmospheric dynamics and the need to couple chemical and radiative
schemes to the next generation of circulation models. With Cassini's
demise, an extended study of Saturn's seasons, from northern summer
to autumn, will require the capabilities of ground- and space-based
observatories, as we eagerly await the next orbital explorer at Saturn.
---------------------------------------------------------
Title: Determining the Global Water Abundance in Jupiter from Juno MWR
Authors: Zhang, Z.; Levin, S.; Adumitroaie, V.; Allison, M. D.;
Arballo, J. K.; Atreya, S. K.; Becker, H. N.; Bjoraker, G. L.;
Bolton, S. J.; Brown, S. T.; Fletcher, L. N.; Guillot, T.; Gulkis,
S.; Hodges, A. L.; Ingersoll, A. P.; Janssen, M. A.; Li, C.; Li, L.;
Lunine, J. I.; Misra, S.; Orton, G.; Oyafuso, F. A.; Santos-Costa,
D.; Sarkissian, E.; Steffes, P. G.; Waite, H., Jr.; Wong, M. H.
2020AGUFMP005.0005Z Altcode:
The global water abundance in Jupiter is pivotal in understanding
Giant-Planet formation and the delivery of volatiles throughout the
solar system. The Microwave Radiometer (MWR) on board Juno provides
the first measurements of Jupiter's deep atmosphere, down to ~250 bars
in pressure. Li et al. (2020) reported the initial results from MWR
on water abundance near Jupiter's equatorial region. The discovery by
Juno that Jupiter's atmosphere is not well mixed at depth and displays
significant variability with latitude suggests that water may vary
with latitude even at depth. We present current plans and status for
Juno's investigation of water beyond equatorial latitudes including
observation plans for Juno's extended mission that will be able to
observe Jupiter's north polar region at improved resolution.
---------------------------------------------------------
Title: Ice giant system exploration in the 2020s: an introduction
Authors: Fletcher, L. N.; Simon, A. A.; Hofstadter, M. D.; Arridge,
C. S.; Cohen, Ian J.; Masters, A.; Mandt, K.; Coustenis, A.
2020RSPTA.37890473F Altcode: 2020RSPTA.37800473F; 2020arXiv200812125F
The international planetary science community met in London in
January 2020, united in the goal of realizing the first dedicated
robotic mission to the distant ice giants, Uranus and Neptune, as the
only major class of solar system planet yet to be comprehensively
explored. Ice-giant-sized worlds appear to be a common outcome of
the planet formation process, and pose unique and extreme tests to
our understanding of exotic water-rich planetary interiors, dynamic
and frigid atmospheres, complex magnetospheric configurations,
geologically-rich icy satellites (both natural and captured), and
delicate planetary rings. This article introduces a special issue on
ice giant system exploration at the start of the 2020s. We review
the scientific potential and existing mission design concepts for
an ambitious international partnership for exploring Uranus and/or
Neptune in the coming decades. <P />This article is part of a discussion
meeting issue `Future exploration of ice giant systems'.
---------------------------------------------------------
Title: Slowly Moving Thermal Waves in Saturn
Authors: Orton, G.; Sinclair, J.; Fletcher, L.; Read, P.; Flasar,
F. M.; Achterberg, R.; Yanamandra-Fisher, P.; Fujiyoshi, T.; Fisher,
B.; Irwin, P.
2020DPS....5220104O Altcode:
We surveyed the global temperature field of Saturn's atmosphere
using the Cassini Composite Infrared Spectrometer (CIRS, 7-1000 µm),
complemented by ground-based mid-infrared observations (7-25 µm),
from 1995 to 2020. We detected and characterized properties of slowly
moving zonal thermal waves and their variability during that period. The
most inclusive CIRS surveys, FIRMAPs (15 cm<SUP>-1</SUP> spectral
resolution), covered the planet from the equator to either north or
south pole, sweeping through the latitude range while the planet rotated
beneath over its ~10-hour rotation. Additional measurements were made by
ground-based observations at the Infrared Telescope Facility using the
MIRSI instrument, the Very Large Telescope using VISIR and the Subaru
Telescope using COMICS. We sampled spectral ranges dominated both by
upper-tropospheric emission (80-200 mbar) and by stratospheric emission
(0.5-3 mbar). Several types of slowly moving zonal thermal waves were
detected: (1) meridionally broad wavenumber-1 through -3 oscillations,
(2) equatorial waves, some of which extend northward to mid-latitudes,
(3) prominent wavenumber-12 oscillations in the southern hemisphere,
which also have components of wavenumbers 1 through 3 and extend over
15°-35°S latitude, (4) mid-latitude wavenumber > 2 oscillations
in both hemispheres with variable time dependence and morphology,
and (5) discrete low-latitude tropospheric features. The prominent
southern-hemisphere waves appear to have distinct periods of maximum
intensity around 2003-2004 from ground-based observations and 2008-2009
from CIRS FIRMAPs. These waves are easily detectable in both the
stratosphere, where the other types of waves are prominent, but also
in the troposphere with no detectable phase shift in longitude. These
waves were also sufficiently coherent to track a mean phase speed,
which is about 0.5° per day, retrograde. After 2009, wavenumber-1
oscillations in the northern hemisphere are joined by higher-wavenumber
oscillations. A local temperature maximum is seen around 2010-2011,
then another in 2016-2017. Further ground-based observations are
required to determine whether the amplitude of northern-hemisphere
waves is influenced by seasonally dependent insolation.
---------------------------------------------------------
Title: The Solar Orbiter magnetometer
Authors: Horbury, T. S.; O'Brien, H.; Carrasco Blazquez, I.; Bendyk,
M.; Brown, P.; Hudson, R.; Evans, V.; Oddy, T. M.; Carr, C. M.; Beek,
T. J.; Cupido, E.; Bhattacharya, S.; Dominguez, J. -A.; Matthews, L.;
Myklebust, V. R.; Whiteside, B.; Bale, S. D.; Baumjohann, W.; Burgess,
D.; Carbone, V.; Cargill, P.; Eastwood, J.; Erdös, G.; Fletcher,
L.; Forsyth, R.; Giacalone, J.; Glassmeier, K. -H.; Goldstein, M. L.;
Hoeksema, T.; Lockwood, M.; Magnes, W.; Maksimovic, M.; Marsch, E.;
Matthaeus, W. H.; Murphy, N.; Nakariakov, V. M.; Owen, C. J.; Owens,
M.; Rodriguez-Pacheco, J.; Richter, I.; Riley, P.; Russell, C. T.;
Schwartz, S.; Vainio, R.; Velli, M.; Vennerstrom, S.; Walsh, R.;
Wimmer-Schweingruber, R. F.; Zank, G.; Müller, D.; Zouganelis, I.;
Walsh, A. P.
2020A&A...642A...9H Altcode:
The magnetometer instrument on the Solar Orbiter mission is designed
to measure the magnetic field local to the spacecraft continuously
for the entire mission duration. The need to characterise not only
the background magnetic field but also its variations on scales from
far above to well below the proton gyroscale result in challenging
requirements on stability, precision, and noise, as well as magnetic
and operational limitations on both the spacecraft and other
instruments. The challenging vibration and thermal environment has
led to significant development of the mechanical sensor design. The
overall instrument design, performance, data products, and operational
strategy are described.
---------------------------------------------------------
Title: Reflection and Shadowing from Saturn's Rings: Influence on
Photochemisty and Heating
Authors: Edgington, S. G.; Atreya, S.; West, R.; Baines, K.;
Fletcher, L.
2020DPS....5220106E Altcode:
Cassini orbited Saturn for over thirteen years, nearly a half Saturn
year. This corresponded to a seasonal configuration where the sub-solar
point was at ~24°S at the time of Saturn Orbit Insertion (July 1, 2004)
and ~27°N at the time of Cassini's Grand Finale. During this period,
the ring shadow moved southward from covering a substantial area of
the northern hemisphere to covering a large swath of territory south
of the equator as solstice approached. At equinox, the rings project
a small sliver of shadow at low latitudes. At its maximum extent, the
ring shadow can reach as far as 48°N/S at the meridian (~58°N/S at the
terminator). <P />Both ultraviolet and visible sunlight penetrating into
any particular latitude will vary greatly depending on both Saturn's
season, the optical thickness of each ring system and its reflective
properties. In essence, the rings act like both semi-transparent
Venetian blinds over the atmosphere of Saturn. At the same time, the
illuminated side of the rings reflect ultraviolet and visible solar
photons onto the fully illuminated hemisphere of the planet. This acts
to enhance both photochemistry and heating and potentially enhancing
seasonal effects. Lastly, the rings, having a temperature themselves,
provides a source of thermal photons impinging onto the atmosphere and
a possible source of heating. <P />The projection of the oscillating
ring shadow onto the planet has been derived as a function of season. In
addition, detailed calculations of geometric parameters important for
light scattering from the rings onto an oblate planet have been worked
for a fine grid of latitudes and longitudes. We will focus on how these
geometric parameters can be used for both photochemical (UV) and thermal
balance (visible and infrared) radiative transfer calculations as a
function of season. <P />The impact of these augmentations on production
and loss rates of hydrocarbons (e.g. acetylene, ethane, and propane),
ammonia, phosphine, and hazes will be examined and attempt to explain
several Saturn observations conducted by Cassini. Comparison with
Jupiter, where seasonal effects are known to be insignificant, will
be made. <P />Acknowledgements: The research described in this paper
was carried out in part at the Jet Propulsion Laboratory, California
Institute of Technology, under a contract with the National Aeronautics
and Space Administration. Government sponsorship is acknowledged.
---------------------------------------------------------
Title: Solar Flare Energy Partitioning and Transport -- the Impulsive
Phase (a Heliophysics 2050 White Paper)
Authors: Kerr, Graham S.; Alaoui, Meriem; Allred, Joel C.; Bian,
Nicholas H.; Dennis, Brian R.; Emslie, A. Gordon; Fletcher, Lyndsay;
Guidoni, Silvina; Hayes, Laura A.; Holman, Gordon D.; Hudson, Hugh
S.; Karpen, Judith T.; Kowalski, Adam F.; Milligan, Ryan O.; Polito,
Vanessa; Qiu, Jiong; Ryan, Daniel F.
2020arXiv200908400K Altcode:
Solar flares are a fundamental component of solar eruptive events (SEEs;
along with solar energetic particles, SEPs, and coronal mass ejections,
CMEs). Flares are the first component of the SEE to impact our
atmosphere, which can set the stage for the arrival of the associated
SEPs and CME. Magnetic reconnection drives SEEs by restructuring the
solar coronal magnetic field, liberating a tremendous amount of energy
which is partitioned into various physical manifestations: particle
acceleration, mass and magnetic-field eruption, atmospheric heating,
and the subsequent emission of radiation as solar flares. To explain
and ultimately predict these geoeffective events, the heliophysics
community requires a comprehensive understanding of the processes that
transform and distribute stored magnetic energy into other forms,
including the broadband radiative enhancement that characterises
flares. This white paper, submitted to the Heliophysics 2050 Workshop,
discusses the flare impulsive phase part of SEEs, setting out the
questions that need addressing via a combination of theoretical,
modelling, and observational research. In short, by 2050 we must
determine the mechanisms of particle acceleration and propagation,
and must push beyond the paradigm of energy transport via nonthermal
electron beams, to also account for accelerated protons & ions
and downward directed Alfven waves.
---------------------------------------------------------
Title: Solar Flare Energy Partitioning and Transport -- the Gradual
Phase (a Heliophysics 2050 White Paper)
Authors: Kerr, Graham S.; Alaoui, Meriem; Allred, Joel C.; Bian,
Nicholas H.; Dennis, Brian R.; Emslie, A. Gordon; Fletcher, Lyndsay;
Guidoni, Silvina; Hayes, Laura A.; Holman, Gordon D.; Hudson, Hugh
S.; Karpen, Judith T.; Kowalski, Adam F.; Milligan, Ryan O.; Polito,
Vanessa; Qiu, Jiong; Ryan, Daniel F.
2020arXiv200908407K Altcode:
Solar flares are a fundamental component of solar eruptive events
(SEEs; along with solar energetic particles, SEPs, and coronal
mass ejections, CMEs). Flares are the first component of the SEE
to impact our atmosphere, which can set the stage for the arrival
of the associated SEPs and CME. Magnetic reconnection drives SEEs
by restructuring the solar coronal magnetic field, liberating a
tremendous amount of energy which is partitioned into various physical
manifestations: particle acceleration, mass and magnetic-field eruption,
atmospheric heating, and the subsequent emission of radiation as solar
flares. To explain and ultimately predict these geoeffective events,
the heliophysics community requires a comprehensive understanding of
the processes that transform and distribute stored magnetic energy
into other forms, including the broadband radiative enhancement that
characterises flares. This white paper, submitted to the Heliophysics
2050 Workshop, discusses the flare gradual phase part of SEEs, setting
out the questions that need addressing via a combination of theoretical,
modelling, and observational research. In short, the flare gradual phase
persists much longer than predicted so, by 2050, we must identify the
characteristics of the significant energy deposition sustaining the
gradual phase, and address the fundamental processes of turbulence
and non-local heat flux.
---------------------------------------------------------
Title: Hot X-ray Onsets of Solar Flares
Authors: Hayes, L.; Hudson, H.; Simoes, P.; Fletcher, L.; Hannah, I.
2020SPD....5121113H Altcode:
The study of the localized plasma conditions before the impulsive phase
of a solar flare can help us understand the physical processes that
occur leading up to the main flare energy release. Here, we present
evidence of a hot X-ray 'onset' interval of enhanced isothermal plasma
temperatures in the range of 10-15 MK up to tens of seconds prior
to the flare's impulsive phase. This 'hot onset' interval occurs
during the pre-flare time during which elevated GOES soft X-ray
flux is detected, but prior to detectable hard X-ray emission. The
isothermal temperatures, estimated by the Geostationary Operational
Environmental Satellite (GOES) X-ray sensor, and confirmed with data
from RHESSI, show no signs of gradual increase, and occurs regardless
of flare classification or configuration. In a small sample of four
representative flare events we identify this early hot onset soft
X-ray emission mainly within footpoint and low-lying loops, rather
than with coronal structures, based on images from the Atmospheric
Imaging Assembly (AIA) and the use of limb occultation. These hot
X-ray onsets appear before there is evidence of collisional heating by
non-thermal electrons, and hence challenges the standard flare heating
modeling techniques.
---------------------------------------------------------
Title: Jupiter's Equatorial Plumes and Hot Spots: Spectral Mapping
from Gemini/TEXES and Juno/MWR
Authors: Fletcher, L. N.; Orton, G. S.; Greathouse, T. K.; Rogers,
J. H.; Zhang, Z.; Oyafuso, F. A.; Eichstädt, G.; Melin, H.; Li, C.;
Levin, S. M.; Bolton, S.; Janssen, M.; Mettig, H. -J.; Grassi, D.;
Mura, A.; Adriani, A.
2020JGRE..12506399F Altcode: 2020arXiv200400072F
We present multiwavelength measurements of the thermal, chemical,
and cloud contrasts associated with the visibly dark formations
(also known as 5-μm hot spots) and intervening bright plumes
on the boundary between Jupiter's Equatorial Zone (EZ) and North
Equatorial Belt (NEB). Observations made by the TEXES 5- to 20-μm
spectrometer at the Gemini North Telescope in March 2017 reveal the
upper-tropospheric properties of 12 hot spots, which are directly
compared to measurements by Juno using the microwave radiometer (MWR),
JIRAM at 5 μm, and JunoCam visible images. MWR and thermal-infrared
spectroscopic results are consistent near 0.7 bar. Mid-infrared-derived
aerosol opacity is consistent with that inferred from visible-albedo
and 5-μm opacity maps. Aerosol contrasts, the defining characteristics
of the cloudy plumes and aerosol-depleted hot spots, are not a good
proxy for microwave brightness. The hot spots are neither uniformly
warmer nor ammonia-depleted compared to their surroundings at p<1
bar. At 0.7 bar, the microwave brightness at the edges of hot spots
is comparable to other features within the NEB. Conversely, hot
spots are brighter at 1.5 bar, signifying either warm temperatures
and/or depleted NH<SUB>3</SUB> at depth. Temperatures and ammonia are
spatially variable within the hot spots, so the precise location of
the observations matters to their interpretation. Reflective plumes
sometimes have enhanced NH<SUB>3</SUB>, cold temperatures, and elevated
aerosol opacity, but each plume appears different. Neither plumes nor
hot spots had microwave signatures in channels sensing p>10 bars,
suggesting that the hot spot/plume wave is a relatively shallow feature.
---------------------------------------------------------
Title: Spatial structure in Neptune's 7.90- μm stratospheric
CH<SUB>4</SUB> emission, as measured by VLT-VISIR
Authors: Sinclair, J. A.; Orton, G. S.; Fletcher, L. N.; Roman, M.;
de Pater, I.; Encrenaz, T.; Hammel, H. B.; Giles, R. S.; Velusamy,
T.; Moses, J. I.; Irwin, P. G. J.; Momary, T. W.; Rowe-Gurney, N.;
Tabataba-Vakili, F.
2020Icar..34513748S Altcode:
We present a comparison of VLT-VISIR images and Keck-NIRC2 images
of Neptune, which highlight the coupling between its troposphere
and stratosphere. VLT-VISIR images were obtained on September 16th
2008 (UT) at 7.90 μm and 12.27 μm, which are primarily sensitive
to 1-mbar CH<SUB>4</SUB> and C<SUB>2</SUB>H<SUB>6</SUB> emission,
respectively. NIRC2 images in the H band were obtained on October 5th,
6th and 9th 2008 (UT) and sense clouds and haze in the upper troposphere
and lower stratosphere (from approximately 600 to 20 mbar). At 7.90 μm,
we observe enhancements of CH<SUB>4</SUB> emission in latitude bands
centered at approximately 25∘S and 48∘S (planetocentric). Within
these zonal bands, tentative detections (< 2 σ) of discrete
hotspots of CH<SUB>4</SUB> emission are also evident at 24∘S,
181∘W and 42∘S, 170∘W. The longitudinal-mean enhancements
in the CH<SUB>4</SUB> emission are also latitudinally-coincident
with bands of bright (presumably CH<SUB>4</SUB> ice) clouds in the
upper troposphere and lower stratosphere evidenced in the H-band
images. This suggests the Neptunian troposphere and stratosphere are
coupled in these specific regions. This could be in the form of (1)
'overshoot' of strong, upwelling plumes and advection of CH<SUB>4</SUB>
ice into the lower stratosphere, which subsequently sublimates into
CH<SUB>4</SUB> gas and/or (2) generation of waves by plumes impinging
from the tropopause below, which impart their energy and heat the lower
stratosphere. We favor the former process since there is no evidence
of similar smaller-scale morphology in the C<SUB>2</SUB>H<SUB>6</SUB>
emission, which probes a similar atmospheric level. However, we
cannot exclude temperature variations as the source of the morphology
observed in CH<SUB>4</SUB> emission. Future, near-infrared imaging of
Neptune performed near-simultaneously with future mid-infrared spectral
observations of Neptune by the James Webb Space Telescope would allow
the coupling of Neptune's troposphere and stratosphere to be confirmed
and studied in greater detail.
---------------------------------------------------------
Title: Monitoring Neptune's atmosphere with a combination of small
and large telescopes: The role of Spanish Telescopes in a global
international campaign
Authors: Hueso, R.; Sánchez-Lavega, A.; Roman, M.; Dhillon, V.; de
Pater, I.; Fletcher, L.; Orton, G. S.; Simon, A.; Wong, M.; Chavez,
E.; Sromovsky, L.; Fry, P.; Delcroix, M.; Hernández-Bernal, J.;
Iñurrigarro, P.; Littlefair, S.; Marsh, T.; Ordonez-Etxeberria, I.;
Pérez-Hoyos, S.; Redwing, E.; Rojas, J. F.; Tollefson, J.
2020sea..confE.102H Altcode:
Neptune's atmosphere is covered by tropospheric clouds and hazes that
evolve in timescales of days, months and years. Given the small apparent
size of Neptune's disk (2.4"), there are outstanding difficulties in
obtaining sufficient high-resolution data to trace Neptune's atmospheric
dynamics and study its variability. Here we present results of an
international campaign to observe Neptune and we focus in the potential
of Spanish Telescopes to advance in the knowledge of its atmosphere.
---------------------------------------------------------
Title: Jupiter in the Ultraviolet: Acetylene and Ethane Abundances
in the Stratosphere of Jupiter from Cassini Observations between
0.15 and 0.19 μm
Authors: Melin, Henrik; Fletcher, L. N.; Irwin, P. G. J.; Edgington,
S. G.
2020AJ....159..291M Altcode: 2020arXiv200509895M
At wavelengths between 0.15 and 0.19 μm, the far-ultraviolet spectrum
of Jupiter is dominated by the scattered solar spectrum, attenuated
by molecular absorptions primarily by acetylene and ethane, and to a
lesser extent ammonia and phosphine. We describe the development of
our radiative transfer code that enables the retrieval of abundances
of these molecular species from ultraviolet reflectance spectra. As a
proof-of-concept we present an analysis of Cassini Ultraviolet Imaging
Spectrograph (UVIS) observations of the disk of Jupiter during the
2000/2001 flyby. The ultraviolet-retrieved acetylene abundances in
the upper stratosphere are lower than those predicted by models based
solely on infrared thermal emission from the mid-stratosphere observed
by the Composite Infrared Spectrometer (CIRS), requiring an adjustment
to the vertical profiles above 1 mbar. We produce a vertical acetylene
abundance profile that is compatible with both CIRS and UVIS, with
reduced abundances at pressures <1 mbar: the 0.1 mbar abundances are
1.21 ± 0.07 ppm for acetylene and 20.8 ± 5.1 ppm for ethane. Finally,
we perform a sensitivity study for the JUICE ultraviolet spectrograph,
which has extended wavelength coverage out to 0.21 μm, enabling the
retrieval of ammonia and phosphine abundances, in addition to acetylene
and ethane.
---------------------------------------------------------
Title: Deep learning for the Sun
Authors: Armstrong, John A.; Osborne, Christopher M. J.; Fletcher,
Lyndsay
2020A&G....61c3.34A Altcode:
John A Armstrong, Christopher M J Osborne and Lyndsay Fletcher examine
how neural networks can be used to explore the nature and location of
solar activity.
---------------------------------------------------------
Title: Demonstration of X-ray Thomson scattering as diagnostics for
miscibility in warm dense matter
Authors: Frydrych, S.; Vorberger, J.; Hartley, N. J.; Schuster,
A. K.; Ramakrishna, K.; Saunders, A. M.; van Driel, T.; Falcone,
R. W.; Fletcher, L. B.; Galtier, E.; Gamboa, E. J.; Glenzer, S. H.;
Granados, E.; MacDonald, M. J.; MacKinnon, A. J.; McBride, E. E.;
Nam, I.; Neumayer, P.; Pak, A.; Voigt, K.; Roth, M.; Sun, P.; Gericke,
D. O.; Döppner, T.; Kraus, D.
2020NatCo..11.2620F Altcode:
The gas and ice giants in our solar system can be seen as a
natural laboratory for the physics of highly compressed matter at
temperatures up to thousands of kelvins. In turn, our understanding
of their structure and evolution depends critically on our ability to
model such matter. One key aspect is the miscibility of the elements
in their interiors. Here, we demonstrate the feasibility of X-ray
Thomson scattering to quantify the degree of species separation in a
1:1 carbon-hydrogen mixture at a pressure of ~150 GPa and a temperature
of ~5000 K. Our measurements provide absolute values of the structure
factor that encodes the microscopic arrangement of the particles. From
these data, we find a lower limit of 2 4<SUB>-7</SUB><SUP>+6</SUP>?% of
the carbon atoms forming isolated carbon clusters. In principle, this
procedure can be employed for investigating the miscibility behaviour
of any binary mixture at the high-pressure environment of planetary
interiors, in particular, for non-crystalline samples where it is
difficult to obtain conclusive results from X-ray diffraction. Moreover,
this method will enable unprecedented measurements of mixing/demixing
kinetics in dense plasma environments, e.g., induced by chemistry or
hydrodynamic instabilities.
---------------------------------------------------------
Title: John Campbell Brown OBE (1947-2019)
Authors: Fletcher, Lyndsay; Labrosse, Nicolas; Mackinnon, Alexander
2020A&G....61b2.14F Altcode:
Astronomer Royal for Scotland and inspirational solar physicist,
by Lyndsay Fletcher, Nicolas Labrosse and Alec MacKinnon.
---------------------------------------------------------
Title: On the Spatial Distribution of Minor Species in Jupiter's
Troposphere as Inferred From Juno JIRAM Data
Authors: Grassi, D.; Adriani, A.; Mura, A.; Atreya, S. K.; Fletcher,
L. N.; Lunine, J. I.; Orton, G. S.; Bolton, S.; Plainaki, C.; Sindoni,
G.; Altieri, F.; Cicchetti, A.; Dinelli, B. M.; Filacchione, G.;
Migliorini, A.; Moriconi, M. L.; Noschese, R.; Olivieri, A.; Piccioni,
G.; Sordini, R.; Stefani, S.; Tosi, F.; Turrini, D.
2020JGRE..12506206G Altcode:
The spatial distribution of water, ammonia, phosphine, germane, and
arsine in the Jupiter's troposphere has been inferred from the Jovian
Infrared Auroral Mapper (JIRAM) Juno data. Measurements allow us to
retrieve the vertically averaged concentration of gases between ~3
and 5 bars from infrared-bright spectra. Results were used to create
latitudinal profiles. The water vapor relative humidity varies with
latitude from <1% to over 15%. At intermediate latitudes (30-70°)
the water vapor maxima are associated with the location of cyclonic
belts, as inferred from mean zonal wind profiles (Porco et al.,
2003). The high-latitude regions (beyond 60°) are drier in the north
(mean relative humidity around 2-3%) than the south, where humidity
reaches 15% around the pole. The ammonia volume mixing ratio varies from
1 × 10<SUP>-4</SUP> to 4 × 10<SUP>-4</SUP>. A marked minimum exists
around 10°N, while data suggest an increase over the equator. The
high-latitude regions are different in the two hemispheres, with a
gradual increase in the south and more constant values with latitude
in the north. The phosphine volume mixing ratio varies from 4 ×
10<SUP>-7</SUP> to 10 × 10<SUP>-7</SUP>. A marked minimum exists in
the North Equatorial Belt. For latitudes poleward 30°S and 30°N,
the northern hemisphere appears richer in phosphine, with a decrease
toward the pole, while the opposite is observed in the south. JIRAM
data indicate an increase of germane volume mixing ratio from 2 ×
10<SUP>-10</SUP> to 8 × 10<SUP>-10</SUP> from both poles to 15°S,
with a depletion centered around the equator. Arsine presents the
opposite trend, with maximum values of 6 × 10<SUP>-10</SUP> at the
two poles and minima below 1 × 10<SUP>-10</SUP> around 20°S.
---------------------------------------------------------
Title: Compositional Mapping of Europa with VLT/SPHERE
Authors: King, O. R. T.; Fletcher, L. N.; Ligier, N.
2020LPI....51.2046K Altcode:
A high spatial resolution ground-based IR observation of Europa has
been fit using a Monte Carlo model to calculate compositional abundances
and uncertainties.
---------------------------------------------------------
Title: New Frontiers-Class Uranus Orbiter: A Case for Exploring the
Feasibility of Achieving Multidisciplinary Science with a Mid-Scale
Mission
Authors: Cohen, I. J.; Beddingfield, C. B.; Chancia, R. O.; DiBraccio,
G. A.; Hedman, M. M.; MacKenzie, S. M.; Mauk, B. H.; Sayanagi,
K. M.; Soderlund, K. M.; Turtle, E. P.; Adams, E. Y.; Ahrens, C. J.;
Arridge, C. S.; Brooks, S. M.; Bunce, E. J.; Charnoz, S.; Clark,
G. B.; Coustenis, A.; Dillman, R. A.; Dutta, S.; Fletcher, L. N.;
Harbison, R. A.; Helled, R.; Holme, R.; Jozwiak, L. M.; Kasaba, Y.;
Kollmann, P.; Luszcz-Cook, S.; Mousis, O.; Mura, A.; Murakami, G.;
Parisi, M.; Rymer, A. M.; Stanley, S.; Stephan, K.; Vervack, R. J.;
Wong, M. H.; Wurz, P.
2020LPI....51.1428C Altcode:
Icy Uranus / Can your system be explored / For New Frontiers cost?
---------------------------------------------------------
Title: Reappraisal and New Constraints on Europa's Surface Composition
with the Near-Infrared Imaging Spectrometer SINFONI of the VLT
Authors: Ligier, N.; Carter, J.; Poulet, F.; Fletcher, L.; King, O.;
Brunetto, R.; Massé, M.; Snodgrass, C.
2020LPI....51.1964L Altcode:
We present the physico-chemical properties of Europa's surface
derived from two complementary datasets acquired with the ground-based
instrument SINFONI (ESO/VLT).
---------------------------------------------------------
Title: CHARISMA: A Space Telescope for Planetary Science
Authors: Young, C. L.; Sayanagi, K. M.; Wong, M. H.; Curry, S.;
Jessup, K. L.; Becker, T.; Hendrix, A.; Chanover, N.; Milam, S.;
Holler, B.; Holsclaw, G.; Peralta, J.; Clarke, J.; Spencer, J.;
Kelley, M.; Luhmann, J.; MacDonnell, D.; Vervack, R.; Rutherford, K.;
Fletcher, L.; de Pater, I.; Vilas, F.; Simon, A.; Siegmund, O.; Bell,
J.; Delory, G.; Pitman, J.; Greathouse, T.; Wishnow, E.; Schneider,
N.; Lillis, R.; Colwell, J.; Bowman, L.; Feaga, L.
2020LPICo2194.6012Y Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Measurement of diamond nucleation rates from hydrocarbons at
conditions comparable to the interiors of icy giant planets
Authors: Schuster, A. K.; Hartley, N. J.; Vorberger, J.; Döppner,
T.; van Driel, T.; Falcone, R. W.; Fletcher, L. B.; Frydrych, S.;
Galtier, E.; Gamboa, E. J.; Gericke, D. O.; Glenzer, S. H.; Granados,
E.; MacDonald, M. J.; MacKinnon, A. J.; McBride, E. E.; Nam, I.;
Neumayer, P.; Pak, A.; Prencipe, I.; Voigt, K.; Saunders, A. M.; Sun,
P.; Kraus, D.
2020PhRvB.101e4301S Altcode:
We present measurements of the nucleation rate into a diamond lattice
in dynamically compressed polystyrene obtained in a pump-probe
experiment using a high-energy laser system and in situ femtosecond
x-ray diffraction. Different temperature-pressure conditions that
occur in planetary interiors were probed. For a single shock reaching
70 GPa and 3000 K no diamond formation was observed, while with a
double shock driving polystyrene to pressures around 150 GPa and
temperatures around 5000 K nucleation rates between 10<SUP>29</SUP>
and 10<SUP>34</SUP>m<SUP>-3</SUP> s<SUP>-1</SUP> were recorded. These
nucleation rates do not agree with predictions of the state-of-the-art
theoretical models for carbon-hydrogen mixtures by many orders of
magnitude. Our data suggest that there is significant diamond formation
to be expected inside icy giant planets like Neptune and Uranus.
---------------------------------------------------------
Title: A Review of the in Situ Probe Designs from Recent Ice Giant
Mission Concept Studies
Authors: Simon, A. A.; Fletcher, L. N.; Arridge, C.; Atkinson, D.;
Coustenis, A.; Ferri, F.; Hofstadter, M.; Masters, A.; Mousis, O.;
Reh, K.; Turrini, D.; Witasse, O.
2020SSRv..216...17S Altcode:
For the Ice Giants, atmospheric entry probes provide critical
measurements not attainable via remote observations. Including the
2013-2022 NASA Planetary Decadal Survey, there have been at least five
comprehensive atmospheric probe engineering design studies performed in
recent years by NASA and ESA. International science definition teams
have assessed the science requirements, and each recommended similar
measurements and payloads to meet science goals with current instrument
technology. The probe system concept has matured and converged on
general design parameters that indicate the probe would include a
1-meter class aeroshell and have a mass around 350 to 400-kg. Probe
battery sizes vary, depending on the duration of a post-release coast
phase, and assumptions about heaters and instrument power needs. The
various mission concepts demonstrate the need for advanced power and
thermal protection system development. The many completed studies show
an Ice Giant mission with an in situ probe is feasible and would be
welcomed by the international science community.
---------------------------------------------------------
Title: Saturn atmospheric dynamics one year after Cassini: Long-lived
features and time variations in the drift of the Hexagon
Authors: Hueso, R.; Sánchez-Lavega, A.; Rojas, J. F.; Simon, A. A.;
Barry, T.; Río-Gaztelurrutia, T. del; Antuñano, A.; Sayanagi, K. M.;
Delcroix, M.; Fletcher, L. N.; García-Melendo, E.; Pérez-Hoyos, S.;
Blalock, J.; Colas, F.; Gómez-Forrellad, J. M.; Gunnarson, J. L.;
Peach, D.; Wong, M. H.
2020Icar..33613429H Altcode: 2019arXiv190913849H
We examine Saturn's atmospheric dynamics with observations in the
visible range from ground-based telescopes and Hubble Space Telescope
(HST). We present a detailed analysis of observations acquired
during 2018 obtaining drift rates of major meteorological systems
from the equator to the north polar hexagon. A system of polar storms
that appeared in the planet in March 2018 and remained active with a
complex phenomenology at least until September is analyzed elsewhere
(Sánchez-Lavega et al., 2019). Many of the regular cloud features
visible in 2018 are long-lived and can be identified in Saturn
images in 2017, and in some cases, for up to a decade using also
Cassini ISS images. Without considering the polar storms, the most
interesting long-lived cloud systems are: <P />i) A bright white spot
in the Equatorial Zone that can be tracked continuously since 2014
with minimal changes in its zonal velocity, which was 444.3 ± 3.1 m
s<SUP>-1</SUP> in 2014 and 452.4 ± 1.7 m s<SUP>-1</SUP> in 2018. This
velocity is remarkably different from the zonal winds at the cloud level
at its latitude during the Cassini mission, and is closer to zonal
winds obtained at the time of the Voyagers flybys and to zonal winds
from Cassini VIMS infrared images of the lower atmosphere. <P />ii)
A large long-lived Anticyclone Vortex, here AV, that formed after the
Great White Spot of 2010-2011. This vortex has changed significantly in
visual contrast, drift rate and latitude with minor changes in size over
the last years. <P />iii) A system of subpolar vortices at latitudes
60-65°N present at least since 2011. These vortices and additional
atmospheric features here studied follow drift rates consistent with
zonal winds obtained by Cassini. <P />We also present a study of the
positions of the vertices of Saturn's north polar hexagon from 2015 to
2018. These measurements are compared with previous analyses during
the Cassini mission (2007-2014), observations with HST in the 90s,
and data from the Voyagers in 1980-1981 to explore the long-term
variability of the hexagon's drift rate. We find variations in the
drift rate of the hexagon through these epochs that can not be fit
by seasonal changes in the polar area. Instead, the different drift
rates reinforce the role of the North Polar Spot that was present in
the Voyager epoch and in the early 90s to cause a faster drift rate
of the hexagon at that time compared with the current slower one.
---------------------------------------------------------
Title: Origins Space Telescope (Origins): Solar System Science
Authors: Ennico-Smith, K.; Milam, S.; Bauer, J.; Cordiner, M.; de
Pater, I.; Fletcher, L.; Lis, D.; Lovell, A.; Moullet, A.; Orton,
G.; Villanueva, G.; Origins Solar System Working Group
2020AAS...23517108E Altcode:
The Origins Space Telescope (Origins) is a 2020 Decadal mission
concept that will trace our cosmic history, from the formation of the
first galaxies and the rise of metals and dust to the development of
habitable worlds and present-day life. With more than three orders of
magnitude improvement in sensitivity over prior far-infrared missions
and access to a spectral range spanning nearly eight octaves (2.8-588
microns), Origins vastly expands the discovery space available to the
community. Origins is also an agile observatory, capable of tracking
moving objects > 60 mas/s, and executing rapid survey science. This
presentation describes a sampling of Solar System science cases to
illustrate the capabilities of this breakthrough mission. For example,
Origins can advance our knowledge of the thermal history and present-day
climate and circulation patterns of the Giant Planets, providing a
ground-truth catalog of giant planet variability as a resource to the
exoplanet community. Origins can deliver a survey of the sizes and
thermal properties of small bodies in the outer Solar System, allowing
us to probe the history and evolution of our Solar System. No survey has
been done on this scale before. Origins can trace the origin of water on
Earth and in our Solar System by determining the D/H ratio in hundreds
of comets, providing, for the first time, a statistically-significant
sample of this critical fingerprint for the origin of water
on Earth. We thank NASA HQ, GSFC, JPL, and NASA-Ames for their
support of the study. To learn more about Origins see our websites (<A
href="https://origins.ipac.caltech.edu">https://origins.ipac.caltech.edu</A>
and <A
href="https://asd.gsfc.nasa.gov/firs/">https://asd.gsfc.nasa.gov/firs/</A>)
and report (<A
href="https://asd.gsfc.nasa.gov/firs/docs/OriginsVolume1MissionConceptStudyReport.pdf">https://asd.gsfc.nasa.gov/firs/docs/OriginsVolume1MissionConceptStudyReport.pdf</A>).
---------------------------------------------------------
Title: A Multi-Spectral Analysis of Recent Perturbations to Jupiter's
Great Red Spot in 2019
Authors: Orton, G. S.; Momary, T.; Sinclair, J. A.; Fujiyoshi, T.;
Honda, M.; Rogers, J.; Foster, C.; Eichstädt, G.; Antuñano, A.;
Fletcher, L. N.; Chowdhury, N.; Stallard, T.; Melin, H.
2019AGUFM.P21G3445O Altcode:
In the early months of 2019, various amateur planetary observers
recorded interactions between the Great Red Spot (GRS) and a series of
ring-like vortices that were transported toward its northeastern side
along the southern boundary of the South Equatorial Belt. Ultimately
these were drawn into the Great Red Spot Hollow, a bright region
surrounding the uniquely red-colored GRS itself. This resulted in their
deformation and dissolution, as well as the formation of red-colored
regions that became known as "flakes" within the Hollow on the western
side of the GRS that appear to be as bright in "methane-band" (~890-nm)
images as the interior of the GRS itself. We will report on the results
of strategic imaging results on May, 27-28, 2019, from 2.3 to 24.5 µ
m from the Subaru Telescope and the Infrared Telescope Facility that
show surprising perturbations to the atmosphere and their aftermath.
---------------------------------------------------------
Title: Saturn's Rings: Atmsopheric Effects of Ring Shadow, Ring Shine,
and Thermal Emission
Authors: Edgington, S. G.; Atreya, S. K.; West, R. A.; Baines, K.;
Fletcher, L. N.
2019AGUFM.P13B3511E Altcode:
Cassini explored for nearly a half Saturnian year. During this epoch,
in addition to seasonal solar inclination changes, the ring shadow moved
from the northern hemisphere to covering a large region of the southern
hemisphere. The intensity of both ultraviolet and visible sunlight
penetrating through the rings varied depending on Saturn's axial tilt
relative to the Sun and the optical thickness of each ring system,
i.e. the rings act like semi-transparent venetian blinds. This effect
magnifies the seasonal effect of axial tilt alone acting to reduce or
even turn off photochemistry and haze generation, an effect exhibited by
the presence of a bluish northern atmosphere in 2004 and color change to
blue in the southern hemisphere after equinox. We report on the impact
of the oscillating ring shadow, seasonal axial tilt, and solar cycle,
on photochemistry of hydrocarbons, ammonia, and phosphine in Saturn's
stratosphere and upper troposphere. The impact on the abundance of
long-lived photochemical products leading to haze formation and on
disequilibrium species is explored. Data from Cassini's CIRS, UVIS,
and VIMS datasets that provide constraints for hazes and molecular
abundances. <P />In addition to visible light reflected from the
rings, UV photons have also been shown to reflect from the rings. This
acts to enhance photolysis on the sunlit hemisphere. We examine the
impact of ultraviolet ring-shine on the photochemistry of the upper
atmosphere. Lastly, we examine the impact of thermal ring photons on
the heating of the hemisphere upon which they shine. <P />The research
described in this paper was carried out in part at the Jet Propulsion
Laboratory, California Institute of Technology, under a contract
with the National Aeronautics and Space Administration. Copyright
2019 California Institute of Technology. Government sponsorship is
acknowledged.
---------------------------------------------------------
Title: Longitudinal Variations in the Stratosphere of Uranus from
the Spitzer Infrared Spectrometer
Authors: Rowe-Gurney, N.; Fletcher, L. N.; Orton, G. S.; Roman, M. T.;
Mainzer, A.; Moses, J. I.; De Pater, I.; Irwin, P. G.
2019AGUFM.P13B3504R Altcode:
NASA's Spitzer Infrared Spectrometer (IRS) acquired mid-infrared
(5-37 μm) disc-averaged spectra of Uranus very near its equinox
over 21.7 hours on 16<SUP>th</SUP> to 17<SUP>th</SUP> of December
2007. A global-mean spectrum was constructed from observations
of multiple longitudes, spaced equally around the planet, and have
provided the opportunity for the most comprehensive globally-averaged
characterisation of Uranus' temperature and composition ever obtained
(Orton et al., 2014a,b). In this work, we analyse the disc-averaged
spectra at four separate longitudes to shed light on the discovery
of longitudinal variability occurring in Uranus' stratosphere
during the 2007 equinox. We detect a variability of up to 15% at
stratospheric altitudes sensitive to methane, ethane, and acetylene
(∼ 0.1 mbar). The tropospheric hydrogen-helium continuum exhibits a
negligible variation of less than 2%, constraining the phenomenon to
the stratosphere. Observations from Keck II NIRCII in December 2007
(Sromovsky et al., 2009; de Pater et al., 2011) and VLT/VISIR in 2009
(Roman et al. in-prep) suggest possible links to these variations in
the form of discrete meteorological features. It now seems clear that
the variations are located in the bright polar cap of emission seen
in the VLT observations. These variations were most obvious at the
boundary between the equator and the polar cap (i.e., somewhere at mid
latitudes). Building on the forward-modelling analysis of the global
average study, we present full optimal estimation inversions (using the
NEMESIS retrieval algorithm, Irwin et al., 2008) of the spectra at each
longitude to distinguish between thermal and compositional variability.
---------------------------------------------------------
Title: IRTF-TEXES observations of stratospheric CH<SUB>3</SUB>
and CH<SUB>4</SUB> emission at Jupiter's high latitudes
Authors: Sinclair, J. A.; Greathouse, T. K.; Giles, R.; Antuñano,
A.; Fouchet, T.; Bezard, B.; Clark, G. B.; Moses, J. I.; Hue, V.;
Orton, G. S.; Fletcher, L. N.; Irwin, P. G.
2019AGUFM.P21G3444S Altcode:
The neutral atmosphere, external magnetosphere and solar-wind
environment of Jupiter are coupled within Jupiter's auroral
regions. Energetic particles deposit their energy as deep as the
1-mbar level (or ~150 km above the 1-bar level) and modify the
thermal structure and chemistry of the atmosphere (Sinclair et
al., 2017, Icarus 292, 182-207, Sinclair et al., 2018, Icarus 300,
305-326). Clark et al., 2018 (JGR Space Physics 123, 7554-7567)
recently performed a comparative analysis of Juno-JEDI (Jovian Electron
Distribution Experiment, Mauk et al., 2017, SSR 213(1-4), 289-346)
and HISAKI-EXCEED (Extreme Ultraviolet Spectroscope for Exospheric
Dynamics, Yoshioka et al., 2013, P&SS 85, 250-260) ultraviolet
observations of Jupiter's aurora. They found that the agreement
between both datasets was optimized when CH<SUB>4</SUB> and other
hydrocarbons were allowed to be transported to higher altitudes in their
atmospheric model. This suggests that a phenomenon within Jupiter's
auroral regions is acting to increase the eddy diffusion coefficient
and the height of the hydrocarbon homopause. In order to test this
hypothesis, we present a retrieval analysis of IRTF-TEXES spectra of
CH<SUB>3</SUB> (methyl radical) and CH<SUB>4</SUB> emission of Jupiter's
high latitudes. Spectra were measured on February 12<SUP>th</SUP>
(coincident with Juno's 18<SUP>th</SUP> perijove), April 16<SUP>th</SUP>
and 21<SUP>st</SUP> 2019 (10 and 15 days after Juno's 19<SUP>th</SUP>
perijove, respectively). A retrieval analysis was performed to derive
the vertical profiles of temperature and CH<SUB>3</SUB> abundance
(from 20 mbar to 1 µbar) and their horizontal variation poleward of
±45º in latitude. Preliminary retrievals of spectra measured on April
16<SUP>th</SUP> 2019 demonstrate that the abundance of CH<SUB>3</SUB>
is enhanced over Jupiter's northern auroral region (60°N - pole,
150-220°W) compared to non-auroral longitudes in the same latitude
band. This is suggestive that the production rate of CH<SUB>3</SUB>
is higher and/or the hydrocarbon homopause altitude is indeed higher
in Jupiter's auroral regions.
---------------------------------------------------------
Title: Science Requirement Document (SRD) for the European Solar
Telescope (EST) (2nd edition, December 2019)
Authors: Schlichenmaier, R.; Bellot Rubio, L. R.; Collados, M.;
Erdelyi, R.; Feller, A.; Fletcher, L.; Jurcak, J.; Khomenko, E.;
Leenaarts, J.; Matthews, S.; Belluzzi, L.; Carlsson, M.; Dalmasse,
K.; Danilovic, S.; Gömöry, P.; Kuckein, C.; Manso Sainz, R.;
Martinez Gonzalez, M.; Mathioudakis, M.; Ortiz, A.; Riethmüller,
T. L.; Rouppe van der Voort, L.; Simoes, P. J. A.; Trujillo Bueno,
J.; Utz, D.; Zuccarello, F.
2019arXiv191208650S Altcode:
The European Solar Telescope (EST) is a research infrastructure
for solar physics. It is planned to be an on-axis solar telescope
with an aperture of 4 m and equipped with an innovative suite of
spectro-polarimetric and imaging post-focus instrumentation. The EST
project was initiated and is driven by EAST, the European Association
for Solar Telescopes. EAST was founded in 2006 as an association
of 14 European countries. Today, as of December 2019, EAST consists
of 26 European research institutes from 18 European countries. The
Preliminary Design Phase of EST was accomplished between 2008 and
2011. During this phase, in 2010, the first version of the EST Science
Requirement Document (SRD) was published. After EST became a project
on the ESFRI roadmap 2016, the preparatory phase started. The goal
of the preparatory phase is to accomplish a final design for the
telescope and the legal governance structure of EST. A major milestone
on this path is to revisit and update the Science Requirement Document
(SRD). The EST Science Advisory Group (SAG) has been constituted by
EAST and the Board of the PRE-EST EU project in November 2017 and has
been charged with the task of providing with a final statement on the
science requirements for EST. Based on the conceptual design, the SRD
update takes into account recent technical and scientific developments,
to ensure that EST provides significant advancement beyond the current
state-of-the-art. The present update of the EST SRD has been developed
and discussed during a series of EST SAG meetings. The SRD develops
the top-level science objectives of EST into individual science
cases. Identifying critical science requirements is one of its main
goals. Those requirements will define the capabilities of EST and the
post-focus instrument suite. The technical requirements for the final
design of EST will be derived from the SRD.
---------------------------------------------------------
Title: Jupiter's Stratosphere in the Ultraviolet: inter-annual
variability of acetylene and ethane
Authors: Melin, H.; Fletcher, L. N.
2019AGUFM.P13B3503M Altcode:
The ultraviolet spectrum of Jupiter between 150 and 200 nm is
dominated by Rayleigh scattered sunlight, augmented by absorption
from stratospheric acetylene and ethane, and tropospheric ammonia
and phosphine. Acetylene and ethane are both photochemical products of
methane, and their meridional distribution traces the global circulation
in the stratosphere. However, they are observed to have very different
distributions on the planet, attributable to their very different
chemical lifetimes - ethane can persist for several Jupiter years,
tracing the stratospheric circulation. Ammonia and phosphine are both
tracers of vertical motions in the atmosphere, lifting these species up
into the upper troposphere where they can be observed. Jupiter's Quasi
Quadrennial Oscillation (QQO) is a four-year semi-regular temperature
variation in the equatorial stratosphere of Jupiter, likely driven by
gravity waves generated by the turbulent troposphere. Here, we analyse
observations from the International Ultraviolet Explorer (IUE) space
telescope and the Astro-1 & 2 Space Shuttle missions that carried
the Hopkins Ultraviolet Telescope (HUT), obtained between 1978 and
1996, at a greater than yearly cadence, covering 1.5 jovian years. We
examine how sensitive these observations are to the abundance of ethane,
acetylene, ammonia and phosphine. Using the NEMESIS radiative transfer
and retrieval code, we examine how the vertical profiles of acetylene
and ethane evolve on jovian inter-annual, annual, seasonal, and QQO
time-scales. We also explore retrievability of ammonia and phosphine
abundance to examine how the vertical mixing changes over this period.
---------------------------------------------------------
Title: Rapid time variability of the UV spectral line profiles in
a small flare - evidence of chromospheric turbulence and heating
Authors: Fletcher, L.; Jeffrey, N. L. S.; Labrosse, N.; Simoes,
P. J. D. A.
2019AGUFMSH13D3424F Altcode:
We present observations of rapid variations in the spectral line
profiles in the B-class flare SOL2016-12-06T10:36:58 detected by the
Interface Region Imaging Spectograph (IRIS). The flare was observed at a
cadence of 1.7s, a time resolution that allows us to detect variations
during the flare rise and its rapid subsequent evolution, as follows:
(i) For Si IV 1402.77Å, the line broadens significantly above its
expected thermal width around 10 seconds prior to the flare's strong
radiative signatures. Modelling shows that in this event the Si IV
line is optically thin, so the evolving line broadening suggests
the development of transition region turbulence, leading to flare
heating; (ii) In the optically thick Mg II k line, formed deeper in
the chromosphere, marked differences appear in the time profiles of
the core and wing intensities, and there are also rapidly varying line
asymmetries and a filling in of the pre-flare central reversal of this
line. An increase in the line core width is also seen. We will discuss
possible interpretations of the evolution these two lines in the context
of evolving turbulence and chromospheric pressure, and opacity effects.
---------------------------------------------------------
Title: Herschel map of Saturn's stratospheric water, delivered by
the plumes of Enceladus
Authors: Cavalié, T.; Hue, V.; Hartogh, P.; Moreno, R.; Lellouch,
E.; Feuchtgruber, H.; Jarchow, C.; Cassidy, T.; Fletcher, L. N.;
Billebaud, F.; Dobrijevic, M.; Rezac, L.; Orton, G. S.; Rengel, M.;
Fouchet, T.; Guerlet, S.
2019A&A...630A..87C Altcode: 2019arXiv190807399C
Context. The origin of water in the stratospheres of giant planets
has been an outstanding question ever since its first detection by
the Infrared Space Observatory some 20 years ago. Water can originate
from interplanetary dust particles, icy rings and satellites, and large
comet impacts. Analyses of Herschel Space Observatory observations have
proven that the bulk of Jupiter's stratospheric water was delivered
by the Shoemaker-Levy 9 impacts in 1994. In 2006, the Cassini mission
detected water plumes at the South Pole of Enceladus, which made the
moon a serious candidate for Saturn's stratospheric water. Further
evidence was found in 2011 when Herschel demonstrated the presence
of a water torus at the orbital distance of Enceladus that was fed by
the moon's plumes. Finally, water falling from the rings onto Saturn's
uppermost atmospheric layers at low latitudes was detected during the
final orbits of Cassini's end-of-mission plunge into the atmosphere. <BR
/> Aims: In this paper, we use Herschel mapping observations of water
in Saturn's stratosphere to identify its source. <BR /> Methods: We
tested several empirical models against the Herschel-HIFI and -PACS
observations, which were collected on December 30, 2010, and January
2, 2011, respectively. <BR /> Results: We demonstrate that Saturn's
stratospheric water is not uniformly mixed as a function of latitude,
but peaks at the equator and decreases poleward with a Gaussian
distribution. We obtain our best fit with an equatorial mole fraction
1.1 ppb and a half width at half maximum of 25°, when accounting
for a temperature increase in the two warm stratospheric vortices
produced by Saturn's Great Storm of 2010-2011. <BR /> Conclusions:
This work demonstrates that Enceladus is the main source of Saturn's
stratospheric water. <P />Herschel is an ESA space observatory with
science instruments provided by European-led Principal Investigator
consortia and with important participation from NASA.
---------------------------------------------------------
Title: Achievements of Hinode in the first eleven years
Authors: Hinode Review Team; Al-Janabi, Khalid; Antolin, Patrick;
Baker, Deborah; Bellot Rubio, Luis R.; Bradley, Louisa; Brooks,
David H.; Centeno, Rebecca; Culhane, J. Leonard; Del Zanna, Giulio;
Doschek, George A.; Fletcher, Lyndsay; Hara, Hirohisa; Harra,
Louise K.; Hillier, Andrew S.; Imada, Shinsuke; Klimchuk, James A.;
Mariska, John T.; Pereira, Tiago M. D.; Reeves, Katharine K.; Sakao,
Taro; Sakurai, Takashi; Shimizu, Toshifumi; Shimojo, Masumi; Shiota,
Daikou; Solanki, Sami K.; Sterling, Alphonse C.; Su, Yingna; Suematsu,
Yoshinori; Tarbell, Theodore D.; Tiwari, Sanjiv K.; Toriumi, Shin;
Ugarte-Urra, Ignacio; Warren, Harry P.; Watanabe, Tetsuya; Young,
Peter R.
2019PASJ...71R...1H Altcode:
Hinode is Japan's third solar mission following Hinotori (1981-1982)
and Yohkoh (1991-2001): it was launched on 2006 September 22 and is in
operation currently. Hinode carries three instruments: the Solar Optical
Telescope, the X-Ray Telescope, and the EUV Imaging Spectrometer. These
instruments were built under international collaboration with the
National Aeronautics and Space Administration and the UK Science and
Technology Facilities Council, and its operation has been contributed
to by the European Space Agency and the Norwegian Space Center. After
describing the satellite operations and giving a performance evaluation
of the three instruments, reviews are presented on major scientific
discoveries by Hinode in the first eleven years (one solar cycle long)
of its operation. This review article concludes with future prospects
for solar physics research based on the achievements of Hinode.
---------------------------------------------------------
Title: Jupiter's auroral-related stratospheric heating and
chemistry III: Abundances of C<SUB>2</SUB>H<SUB>4</SUB>,
CH<SUB>3</SUB>C<SUB>2</SUB>H, C<SUB>4</SUB>H<SUB>2</SUB> and
C<SUB>6</SUB>H<SUB>6</SUB> from Voyager-IRIS and Cassini-CIRS
Authors: Sinclair, J. A.; Moses, J. I.; Hue, V.; Greathouse, T. K.;
Orton, G. S.; Fletcher, L. N.; Irwin, P. G. J.
2019Icar..328..176S Altcode:
We present an analysis of Voyager-1-IRIS and Cassini-CIRS
spectra of Jupiter's high latitudes acquired during the
spacecrafts' respective flybys in November 1979 and January
2001. We performed a forward-model analysis in order to derive the
abundances of ethylene (C<SUB>2</SUB>H<SUB>4</SUB>), methylacetylene
(CH<SUB>3</SUB>C<SUB>2</SUB>H), diacetylene (C<SUB>4</SUB>H<SUB>2</SUB>)
and benzene (C<SUB>6</SUB>H<SUB>6</SUB>) in Jupiter's northern and
southern auroral regions. We also compared these abundances to:
1) lower-latitude abundances predicted by the Moses et al. (2005)
'Model A' photochemical model, henceforth 'Moses 2005A', and
2) abundances derived at non-auroral longitudes in the same
latitude band. This paper serves as an extension of Sinclair et
al. (2017b), where we retrieved the vertical profiles of temperature,
C<SUB>2</SUB>H<SUB>2</SUB> and C<SUB>2</SUB>H<SUB>6</SUB> from similar
datasets. We find that an enrichment of C<SUB>2</SUB>H<SUB>4</SUB>,
CH<SUB>3</SUB>C<SUB>2</SUB>H and C<SUB>6</SUB>H<SUB>6</SUB> with
respect to lower-latitude abundances is required to fit the spectra
of Jupiter's northern and southern auroral regions. For example, for
CIRS 0.5 cm<SUP>-1</SUP> spectra of Jupiter's southern auroral region,
scale factor enrichments of 6.40<SUB>-1.15</SUB><SUP>+1.30</SUP>
and 9.60<SUB>-3.67</SUB><SUP>+3.98</SUP> are required with respect
to the Moses 2005A vertical profiles of C<SUB>2</SUB>H<SUB>4</SUB>
and C<SUB>6</SUB>H<SUB>6</SUB>, respectively, in order to fit
the spectral emission features of these species at ∼950 and
∼674 cm<SUP>-1</SUP>. Similarly, in order to fit the CIRS 2.5
cm<SUP>-1</SUP> spectra of Jupiter's northern auroral region, scale
factor enrichments of 1.60<SUB>-0.21</SUB><SUP>+0.37</SUP>,
3.40<SUB>-1.69</SUB><SUP>+1.89</SUP> and
15.00<SUB>-4.02</SUB><SUP>+4.01</SUP> with respect to the
Moses 2005A vertical profiles of C<SUB>2</SUB>H<SUB>4</SUB>,
CH<SUB>3</SUB>C<SUB>2</SUB>H and C<SUB>6</SUB>H<SUB>6</SUB>
were required, respectively. Outside of Jupiter's auroral
region in the same latitude bands, only upper-limit abundances
of C<SUB>2</SUB>H<SUB>4</SUB>, CH<SUB>3</SUB>C<SUB>2</SUB>H and
C<SUB>6</SUB>H<SUB>6</SUB> could be determined due to the limited
sensitivity of the measurements, the weaker emission features combined
with cooler stratospheric temperatures (and therefore decreased
thermal emission) of these regions. Nevertheless, for a subset of the
observations, derived abundances of C<SUB>2</SUB>H<SUB>4</SUB> and
C<SUB>6</SUB>H<SUB>6</SUB> in Jupiter's auroral regions were higher
(by 1 σ) with respect to upper-limit abundances derived outside
the auroral region in the same latitude band. This is suggestive
that the influx of energetic ions and electrons from the Jovian
magnetosphere and external solar-wind environment into the neutral
atmosphere in Jupiter's auroral regions drives enhanced ion-related
chemistry, as has also been inferred from Cassini observations of
Saturn's high latitudes (Fletcher et al., 2018; Guerlet et al., 2015;
Koskinen et al., 2016). We were not able to constrain the abundance
of C<SUB>4</SUB>H<SUB>2</SUB> in either Jupiter's auroral regions or
non-auroral regions due to its lower (predicted) abundance and weaker
emission feature. Thus, only upper-limit abundances were derived in
both locations. From CIRS 2.5 cm<SUP>-1</SUP> spectra, the upper limit
abundance of C<SUB>4</SUB>H<SUB>2</SUB> corresponds to a scale factor
enhancement of 45.6 and 23.8 with respect to the Moses 2005A vertical
profile in Jupiter's non-auroral and auroral regions.
---------------------------------------------------------
Title: The Role of Energy Diffusion in the Deposition of Energetic
Electron Energy in Solar and Stellar Flares
Authors: Jeffrey, Natasha L. S.; Kontar, Eduard P.; Fletcher, Lyndsay
2019ApJ...880..136J Altcode: 2019arXiv190601887J
During solar flares, a large fraction of the released magnetic energy
is carried by energetic electrons that transfer and deposit energy
in the Sun’s atmosphere. Electron transport is often approximated
by a cold thick-target model, assuming that electron energy is much
larger than the temperature of the ambient plasma, and electron energy
evolution is modeled as a systematic loss. Using kinetic modeling
of electrons, we reevaluate the transport and deposition of flare
energy. Using a full collisional warm-target model (WTM), we account
for electron thermalization and for the properties of the ambient
coronal plasma such as its number density, temperature and spatial
extent. We show that the deposition of nonthermal electron energy in the
lower atmosphere is highly dependent on the properties of the flaring
coronal plasma. In general, thermalization and a reduced WTM energy
loss rate leads to an increase of nonthermal energy transferred to
the chromosphere, and the deposition of nonthermal energy at greater
depths. The simulations show that energy is deposited in the lower
atmosphere initially by high-energy nonthermal electrons, and later by
lower energy nonthermal electrons that partially or fully thermalize
in the corona, over timescales of seconds, unaccounted for in previous
studies. This delayed heating may act as a diagnostic of both the
injected nonthermal electron distribution and the coronal plasma,
vital for constraining flare energetics.
---------------------------------------------------------
Title: The plasmoid instability in a confined solar flare
Authors: MacTaggart, David; Fletcher, Lyndsay
2019MNRAS.486L..96M Altcode: 2019MNRAS.tmpL..70M; 2019arXiv190501201M
Eruptive flares (EFs) are associated with erupting filaments and, in
some models, filament eruption drives flare reconnection. Recently,
however, observations of a confined flare (CF) have revealed all the
hallmarks of an EF (impulsive phase, flare ribbons, etc.) without the
filament eruption itself. Therefore, if the filament is not primarily
responsible for impulsive flare reconnection, what is? In this Letter,
we argue, based on mimimal requirements, that the plasmoid instability
is a strong candidate for explaining the impulsive phase in the observed
CF. We present magnetohydrodynamic simulation results of the non-linear
development of the plasmoid instability, in a model active region
magnetic field geometry, to strengthen our claim. We also discuss
how the ideas described in this Letter can be generalized to other
situations, including EFs.
---------------------------------------------------------
Title: Fast Solar Image Classification Using Deep Learning and Its
Importance for Automation in Solar Physics
Authors: Armstrong, John A.; Fletcher, Lyndsay
2019SoPh..294...80A Altcode: 2019arXiv190513575A
The volume of data being collected in solar physics has exponentially
increased over the past decade and with the introduction of the
Daniel K. Inouye Solar Telescope (DKIST) we will be entering the
age of petabyte solar data. Automated feature detection will be
an invaluable tool for post-processing of solar images to create
catalogues of data ready for researchers to use. We propose a deep
learning model to accomplish this; a deep convolutional neural network
is adept at feature extraction and processing images quickly. We train
our network using data from Hinode/Solar Optical Telescope (SOT) Hα
images of a small subset of solar features with different geometries:
filaments, prominences, flare ribbons, sunspots and the quiet Sun
(i.e. the absence of any of the other four features). We achieve near
perfect performance on classifying unseen images from SOT (≈ 99.9%)
in 4.66 seconds. We also for the first time explore transfer learning
in a solar context. Transfer learning uses pre-trained deep neural
networks to help train new deep learning models i.e. it teaches a new
model. We show that our network is robust to changes in resolution
by degrading images from SOT resolution (≈0.33<SUP>″</SUP> at λ
=6563 Å) to Solar Dynamics Observatory/Atmospheric Imaging Assembly
(SDO/AIA) resolution (≈1.2<SUP>″</SUP>) without a change in
performance of our network. However, we also observe where the network
fails to generalise to sunspots from SDO/AIA bands 1600/1700 Å due
to small-scale brightenings around the sunspots and prominences in
SDO/AIA 304 Å due to coronal emission.
---------------------------------------------------------
Title: Spectral Evidence for Heating at Large Column Mass in Umbral
Solar Flare Kernels. I. IRIS Near-UV Spectra of the X1 Solar Flare
of 2014 October 25
Authors: Kowalski, Adam F.; Butler, Elizabeth; Daw, Adrian N.;
Fletcher, Lyndsay; Allred, Joel C.; De Pontieu, Bart; Kerr, Graham S.;
Cauzzi, Gianna
2019ApJ...878..135K Altcode: 2019arXiv190502111K
The GOES X1 flare SOL2014-10-25T17:08:00 was a three-ribbon solar
flare observed with the Interface Region Imaging Spectrograph (IRIS)
in the near-UV (NUV) and far-UV. One of the flare ribbons crossed
a sunspot umbra, producing a dramatic, ∼1000% increase in the NUV
continuum radiation. We comprehensively analyze the UV spectral data
of the umbral flare brightenings, which provide new challenges for
radiative-hydrodynamic modeling of the chromospheric velocity field and
the white-light continuum radiation. The emission line profiles in the
umbral flare brightenings exhibit redshifts and profile asymmetries,
but these are significantly smaller than in another, well-studied
X-class solar flare. We present a ratio of the NUV continuum intensity
to the Fe II λ2814.45 intensity. This continuum-to-line ratio is a
new spectral diagnostic of significant heating at high column mass
(log m/[g cm<SUP>-2</SUP>] > -2) during solar flares because the
continuum and emission line radiation originate from relatively similar
temperatures but moderately different optical depths. The full spectral
readout of these IRIS data also allow for a comprehensive survey of the
flaring NUV landscape: in addition to many lines of Fe II and Cr II, we
identify a new solar flare emission line, He I λ2829.91 (as previously
identified in laboratory and early-type stellar spectra). The Fermi/GBM
hard X-ray data provide inputs to radiative-hydrodynamic models (which
will be presented in Paper II) in order to better understand the large
continuum-to-line ratios, the origin of the white-light continuum
radiation, and the role of electron beam heating in the low atmosphere.
---------------------------------------------------------
Title: A brightening of Jupiter's auroral 7.8-μm CH<SUB>4</SUB>
emission during a solar-wind compression
Authors: Sinclair, J. A.; Orton, G. S.; Fernandes, J.; Kasaba,
Y.; Sato, T. M.; Fujiyoshi, T.; Tao, C.; Vogt, M. F.; Grodent, D.;
Bonfond, B.; Moses, J. I.; Greathouse, T. K.; Dunn, W.; Giles, R. S.;
Tabataba-Vakili, F.; Fletcher, L. N.; Irwin, P. G. J.
2019NatAs...3..607S Altcode: 2019NatAs.tmp..243S
Enhanced mid-infrared emission from CH<SUB>4</SUB> and other
stratospheric hydrocarbons has been observed coincident with Jupiter's
ultraviolet auroral emission<SUP>1-3</SUP>. This suggests that auroral
processes and the neutral stratosphere of Jupiter are coupled; however,
the exact nature of this coupling is unknown. Here we present a time
series of Subaru-COMICS images of Jupiter measured at a wavelength
of 7.80 μm on 11-14 January, 4-5 February and 17-20 May 2017. These
data show that both the morphology and magnitude of the auroral
CH<SUB>4</SUB> emission vary on daily timescales in relation to external
solar-wind conditions. The southern auroral CH<SUB>4</SUB> emission
increased in brightness temperature by about 3.8 K between 15:50 ut,
11 January and 12:57 ut, 12 January, during a predicted solar-wind
compression. During the same compression, the northern auroral
emission exhibited a duskside brightening, which mimics the morphology
observed in the ultraviolet auroral emission during periods of enhanced
solar-wind pressure<SUP>4,5</SUP>. These results suggest that changes
in external solar-wind conditions perturb the Jovian magnetosphere in
such a way that energetic particles are accelerated into the planet's
atmosphere, deposit their energy as deep as the neutral stratosphere,
and modify the thermal structure, the abundance of CH<SUB>4</SUB> or
the population of energy states of CH<SUB>4</SUB>. We also find that
the northern and southern auroral CH<SUB>4</SUB> emission evolved
independently between the January, February and May images, as has
been observed at X-ray wavelengths over shorter timescales<SUP>6</SUP>
and at mid-infrared wavelengths over longer timescales<SUP>7</SUP>.
---------------------------------------------------------
Title: First Spectral Analysis of a Solar Plasma Eruption Using ALMA
Authors: Rodger, Andrew S.; Labrosse, Nicolas; Wedemeyer, Sven;
Szydlarski, Mikolaj; Simões, Paulo J. A.; Fletcher, Lyndsay
2019ApJ...875..163R Altcode: 2019arXiv190201319R
The aim of this study is to demonstrate how the logarithmic
millimeter continuum gradient observed using the Atacama Large
Millimeter/submillimeter Array (ALMA) may be used to estimate optical
thickness in the solar atmosphere. We discuss how using multiwavelength
millimeter measurements can refine plasma analysis through knowledge
of the absorption mechanisms. Here we use subband observations from
the publicly available science verification (SV) data, while our
methodology will also be applicable to regular ALMA data. The spectral
resolving capacity of ALMA SV data is tested using the enhancement
coincident with an X-ray bright point and from a plasmoid ejection
event near active region NOAA12470 observed in Band 3 (84-116 GHz) on
2015 December 17. We compute the interferometric brightness temperature
light curve for both features at each of the four constituent subbands
to find the logarithmic millimeter spectrum. We compared the observed
logarithmic spectral gradient with the derived relationship with optical
thickness for an isothermal plasma to estimate the structures’
optical thicknesses. We conclude, within 90% confidence, that the
stationary enhancement has an optical thickness between 0.02 ≤ τ
≤ 2.78, and that the moving enhancement has 0.11 ≤ τ ≤ 2.78,
thus both lie near to the transition between optically thin and thick
plasma at 100 GHz. From these estimates, isothermal plasmas with
typical Band 3 background brightness temperatures would be expected
to have electron temperatures of ∼7370-15300 K for the stationary
enhancement and between ∼7440 and 9560 K for the moving enhancement,
thus demonstrating the benefit of subband ALMA spectral analysis.
---------------------------------------------------------
Title: RADYNVERSION: Learning to Invert a Solar Flare Atmosphere
with Invertible Neural Networks
Authors: Osborne, Christopher M. J.; Armstrong, John A.; Fletcher,
Lyndsay
2019ApJ...873..128O Altcode: 2019arXiv190108626O
During a solar flare, it is believed that reconnection takes place in
the corona followed by fast energy transport to the chromosphere. The
resulting intense heating strongly disturbs the chromospheric structure
and induces complex radiation hydrodynamic effects. Interpreting the
physics of the flaring solar atmosphere is one of the most challenging
tasks in solar physics. Here we present a novel deep-learning approach,
an invertible neural network, to understanding the chromospheric
physics of a flaring solar atmosphere via the inversion of observed
solar line profiles in Hα and Ca II λ8542. Our network is trained
using flare simulations from the 1D radiation hydrodynamic code RADYN as
the expected atmosphere and line profile. This model is then applied
to single pixels from an observation of an M1.1 solar flare taken
with the Swedish 1 m Solar Telescope/CRisp Imaging SpectroPolarimeter
instrument just after the flare onset. The inverted atmospheres obtained
from observations provide physical information on the electron number
density, temperature, and bulk velocity flow of the plasma throughout
the solar atmosphere ranging from 0 to 10 Mm in height. The density and
temperature profiles appear consistent with the expected atmospheric
response, and the bulk plasma velocity provides the gradients needed
to produce the broad spectral lines while also predicting the expected
chromospheric evaporation from flare heating. We conclude that we have
taught our novel algorithm the physics of a solar flare according
to RADYN and that this can be confidently used for the analysis of
flare data taken in these two wavelengths. This algorithm can also be
adapted for a menagerie of inverse problems providing extremely fast
(∼10 μs) inversion samples.
---------------------------------------------------------
Title: Photochemistry in Saturn's Atmosphere: Ring Shadow and Ring
Reflection
Authors: Edgington, S. G.; Atreya, S. K.; Wilson, E. H.; Baines,
K. H.; West, R. A.; Bjoraker, G. L.; Fletcher, L. N.; Momary, T. W.
2019LPI....50.3053E Altcode:
This work studies the generation and variation of haze in Saturn's
atmosphere and the chemistry and solar-seasonal insolation that
modulates it.
---------------------------------------------------------
Title: The Europa Imaging System (EIS): High-Resolution, 3-D Insight
into Europa's Geology, Ice Shell, and Potential for Current Activity
Authors: Turtle, E. P.; McEwen, A. S.; Collins, G. C.; Daubar,
I. J.; Ernst, C. M.; Fletcher, L.; Hansen, C. J.; Hawkins, S. E.;
Hayes, A. G.; Humm, D.; Hurford, T. A.; Kirk, R. L.; Kutsop, N.;
Barr Mlinar, A. C.; Nimmo, F.; Patterson, G. W.; Phillips, C. B.;
Pommerol, A.; Prockter, L.; Quick, L. C.; Reynolds, E. L.; Slack,
K. A.; Soderblom, J. M.; Sutton, S.; Thomas, N.; Bland, M.
2019LPI....50.3065T Altcode:
Cameras to observe / Europa's fractured landscapes / Ice shell
mysteries.
---------------------------------------------------------
Title: Radynversion: Solar atmospheric properties during a solar flare
Authors: Osborne, Christopher M. J.; Armstrong, John A.; Fletcher,
Lyndsay
2019ascl.soft02008O Altcode:
Radynversion infers solar atmospheric properties during a solar
flare. The code is based on an Invertible Neural Network (INN) that
is trained to learn an approximate bijective mapping between the
atmospheric properties of electron density, temperature, and bulk
velocity (all as a function of altitude), and the observed Hα and Ca
II λ8542 line profiles. As information is lost in the forward process
of radiation transfer, this information is injected back into the model
during the inverse process by means of a latent space; the training
allows this latent space to be filled using an n-dimensional unit
Gaussian distribution, where n is the dimensionality of the latent
space. The code is based on a model trained by simulations made by
RADYN, a 1D non-equilibrium radiation hydrodynamic model with good
optically thick radiation treatment that does not consider magnetic
effects.
---------------------------------------------------------
Title: The Spectral Content of SDO/AIA 1600 and 1700 Å Filters from
Flare and Plage Observations
Authors: Simões, Paulo J. A.; Reid, Hamish A. S.; Milligan, Ryan O.;
Fletcher, Lyndsay
2019ApJ...870..114S Altcode: 2018arXiv180801488S
The strong enhancement of the ultraviolet emission during solar flares
is usually taken as an indication of plasma heating in the lower solar
atmosphere caused by the deposition of the energy released during
these events. Images taken with broadband ultraviolet filters by the
Transition Region and Coronal Explorer and Atmospheric Imaging Assembly
(AIA; 1600 and 1700 Å) have revealed the morphology and evolution of
flare ribbons in great detail. However, the spectral content of these
images is still largely unknown. Without knowledge of the spectral
contribution to these UV filters, the use of these rich imaging data
sets is severely limited. Aiming to solve this issue, we estimate
the spectral contributions of the AIA UV flare and plage images using
high-resolution spectra in the range 1300-1900 Å from the Skylab NRL
SO82B spectrograph. We find that the flare excess emission in AIA 1600
Å is dominated by the C IV 1550 Å doublet (26%), Si I continua (20%),
with smaller contributions from many other chromospheric lines such
as C I 1561 and 1656 Å multiplets, He II 1640 Å, and Si II 1526 and
1533 Å. For the AIA 1700 Å band, the C I 1656 Å multiplet is the
main contributor (38%), followed by He II 1640 (17%), and accompanied
by a multitude of other, weaker chromospheric lines, with minimal
contribution from the continuum. Our results can be generalized to
state that the AIA UV flare excess emission is of chromospheric origin,
while plage emission is dominated by photospheric continuum emission
in both channels.
---------------------------------------------------------
Title: Water and Volatiles in the Outer Solar System
Authors: Grasset, O.; Castillo-Rogez, J.; Guillot, T.; Fletcher,
L. N.; Tosi, F.
2019dwpp.book..191G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Continuum emission enhancements and penumbral changes observed
during flares by IRIS, ROSA, and Hinode
Authors: Zuccarello, F.; Guglielmino, S. L.; Capparelli, V.;
Mathioudakis, M.; Keys, P.; Fletcher, L.; Criscuoli, S.; Falco, M.;
Murabito, M.
2019NCimC..42...13Z Altcode: 2019arXiv190101732Z
In this paper we describe observations acquired by satellite instruments
( Hinode/SOT and IRIS) and ground-based telescopes (ROSA@DST) during
two consecutive C7.0 and X1.6 flares occurred in active region NOAA
12205 on 2014 November 7. The analysis of these data show the presence
of continuum enhancements during the evolution of the events, observed
both in ROSA images and in IRIS spectra. Moreover, we analyze the role
played by the evolution of the δ sunspots of the active region in the
flare triggering, indicating the disappearance of a large portion of
penumbra around these sunspots.
---------------------------------------------------------
Title: Contemporaneous VLA and ALMA observations of Jupiter during
the Juno mission
Authors: De Pater, I.; Sault, R. J.; Mockel, C.; Moullet, A.; Butler,
B. J.; Fletcher, L. N.; deBoer, D.; Wong, M. H.; Orton, G.; Janssen,
M. A.; Cosentino, R.; Villard, E.; Bjoraker, G. L.
2018AGUFM.P33F3897D Altcode:
In early January 2017, between Juno's perijoves PJ3 and PJ4 (near
its originally planned PJ8) we imaged Jupiter with the Very Large
Array (VLA) at 8-12 GHz and with ALMA at 100 and 230 GHz. We will
inter-compare these datasets, and compare them with VLA data obtained
in 2014, and the Juno Microwave Radiometer (MWR) data obtained during
PJ1. We will further compare these data with contemporaneous HST,
Gemini 5-micron, near-IR IRTF, and mid-IR VLT and Subaru data. The
prior VLA maps of Jupiter, obtained in 2014 at frequencies between 3
and 37 GHz, were analyzed in detail to derive the ammonia abundance as
a function of depth and latitude for our longitude-smeared maps. With
these ammonia profiles, we can match the nadir brightness temperatures
as measured by Juno/MWR during PJ1 very well. Although our VLA ammonia
profiles match the NH3 profiles derived from the Juno data by the Juno
team reasonably well in the Equatorial Zone and North Equatorial Belt,
there are noticeable differences at other latitudes. <P />References:
<P />de Pater et al., 2016. Science, 352, 1198-1201. <P />de
Pater et al., 2018. Icarus, submitted. <P />Li et al., 2017. GRL,
10.1002/2017GL073159.
---------------------------------------------------------
Title: Meeting contribution: Exploring the weather of the giant
planets via professional-amateur collaboration
Authors: Fletcher, L.
2018JBAA..128..374F Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Mid-infrared spectra and images of Jupiter's auroral regions
during perijoves 11 - 15
Authors: Sinclair, J. A.; Orton, G.; Greathouse, T. K.; Giles, R.;
Kasaba, Y.; Sato, T. M.; Watanabe, H.; Tao, C.; Gladstone, R.; Clark,
G. B.; Fletcher, L. N.; Moses, J. I.; Irwin, P. G.; Tabataba-Vakili, F.
2018AGUFM.P33F3892S Altcode:
Energetic charged particles from the Jovianmagnetosphere penetrate
the atmosphere in the polar regions and deposit their energy into
the neutral atmosphere to pressures as deep as the 1-mbar level
(or approximately 150 km above the 1 bar level). The resulting
precipitation, ion drag and joule heating warms the neutral stratosphere
and modifies the hydrocarbon chemistry (e.g. Sinclair et al., 2017a,
Icarus 292, 182-207, Sinclair et al., 2018, Icarus 300, 305-326). This
coupling of the neutral stratosphere and the magnetosphere can be
sensed by the mid-infrared emission of stratospheric CH<SUB>4</SUB>,
C<SUB>2</SUB>H<SUB>2</SUB>, C<SUB>2</SUB>H<SUB>4</SUB>and further
hydrocarbon species. Mid-infrared measurements of Jupiter's auroral
regions were performed near-contemporaneously with perijoves (PJ)
11-15 in order to sense the atmosphere-magnetosphere coupling
at stratospheric altitudes, a region poorly sampled by Juno's
instrumentation. High-spatial resolution 7.8-μm images of Jupiter's
stratospheric CH<SUB>4</SUB>emission were measured by Subaru-COMICS
(Kataza et al., 2000, Optical and IR Telescope Instrumentation and
Detectors, 4008 1144-1152) on March 31-April 1<SUP>st</SUP>(PJ12),
May 24-25<SUP>th</SUP>(PJ13). The morphology of CH<SUB>4</SUB>auroral
emission will be compared with Juno and HST measurements of the
ultraviolet auroral emission to explore the correlation of high UV
color ratios, inferred to be driven by lateral Pedersen currents,
with heating of the neutrals. High-spectral resolution IRTF-TEXES
(Lacy et al., 2002, PASP 114, 153-168) measurements of CH<SUB>4</SUB>,
C<SUB>2</SUB>H<SUB>2</SUB>, C<SUB>2</SUB>H<SUB>4</SUB>emission were
acquired on February 9-12 (PJ11) and July 11-16 (PJ14). A retrieval
analysis will be conducted to derive three-dimensional maps (altitude,
latitude, longitude) of temperature and hydrocarbon abundances at
Jupiter's high latitudes. New constraints on the vertical profile of
CH<SUB>4</SUB>in Jupiter's auroral region (Clark et al., 2018, under
review) will be adopted in this analysis to explore the effects on
retrieved parameters. Both datasets will be compared with measurements
supporting previous perijoves and the approach phase of Juno to Jupiter
to explore the longer-term variability of the auroral stratosphere.
---------------------------------------------------------
Title: Notes and News: 'New Views of Jupiter': Pro-Am collaborations
during and beyond the NASA Juno mission
Authors: Rogers, J. H.; Fletcher, L.
2018JBAA..128..321R Altcode:
An illustrated report of a pro-am workshop hosted by the Royal
Astronomical Society in Burlington House, London, on 2018 May 10-11
and on the second day in the equally handsome and historic rooms of
the Linnean Society next door. It was organised by Dr John Rogers
(BAA) and Dr Leigh Fletcher (University of Leicester), as a follow-up
to the workshop in Nice two years earlier [BAA Journal vol.126 p.199,
2016]. The workshop was principally funded by EuroPlanet with funding
from the European Union, with a contribution from the European Research
Council, and the RAS provided the venue and staff free of charge.
---------------------------------------------------------
Title: Photochemistry in Saturn's Atmosphere: Ring Shadow and Ring
Reflection
Authors: Edgington, S. G.; Atreya, S. K.; Wilson, E. H.; Baines,
K. H.; West, R. A.; Bjoraker, G. L.; Fletcher, L. N.; Momary, T.
2018AGUFM.P43E3814E Altcode:
After over thirteen years in Saturn orbit, Cassini observed for half
a Saturnian year. During this epoch, the ring shadow moved from its
northernmost extent to its southernmost. Acting like Venetian blinds,
the rings would modulate both ultraviolet and visible sunlight
penetrating through the rings. At the same time, both visible and
ultraviolet light would be reflected from the sunlit side of the rings
on the already sunlit hemisphere. Total insolation at any particular
latitude would vary depending on Saturn's axis relative to the Sun,
the optical thickness of each ring system, and ring reflectivity. These
factors effectively magnify seasonal effects due to axial tilt alone,
further influencing photochemical cycles and haze generation. This
effect was observed with the transformation of the northern hemisphere
from a relatively clear, blue Rayleigh-scattering atmosphere in 2004
to a smoggy, salmon color over the mission. We report on insolation
over Saturn's disk accounting for axis tilt, ring transmission and
reflectance, and solar cycle over Voyager and Cassini epochs. Impact on
photolysis of key hydrocarbons in Saturn's thermosphere, stratosphere,
and troposphere are explored and limits on production-loss rates
and abundance of long-lived photochemical products leading to
haze formation are placed. We assess the impact of insolation on a
disequilibrium species (e.g. phosphine) whose presence in the upper
troposphere can be used as a tracer of convective processes in the
deeper atmosphere. Analysis of Cassini's CIRS, UVIS, and VIMS datasets
are used to provide constrains on evolving haze content. Comparison
of hazes at mid-latitudes will be contrasted to those within Saturn's
hexagonal jet stream to understand evolution from a hazeless atmosphere
to a hazy one. We explore how this jet stream acts like a barrier to
transport, isolating the north polar region from photochemical hazes
generate outside of it. <P />The research described in this paper
was carried out in part at the Jet Propulsion Laboratory, California
Institute of Technology, under a contract with the National Aeronautics
and Space Administration. Copyright 2018 California Institute of
Technology. Government sponsorship is acknowledged.
---------------------------------------------------------
Title: The development of lower-atmosphere turbulence early in a
solar flare
Authors: Jeffrey, N. L. S.; Fletcher, L.; Labrosse, N.; Simões,
P. J. A.
2018SciA....4.2794J Altcode: 2018arXiv181209906J
We present the first observational study of the onset and evolution of
solar flare turbulence in the lower solar atmosphere on an unprecedented
time scale of 1.7 s using the Interface Region Imaging Spectrograph
observing plasma at a temperature of 80,000 K. At this time resolution,
nonthermal spectral line broadening, indicating turbulent velocity
fluctuations, precedes the flare onset at this temperature and is
coincident with net blue-shifts. The broadening decreases as the flare
brightens and then oscillates with a period of 10 s. These observations
are consistent with turbulence in the lower solar atmosphere at the
flare onset, heating that region as it dissipates. This challenges the
current view of energy release and transport in the standard solar flare
model, suggesting that turbulence partly heats the lower atmosphere.
---------------------------------------------------------
Title: Spatially-Resolved Spectroscopy of the Ice Giants Atmospheres:
Clouds, Seasonal Changes, and the Future in IR with JWST MIRI
Authors: Roman, M. T.; Fletcher, L. N.; Banfield, D. J.; Gierasch,
P. J.
2018AGUFM.P31B..05R Altcode:
We present results from an analysis of spatially-resolved near-IR
spectra of Uranus and Neptune and compare aerosol distributions and
observed changes over a period of six years. Data were acquired
from 2001 to 2007 using the 200-inch ( 5.1m) Hale Telescope and
the Palomar High Angular Resolution Observer (PHARO) near-infrared
adaptive optics (AO) camera system. Latitudinal variations in
aerosols are interpreted in context of notional circulation models,
while temporal changes suggest potential seasonal effects. We infer
significant reduction in aerosol scattering optical thickness in
southern latitudes between 2001 and 2007 on Uranus, in agreement with
trends reported in studies covering part of the same period using
different data and retrieval algorithms. For Neptune, latitudinal
variations in the higher aerosols are consistent with upwelling at
mid-latitudes, consistent with circulation inferred from IR spectra,
with the greatest aerosol abundances in peaking in 2002 before reaching
a minimum in 2006/2007. Best fits to both planets are consistent with
polar depletion of methane in the tropopause (>2 bar). Stratospheric
methane abundances are poorly constrained in the near IR, but generally
consistent with lower values on Uranus and values near saturation
Neptune. <P />A far greater understanding of the cloud level and
stratosphere will come with observations from the James Webb Space
Telescope (JWST). We look ahead to how the JWST MIRI instrument will
provide global, spatially resolved 5-30 μm spectroscopy of Uranus
and Neptune, thus providing an unprecedented picture of atmospheric
temperatures, winds, and composition from the troposphere to the
stratosphere. MIRI spectra will offer unique constraints for radiative,
dynamical, and chemical models of the ice giant atmospheres and lead
the way for future spacecraft missions.
---------------------------------------------------------
Title: Cyclone-related lightning near Juno's 6th orbit
Authors: Wong, M. H.; Brown, S. T.; Fletcher, L. N.; Bjoraker, G. L.;
De Pater, I.; Simon, A. A.
2018AGUFM.P33F3891W Altcode:
The densest cluster of Juno MWR lightning strikes on perijove
6 (PJ6) occurred near 49 N planetographic latitude (Brown et
al. 2018; DOI:10.1038/s41586-018-0156-5). Hubble imaging reveals
a cyclonic vortex at this location. <P />Assuming the results
of Romps et al. (2014; DOI:10.1126/science.1259100) apply to
Jupiter as well as the Earth, Jupiter's cyclones are likely to be
heavily-precipitating systems, explaining observations of depleted
volatiles in microwave spectral imaging data (de Pater et al. 2016;
DOI:10.1126/science.aaf2210). Ground-based thermal infrared imaging
and spectra show that anomalies in temperature, composition, and
cloud structure are common in low-latitude cyclonic vortices of
different types. These infrared data were acquired in early 2017
using VLT/VISIR, Gemini NIRI, Keck NIRSPEC, and IRTF iSHELL. Hubble
imaging data constrain some clouds to be deeper than 4 bar (presumably
water clouds), particularly in the PJ6 cyclone with strong lightning
activity. Large cyclones feature differences in high-altitude particle
properties relative to their surroundings, consistent with downwelling
and sublimation of haze particles in the upper troposphere. Warm, dry,
and less-hazy conditions in the upper part of cyclones are consistent
with downwelling aloft, while deep water clouds and lightning are
consistent with upwelling at depth, precisely the inverse of the
circulation within anticyclonic vortices according to Marcus et
al. (2013; DOI:10.1115/1.4007666). This vortex structure suggests that
midplanes of cyclones with lightning activity lie between the upper
troposphere and the water cloud layer. Cyclones without water clouds
and lightning may exist if their midplanes lie deeper than the water
cloud layer.
---------------------------------------------------------
Title: Detection of Three-minute Oscillations in Full-disk Lyman-alpha
Emission during a Solar Flare
Authors: Milligan, Ryan O.; Fleck, Bernhard; Ireland, Jack; Fletcher,
Lyndsay; Dennis, Brian R.
2018csc..confE..36M Altcode:
In a recent study of spatially-integrated Lyman-alpha line emission
(Lya, 1216A) from GOES/EUVS, we detected the presence of acoustic
3-minute oscillations during an X-class solar flare. Similar
periodicities were also found - in phase - in Lyman continuum data from
SDO/EVE, and the 1600A and 1700A channels on SDO/AIA. The implication
is that the chromosphere responds dynamically at its acoustic cutoff
frequency to an impulsive injection of energy. Since the 3-minute
period was not detected at hard X-ray energies in RHESSI data we can
state that this 3-minute oscillation does not depend on the rate of
energisation of non-thermal electrons. This finding suggests that
chromospheric mechanical energy should be included in the flare
energy budget, and that fluctuations in Lya emission may influence
the composition and dynamics of planetary atmospheres during periods
of high activity. Knowledge of the behaviour of this emission during
flares could be important when interpreting future science results
from the EUI instrument on Solar Orbiter which will obtain high cadence
images in Lya.
---------------------------------------------------------
Title: The spectral content of SDO/AIA 1600 and 1700 A filters from
flare and plage observations
Authors: Simoes, Paulo; Reid, Hamish; Milligan, Ryan; Fletcher, Lyndsay
2018csc..confE.125S Altcode:
The strong enhancement of the ultraviolet emission during solar
flares is usually taken as an indication of plasma heating in the
low solar atmosphere caused by the deposition of the energy released
during these events. Images taken with broadband ultraviolet filters
by the Transition Region and Coronal Explorer (TRACE) and Atmospheric
Imaging Assembly (AIA 1600 and 1700 Å) have revealed the morphology
and evolution of flare ribbons in great detail. However, the spectral
content of these images is still largely unknown. Without the knowledge
of the spectral contribution to these UV filters, the use of these rich
imaging datasets is severely limited. Aiming to solve this issue, we
estimate the spectral contributions of the AIA UV flare and plage images
using high-resolution spectra in the range 1300 to 1900 Å from the
Skylab NRL SO82B spectrograph. We find that the flare excess emission in
AIA 1600 Å is composed of the C IV 1550 Å doublet (26%), Si I continua
(20%), with smaller contributions from many other chromospheric lines
such as C I 1561 and 1656 Å multiplets, He II 1640 Å, Si II 1526 and
1533 Å. For the AIA 1700 Å band, C I 1656 Å multiplet is the main
contributor (38%), followed by He II 1640 (17%), and accompanied by a
multitude of other chromospheric lines, with minimal contribution from
the continuum. Our results can be generalized to state that the AIA UV
flare excess emission is of chromospheric origin, while plage emission
is dominated by photospheric continuum emission in both channels.
---------------------------------------------------------
Title: Characterization of Mesoscale Waves in the Jupiter NEB by
Jupiter InfraRed Auroral Mapper on board Juno
Authors: Adriani, A.; Moriconi, M. L.; Altieri, F.; Sindoni, G.;
Ingersoll, A. P.; Grassi, D.; Mura, A.; Atreya, S. K.; Orton, G.;
Lunine, J. I.; Fletcher, L. N.; Simon, A. A.; Melin, H.; Tosi, F.;
Cicchetti, A.; Noschese, R.; Sordini, R.; Levin, S.; Bolton, J.;
Plainaki, C.; Olivieri, A.
2018AJ....156..246A Altcode:
In 2017, the Jupiter InfraRed Auroral Mapper (JIRAM), on board the
NASA-ASI Juno mission, observed a wide longitude region (50° W-80° E
in System III) that was perturbed by a wave pattern centered at 15° N
in the Jupiter’s North Equatorial Belt (NEB). We analyzed JIRAM data
acquired on 2017 July 10 using the M-channel and on 2017 February 2 with
the spectrometer. The two observations occurred at different times and
at slightly different latitudes. The waves appear as clouds blocking
the deeper thermal emission. The wave crests are oriented north-south,
and the typical wave packet contains 10 crests and 10 troughs. We used
Fourier analysis to rigorously determine the wavenumbers associated
with the observed patterns at a confidence level of 90%. Wavelet
analysis was also used to constrain the spatial localization of the
largest energies involved in the process and determine the wavelengths
carrying the major contribution. We found wavelengths ranging from 1400
to 1900 km, and generally decreasing toward the west. Where possible,
we also computed a vertical location of the cloud pressure levels
from the inversion of the spectral radiances measured by the JIRAM
spectrometer. The waves were detected at pressure levels consistent with
the NH<SUB>3</SUB> as well as NH<SUB>4</SUB>SH clouds. Phase velocities
could not be determined with sufficient confidence to discriminate
whether the alternating crests and troughs are a propagating wave or
a manifestation of a fluid dynamical instability.
---------------------------------------------------------
Title: A hexagon in Saturn's northern stratosphere surrounding the
emerging summertime polar vortex
Authors: Fletcher, L. N.; Orton, G. S.; Sinclair, J. A.; Guerlet,
S.; Read, P. L.; Antuñano, A.; Achterberg, R. K.; Flasar, F. M.;
Irwin, P. G. J.; Bjoraker, G. L.; Hurley, J.; Hesman, B. E.; Segura,
M.; Gorius, N.; Mamoutkine, A.; Calcutt, S. B.
2018NatCo...9.3564F Altcode: 2018arXiv180900572F
Saturn's polar stratosphere exhibits the seasonal growth and dissipation
of broad, warm vortices poleward of 75° latitude, which are strongest
in the summer and absent in winter. The longevity of the exploration
of the Saturn system by Cassini allows the use of infrared spectroscopy
to trace the formation of the North Polar Stratospheric Vortex (NPSV),
a region of enhanced temperatures and elevated hydrocarbon abundances at
millibar pressures. We constrain the timescales of stratospheric vortex
formation and dissipation in both hemispheres. Although the NPSV formed
during late northern spring, by the end of Cassini's reconnaissance
(shortly after northern summer solstice), it still did not display the
contrasts in temperature and composition that were evident at the south
pole during southern summer. The newly formed NPSV was bounded by a
strengthening stratospheric thermal gradient near 78°N. The emergent
boundary was hexagonal, suggesting that the Rossby wave responsible
for Saturn's long-lived polar hexagon—which was previously expected
to be trapped in the troposphere—can influence the stratospheric
temperatures some 300 km above Saturn's clouds.
---------------------------------------------------------
Title: Modeling of the Hydrogen Lyman Lines in Solar Flares
Authors: Brown, Stephen A.; Fletcher, Lyndsay; Kerr, Graham S.;
Labrosse, Nicolas; Kowalski, Adam F.; De La Cruz Rodríguez, Jaime
2018ApJ...862...59B Altcode: 2018arXiv180703373B
The hydrogen Lyman lines (91.2 nm < λ < 121.6 nm) are significant
contributors to the radiative losses of the solar chromosphere, and
they are enhanced during flares. We have shown previously that the Lyman
lines observed by the Extreme Ultraviolet Variability instrument onboard
the Solar Dynamics Observatory exhibit Doppler motions equivalent
to speeds on the order of 30 km s<SUP>-1</SUP>. However, contrary to
expectations, both redshifts and blueshifts were present and no dominant
flow direction was observed. To understand the formation of the Lyman
lines, particularly their Doppler motions, we have used the radiative
hydrodynamic code, RADYN, along with the radiative transfer code, RH,
to simulate the evolution of the flaring chromosphere and the response
of the Lyman lines during solar flares. We find that upflows in the
simulated atmospheres lead to blueshifts in the line cores, which
exhibit central reversals. We then model the effects of the instrument
on the profiles, using the Extreme Ultraviolet Variability Experiment
(EVE) instrument's properties. What may be interpreted as downflows
(redshifted emission) in the lines, after they have been convolved
with the instrumental line profile, may not necessarily correspond to
actual downflows. Dynamic features in the atmosphere can introduce
complex features in the line profiles that will not be detected by
instruments with the spectral resolution of EVE, but which leave more
of a signature at the resolution of the Spectral Investigation of the
Coronal Environment instrument onboard the Solar Orbiter.
---------------------------------------------------------
Title: Observing turbulence early in a solar flare with the high
time resolution of IRIS
Authors: Jeffrey, Natasha; Simões, Paulo; Fletcher, Lyndsay;
Labrosse, Nicolas
2018cosp...42E1609J Altcode:
Wave and turbulent dissipation play a key role in the transfer of energy
in magnetized plasmas. Here we report the first high time-resolution,
<2 s, spectroscopic study of flare turbulence in the lower solar
atmosphere, using the Interface Region Imaging Spectrograph (IRIS). We
observe the line Si IV 1402.77 Å, formed at a transition region
temperature of 80000 K, at the eastern flare footpoint, over a region
of <0.3” during the flare duration. The non-thermal broadening
indicates turbulent motions with velocities of 60-70 km/s. The line
broadening rises sharply, and precedes the flare onset as indicated
by its impulsive radiation signatures in Si IV intensity, extreme
ultraviolet (EUV) and X-rays. The <2 s cadence shows that the
line broadening oscillates with a period of ∼10 s before its decay,
coinciding with motions in the Si IV line centroid position. The results
are consistent with the dissipation of turbulent energy in the lower
atmosphere, early in the solar flare, and before the flare brightening.
---------------------------------------------------------
Title: Spectroscopic measurements of the ion velocity distribution
at the base of the fast solar wind
Authors: Jeffrey, Natasha; Savin, Daniel W.; Hahn, Michael; Fletcher,
Lyndsay
2018cosp...42E1608J Altcode:
In situ measurements of the fast solar wind reveal non-thermal
distributions of electrons, protons and, minor ions extending from
0.3 AU to the heliopause. The physical mechanisms responsible for
these non-thermal properties and the location where these properties
originate remain open questions. Here we present spectroscopic evidence,
from extreme ultraviolet spectroscopy, that the velocity distribution
functions (VDFs) of minor ions are already non-Gaussian at the base
of the fast solar wind in a coronal hole, at altitudes of < 1.1
R_{⊙}. Analysis of Fe, Si, and Mg spectral lines reveal a peaked
line-shape core and broad wings that can be characteristed by a kappa
VDF. A kappa distribution fit gives very small kappa indices off-limb
of κ≈ 1.9-2.5, indicating either (a) ion populations far from
thermal equilibrium, (b) fluid motions such as non-Gaussian turbulent
fluctuations or non-uniform wave motions, or (c) some combination
of both. These observations provide important empirical constraints
for the source region of the fast solar wind and for the theoretical
models of the different acceleration, heating, and energy deposition
processes therein. To the best of our knowledge, this is the first
time that the ion VDF in the fast solar wind has been probed so close
to its source region. The findings are also a timely precursor to the
upcoming 2018 launch of the Parker Solar Probe, which will provide the
closest in situ measurements of the solar wind at approximately 0.04 AU
(8.5 solar radii).
---------------------------------------------------------
Title: Thermal Emission From Saturn's Polar Cyclones
Authors: Achterberg, R. K.; Flasar, F. M.; Bjoraker, G. L.; Hesman,
B. E.; Gorius, N. J. P.; Mamoutkine, A. A.; Fletcher, L. N.; Segura,
M. E.; Edgington, S. G.; Brooks, S. M.
2018GeoRL..45.5312A Altcode:
We have used data from the Cassini Composite Infrared Spectrometer to
map the temperatures in Saturn's polar cyclones at the highest spatial
resolution obtained during the Cassini mission. We find temperature
contrasts of 7 K in the upper troposphere within 1.4° of both poles,
roughly 50 percent larger than earlier measurements at lower spatial
resolution. The polar hot spots weaken with depth, disappearing near
500 mbar. In the stratosphere, the polar hot spot becomes broader,
extending 4° from the poles, and weakens with altitude disappearing
near 1 mbar. A thermal relaxation model shows that the tropospheric
hot spot is consistent with adiabatic heating from subsidence with
a vertical velocity of about -0.05 mm/s above 500 mbar. The observed
temperature gradients imply that the winds in the polar cyclone decay
with increasing altitude over roughly three pressure scale heights
above the 200-mbar level.
---------------------------------------------------------
Title: Scientific rationale for Uranus and Neptune in situ
explorations
Authors: Mousis, O.; Atkinson, D. H.; Cavalié, T.; Fletcher, L. N.;
Amato, M. J.; Aslam, S.; Ferri, F.; Renard, J. -B.; Spilker, T.;
Venkatapathy, E.; Wurz, P.; Aplin, K.; Coustenis, A.; Deleuil, M.;
Dobrijevic, M.; Fouchet, T.; Guillot, T.; Hartogh, P.; Hewagama, T.;
Hofstadter, M. D.; Hue, V.; Hueso, R.; Lebreton, J. -P.; Lellouch,
E.; Moses, J.; Orton, G. S.; Pearl, J. C.; Sánchez-Lavega, A.;
Simon, A.; Venot, O.; Waite, J. H.; Achterberg, R. K.; Atreya, S.;
Billebaud, F.; Blanc, M.; Borget, F.; Brugger, B.; Charnoz, S.;
Chiavassa, T.; Cottini, V.; d'Hendecourt, L.; Danger, G.; Encrenaz,
T.; Gorius, N. J. P.; Jorda, L.; Marty, B.; Moreno, R.; Morse, A.;
Nixon, C.; Reh, K.; Ronnet, T.; Schmider, F. -X.; Sheridan, S.; Sotin,
C.; Vernazza, P.; Villanueva, G. L.
2018P&SS..155...12M Altcode: 2017arXiv170800235M
The ice giants Uranus and Neptune are the least understood class
of planets in our solar system but the most frequently observed
type of exoplanets. Presumed to have a small rocky core, a deep
interior comprising ∼70% heavy elements surrounded by a more
dilute outer envelope of H<SUB>2</SUB> and He, Uranus and Neptune
are fundamentally different from the better-explored gas giants
Jupiter and Saturn. Because of the lack of dedicated exploration
missions, our knowledge of the composition and atmospheric processes
of these distant worlds is primarily derived from remote sensing
from Earth-based observatories and space telescopes. As a result,
Uranus's and Neptune's physical and atmospheric properties remain
poorly constrained and their roles in the evolution of the Solar System
not well understood. Exploration of an ice giant system is therefore
a high-priority science objective as these systems (including the
magnetosphere, satellites, rings, atmosphere, and interior) challenge
our understanding of planetary formation and evolution. Here we
describe the main scientific goals to be addressed by a future in
situ exploration of an ice giant. An atmospheric entry probe targeting
the 10-bar level, about 5 scale heights beneath the tropopause, would
yield insight into two broad themes: i) the formation history of the
ice giants and, in a broader extent, that of the Solar System, and ii)
the processes at play in planetary atmospheres. The probe would descend
under parachute to measure composition, structure, and dynamics, with
data returned to Earth using a Carrier Relay Spacecraft as a relay
station. In addition, possible mission concepts and partnerships are
presented, and a strawman ice-giant probe payload is described. An
ice-giant atmospheric probe could represent a significant ESA
contribution to a future NASA ice-giant flagship mission.
---------------------------------------------------------
Title: The Origin of White Light Flares: A parameter study of standard
model solar flare RHD Simulations
Authors: Kerr, Graham Stewart; de Aguiar Simoes, Paulo Jose; Fletcher,
Lyndsay; Allred, Joel C.; Kowalski, Adam F.
2018tess.conf30490K Altcode:
The bulk of the enhanced radiation emitted during solar flares
originates from the lower atmosphere, making it a crucial region for
understanding energy and radiation transport during flares. Of the
radiation emitted from the lower atmosphere a significant contribution
is from enhancements to the optical continuum (white light flares;
WLFs). There is still no consensus regarding the emission mechanism
responsible for WLFs, in part due to the paucity of broadband WLF
spectra, leading to ambiguity. Two commonly proposed mechanisms are
optically thin recombination radiation in the chromosphere resulting
from overionisation during the flare or optically thick radiation from
the photosphere/upper photosphere resulting from enhanced H- opacity
(an enhanced blackbody spectrum). Each mechanism can impose strong
constraints on models of energy transport. Of course a combination of
mechanisms is also possible. In the standard flare model, energy is
transported to the chromosphere via a beam of non-thermal electrons. To
address how WLFs would be produced in this standard model we performed
a parameter study, simulating 43 flares using RADYN, a radiation
hydrodynamics flare code. This study covered a range of typical
non-thermal electron beam distributions and energy fluxes. It was
found that in all cases the peak flare contribution to WLFs originated
in the upper chromosphere as a result of recombinations. For harder
non-thermal electron distributions there was also a non-negligible
contribution of H- emission from the lower chromosphere and upper
photosphere owing to an extended region of increased electron density
(itself resulting from stronger, more deeply penetrating, non-thermal
collisional ionisation rates). From this we predict that flares with a
harder non-thermal electron distribution may exhibit a larger vertical
extent when viewed on the limb. We were unable to simulate solely
optically thick sources of WLFs. Our simulated WLF spectra are in
good agreement with recent observations. Not all of our simulations
resulted in an observable WLF. In lower energy simulations, flare
energy input resulted in an enhanced opacity in the upper atmosphere
but without sufficient ionization/recombination to produce a strong
enough emissivity to counter the opacity. Thus we find that not all
flares are white light flares.
---------------------------------------------------------
Title: Unambiguous Evidence of Coronal Implosions during Solar
Eruptions and Flares
Authors: Wang, Juntao; Simões, P. J. A.; Fletcher, L.
2018ApJ...859...25W Altcode: 2018arXiv180402354W
In the implosion conjecture, coronal loops contract as the result
of magnetic energy release in solar eruptions and flares. However,
after almost two decades, observations of this phenomenon are still
rare and most previous reports are plagued by projection effects so
that loop contraction could be either true implosion or just a change
in loop inclination. In this paper, to demonstrate the reality of loop
contractions in the global coronal dynamics, we present four events
with the continuously contracting loops in an almost edge-on geometry
from the perspective of SDO/AIA, which are free from the ambiguity
caused by the projection effects, also supplemented by contemporary
observations from STEREO for examination. In the wider context of
observations, simulations and theories, we argue that the implosion
conjecture is valid in interpreting these events. Furthermore, distinct
properties of the events allow us to identify two physical categories of
implosion. One type demonstrates a rapid contraction at the beginning of
the flare impulsive phase, as magnetic free energy is removed rapidly
by a filament eruption. The other type, which has no visible eruption,
shows a continuous loop shrinkage during the entire flare impulsive
phase, which we suggest shows the ongoing conversion of magnetic free
energy in a coronal volume. Corresponding scenarios are described that
can provide reasonable explanations for the observations. We also
point out that implosions may be suppressed in cases when a heavily
mass-loaded filament is involved, possibly serving as an alternative
account for their observational rarity.
---------------------------------------------------------
Title: Assessing the long-term variability of acetylene and ethane
in the stratosphere of Jupiter
Authors: Melin, Henrik; Fletcher, L. N.; Donnelly, P. T.; Greathouse,
T. K.; Lacy, J. H.; Orton, G. S.; Giles, R. S.; Sinclair, J. A.;
Irwin, P. G. J.
2018Icar..305..301M Altcode: 2018arXiv180100652M
Acetylene (C<SUB>2</SUB>H<SUB>2</SUB>) and ethane
(C<SUB>2</SUB>H<SUB>6</SUB>) are both produced in the stratosphere
of Jupiter via photolysis of methane (CH<SUB>4</SUB>). Despite this
common source, the latitudinal distribution of the two species is
radically different, with acetylene decreasing in abundance towards
the pole, and ethane increasing towards the pole. We present six years
of NASA IRTF TEXES mid-infrared observations of the zonally-averaged
emission of methane, acetylene and ethane. We confirm that the
latitudinal distributions of ethane and acetylene are decoupled, and
that this is a persistent feature over multiple years. The acetylene
distribution falls off towards the pole, peaking at ∼ 30°N with
a volume mixing ratio (VMR) of ∼ 0.8 parts per million (ppm) at 1
mbar and still falling off at ± 70° with a VMR of ∼ 0.3 ppm. The
acetylene distributions are asymmetric on average, but as we move from
2013 to 2017, the zonally-averaged abundance becomes more symmetric
about the equator. We suggest that both the short term changes in
acetylene and its latitudinal asymmetry is driven by changes to the
vertical stratospheric mixing, potentially related to propagating
wave phenomena. Unlike acetylene, ethane has a symmetric distribution
about the equator that increases toward the pole, with a peak mole
fraction of ∼ 18 ppm at about ± 50° latitude, with a minimum at
the equator of ∼ 10 ppm at 1 mbar. The ethane distribution does not
appear to respond to mid-latitude stratospheric mixing in the same
way as acetylene, potentially as a result of the vertical gradient of
ethane being much shallower than that of acetylene. The equator-to-pole
distributions of acetylene and ethane are consistent with acetylene
having a shorter lifetime than ethane that is not sensitive to longer
advective timescales, but is augmented by short-term dynamics, such
as vertical mixing. Conversely, the long lifetime of ethane allows it
to be transported to higher latitudes faster than it can be chemically
depleted.
---------------------------------------------------------
Title: Spectroscopic Measurements of the Ion Velocity Distribution
at the Base of the Fast Solar Wind
Authors: Jeffrey, Natasha L. S.; Hahn, Michael; Savin, Daniel W.;
Fletcher, Lyndsay
2018EGUGA..20.1620J Altcode:
In situ measurements of the fast solar wind reveal non-thermal
distributions of electrons, protons and, minor ions extending from
0.3 AU to the heliopause. The physical mechanisms responsible for
these non-thermal properties and the location where these properties
originate remain open questions. Here we present spectroscopic
evidence, from extreme ultraviolet spectroscopy, that the velocity
distribution functions (VDFs) of minor ions are already non-Gaussian
at the base of the fast solar wind in a coronal hole, at altitudes of
< 1.1R⊙. Analysis of Fe, Si, and Mg spectral lines reveal a peaked
line-shape core and broad wings that can be characteristed by a kappa
VDF. A kappa distribution fit gives very small kappa indices off-limb
of κ ≈ 1.9 - 2.5, indicating either (a) ion populations far from
thermal equilibrium, (b) fluid motions such as non-Gaussian turbulent
fluctuations or non-uniform wave motions, or (c) some combination
of both. These observations provide important empirical constraints
for the source region of the fast solar wind and for the theoretical
models of the different acceleration, heating, and energy deposition
processes therein. To the best of our knowledge, this is the first
time that the ion VDF in the fast solar wind has been probed so close
to its source region. The findings are also a timely precursor to the
upcoming 2018 launch of the Parker Solar Probe, which will provide the
closest in situ measurements of the solar wind at approximately 0.04 AU
(8.5 solar radii).
---------------------------------------------------------
Title: The quest for H_3^+ at Neptune: deep burn observations with
NASA IRTF iSHELL
Authors: Melin, H.; Fletcher, L. N.; Stallard, T. S.; Johnson, R. E.;
O'Donoghue, J.; Moore, L.; Donnelly, P. T.
2018MNRAS.474.3714M Altcode: 2017arXiv171108978M
Emission from the molecular ion H_3^+ is a powerful diagnostic
of the upper atmosphere of Jupiter, Saturn, and Uranus, but it
remains undetected at Neptune. In search of this emission, we present
near-infrared spectral observations of Neptune between 3.93 and 4.00 μm
taken with the newly commissioned iSHELL instrument on the NASA Infrared
Telescope Facility in Hawaii, obtained 2017 August 17-20. We spent
15.4 h integrating across the disc of the planet, yet were unable to
unambiguously identify any H_3^+ line emissions. Assuming a temperature
of 550 K, we derive an upper limit on the column integrated density of
1.0^{+1.2}_{-0.8}× 10^{13} m<SUP>-2</SUP>, which is an improvement of
30 per cent on the best previous observational constraint. This result
means that models are overestimating the density by at least a factor
of 5, highlighting the need for renewed modelling efforts. A potential
solution is strong vertical mixing of polyatomic neutral species from
Neptune's upper stratosphere to the thermosphere, reacting with H_3^+,
thus greatly reducing the column integrated H_3^+ densities. This upper
limit also provide constraints on future attempts at detecting H_3^+
using the James Webb Space Telescope.
---------------------------------------------------------
Title: Spectroscopic Measurements of the Ion Velocity Distribution
at the Base of the Fast Solar Wind
Authors: Jeffrey, Natasha L. S.; Hahn, Michael; Savin, Daniel W.;
Fletcher, Lyndsay
2018ApJ...855L..13J Altcode: 2018arXiv180207104J
In situ measurements of the fast solar wind reveal non-thermal
distributions of electrons, protons, and minor ions extending from
0.3 au to the heliopause. The physical mechanisms responsible for
these non-thermal properties and the location where these properties
originate remain open questions. Here, we present spectroscopic
evidence, from extreme ultraviolet spectroscopy, that the velocity
distribution functions (VDFs) of minor ions are already non-Gaussian
at the base of the fast solar wind in a coronal hole, at altitudes
of <1.1 R <SUB>⊙</SUB>. Analysis of Fe, Si, and Mg spectral
lines reveals a peaked line-shape core and broad wings that can be
characterized by a kappa VDF. A kappa distribution fit gives very
small kappa indices off-limb of κ ≈ 1.9-2.5, indicating either (a)
ion populations far from thermal equilibrium, (b) fluid motions such
as non-Gaussian turbulent fluctuations or non-uniform wave motions,
or (c) some combination of both. These observations provide important
empirical constraints for the source region of the fast solar wind
and for the theoretical models of the different acceleration, heating,
and energy deposition processes therein. To the best of our knowledge,
this is the first time that the ion VDF in the fast solar wind has
been probed so close to its source region. The findings are also a
timely precursor to the upcoming 2018 launch of the Parker Solar Probe,
which will provide the closest in situ measurements of the solar wind
at approximately 0.04 au (8.5 solar radii).
---------------------------------------------------------
Title: Equatorial Oscillation and Planetary Wave Activity in Saturn's
Stratosphere Through the Cassini Epoch
Authors: Guerlet, S.; Fouchet, T.; Spiga, A.; Flasar, F. M.; Fletcher,
L. N.; Hesman, B. E.; Gorius, N.
2018JGRE..123..246G Altcode:
Thermal infrared spectra acquired by Cassini/Composite InfraRed
Spectrometer (CIRS) in limb-viewing geometry in 2015 are used to derive
2-D latitude-pressure temperature and thermal wind maps. These maps
are used to study the vertical structure and evolution of Saturn's
equatorial oscillation (SEO), a dynamical phenomenon presenting
similarities with the Earth's quasi-biennal oscillation (QBO) and
semi-annual oscillation (SAO). We report that a new local wind maximum
has appeared in 2015 in the upper stratosphere and derive the descent
rates of other wind extrema through time. The phase of the oscillation
observed in 2015, as compared to 2005 and 2010, remains consistent with
a ∼15 year period. The SEO does not propagate downward at a regular
rate but exhibits faster descent rate in the upper stratosphere,
combined with a greater vertical wind shear, compared to the lower
stratosphere. Within the framework of a QBO-type oscillation, we
estimate the absorbed wave momentum flux in the stratosphere to be
on the order of ∼7 × 10<SUP>-6</SUP> N m<SUP>-2</SUP>. On Earth,
interactions between vertically propagating waves (both planetary
and mesoscale) and the mean zonal flow drive the QBO and SAO. To
broaden our knowledge on waves potentially driving Saturn's equatorial
oscillation, we searched for thermal signatures of planetary waves
in the tropical stratosphere using CIRS nadir spectra. Temperature
anomalies of amplitude 1-4 K and zonal wave numbers 1 to 9 are
frequently observed, and an equatorial Rossby (n = 1) wave of zonal
wave number 3 is tentatively identified in November 2009.
---------------------------------------------------------
Title: Jupiter's auroral-related stratospheric heating and chemistry
II: Analysis of IRTF-TEXES spectra measured in December 2014
Authors: Sinclair, J. A.; Orton, G. S.; Greathouse, T. K.; Fletcher,
L. N.; Moses, J. I.; Hue, V.; Irwin, P. G. J.
2018Icar..300..305S Altcode:
We present a retrieval analysis of TEXES (Texas Echelon Cross
Echelle Spectrograph (Lacy et al., 2002)) spectra of Jupiter's high
latitudes obtained on NASA's Infrared Telescope Facility on December
10 and 11th 2014. The vertical temperature profile and vertical
profiles of C<SUB>2</SUB>H<SUB>2</SUB>, C<SUB>2</SUB>H<SUB>4</SUB>
and C<SUB>2</SUB>H<SUB>6</SUB> were retrieved at both high-northern
and high-southern latitudes and results were compared in 'quiescent'
regions and regions known to be affected by Jupiter's aurora in order
to highlight how auroral processes modify the thermal structure
and hydrocarbon chemistry of the stratosphere. In qualitative
agreement with Sinclair et al. (2017a), we find temperatures in
auroral regions to be elevated with respect to quiescent regions
at two discrete pressures levels at approximately 1 mbar and 0.01
mbar. For example, in comparing retrieved temperatures at 70°N,
60°W (a representative quiescent region) and 70°N, 180°W (centred
on the northern auroral oval), temperatures increase by 19.0 ± 4.2
K at 0.98 mbar, 20.8 ± 3.9 K at 0.01 mbar but only by 8.3 ± 4.9
K at the intermediate level of 0.1 mbar. We conclude that elevated
temperatures at 0.01 mbar result from heating by joule resistance
of the atmosphere and the energy imparted by electron and ion
precipitation. However, temperatures at 1 mbar are considered to result
either from heating by shortwave radiation of aurorally-produced haze
particulates or precipitation of higher energy population of charged
particles. Our former conclusion would be consistent with results of
auroral-chemistry models, that predict the highest number densities of
aurorally-produced haze particles at this pressure level (Wong et al.,
2000, 2003). C<SUB>2</SUB>H<SUB>2</SUB> and C<SUB>2</SUB>H<SUB>4</SUB>
exhibit enrichments but C<SUB>2</SUB>H<SUB>6</SUB> remains constant
within uncertainty when comparing retrieved concentrations in the
northern auroral region with quiescent longitudes in the same latitude
band. At 1 mbar, C<SUB>2</SUB>H<SUB>2</SUB> increases from 278.4 ± 40.3
ppbv at 70°N, 60°W to 564.4 ± 72.0 ppbv at 70°N, 180°W and at 0.01
mbar, over the same longitude range at 70°N, C<SUB>2</SUB>H<SUB>4</SUB>
increases from 0.669 ± 0.129 ppmv to 6.509 ± 0.811 ppmv. However,
we note that non-LTE (local thermodynamic equilibrium) emission
may affect the cores of the strongest C<SUB>2</SUB>H<SUB>2</SUB> and
C<SUB>2</SUB>H<SUB>4</SUB> lines on the northern auroral region, which
may be a possible source of error in our derived concentrations. We
retrieved concentrations of C<SUB>2</SUB>H<SUB>6</SUB> at 1 mbar of
9.03 ± 0.98 ppmv at 70°N, 60°W and 7.66 ± 0.70 ppmv at 70°N,
180°W. Thus, C<SUB>2</SUB>H<SUB>6</SUB>'s concentration appears
constant (within uncertainty) as a function of longitude at 70°N.
---------------------------------------------------------
Title: Detection of 3-Minute Oscillations in Full-Disk Lyman-alpha
Emission During A Solar Flare
Authors: Milligan, R. O.; Ireland, J.; Fleck, B.; Hudson, H. S.;
Fletcher, L.; Dennis, B. R.
2017AGUFMSH41A2739M Altcode:
We report the detection of chromospheric 3-minute oscillations in
disk-integrated EUV irradiance observations during a solar flare. A
wavelet analysis of detrended Lyman-alpha (from GOES/EUVS) and
Lyman continuum (from SDO/EVE) emission from the 2011 February 15
X-class flare revealed a 3-minute period present during the flare's
main phase. The formation temperature of this emission locates this
radiation to the flare's chromospheric footpoints, and similar behaviour
is found in the SDO/AIA 1600A and 1700A channels, which are dominated
by chromospheric continuum. The implication is that the chromosphere
responds dynamically at its acoustic cutoff frequency to an impulsive
injection of energy. Since the 3-minute period was not found at hard
X-ray energies (50-100 keV) in RHESSI data we can state that this
3-minute oscillation does not depend on the rate of energization of, or
energy deposition by, non-thermal electrons. However, a second period of
120 s found in both hard X-ray and chromospheric emission is consistent
with episodic electron energization on 2-minute timescales. Our
finding on the 3-minute oscillation suggests that chromospheric
mechanical energy should be included in the flare energy budget, and
the fluctuations in the Lyman-alpha line may influence the composition
and dynamics of planetary atmospheres during periods of high activity.
---------------------------------------------------------
Title: Hα and Hβ emission in a C3.3 solar flare: comparison between
observations and simulations
Authors: Zuccarello, F.; Simoes, P. J. D. A.; Capparelli, V.; Fletcher,
L.; Romano, P.; Mathioudakis, M.; Cauzzi, G.; Carlsson, M.; Kuridze,
D.; Keys, P.
2017AGUFMSH41A2742Z Altcode:
This work is based on the analysis of an extremely rare set of
simultaneous observations of a C3.3 solar flare in the Hα and Hβ lines
at high spatial and temporal resolution, which were acquired at the
Dunn Solar Telescope. Images of the C3.3 flare (SOL2014-04-22T15:22)
made at various wavelengths along the Hα line profile by the
Interferometric Bidimensional Spectrometer (IBIS) and in the Hβ
with the Rapid Oscillations in the Solar Atmosphere (ROSA) broadband
imager are analyzed to obtain the intensity evolution. The analysis
shows that Hα and Hβ intensity excesses in three identified flare
footpoints are well correlated in time. In the stronger footpoints,
the typical value of the the Hα/Hβ intensity ratio observed is ∼
0.4 - 0.5, in broad agreement with values obtained from a RADYN non-LTE
simulation driven by an electron beam with parameters constrained by
observations. The weaker footpoint has a larger Hα/Hβ ratio, again
consistent with a RADYN simulation but with a smaller energy flux.
---------------------------------------------------------
Title: Dynamical and Chemical Tracers in Jupiter's Troposphere and
Stratosphere from the Earth-Based Infrared Juno Support Campaign
Authors: Melin, H.; Fletcher, L. N.; Donnelly, P. T.; Greathouse,
T.; Lacy, J.; Orton, G.; Giles, R.; Sinclair, J. A.; Irwin, P. G.
2017AGUFM.P31C2841M Altcode:
The three-dimensional distribution of temperatures, chemical tracers
and aerosol opacity in Jupiter's troposphere and stratosphere
can be characterised by inverting spectra and images taken the
mid-infrared. We present NASA IRTF TEXES, Gemini TEXES and VLT VISIR
5-25 µm spectral maps of Jupiter obtained in the run-up, and during
the Juno mission at Jupiter, providing crucial observations in the
mid-infrared, a wavelength region not covered by Juno's suite of
instruments. The NASA IRTF TEXES observations form a long baseline of
spectroscopic maps between 2012 and 2017, providing temporal context
for Juno's observations. Using this dataset we investigate the zonal
abundance distribution of acetylene and ethane, and how these change
over time. Using the methane channel, we can retrieve the vertical
temperature profile between 1 and 10 mbar and track a full cycle of
Jupiter's equatorial stratospheric oscillation. We confirm that the
acetylene abundance decreases towards the pole, whilst ethane increases
towards the pole. We find that the data supports the hypothesis
that acetylene is asymmetric about the equator, and varies with time
in response to short-lived dynamical changes. We suggest that this
asymmetry, which changes over time, is driven by stratospheric wave
activity. Conversely, ethane appears to be symmetric about the equator,
and does not vary with time. The stark difference between acetylene
and ethane is likely linked to the two species having very different
chemical life-times and vertical abundance gradients. Gemini TEXES
spectral mapping in March 2017 reveals - in addition to temperatures -
the spatial distribution of ammonia, phosphine and upper tropospheric
aerosols at high spatial resolution. We confirm the equatorial NH3
enhancement observed by Juno, and investigate the distribution of
these dynamical tracers in the vicinity of NEB hotspots, an SEB plume
outbreak, and the Great Red Spot.
---------------------------------------------------------
Title: Ammonia in Jupiter's troposphere: a comparison of ground-based
5-μm high-resolution spectroscopy and Juno MWR observations
Authors: Giles, R.; Orton, G.; Fletcher, L. N.; Irwin, P. G.; Sinclair,
J. A.
2017AGUFM.P31C2812G Altcode:
Latitudinally-resolved 5-micron observations of Jupiter from the
CRIRES instrument at the Very Large Telescope are used to measure
the spatial variability in Jupiter's tropospheric ammonia (NH3)
abundance and these results are compared to the results from Juno's
Microwave Radiometer (MWR). The 5-micron spectral region is an
atmospheric window, allowing us to probe down to Jupiter's middle
troposphere. The high-resolution 2012 CRIRES observations include
several spectrally-resolved NH3 absorption features; these features
probe slightly different pressure levels, allowing the NH3 vertical
profile at 1-4 bar to be constrained. We find that in regions of low
cloud opacity, the NH3 abundance must decrease with altitude within
this pressure range. The CRIRES observations do not provide evidence for
any significant belt-zone variability in NH3, as any difference in the
spectral shape can be accounted for by the large differences in cloud
opacity between the cloudy zones and the cloud-free belts. However,
we do find evidence for a strong localised enhancement in NH3 on the
southern edge of the North Equatorial Belt (4-6°N). These results
can be directly compared with observations from the Juno mission's MWR
experiment. Li et al. (2017, doi 10.1002/2017GL073159) have used MWR
data to retrieve NH3 abundances at pressure levels of 1-100 bar. In
bright, cloud-free regions of the planet, the two datasets are broadly
consistent, including the asymmetrical enhancement on the southern
edge of the NEB. However, in the cool, cloudy Equatorial Zone, the MWR
retrieved abundances are significantly higher than those from CRIRES and
forward modeling shows that the MWR vertical distributions are unable
to fit the CRIRES data. We will investigate possible explanations
for this discrepancy, including the role of tropospheric clouds and
temperature variations.
---------------------------------------------------------
Title: Non-thermal Power-Law Distributions in Solar and Space Plasmas
Authors: Oka, M.; Battaglia, M.; Birn, J.; Chaston, C. C.; Effenberger,
F.; Eriksson, E.; Fletcher, L.; Hatch, S.; Imada, S.; Khotyaintsev,
Y. V.; Kuhar, M.; Livadiotis, G.; Miyoshi, Y.; Retino, A.
2017AGUFMSH51C2518O Altcode:
Particles are accelerated to very high, non-thermal energies in solar
and space plasma environments. While energy spectra of accelerated
particles often exhibit a power-law and are characterized by the
power-law index δ, it remains unclear how particles are accelerated
to high energies and how δ is determined. Here, we review previous
observations of the power-law index δ in a variety of different plasma
environments with a particular focus on sub-relativistic electrons. It
appears that in regions more closely related to magnetic reconnection
(such as the "above-the-looptop" solar hard X-ray source and the plasma
sheet in Earth's magnetotail), the spectra are typically soft (δ>
4). This is in contrast to the typically hard spectra (δ< 4)
that are observed in coincidence with shocks. The difference implies
that shocks are more efficient in producing a larger fraction of
non-thermal electron energies than magnetic reconnection. A caveat
is that during active times in Earth's magnetotail, δ values seem
spatially uniform in the plasma sheet, while power-law distributions
still exist even in quiet times. The role of magnetotail reconnection
in the electron power-law formation could therefore be confounded
with these background conditions. Because different regions have been
studied with different instrumentations and methodologies, we point
out a need for more systematic and coordinated studies of power-law
distributions for a better understanding of possible scaling laws in
particle acceleration as well as their universality.
---------------------------------------------------------
Title: High spatial and spectral resolution measurements of Jupiter's
auroral regions using Gemini-North-TEXES
Authors: Sinclair, J. A.; Orton, G. S.; Greathouse, T. K.; Lacy, J.;
Giles, R.; Fletcher, L. N.; Vogt, M.; Irwin, P. G.
2017AGUFM.P24A..08S Altcode:
Jupiter exhibits auroral emission at a multitude of wavelengths. Auroral
emission at X-ray, ultraviolet and near-infrared wavelengths demonstrate
the precipitation of ion and electrons in Jupiter's upper atmosphere, at
altitudes exceeding 250 km above the 1-bar level. Enhanced mid-infrared
emission of CH4, C2H2, C2H4 and further hydrocarbons is also observed
coincident with Jupiter's auroral regions. Retrieval analyses
of infrared spectra from IRTF-TEXES (Texas Echelon Cross Echelle
Spectrograph on NASA's Infrared Telescope Facility) indicate strong
heating at the 1-mbar level and evidence of ion-neutral chemistry,
which enriches the abundances of unsaturated hydrocarbons (Sinclair
et al., 2017b, doi:10.1002/2017GL073529, Sinclair et al., 2017c (under
review)). The extent to which these phenomena in the stratosphere are
correlated and coupled physically with the shorter-wavelength auroral
emission originating from higher altitudes has been a challenge due
to the limited spatial resolution available on the IRTF. Smaller-scale
features observed in the near-infrared and ultraviolet emission, such as
the main `oval', transient `swirls' and dusk-active regions within the
main oval (e.g. Stallard et al., 2014, doi:10.1016/j/Icarus.2015.12.044,
Nichols et al., 2017, doi: 10.1002/2017GL073029) are potentially being
blurred in the mid-infrared by the diffraction-limited resolution
(0.7") of IRTF's 3-metre primary aperture. However, on March 17-19th
2017, we obtained spectral measurements of H2 S(1), CH4, C2H2, C2H4 and
C2H6 emission of Jupiter's high latitudes using TEXES on Gemini-North,
which has a 8-metre primary aperture. This rare opportunity combines
the superior spectral resolving power of TEXES and the high spatial
resolution provided by Gemini-North's 8-metre aperture. We will
perform a retrieval analyses to determine the 3D distributions of
temperature, C2H2, C2H4 and C2H6. The morphology will be compared
with near-contemporaneous measurements of H3+ emission from IRTF-SpeX
and Juno-JIRAM/UVS to assess the extent of coupling between the
stratosphere and ionosphere. In addition, a magnetospheric mapping tool
(Vogt et al. 2011, doi:10.1029/2010JA016148) will be used to determine
whether small-scale features are likely linked to the solar wind or
the magnetosphere.
---------------------------------------------------------
Title: Characterization of Jupiter's Atmosphere from Observation of
Thermal Emission by Juno and Ground-Based Supporting Observations
Authors: Orton, G. S.; Momary, T.; Tabataba-Vakili, F.; Janssen, M. A.;
Hansen, C. J.; Bolton, S. J.; Li, C.; Adriani, A.; Mura, A.; Grassi,
D.; Fletcher, L. N.; Brown, S. T.; Fujiyoshi, T.; Greathouse, T. K.;
Kasaba, Y.; Sato, T. M.; Stephens, A.; Donnelly, P.; Eichstädt, G.;
Rogers, J.
2017AGUFM.P23E..02O Altcode:
Ground-breaking measurements of thermal emission at very long
wavelengths have been made by the Juno mission's Microwave Radiometer
(MWR). We examine the relationship between these and other thermal
emission measurements by the Jupiter Infrared Auroral Mapper (JIRAM)
at 5 µm and ground-based supporting observations in the thermal
infrared that cover the 5-25 µm range. The relevant ground-based
observations of thermal emission are constituted from imaging and
scanning spectroscopy obtained at the NASA Infrared Telescope Facility
(IRTF), the Gemini North Telescope, the Subaru Telescope and the Very
Large Telescope. A comparison of these results clarifies the physical
properties responsible for the observed emissions, i.e. variability of
the temperature field, the cloud field or the distribution of gaseous
ammonia. Cross-references to the visible cloud field from Juno's
JunoCam experiment and Earth-based images are also useful. This work
continues an initial comparison by Orton et al. (2017, GRL 44, doi:
10.1002/2017GL073019) between MWR and JIRAM results, together with
ancillary 5-µm IRTF imaging and with JunoCam and ground-based visible
imaging. These showed a general agreement between MWR and JIRAM results
for the 5-bar NH3 abundance in specific regions of low cloud opacity
but only a partial correlation between MWR and 5-µm radiances emerging
from the 0.5-5 bar levels of the atmosphere in general. Similar to the
latter, there appears to be an inconsistent correlation between MWR
channels sensitive to 0.5-10 bars and shorter-wavelength radiances
in the "tails" of 5-µm hot spots , which may be the result of the
greater sensitivity of the latter to particulate opacity that could
depend on the evolution history of the particular features sampled. Of
great importance is the interpretation of MWR radiances in terms
of the variability of temperature vs. NH3 abundances in the 0.5-5
bar pressure range. This is particularly important to understand
MWR results in Jupiter's Great Red Spot. It may also be important
to understand apparent differences between MWR and high-resolution
spectroscopic observations around Jupiter's equator.
---------------------------------------------------------
Title: D/H Ratios on Saturn and Jupiter from Cassini CIRS
Authors: Pierel, J. D. R.; Nixon, C. A.; Lellouch, E.; Fletcher, L. N.;
Bjoraker, G. L.; Achterberg, R. K.; Bézard, B.; Hesman, B. E.; Irwin,
P. G. J.; Flasar, F. M.
2017AJ....154..178P Altcode:
We present new measurements of the deuterium abundance on Jupiter
and Saturn, showing evidence that Saturn's atmosphere contains less
deuterium than Jupiter's. We analyzed far-infrared spectra from the
Cassini Composite Infrared Spectrometer to measure the abundance of
HD on both giant planets. Our estimate of the Jovian D/H = (2.95 ±
0.55) × 10<SUP>-5</SUP> is in agreement with previous measurements
by ISO/SWS: (2.25 ± 0.35) × 10<SUP>-5</SUP>, and the Galileo probe:
(2.6 ± 0.7) × 10<SUP>-5</SUP>. In contrast, our estimate of the
Saturn value of (2.10 ± 0.13) × 10<SUP>-5</SUP> is somewhat lower
than on Jupiter (by a factor of 0.71<SUB>-0.15</SUB><SUP>+0.22</SUP>),
contrary to model predictions of a higher ratio: Saturn/Jupiter =
1.05-1.20. The Saturn D/H value is consistent with estimates for
hydrogen in the protosolar nebula (2.1 ± 0.5) × 10<SUP>-5</SUP>,
but its apparent divergence from the Jovian value suggests that our
understanding of planetary formation and evolution is incomplete,
which is in agreement with previous work.
---------------------------------------------------------
Title: Hα and Hβ Emission in a C3.3 Solar Flare: Comparison between
Observations and Simulations
Authors: Capparelli, Vincenzo; Zuccarello, Francesca; Romano, Paolo;
Simões, Paulo J. A.; Fletcher, Lyndsay; Kuridze, David; Mathioudakis,
Mihalis; Keys, Peter H.; Cauzzi, Gianna; Carlsson, Mats
2017ApJ...850...36C Altcode: 2017arXiv171004067C
The hydrogen Balmer series is a basic radiative loss channel from
the flaring solar chromosphere. We report here on the analysis of an
extremely rare set of simultaneous observations of a solar flare in the
{{H}}α and {{H}}β lines, at high spatial and temporal resolutions,
that were acquired at the Dunn Solar Telescope. Images of the C3.3 flare
(SOL2014-04-22T15:22) made at various wavelengths along the {{H}}α line
profile by the Interferometric Bidimensional Spectrometer (IBIS) and in
the {{H}}β with the Rapid Oscillations in the Solar Atmosphere (ROSA)
broadband imager are analyzed to obtain the intensity evolution. The
{{H}}α and {{H}}β intensity excesses in three identified flare
footpoints are well-correlated in time. We examine the ratio of {{H}}α
to {{H}}β flare excess, which was proposed by previous authors as
a possible diagnostic of the level of electron-beam energy input. In
the stronger footpoints, the typical value of the the {{H}}α /H β
intensity ratio observed is ∼0.4-0.5, in broad agreement with values
obtained from a RADYN non-LTE simulation driven by an electron beam
with parameters constrained (as far as possible) by observation. The
weaker footpoint has a larger {{H}}α /H β ratio, again consistent
with a RADYN simulation, but with a smaller energy flux. The {{H}}α
line profiles observed have a less prominent central reversal than is
predicted by the RADYN results, but can be brought into agreement if
the {{H}}α -emitting material has a filling factor of around 0.2-0.3.
---------------------------------------------------------
Title: Can Substorm Particle Acceleration Be Applied to Solar Flares?
Authors: Birn, J.; Battaglia, M.; Fletcher, L.; Hesse, M.; Neukirch, T.
2017ApJ...848..116B Altcode:
Using test particle studies in the electromagnetic fields of
three-dimensional magnetohydrodynamic (MHD) simulations of magnetic
reconnection, we study the energization of charged particles in the
context of the standard two-ribbon flare picture in analogy to the
standard magnetospheric substorm paradigm. In particular, we investigate
the effects of the collapsing field (“collapsing magnetic trap”)
below a reconnection site, which has been demonstrated to be the major
acceleration mechanism that causes energetic particle acceleration and
injections observed in Earth’s magnetotail associated with substorms
and other impulsive events. We contrast an initially force-free,
high-shear field (low beta) with low and moderate shear, finite-pressure
(high-beta) arcade structures, where beta represents the ratio between
gas (plasma) and magnetic pressure. We demonstrate that the energization
affects large numbers of particles, but the acceleration is modest in
the presence of a significant shear field. Without incorporating loss
mechanisms, the effect on particles at different energies is similar,
akin to adiabatic heating, and thus is not a likely mechanism to
generate a power-law tail onto a (heated or not heated) Maxwellian
velocity distribution.
---------------------------------------------------------
Title: Comparing UV/EUV line parameters and magnetic field in a
quiescent prominence with tornadoes
Authors: Levens, P. J.; Labrosse, N.; Schmieder, B.; López Ariste,
A.; Fletcher, L.
2017A&A...607A..16L Altcode: 2017arXiv170804606L
Context. Understanding the relationship between plasma and the
magnetic field is important for describing and explaining the
observed dynamics of solar prominences. <BR /> Aims: We determine
if a close relationship can be found between plasma and magnetic
field parameters, measured at high resolution in a well-observed
prominence. <BR /> Methods: A prominence observed on 15 July 2014 by
the Interface Region Imaging Spectrograph (IRIS), Hinode, the Solar
Dynamics Observatory (SDO), and the Télescope Héliographique pour
l'Étude du Magnétisme et des Instabilités Solaires (THEMIS) is
selected. We perform a robust co-alignment of data sets using a 2D
cross-correlation technique. Magnetic field parameters are derived
from spectropolarimetric measurements of the He I D<SUB>3</SUB> line
from THEMIS. Line ratios and line-of-sight velocities from the Mg II h
and k lines observed by IRIS are compared with magnetic field strength,
inclination, and azimuth. Electron densities are calculated using Fe xii
line ratios from the Hinode Extreme-ultraviolet Imaging Spectrometer,
which are compared to THEMIS and IRIS data. <BR /> Results: We find
Mg II k/h ratios of around 1.4 everywhere, similar to values found
previously in prominences. Also, the magnetic field is strongest (
30 G) and predominantly horizontal in the tornado-like legs of the
prominence. The k<SUB>3</SUB> Doppler shift is found to be between
±10 km s<SUP>-1</SUP> everywhere. Electron densities at a temperature
of 1.5 × 10<SUP>6</SUP> K are found to be around 10<SUP>9</SUP>
cm<SUP>-3</SUP>. No significant correlations are found between the
magnetic field parameters and any of the other plasma parameters
inferred from spectroscopy, which may be explained by the large
differences in the temperatures of the lines used in this study. <BR />
Conclusions: This is the first time that a detailed statistical study of
plasma and magnetic field parameters has been performed at high spatial
resolution in a prominence. Our results provide important constraints
on future models of the plasma and magnetic field in these structures.
---------------------------------------------------------
Title: Detection of Three-minute Oscillations in Full-disk Lyα
Emission during a Solar Flare
Authors: Milligan, Ryan O.; Fleck, Bernhard; Ireland, Jack; Fletcher,
Lyndsay; Dennis, Brian R.
2017ApJ...848L...8M Altcode: 2017arXiv170909037M
In this Letter we report the detection of chromospheric 3-minute
oscillations in disk-integrated EUV irradiance observations during a
solar flare. A wavelet analysis of detrended Lyα (from GOES/EUVS) and
Lyman continuum (from Solar Dynamics Observatory (SDO)/EVE) emission
from the 2011 February 15 X-class flare (SOL2011-02-15T01:56) revealed
a ∼3 minute period present during the flare’s main phase. The
formation temperature of this emission locates this radiation at the
flare’s chromospheric footpoints, and similar behavior is found
in the SDO/Atmospheric Imaging Assembly 1600 and 1700 Å channels,
which are dominated by chromospheric continuum. The implication is
that the chromosphere responds dynamically at its acoustic cutoff
frequency to an impulsive injection of energy. Since the 3-minute
period was not found at hard X-ray (HXR) energies (50-100 keV) in
Reuven Ramaty High Energy Solar Spectroscopic Imager data we can
state that this 3-minute oscillation does not depend on the rate of
energization of non-thermal electrons. However, a second period of 120
s found in both HXR and chromospheric lightcurves is consistent with
episodic electron energization on 2-minute timescales. Our finding on
the 3-minute oscillation suggests that chromospheric mechanical energy
should be included in the flare energy budget, and the fluctuations in
the Lyα line may influence the composition and dynamics of planetary
atmospheres during periods of high activity.
---------------------------------------------------------
Title: Water and Volatiles in the Outer Solar System
Authors: Grasset, O.; Castillo-Rogez, J.; Guillot, T.; Fletcher,
L. N.; Tosi, F.
2017SSRv..212..835G Altcode: 2017SSRv..tmp..135G
Space exploration and ground-based observations have provided
outstanding evidence of the diversity and the complexity of the outer
solar system. This work presents our current understanding of the
nature and distribution of water and water-rich materials from the
water snow line to the Kuiper Belt. This synthesis is timely, since
a thorough exploration of at least one object in each region of the
outer solar system has now been achieved. Next steps, starting with
the Juno mission now in orbit around Jupiter, will be more focused on
understanding the processes at work than on describing the general
characteristics of each giant planet systems. <P />This review is
organized in three parts. First, the nature and the distribution of
water and volatiles in giant and intermediary planets are described
from their inner core to their outer envelopes. A special focus is
given to Jupiter and Saturn, which are much better understood than the
two ice giants (Uranus and Neptune) thanks to the Galileo and Cassini
missions. Second, the icy moons will be discussed. Space missions and
ground-based observations have revealed the variety of icy surfaces
in the outer system. While Europa, Enceladus, and maybe Titan present
past or even active tectonic and volcanic activities, many other moons
have been dead worlds for more than 3 billion years. Ice compositions
found at these bodies are also complex and it is now commonly admitted
that icy surfaces are never composed of pure ices. A detailed review
of the distribution of non-ice materials on the surfaces and in the
tenuous atmospheres of the moons is proposed, followed by a more focused
discussion on the nature and the characteristics of the liquid layers
trapped below the cold icy crusts that have been suggested in the icy
Galilean moons, and in Enceladus, Dione, and Titan at Saturn. Finally,
the recent observations collected by Dawn at Ceres and New Horizons
at Pluto, as well as the state of knowledge of other transneptunian
objects, are summarized, and complete this overview of the nature and
distribution of ice-rich material in the outer solar system.
---------------------------------------------------------
Title: Seismology of contracting and expanding coronal loops using
damping of kink oscillations by mode coupling
Authors: Pascoe, D. J.; Russell, A. J. B.; Anfinogentov, S. A.;
Simões, P. J. A.; Goddard, C. R.; Nakariakov, V. M.; Fletcher, L.
2017A&A...607A...8P Altcode:
<BR /> Aims: We extend recently developed seismological methods to
analyse oscillating loops which feature a large initial shift in the
equilibrium position and investigate additional observational signatures
related to the loop environment and oscillation driver. <BR /> Methods:
We model the motion of coronal loops as a kink oscillation damped by
mode coupling, accounting for any change in loop length and the possible
presence of parallel harmonics in addition to the fundamental mode. We
apply our model to a loop which rapidly contracts due to a post-flare
implosion (SOL2012-03-09) and a loop with a large lateral displacement
(SOL2012-10-20). <BR /> Results: The seismological method is used to
calculate plasma parameters of the oscillating loops including the
transverse density profile, magnetic field strength, and phase mixing
timescale. For SOL2012-03-09 the period of oscillation has a linear
correlation with the contracting motion and suggests the kink speed
remains constant during the oscillation. The implosion excitation
mechanism is found to be associated with an absence of additional
parallel harmonics. <BR /> Conclusions: The improved Bayesian
analysis of the coronal loop motion allows for accurate seismology
of plasma parameters, and the evolution of the period of oscillation
compared with the background trend can be used to distinguish between
loop motions in the plane of the loop and those perpendicular to
it. The seismologically inferred kink speed and density contrast
imply sub-Alfvénic (M<SUB>A</SUB> = 0.16 ± 0.03) propagation of the
magnetic reconfiguration associated with the implosion, as opposed to
triggering by a wave propagating at the Alfvén speed.
---------------------------------------------------------
Title: Observations of Reconnection Flows in a Flare on the Solar Disk
Authors: Wang, Juntao; Simões, P. J. A.; Jeffrey, N. L. S.; Fletcher,
L.; Wright, P. J.; Hannah, I. G.
2017ApJ...847L...1W Altcode: 2017arXiv170808706W
Magnetic reconnection is a well-accepted part of the theory of solar
eruptive events, though the evidence is still circumstantial. Intrinsic
to the reconnection picture of a solar eruptive event, particularly
in the standard model for two-ribbon flares (CSHKP model), are an
advective flow of magnetized plasma into the reconnection region,
expansion of field above the reconnection region as a flux rope
erupts, retraction of heated post-reconnection loops, and downflows
of cooling plasma along those loops. We report on a unique set of
Solar Dynamics Observatory/Atmospheric Imaging Assembly imaging and
Hinode/EUV Imaging Spectrometer spectroscopic observations of the
disk flare SOL2016-03-23T03:54 in which all four flows are present
simultaneously. This includes spectroscopic evidence for a plasma
upflow in association with large-scale expanding closed inflow
field. The reconnection inflows are symmetric, and consistent with
fast reconnection, and the post-reconnection loops show a clear cooling
and deceleration as they retract. Observations of coronal reconnection
flows are still rare, and most events are observed at the solar limb,
obscured by complex foregrounds, making their relationship to the
flare ribbons, cusp field, and arcades formed in the lower atmosphere
difficult to interpret. The disk location and favorable perspective
of this event have removed these ambiguities giving a clear picture
of the reconnection dynamics.
---------------------------------------------------------
Title: Identifying the source of colour and featural changes in
Jupiter's atmosphere from MUSE/VLT
Authors: Braude, A. S.; Irwin, P. G. J.; Orton, G. S.; Fletcher, L. N.
2017EPSC...11..806B Altcode:
We use ground-based observations from the MUSE/VLT instrument to
characterise changes in cloud structure and colour in Jupiter's
atmosphere between 2014-2017, and providing global context
to observations of Jupiter from the Juno spacecraft. We witness
significant changes in Jupiter's banded structure in the northern
hemisphere in 2017, and we also confirm that the colour in Jupiter's
red regions can be well-modelled using a red substance produced through
the photochemical reaction of ammonia with acetylene. This implies a
high-altitude source of colour in Jupiter's atmosphere.
---------------------------------------------------------
Title: Exploration of Jupiter's atmosphere and magnetosphere with
the European Jupiter Icy Moons Explorer (JUICE)
Authors: Cavalié, T.; Fletcher, L.; Krupp, N.; Masters, A.;
Witasse, O.
2017EPSC...11..420C Altcode:
JUICE - JUpiter ICy moons Explorer - is the first large mission in ESA's
Cosmic Vision 2015-2025 programme. The mission was selected in May 2012
and adopted in November 2014. The implementation phase started in July
2015. Planned for launch in June 2022 and arrival at Jupiter in October
2029, it will spend at least three years making detailed observations
of Jupiter and three of its largest moons, Ganymede, Callisto and
Europa. JUICE will then orbit Ganymede for almost a year. JUICE
will perform a varied and extensive orbital tour with access to high
latitudes to provide a comprehensive study of the unique environmental
conditions at Jupiter's poles. The overarching theme for JUICE is:
The emergence of habitable worlds around gas giants. JUICE will also
perform a multidisciplinary investigation of the Jupiter as an archetype
for gas giants. In this paper, we will present the science objectives
and key measurements performed by the instrument suite, relevant to
the study of the atmosphere and magnetosphere of Jupiter. We will also
present the first steps of the science implementation, as performed
by the ESA Working Groups and Science Working Team.
---------------------------------------------------------
Title: Detection of Compact Baroclinic Waves in Jupiter's Deep Clouds
at 5-microns from the VLT
Authors: Fletcher, L. N.; Donnelly, P.; Melin, H.; Orton, G. S.;
Greathouse, T. K.; Sinclair, J. A.; Giles, R. S.; Simon, A. A.;
de Pater, I.; Wong, M.
2017EPSC...11..454F Altcode:
A campaign of Earth-based supporting observations is providing spatial,
temporal and spectral context to the close-in orbital exploration of
Jupiter by the Juno mission. This campaign, utilising 8-m observatories
on Earth, is providing some of the highest resolution mid-infrared
observations of Jupiter ever obtained, allowing us to probe the scale
of compact wave patterns for the first time. We report the detection
of a compact (1-degree longitude) wave in the deep clouds of the North
Equatorial Belt at 5-microns, coincident with a structure observed by
Hubble in reflected sunlight at higher altitudes.
---------------------------------------------------------
Title: The Hera Saturn Entry Probe Mission: a Proposal in Response
to the ESA M5 Call
Authors: Mousis, O.; Atkinson, D.; Amato, M.; Aslam, S.; Atreya,
S.; Blanc, M.; Bolton, S.; Brugger, B.; Calcutt, S.; Cavalié, T.;
Charnoz, S.; Coustenis, A.; Deleuil, M.; Dobrijevic, M.; Ferri, F.;
Fletcher, L.; Gautier, D.; Guillot, T.; Hartogh, P.; Holland, A.
2017EPSC...11..305M Altcode:
The Hera Saturn entry probe mission is proposed as an ESA M-class
mission to be piggybacked on a NASA spacecraft sent to or past the
Saturn system. Hera consists of an atmospheric probe built by ESA and
released into the atmosphere of Saturn by its NASA companion Saturn
Carrier-Relay spacecraft. Hera will perform in situ measurements of the
chemical and isotopic composition as well as the structure and dynamics
of Saturn's atmosphere using a single probe, with the goal of improving
our understanding of the origin, formation, and evolution of Saturn,
the giant planets and their satellite systems, with extrapolation to
extrasolar planets. Hera will probe well into and possibly beneath the
cloud-forming region of the troposphere, below the region accessible
to remote sensing, to locations where certain cosmogenically abundant
species are expected to be well mixed.
---------------------------------------------------------
Title: Formation of the thermal infrared continuum in solar flares
Authors: Simões, Paulo J. A.; Kerr, Graham S.; Fletcher, Lyndsay;
Hudson, Hugh S.; Giménez de Castro, C. Guillermo; Penn, Matt
2017A&A...605A.125S Altcode: 2017arXiv170609867S
<BR /> Aims: Observations of the Sun with the Atacama Large Millimeter
Array have now started, and the thermal infrared will regularly be
accessible from the NSF's Daniel K. Inouye Solar Telescope. Motivated by
the prospect of these new data, and by recent flare observations in the
mid infrared, we set out here to model and understand the source of the
infrared continuum in flares, and to explore its diagnostic capability
for the physical conditions in the flare atmosphere. <BR /> Methods:
We use the one-dimensional (1D) radiation hydrodynamics code RADYN
to calculate mid-infrared continuum emission from model atmospheres
undergoing sudden deposition of energy by non-thermal electrons. <BR
/> Results: We identify and characterise the main continuum thermal
emission processes relevant to flare intensity enhancement in the
mid- to far-infrared (2-200 μm) spectral range as free-free emission
on neutrals and ions. We find that the infrared intensity evolution
tracks the energy input to within a second, albeit with a lingering
intensity enhancement, and provides a very direct indication of the
evolution of the atmospheric ionisation. The prediction of highly
impulsive emission means that, on these timescales, the atmospheric
hydrodynamics need not be considered in analysing the mid-IR signatures.
---------------------------------------------------------
Title: Characterising Jupiter's Temperatures, Aerosols and Ammonia
via VLT/VISIR Spatial Mapping 2016-17
Authors: Donnelly, P. T.; Fletcher, L. N.; Orton, G. S.; Melin, H.
2017EPSC...11..581D Altcode:
The VISIR mid-IR imager (5-25 µm) on the Very Large Telescope (VLT)
has been providing infrared spatial and temporal support for NASA's
Juno spacecraft, constraining atmospheric thermal conditions in the
upper troposphere (100-700 mbar) and stratosphere (1-10 mbar). Our
pre-Juno-arrival dataset (January-August 2016) demonstrated that
Jupiter's North Equatorial Belt (NEB) began a northward expansion in
late 2015, consistent with the 3-5 year cycle of NEB activity. VISIR
detected two new thermal waves during this period; an upper tropospheric
wave in the mid-NEB and a stratospheric wave centred on the eastward
jet at 23.9°N. The latter was quasi-stationary and both waves are
morphologically similar to those observed during the 2000 expansion
event by Cassini. We now extend this analysis to coincide with Juno's
perijove encounters, once every 53.5 days. We report (i) the continued
existence of the mid-NEB wave; (ii) evolution of Jupiter's North
Temperate Belt (NTB) following the October 2016 outbreak; and (iii)
complex thermal variability associated with a mid-SEB outbreak during
2017. We discuss zonally-averaged temperatures, aerosols and ammonia
distributions derived from VLT data (taking centre-to-limb variations
into account), comparing the upper-tropospheric aerosols and ammonia
to the findings of Juno's near-infrared and microwave observations.
---------------------------------------------------------
Title: The New Frontiers Saturn PRobe Interior and aTmosphere Explorer
(SPRITE) Mission Proposal
Authors: Atkinson, D. H.; Simon, A. A.; Banfield, D.; Atreya, S.;
Blacksberg, J.; Brinckerhoff, W.; Colaprete, A.; Coustenis, A.;
Fletcher, L.; Guillot, T.; Hofstadter, M.; Lunine, J.; Mahaffy, P.;
Marley, M.; Mousis, O.; Spilker, T.; Trainer, M.; Webster, C.
2017EPSC...11..356A Altcode:
SPRITE is a Saturn Probe mission proposal submitted to NASA under the
New Frontiers 4 program.
---------------------------------------------------------
Title: Scientific rationale and concepts for in situ probe exploration
of Uranus and Neptune
Authors: Mousis, O.; Atkinson, D.; Amato, M.; Aslam, S.; Atreya,
S.; Blanc, M.; Brugger, B.; Calcutt, S.; Cavalié, T.; Charnoz, S.;
Coustenis, A.; Deleuil, M.; Dobrijevic, M.; Encrenaz, T.; Ferri, F.;
Fletcher, L.; Guillot, T.; Hartogh, P.; Hofstadter, M.; Hueso, R.
2017EPSC...11..299M Altcode:
Uranus and Neptune, referred to as ice giants, are fundamentally
different from the better-known gas giants (Jupiter and
Saturn). Exploration of an ice giant system is a high-priority science
objective, as these systems (including the magnetosphere, satellites,
rings, atmosphere, and interior) challenge our understanding of
planetary formation and evolution. The importance of the ice giants is
reflected in NASA's 2011 Decadal Survey, comments from ESA's SSC in
response to L2/L3 mission proposals and results of the 2017 NASA/ESA
Ice Giants study. A crucial part of exploration of the ice giants is
in situ sampling of the atmosphere via an atmospheric probe. A probe
would bring insights in two broad themes: the formation history of our
Solar System and the processes at play in planetary atmospheres. Here
we summarize the science driver for in situ measurements at these two
planets and discuss possible mission concepts that would be consistent
with the constraints of ESA M-class missions.
---------------------------------------------------------
Title: Saturn at Northern Summer Solstice: Thermal Structure during
the Finale of the Cassini Mission
Authors: Fletcher, L. N.; Guelet, S.; Orton, G. S.; Sinclair, J. A.;
Fouchet, T.; Irwin, P.; Li, L.; Flasar, F. M.
2017EPSC...11..450F Altcode:
With the culmination of 13 years of orbital exploration of Saturn by the
Cassini spacecraft, we now have the most comprehensive characterisation
of a seasonal giant planet ever obtained. The longevity of Cassini
has meant that we can explore atmospheric processes from solstice
to solstice using infrared remote sensing, including: the formation
and dissipation of stratospheric polar vortices; the evolution of
Saturn's equatorial oscillation; and the aftermath of the 2010-11
springtime storm.
---------------------------------------------------------
Title: Saturn's stratospheric equatorial oscillation and wave activity
through the Cassini epoch
Authors: Guerlet, S.; Fouchet, T.; Spiga, A.; Hesman, B.; Gorius,
N.; Fletcher, L.; Flasar, F. M.
2017EPSC...11..172G Altcode:
We study the evolution of Saturn's Quasi-Periodic Oscillation,
a dynamical phenomenon observed in Saturn's stratosphere that has
counterparts in Jupiter and the Earth stratospheres as well. Thermal
infrared spectra acquired by Cassini/CIRS in limb viewing geometry
in 2015 are used to derive 2-D latitude-pressure temperature and
thermal wind maps in Saturn's stratosphere. These maps are compared
to previous observations from 2005 and 2010 to characterize and
study the evolution of the vertical structure of Saturn's equatorial
oscillation. This phenomenon is thought to result from the interaction
between upward-propagating waves and the mean zonal flow, but little
is known on Saturn's stratospheric wave activity. CIRS nadir spectra
are then used to map stratospheric temperatures with longitude and
characterize planetary waves in the tropical region (20N-20S).
---------------------------------------------------------
Title: Saturn's Atmospheric Photochemistry: Haze Production in
Ring-Shadowed Atmosphere and within the Hexagon
Authors: Edgington, S. G.; Atreya, S. K.; Wilson, E. H.; Baines,
K. H.; West, R. A.; Bjoraker, G. L.; Fletcher, L. N.; Momary, T.
2017EPSC...11..386E Altcode:
This research explores the impact of seasonal changes within Saturn's
atmosphere and the evolution of hazes within it.
---------------------------------------------------------
Title: The thermal infrared continuum in solar flares
Authors: Fletcher, Lyndsay; Simoes, Paulo; Kerr, Graham Stewart;
Hudson, Hugh S.; Gimenez de Castro, C. Guillermo; Penn, Matthew J.
2017SPD....4810821F Altcode:
Observations of the Sun with the Atacama Large Millimeter Array have
now started, and the thermal infrared will regularly be accessible
from the NSF’s Daniel K. Inouye Solar Telescope. Motivated by the
prospect of these new observations, and by recent flare detections in
the mid infrared, we set out here to model and understand the source
of the infrared continuum in flares, and to explore its diagnostic
capability for the physical conditions in the flare atmosphere. We use
the 1D radiation hydrodynamics code RADYN to calculate mid-infrared
continuum emission from model atmospheres undergoing sudden deposition
of energy by non-thermal electrons. We identify and characterise the
main continuum thermal emission processes relevant to flare intensity
enhancement in the mid- to far-infrared (2-200 micron) spectral range
as free-free emission on neutrals and ions. We find that the infrared
intensity evolution tracks the energy input to within a second,
albeit with a lingering intensity enhancement, and provides a very
direct indication of the evolution of the atmospheric ionization. The
prediction of highly impulsive emission means that, on these timescales,
the atmospheric hydrodynamics need not be considered in analysing the
mid-IR signatures.
---------------------------------------------------------
Title: Jupiter's auroral-related stratospheric heating and chemistry
I: Analysis of Voyager-IRIS and Cassini-CIRS spectra
Authors: Sinclair, J. A.; Orton, G. S.; Greathouse, T. K.; Fletcher,
L. N.; Moses, J. I.; Hue, V.; Irwin, P. G. J.
2017Icar..292..182S Altcode:
Auroral processes are evident in Jupiter's polar atmosphere over
a large range in wavelength (X-ray to radio). In particular,
previous observations in the mid-infrared (5-15 μm) have shown
enhanced emission from CH<SUB>4</SUB>, C<SUB>2</SUB>H<SUB>2</SUB>
and C<SUB>2</SUB>H<SUB>4</SUB> and further stratospheric hydrocarbon
species in spatial regions coincident with auroral processes observed at
other wavelengths. These regions, described as auroral-related hotspots,
observed at approximately 160°W to 200°W (System III) at high-northern
latitudes and 330°W to 80°W at high-southern latitudes, indicate
that auroral processes modify the thermal structure and composition
of the neutral atmosphere. However, previous studies have struggled to
differentiate whether the aforementioned enhanced emission is a result
of either temperature changes and/or changes in the concentration of
the emitting species. We attempt to address this degeneracy in this
work by performing a retrieval analysis of Voyager 1-IRIS spectra
(acquired in 1979) and Cassini-CIRS spectra (acquired in 2000/2001) of
Jupiter. Retrievals of the vertical temperature profile in Cassini-CIRS
spectra covering the auroral-related hotspots indicate the presence
of two discrete vertical regions of heating at the 1-mbar level and
at pressures of 10-μbar and lower. For example, in Cassini-CIRS
2.5 cm-<SUP>1</SUP> 'MIRMAP' spectra at 70°N (planetographic)
180°W (centred on the auroral oval), we find temperatures at the
1-mbar level and 10-μbar levels are enhanced by 15.3 ± 5.2 K and
29.6 ± 15.0 K respectively, in comparison to results at 70°N,
60°W in the same dataset. High temperatures at 10 μbar and lower
pressures were considered indicative of joule heating, ion and/or
electron precipitation, ion-drag and energy released form exothermic
ion-chemistry. However, we conclude that the heating at the 1-mbar
level is the result of either a layer of aurorally-produced haze
particles, which are heated by incident sunlight and/or adiabatic
heating by downwelling within the auroral hot-spot region. The
former mechanism would be consistent with the vertical profiles of
polycyclic aromatic hydrocarbons (PAHs) and haze particles predicted
in auroral-chemistry models (Wong et al., 2000; 2003). Retrievals of
C<SUB>2</SUB>H<SUB>2</SUB> and C<SUB>2</SUB>H<SUB>6</SUB> were also
performed and indicate C<SUB>2</SUB>H<SUB>2</SUB> is enriched but
C<SUB>2</SUB>H<SUB>6</SUB> is depleted in auroral regions relative to
quiescent regions. For example, using CIRS Δν∼ = 2.5 cm-<SUP>1</SUP>
spectra, we determined that C<SUB>2</SUB>H<SUB>2</SUB> at 0.98 mbar
increases by 175.3 ± 89.3 ppbv while C<SUB>2</SUB>H<SUB>6</SUB> at
4.7 mbar decreases by 0.86 ± 0.59 ppmv in comparing results at 70°N,
180°W and 70°N, 60°W. These results represent a mean of values
retrieved from different initial assumptions and thus we believe they
are robust. We believe these contrasts in C<SUB>2</SUB>H<SUB>2</SUB> and
C<SUB>2</SUB>H<SUB>6</SUB> between auroral and quiescent regions can
be explained by a coupling of auroral-driven chemistry and horizontal
advection. Ion-neutral and electron recombination chemistry in
the auroral region enriches all C<SUB>2</SUB> hydrocarbons but
in particular, the unsaturated C<SUB>2</SUB>H<SUB>2</SUB> and
C<SUB>2</SUB>H<SUB>4</SUB> hydrocarbons. Once advected outside of
the auroral region, the unsaturated C<SUB>2</SUB> hydrocarbons are
converted into C<SUB>2</SUB>H<SUB>6</SUB> by neutral photochemistry
thereby enriching C<SUB>2</SUB>H<SUB>6</SUB> in quiescent regions,
which gives the impression it is depleted inside the auroral region.
---------------------------------------------------------
Title: Modelling of the hydrogen Lyman lines during solar flares
Authors: Brown, Stephen Alistair; Fletcher, Lyndsay; Labrosse, Nicolas
2017SPD....4810303B Altcode:
The hydrogen Lyman series and continuum are both observed with high
cadence and spectral resolution by the EVE instrument on NASA’s
solar dynamics observatory. The Lyman lines, some of which will also be
observed by the SPICE spectrometer on Solar Orbiter, can provide useful
information about the dynamics of the solar chromosphere during a flare,
where most of the event’s energy is deposited. In Brown et al (2016),
we measured line shifts in the Lyman lines using the EVE instrument and
calculated corresponding plasma flow speeds of around 30 kilometres
per second. However, the observed signs of these shifts varied. We
have also modelled Lyman line profiles output from the radiative
hydrodynamic code RADYN (Carlsson & Stein 1997, Allred et al 2015)
and the radiative transfer code RH (Uitenbroek 2001) and present our
initial findings. We show that the dynamics of the plasma are reflected
in complex features in the true line profile, but that the detection of
a line shift in a particular direction from EVE observations may not
be indicative of the true plasma flow, particularly when these model
profiles are passed through the EVE instrumental response. We present
several cases of atmospheric responses for differing amounts of energy
input, and outline interesting features in the Lyman line profiles which
are thought to be linked to the response of the dynamic atmosphere.
---------------------------------------------------------
Title: Formation of diamonds in laser-compressed hydrocarbons at
planetary interior conditions
Authors: Kraus, D.; Vorberger, J.; Pak, A.; Hartley, N. J.; Fletcher,
L. B.; Frydrych, S.; Galtier, E.; Gamboa, E. J.; Gericke, D. O.;
Glenzer, S. H.; Granados, E.; MacDonald, M. J.; MacKinnon, A. J.;
McBride, E. E.; Nam, I.; Neumayer, P.; Roth, M.; Saunders, A. M.;
Schuster, A. K.; Sun, P.; van Driel, T.; Döppner, T.; Falcone, R. W.
2017NatAs...1..606K Altcode:
The effects of hydrocarbon reactions and diamond precipitation on
the internal structure and evolution of icy giant planets such
as Neptune and Uranus have been discussed for more than three
decades<SUP>1</SUP>. Inside these celestial bodies, simple
hydrocarbons such as methane, which are highly abundant in
the atmospheres<SUP>2</SUP>, are believed to undergo structural
transitions<SUP>3,4</SUP> that release hydrogen from deeper layers
and may lead to compact stratified cores<SUP>5-7</SUP>. Indeed,
from the surface towards the core, the isentropes of Uranus and
Neptune intersect a temperature-pressure regime in which methane
first transforms into a mixture of hydrocarbon polymers<SUP>8</SUP>,
whereas, in deeper layers, a phase separation into diamond and
hydrogen may be possible. Here we show experimental evidence for
this phase separation process obtained by in situ X-ray diffraction
from polystyrene (C<SUB>8</SUB>H<SUB>8</SUB>)<SUB>n</SUB> samples
dynamically compressed to conditions around 150 GPa and 5,000 K;
these conditions resemble the environment around 10,000 km below the
surfaces of Neptune and Uranus<SUP>9</SUP>. Our findings demonstrate
the necessity of high pressures for initiating carbon-hydrogen
separation<SUP>3</SUP> and imply that diamond precipitation may require
pressures about ten times as high as previously indicated by static
compression experiments<SUP>4,8,10</SUP>. Our results will inform
mass-radius relationships of carbon-bearing exoplanets<SUP>11</SUP>,
provide constraints for their internal layer structure and improve
evolutionary models of Uranus and Neptune, in which carbon-hydrogen
separation could influence the convective heat transport<SUP>7</SUP>.
---------------------------------------------------------
Title: Jupiter's North Equatorial Belt expansion and thermal wave
activity ahead of Juno's arrival
Authors: Fletcher, L. N.; Orton, G. S.; Sinclair, J. A.; Donnelly, P.;
Melin, H.; Rogers, J. H.; Greathouse, T. K.; Kasaba, Y.; Fujiyoshi,
T.; Sato, T. M.; Fernandes, J.; Irwin, P. G. J.; Giles, R. S.; Simon,
A. A.; Wong, M. H.; Vedovato, M.
2017GeoRL..44.7140F Altcode: 2017arXiv170805179F
The dark colors of Jupiter's North Equatorial Belt (NEB, 7-17°N)
appeared to expand northward into the neighboring zone in 2015,
consistent with a 3-5 year cycle. Inversions of thermal-IR imaging from
the Very Large Telescope revealed a moderate warming and reduction of
aerosol opacity at the cloud tops at 17-20°N, suggesting subsidence and
drying in the expanded sector. Two new thermal waves were identified
during this period: (i) an upper tropospheric thermal wave (wave
number 16-17, amplitude 2.5 K at 170 mbar) in the mid-NEB that was
anticorrelated with haze reflectivity; and (ii) a stratospheric wave
(wave number 13-14, amplitude 7.3 K at 5 mbar) at 20-30°N. Both
were quasi-stationary, confined to regions of eastward zonal flow,
and are morphologically similar to waves observed during previous
expansion events.
---------------------------------------------------------
Title: Independent evolution of stratospheric temperatures in
Jupiter's northern and southern auroral regions from 2014 to 2016
Authors: Sinclair, J. A.; Orton, G. S.; Greathouse, T. K.; Fletcher,
L. N.; Tao, C.; Gladstone, G. R.; Adriani, A.; Dunn, W.; Moses, J. I.;
Hue, V.; Irwin, P. G. J.; Melin, H.; Giles, R. S.
2017GeoRL..44.5345S Altcode:
We present retrievals of the vertical temperature profile of Jupiter's
high latitudes from Infrared Telescope Facility-Texas Echelon Cross
Echelle Spectrograph measurements acquired on 10-11 December 2014 and
30 April to 1 May 2016. Over this time range, 1 mbar temperature in
Jupiter's northern and southern auroral regions exhibited independent
evolution. The northern auroral hot spot exhibited negligible net
change in temperature at 1 mbar and its longitudinal position remained
fixed at 180°W (System III), whereas the southern auroral hot spot
exhibited a net increase in temperature of 11.1 ± 5.2 K at 0.98
mbar and its longitudinal orientation moved west by approximately
30°. This southern auroral stratospheric temperature increase might
be related to (1) near-contemporaneous brightening of the southern
auroral ultraviolet/near-infrared H3+ emission measured by the Juno
spacecraft and (2) an increase in the solar dynamical pressure in the
preceding 3 days. We therefore suggest that 1 mbar temperature in the
southern auroral region might be modified by higher-energy charged
particle precipitation.
---------------------------------------------------------
Title: Latitudinal variability in Jupiter's tropospheric
disequilibrium species: GeH<SUB>4</SUB>, AsH<SUB>3</SUB> and
PH<SUB>3</SUB>
Authors: Giles, R. S.; Fletcher, L. N.; Irwin, P. G. J.
2017Icar..289..254G Altcode: 2016arXiv161009073G
Jupiter's tropospheric composition is studied using high-resolution,
spatially-resolved 5-μm observations from the CRIRES instrument
at the Very Large Telescope. The high resolving power (R = 96,000)
allows us to spectrally resolve the line shapes of individual
molecular species in Jupiter's troposphere and, by aligning the slit
north-south along Jupiter's central meridian, we are able to search
for any latitudinal variability. Despite the high spectral resolution,
we find that there are significant degeneracies between the cloud
structure and aerosol scattering properties that complicate the
retrievals of tropospheric gaseous abundances and limit conclusions
on any belt-zone variability. However, we do find evidence for
variability between the equatorial regions of the planet and the polar
regions. Arsine (AsH<SUB>3</SUB>) and phosphine (PH<SUB>3</SUB>) both
show an enhancement at high latitudes, while the abundance of germane
(GeH<SUB>4</SUB>) remains approximately constant. These observations
contrast with the theoretical predictions from Wang et al. (2016)
and we discuss the possible explanations for this difference.
---------------------------------------------------------
Title: Cycles of activity in the Jovian atmosphere
Authors: Fletcher, L. N.
2017GeoRL..44.4725F Altcode: 2017arXiv170805180F
Jupiter's banded appearance may appear unchanging to the casual
observer, but closer inspection reveals a dynamic, ever-changing system
of belts and zones with distinct cycles of activity. Identification
of these long-term cycles requires access to data sets spanning
multiple Jovian years, but explaining them requires multispectral
characterization of the thermal, chemical, and aerosol changes
associated with visible color variations. The Earth-based support
campaign for Juno's exploration of Jupiter has already characterized
two upheaval events in the equatorial and temperate belts that are
part of long-term Jovian cycles, whose underlying sources could be
revealed by Juno's exploration of Jupiter's deep atmosphere.
---------------------------------------------------------
Title: Non-Gaussian Velocity Distributions in Solar Flares from
Extreme Ultraviolet Lines: A Possible Diagnostic of Ion Acceleration
Authors: Jeffrey, Natasha L. S.; Fletcher, Lyndsay; Labrosse, Nicolas
2017ApJ...836...35J Altcode: 2017arXiv170102196J
In a solar flare, a large fraction of the magnetic energy released
is converted rapidly to the kinetic energy of non-thermal particles
and bulk plasma motion. This will likely result in non-equilibrium
particle distributions and turbulent plasma conditions. We investigate
this by analyzing the profiles of high temperature extreme ultraviolet
emission lines from a major flare (SOL2014-03-29T17:44) observed by
the EUV Imaging Spectrometer (EIS) on Hinode. We find that in many
locations the line profiles are non-Gaussian, consistent with a kappa
distribution of emitting ions with properties that vary in space and
time. At the flare footpoints, close to sites of hard X-ray emission
from non-thermal electrons, the κ index for the Fe xvi 262.976 Å
line at 3 MK takes values of 3-5. In the corona, close to a low-energy
HXR source, the Fe xxiii 263.760 Å line at 15 MK shows κ values of
typically 4-7. The observed trends in the κ parameter show that we are
most likely detecting the properties of the ion population rather than
any instrumental effects. We calculate that a non-thermal ion population
could exist if locally accelerated on timescales ≤0.1 s. However,
observations of net redshifts in the lines also imply the presence of
plasma downflows, which could lead to bulk turbulence, with increased
non-Gaussianity in cooler regions. Both interpretations have important
implications for theories of solar flare particle acceleration.
---------------------------------------------------------
Title: Summer at Saturn's North Pole: Seasonal Changes Seen by ISS
& CIRS on Cassini, and VLT on the Ground
Authors: Sayanagi, K. M.; Blalock, J.; Fletcher, L. N.; Ingersoll,
A. P.; Dyudina, U.; Ewald, S. P.
2016AGUFM.P33B2137S Altcode:
We report seasonal changes in Saturn's north polar vortex seen by
Cassini ISS, Cassini CIRS, and ground-based VLT VISIR thermal infrared
observations. ISS observation of Saturn's northern high latitudes show
that a reflective, bright polar spot has formed over the north pole,
seen first in images captured in 2016. This coincides with the warm
cyclonic north polar vortex that has been steadily warming since it
was first discovered in 2007 by Cassini CIRS. The reflective spot was
not present when the north pole was observed during the previous period
of Cassini spacecraft's high-inclination orbits in 2012. In 2012, the
concentration of light-scattering aerosols within 2-degree latitude of
the north pole appeared to be less than that of the surrounding region,
and appeared dark in all ISS filters. The new bright spot over the north
pole is similar to that over the south pole seen in 2007. In 2007,
Saturn was approaching the equinox of 2009 and south pole had been
continuously illuminated since the previous equinox in 1995. The bright
spot over the summer south pole in 2007 was hypothesized to consist
of aerosols produced by ultraviolet photodissociation of hydrocarbon
molecules; we follow this hypothesis to propose that the new bright spot
over the north pole is also produced by the same mechanism. We argue
that, in 2012 (3 years after equinox), the north polar bright spot
hadn't formed because the ultraviolet insolation was not sufficient
to produce enough photochemical aerosols. The new polar bright cloud
formation is consistent with the rising abundances of stratospheric
hydrocarbons (potential precursors to aerosol formation) over the north
polar region as tracked by CIRS (Fletcher et al., 2015). In addition
to ISS images, we also present CIRS and VLT-VISIR thermal maps of the
northern high latitudes as the new north polar bright spot is expected
to have implications on radiative energy balance. Our research has
been supported by the Cassini Project, NASA grants OPR NNX11AM45G,
CDAPS NNX15AD33G, PATM NNX14AK07G, and NSF grant AAG 1212216.
---------------------------------------------------------
Title: The strength and evolution of stratospheric-auroral processes
on Jupiter, as observed by IRTF-TEXES
Authors: Sinclair, J. A.; Orton, G. S.; Greathouse, T. K.; Fletcher,
L. N.; Moses, J. I.; Hue, V.; Irwin, P. G.; Melin, H.; Giles, R.
2016AGUFM.P33C2149S Altcode:
Auroral processes on Jupiter are evident over a large range of
wavelengths. Juno's JIRAM (Jovian Infrared Auroral Mapper) and UVS
(Ultraviolet Spectrometer) instruments will observe Jupiter's auroral
emission at near-infrared and ultraviolet wavelengths, highlighting the
precipitation of charged particles in Jupiter's thermosphere. These
observations can then be related to measurements by Juno's MAG
(magnetometer), JADE (Jovian Auroral Distributions Experiment) and
JEDI instruments (Jovian Energetic Particle Detector Instrument),
which will prove a powerful tool in studying the interaction of
Jupiter's atmosphere with the external magnetosphere. However, Juno's
scientific payload does not include a mid-infrared instrument (5 -
15 microns) capable of sounding Jupiter's stratosphere in which a
significant amount of energy associated with auroral processes is
deposited. As demonstrated by Sinclair et al., 2016a (under review)
from a retrieval analysis of Voyager-IRIS (Infrared Interferometer
Spectrometer) observations in 1979, Cassini-CIRS (Composite Infrared
Spectrometer) observations in 2001 and IRTF-TEXES (Texas Echelon Cross
Echelle Spectrograph) observations in 2014, temperatures in the northern
auroral region at 70°N, 180°W are elevated by up to approximately 20
K and 35 K at the 1-mbar and 10-ubar levels respectively, in comparison
to quiescent longitudes (see attached Figure). However, the physical
mechanisms responsible for modifications of the thermal structure
and composition of the stratosphere in auroral regions are still not
well understood. We hope to better understand the processes driving
the auroral-stratosphere interaction on Jupiter by characterizing
whether and by what magnitude the thermal structure and composition
of the stratosphere evolve at Jupiter's high latitudes. In April 2016,
we obtained IRTF-TEXES measurements of Jupiter's high-latitudes under
similar conditions to those obtained in December 2014. We will perform
a retrieval analysis to determine the vertical profiles of temperature,
C2H2, C2H4 and C2H6. Results will be compared with those in December
2014 to determine the 3D evolution of the thermal structure and
composition in proximity to the auroral regions: the attached Figure
shows preliminary temperature results.
---------------------------------------------------------
Title: Arcade Implosion Caused by a Filament Eruption in a Flare
Authors: Wang, Juntao; Simões, P. J. A.; Fletcher, L.; Thalmann,
J. K.; Hudson, H. S.; Hannah, I. G.
2016ApJ...833..221W Altcode: 2016arXiv161005931W
Coronal implosions—the convergence motion of plasmas and entrained
magnetic field in the corona due to a reduction in magnetic
pressure—can help to locate and track sites of magnetic energy
release or redistribution during solar flares and eruptions. We report
here on the analysis of a well-observed implosion in the form of an
arcade contraction associated with a filament eruption, during the
C3.5 flare SOL2013-06-19T07:29. A sequence of events including the
magnetic flux-rope instability and distortion, followed by a filament
eruption and arcade implosion, lead us to conclude that the implosion
arises from the transfer of magnetic energy from beneath the arcade
as part of the global magnetic instability, rather than due to local
magnetic energy dissipation in the flare. The observed net contraction
of the imploding loops, which is found also in nonlinear force-free
field extrapolations, reflects a permanent reduction of magnetic
energy underneath the arcade. This event shows that, in addition to
resulting in the expansion or eruption of an overlying field, flux-rope
instability can also simultaneously implode an unopened field due to
magnetic energy transfer. It demonstrates the “partial opening of
the field” scenario, which is one of the ways in 3D to produce a
magnetic eruption without violating the Aly-Sturrock hypothesis. In
the framework of this observation, we also propose a unification of
three main concepts for active region magnetic evolution, namely the
metastable eruption model, the implosion conjecture, and the standard
“CSHKP” flare model.
---------------------------------------------------------
Title: SPRITE - The Saturn PRobe Interior and aTmosphere Explorer
Mission.
Authors: Atkinson, D. H.; Simon, A. A.; Banfield, D. J.; Atreya,
S. K.; Blacksberg, J.; Brinckerhoff, W. B.; Colaprete, A.; Coustenis,
A.; Danner, R. M.; Fletcher, L. N.; Guillot, T.; Hofstadter, M. D.;
Keithly, D.; Lobbia, M. A.; Lunine, J. I.; Mahaffy, P. R.; Marley,
M. S.; Mousis, O.; Spilker, T. R.; Trainer, M. G.; Webster, C. R.;
Youmans, T. A.
2016AGUFM.P33B2132A Altcode:
The 2013-2022 Planetary Science Decadal Survey (PSDS) Vision and Voyages
Planetary identified a Saturn Probe mission as a high priority mission
target for the NASA New Frontiers program. Fundamental measurements of
noble gas abundances and isotope ratios of hydrogen, carbon, oxygen,
and nitrogen, as well as the interior structure of Saturn are needed to
help constrain Solar System formation models and to provide an improved
context for understanding exoplanet systems. The SPRITE mission would
fulfill the PSDS scientific goals for in situ exploration of Saturn, and
would additionally provide ground truth for remote sensing that would
improve the understanding of the composition and interior structure of
Saturn and, by proxy, extrasolar giant planets. In Situ measurements are
the only means to address many key questions regarding the structure
and composition of Saturn's atmosphere including the abundance of
noble gases and key isotopes, the abundance of helium needed to
understand the formation history and thermal evolution of Saturn,
and the abundance of water in the deep atmosphere, a key diagnostic
of Saturn's formation since it is thought that the heavy elements were
delivered by water-bearing planetesimals. The SPRITE atmospheric entry
probe mission including remote sensing from a carrier-relay spacecraft
would measure many of these key atmospheric constituents as well as
the atmospheric structure of Saturn including temperature, pressure
and wind speeds along the probe descent path thereby providing interior
science not accessible to remote sensing measurements. Additionally, the
SPRITE carrier-relay spacecraft would make remote sensing measurements
to support probe measurements in the upper troposphere of Saturn.
---------------------------------------------------------
Title: Analysis of Saturn's Hexagon between 2012 and 2016: Dynamical
and Morphological Changes
Authors: Blalock, J.; Sayanagi, K. M.; Fletcher, L. N.; Ingersoll,
A. P.; Dyudina, U.; Ewald, S. P.
2016AGUFM.P31D..06B Altcode:
We present analyses of Saturn's wind fields and cloud morphology in
the northern Hexagon region, combining visible-light imaging from the
Cassini ISS instrument with measurements of Saturn's thermal structure
and zonal wind shear from the Cassini CIRS instrument and ground-based
VLT/VISIR imaging. Our study focuses on temporal changes occurring
in the region around 77 degree N planetocentric latitude, which has
been illuminated by sunlight since 2008, and captured by ISS with good
observation geometries in 2012-2013 and 2016. The goal of our analysis
is to detect any change in the cloud morphology, atmospheric dynamics
and thermal structure. To measure the wind field in the Hexagon region,
we utilize the two-dimensional correlation imaging velocimetry (CIV)
technique. We also calculate the relative vorticity and divergence from
the wind field. To detect changes in the dynamics of the Hexagon, we
compare measurements of the wind, relative vorticity, and divergence
in 2012 with those from 2016, as well as evaluating changes in the
zonal mean temperature gradient across the Hexagon boundaries. We
compare cloud reflectivity between 2012 and 2016 in images that
show the Hexagon under similar illumination conditions, calculating
the zonal mean reflectivity as a function of latitude. Furthermore,
we assess the winds and cloud reflectivity at several wavelengths in
order to look for changes occurring at different altitudes, and relate
this to temperature variations in the 100-700 mbar region assessed from
Cassini and ground-based VLT imaging. Specifically, we focus on the CB2
continuum filter which senses thick tropospheric clouds and the MT2 and
MT3 methane filters which sense the upper tropospheric and stratospheric
haze layers. Our work has been supported by NASA PATM NNX14AK07G,
CDAPS NNX15AD33G, NSF AAG 1212216, and NASA NESSF NNX15AQ70H.
---------------------------------------------------------
Title: Photochemistry in Saturn's Ring-Shadowed Atmosphere: Modulation
of Hydrocarbons and Observations of Dust Content
Authors: Edgington, S. G.; Atreya, S. K.; Wilson, E. H.; Baines,
K. H.; West, R. A.; Bjoraker, G. L.; Fletcher, L. N.; Momary, T.
2016AGUFM.P33B2133E Altcode:
Cassini has been orbiting Saturn for over twelve years now. During this
epoch, the ring shadow has moved from covering much of the northern
hemisphere with solar inclination of 24 degrees to covering a large
swath south of the equator and it continues to move southward. At
Saturn Orbit Insertion in 2004, the projection of the A-ring onto
Saturn reached as far as 40N along the central meridian (52N at
the terminator). At its maximum extent, the ring shadow can reach
as far as 48N/S (58N/S at the terminator). The net effect is that
the intensity of both ultraviolet and visible sunlight penetrating
through the rings to any particular latitude will vary depending on
both Saturn's axis relative to the Sun and the optical thickness of
each ring system. In essence, the rings act like semi-transparent
venetian blinds.Previous work examined the variation of the solar
flux as a function of solar inclination, i.e. for each 7.25-year
season at Saturn. Here, we report on the impact of the oscillating
ring shadow on the photolysis and production rates of hydrocarbons
(acetylene, ethane, propane, and benzene) and phosphine in Saturn's
stratosphere and upper troposphere. The impact of these production
and loss rates on the abundance of long-lived photochemical products
leading to haze formation are explored. We assess their impact on
phosphine abundance, a disequilibrium species whose presence in the
upper troposphere can be used as a tracer of convective processes in
the deeper atmosphere.We will also present our ongoing analysis of
Cassini's CIRS, UVIS, and VIMS datasets that provide an estimate of the
evolving haze content of the northern hemisphere and we will begin to
assess the implications for dynamical mixing. In particular, we will
examine how the now famous hexagonal jet stream acts like a barrier to
transport, isolating Saturn's north polar region from outside transport
of photochemically-generated molecules and haze.The research described
in this paper was carried out in part at the Jet Propulsion Laboratory,
California Institute of Technology, under a contract with the National
Aeronautics and Space Administration. Copyright 2016 California
Institute of Technology. Government sponsorship is acknowledged.
---------------------------------------------------------
Title: Evidence for kappa distributions of ions in the flaring solar
atmosphere from extreme ultraviolet spectroscopy
Authors: Fletcher, L.; Jeffrey, N. L. S.; Labrosse, N.
2016AGUFMSH13D..02F Altcode:
We present new evidence for ion kappa distributions in the lower
solar atmosphere, and in the solar corona, during the impulsive
energy release phase of solar flares. The existence of non-Maxwellian
electron distributions during flares is well established from X-ray
spectroscopy, but ion populations are harder to diagnose. By careful
fitting of the spectral line profiles from highly ionised states
of iron observed during flares by the Extreme Ultraviolet Imaging
Spectrometer (EIS) on the Hinode spacecraft, and taking into account
the spectrometer's known instrumental characteristics, we establish
that the physical line profile is consistent with that emitted by a
kappa distribution of ions. Kappa distributions provide a far better
fit than Maxwellian distributions in many cases, and are detected both
at the chromospheric footpoints and in the corona during flares, but
with different parameters. We discuss the possible origins of these ion
distributions, and their implications for solar flare ion acceleration.
---------------------------------------------------------
Title: Tapping the Core - a study of Alfvénic energy flow in an
erupting flux-rope configuration
Authors: Fletcher, L.; Dalmasse, K.; Gibson, S. E.; Fan, Y.
2016AGUFMSH31B2564F Altcode:
We analyze the evolution of reconnecting magnetic field in a 3-D
numerical simulation of a partially-ejected solar flux rope, with a
focus on understanding how the flux rope dynamics is linked to the
flow of energy through the field and the solar atmosphere as Alfvénic
Poynting flux. The magnetic flux rope splits in two during its eruption,
with reconnection taking place between the erupting rope and surrounding
fields, and internally in the strong field of the rope. We track the
Poynting flux entering and leaving the simulation current sheets,
and by mapping this down to the solar surface we identify locations of
weak and strong energy deposition in the lower atmosphere. Our tracking
method enables us to link the lower atmosphere signatures to different
stages of the coronal reconnection. We find a predominantly two-ribbon
morphology in the locations of Poynting flux deposition in the lower
atmosphere, in which the transition from reconnection involving weaker
field external to the flux rope, to reconnection involving the flux rope
core field, is accompanied by rapid ribbon spreading. In the core-field
reconnection phase, ribbons move into strong field regions on the
solar surface, and locations of highly concentrated downward-directed
Poynting flux are found, which may be linked to the most energetic flare
`footpoints' seen in optical and hard X-ray emission.
---------------------------------------------------------
Title: Recruiting flare hunters for citizen science
Authors: Fletcher, Lyndsay; Berlicki, Arkadiusz; Awasthi, Arun Kumar;
Gronkiewicz, Dominik
2016A&G....57f6.21F Altcode:
Lyndsay Fletcher, Arkadiusz Berlicki, Arun Kumar Awasthi and Dominik
Gronkiewicz describe how they established F-HUNTERS, a pro-am solar
flare observing campaign.
---------------------------------------------------------
Title: Doppler speeds of the hydrogen Lyman lines in solar flares
from EVE
Authors: Brown, Stephen A.; Fletcher, Lyndsay; Labrosse, Nicolas
2016A&A...596A..51B Altcode: 2016arXiv161004007B
<BR /> Aims: The hydrogen Lyman lines provide important diagnostic
information about the dynamics of the chromosphere, but there have
been few systematic studies of their variability during flares. We
investigate Doppler shifts in these lines in several flares, and use
these to calculate plasma speeds. <BR /> Methods: We use spectral data
from the Multiple EUV Grating Spectrograph B (MEGS-B) detector of the
Extreme-Ultraviolet Variability Experiment (EVE) instrument on the Solar
Dynamics Observatory. MEGS-B obtains full-disk spectra of the Sun at
a resolution of 0.1 nm in the range 37-105 nm, which we analyse using
three independent methods. The first method performs Gaussian fits to
the lines, and compares the quiet-Sun centroids with the flaring ones
to obtain the Doppler shifts. The second method uses cross-correlation
to detect wavelength shifts between the quiet-Sun and flaring line
profiles. The final method calculates the "center-of-mass" of the line
profile, and compares the quiet-Sun and flaring centroids to obtain the
shift. <BR /> Results: In a study of 6 flares we find strong signatures
of both upflow and downflow in the Lyman lines, with speeds measured
in Sun-as-a-Star data of around 10 km s<SUP>-1</SUP>, and speeds in the
flare excess signal of around 30 km s<SUP>-1</SUP>. <BR /> Conclusions:
All events showing upflows in Lyman lines are associated with some kind
of eruption or coronal flow in imaging data, which may be responsible
for the net blueshifts. Events showing downflows in the Lyman lines
may be associated with loop contraction or faint downflows, but it is
likely that chromospheric condensation flows are also contributing.
---------------------------------------------------------
Title: Doppler speeds of the hydrogen Lyman lines in solar flares
from EVE
Authors: Brown, Stephen; Fletcher, Lyndsay; Labrosse, Nicolas
2016usc..confE...7B Altcode:
The hydrogen Lyman lines provide important diagnostic information
about the dynamics of the chromosphere, but until recently there have
been few systematic studies of their variability during flares. We
investigate Doppler shifts in these lines in several flares, and
use these to calculate plasma speeds. We use spectral data from the
Multiple EUV Grating Spectrograph B (MEGS-B) detector on board the
Extreme-Ultraviolet Variability Experiment (EVE) instrument on the Solar
Dynamics Observatory. MEGS-B obtains full-disk spectra of the Sun at
a resolution of 0.1nm in the range 37-105nm, which we analyse using
three independent methods. The first method performs Gaussian fits to
the lines, and compares the quiet-Sun centroids with the flaring ones
to obtain the Doppler shifts. The second method uses cross-correlation
to detect wavelength shifts between the quiet-Sun and flaring line
profiles. The final method calculates the "center-of-mass" of the line
profile, and compares the quiet-Sun and flaring centroids to obtain
the shift. In a study of 6 flares we find signatures of both upflow
and downflow in the Lyman lines, with speeds of around 10 km s^-1 in
the line profiles that have not undergone pre-flare subtraction, and
speeds in the flare-excess profiles of around 30 km s^-1 . We include
analysis of AIA images of these events in order to understand potential
contributions from material ejections, and find that not all upflows
can be explained by ejecta. We discuss current and future attempts at
modelling these line profiles.
---------------------------------------------------------
Title: The Hera Saturn entry probe mission
Authors: Mousis, O.; Atkinson, D. H.; Spilker, T.; Venkatapathy, E.;
Poncy, J.; Frampton, R.; Coustenis, A.; Reh, K.; Lebreton, J. -P.;
Fletcher, L. N.; Hueso, R.; Amato, M. J.; Colaprete, A.; Ferri, F.;
Stam, D.; Wurz, P.; Atreya, S.; Aslam, S.; Banfield, D. J.; Calcutt,
S.; Fischer, G.; Holland, A.; Keller, C.; Kessler, E.; Leese, M.;
Levacher, P.; Morse, A.; Muñoz, O.; Renard, J. -B.; Sheridan, S.;
Schmider, F. -X.; Snik, F.; Waite, J. H.; Bird, M.; Cavalié, T.;
Deleuil, M.; Fortney, J.; Gautier, D.; Guillot, T.; Lunine, J. I.;
Marty, B.; Nixon, C.; Orton, G. S.; Sánchez-Lavega, A.
2016P&SS..130...80M Altcode: 2015arXiv151007685M
The Hera Saturn entry probe mission is proposed as an M-class mission
led by ESA with a contribution from NASA. It consists of one atmospheric
probe to be sent into the atmosphere of Saturn, and a Carrier-Relay
spacecraft. In this concept, the Hera probe is composed of ESA
and NASA elements, and the Carrier-Relay Spacecraft is delivered
by ESA. The probe is powered by batteries, and the Carrier-Relay
Spacecraft is powered by solar panels and batteries. We anticipate
two major subsystems to be supplied by the United States, either by
direct procurement by ESA or by contribution from NASA: the solar
electric power system (including solar arrays and the power management
and distribution system), and the probe entry system (including the
thermal protection shield and aeroshell). Hera is designed to perform
in situ measurements of the chemical and isotopic compositions as
well as the dynamics of Saturn's atmosphere using a single probe, with
the goal of improving our understanding of the origin, formation, and
evolution of Saturn, the giant planets and their satellite systems,
with extrapolation to extrasolar planets. Hera's aim is to probe
well into the cloud-forming region of the troposphere, below the
region accessible to remote sensing, to the locations where certain
cosmogenically abundant species are expected to be well mixed. By
leading to an improved understanding of the processes by which giant
planets formed, including the composition and properties of the local
solar nebula at the time and location of giant planet formation,
Hera will extend the legacy of the Galileo and Cassini missions by
further addressing the creation, formation, and chemical, dynamical,
and thermal evolution of the giant planets, the entire solar system
including Earth and the other terrestrial planets, and formation of
other planetary systems.
---------------------------------------------------------
Title: A dispersive wave pattern on Jupiter's fastest retrograde
jet at 20°S
Authors: Rogers, J. H.; Fletcher, L. N.; Adamoli, G.; Jacquesson,
M.; Vedovato, M.; Orton, G. S.
2016Icar..277..354R Altcode: 2016arXiv160507883R
A compact wave pattern has been identified on Jupiter's fastest
retrograding jet at 20°S (the SEBs) on the southern edge of the
South Equatorial Belt. The wave has been identified in both reflected
sunlight from amateur observations between 2010 and 2015, thermal
infrared imaging from the Very Large Telescope and near infrared
imaging from the Infrared Telescope Facility. The wave pattern is
present when the SEB is relatively quiescent and lacking large-scale
disturbances, and is particularly notable when the belt has undergone a
fade (whitening). It is generally not present when the SEB exhibits its
usual large-scale convective activity ('rifts'). Tracking of the wave
pattern and associated white ovals on its southern edge over several
epochs have permitted a measure of the dispersion relationship, showing
a strong correlation between the phase speed (-43.2 to -21.2 m/s) and
the longitudinal wavelength, which varied from 4.4 to 10.0° longitude
over the course of the observations. Infrared imaging sensing low
pressures in the upper troposphere suggest that the wave is confined
to near the cloud tops. The wave is moving westward at a phase speed
slower (i.e., less negative) than the peak retrograde wind speed
(-62 m/s), and is therefore moving east with respect to the SEBs jet
peak. Unlike the retrograde NEBn jet near °N, which is a location of
strong vertical wind shear that sometimes hosts Rossby wave activity,
the SEBs jet remains retrograde throughout the upper troposphere,
suggesting the SEBs pattern cannot be interpreted as a classical Rossby
wave. 2D windspeeds and thermal gradients measured by Cassini in 2000
are used to estimate the quasi-geostrophic potential vorticity gradient
as a means of understanding the origin of the a wave. We find that
the vorticity gradient is dominated by the baroclinic term and becomes
negative (changes sign) in a region near the cloud-top level (400-700
mbar) associated with the SEBs. Such a sign reversal is a necessary (but
not sufficient) condition for the growth of baroclinic instabilities,
which is a potential source of the meandering wave pattern.
---------------------------------------------------------
Title: A pioneer of solar astronomy
Authors: Dalla, Silvia; Fletcher, Lyndsay
2016A&G....57e5.21D Altcode:
Silvia Dalla and Lyndsay Fletcher assess the work of Annie Maunder,
an outstanding observer and interpreter of observations, who argued
for her innovative ideas with power and eloquence.
---------------------------------------------------------
Title: Simulations of the Mg II k and Ca II 8542 lines from an
AlfvÉn Wave-heated Flare Chromosphere
Authors: Kerr, Graham S.; Fletcher, Lyndsay.; Russell, Alexander J. B.;
Allred, Joel C.
2016ApJ...827..101K Altcode: 2016arXiv160505888K
We use radiation hydrodynamic simulations to examine two models of solar
flare chromospheric heating: Alfvén wave dissipation and electron beam
collisional losses. Both mechanisms are capable of strong chromospheric
heating, and we show that the distinctive atmospheric evolution in
the mid-to-upper chromosphere results in Mg II k-line emission that
should be observably different between wave-heated and beam-heated
simulations. We also present Ca II 8542 Å profiles that are formed
slightly deeper in the chromosphere. The Mg II k-line profiles from our
wave-heated simulation are quite different from those from a beam-heated
model and are more consistent with Interface Region Imaging Spectrograph
observations. The predicted differences between the Ca II 8542 Å in
the two models are small. We conclude that careful observational and
theoretical study of lines formed in the mid-to-upper chromosphere
holds genuine promise for distinguishing between competing models for
chromospheric heating in flares.
---------------------------------------------------------
Title: Flares In Time-Domain Surveys
Authors: Kowalski, Adam; Hawley, Suzanne; Davenport, James; Berlicki,
Arkadiusz; Cauzzi, Gianna; Fletcher, Lyndsay; Heinzel, Petr; Notsu,
Yuta; Loyd, Parke; Martinez Oliveros, Juan Carlos; Pugh, Chloe;
Schmidt, Sarah Jane; Karmakar, Subhajeet; Pye, John; Flaccomio, Ettore
2016csss.confE.126K Altcode:
Proceedings for the splinter session "Flares in Time-Domain Surveys"
convened at Cool Stars 19 on June 07, 2016 in Uppsala, Sweden. Contains
a two page summary of the splinter session, links to YouTube talks,
and a PDF copy of the slides from the presenters.
---------------------------------------------------------
Title: Probing Saturn's tropospheric cloud with Cassini/VIMS
Authors: Barstow, J. K.; Irwin, P. G. J.; Fletcher, L. N.; Giles,
R. S.; Merlet, C.
2016Icar..271..400B Altcode: 2016arXiv160102978B
In its decade of operation the Cassini mission has allowed us to look
deep into Saturn's atmosphere and investigate the processes occurring
below its enshrouding haze. We use Visual and Infrared Mapping
Spectrometer (VIMS) 4.6-5.2 μm data from early in the mission to
investigate the location and properties of Saturn's cloud structure
between 0.6 and 5 bar. We average nightside spectra from 2006 over
latitude circles and model the spectral limb darkening using the NEMESIS
radiative transfer and retrieval tool. We present our best-fit deep
cloud model for latitudes -40<SUP>∘</SUP> < λ <50<SUP>∘</SUP>
, along with retrieved abundances for NH<SUB>3</SUB>, PH<SUB>3</SUB> and
AsH<SUB>3</SUB>. We find an increase in NH<SUB>3</SUB> abundance at the
equator, a cloud base at ∼2.3 bar and no evidence for cloud particles
with strong absorption features in the 4.6-5.2 μm wavelength range, all
of which are consistent with previous work. Non-scattering cloud models
assuming a composition of either NH<SUB>3</SUB> or NH<SUB>4</SUB>SH,
with a scattering haze overlying, fit limb darkening curves and
spectra at all latitudes well; the retrieved optical depth for the
tropospheric haze is decreased in the northern (winter) hemisphere,
implying that the haze has a photochemical origin. Our ability to test
this hypothesis by examining spectra at different seasons is restricted
by the varying geometry of VIMS observations over the life of the
mission, and the appearance of the Saturn storm towards the end of 2010.
---------------------------------------------------------
Title: Time variability of Neptune's horizontal and vertical cloud
structure revealed by VLT/SINFONI and Gemini/NIFS from 2009 to 2013
Authors: Irwin, P. G. J.; Fletcher, L. N.; Tice, D.; Owen, S. J.;
Orton, G. S.; Teanby, N. A.; Davis, G. R.
2016Icar..271..418I Altcode:
New observations of Neptune's clouds in the near infrared were acquired
in October 2013 with SINFONI on ESO's Very Large Telescope (VLT) in
Chile. SINFONI is an Integral Field Unit spectrometer returning a 64
× 64 pixel image with 2048 wavelengths. Image cubes in the J-band
(1.09-1.41 μm) and H-band (1.43-1.87 μm) were obtained at spatial
resolutions of 0.1″and 0.025″per pixel, while SINFONI's adaptive
optics provided an effective resolution of approximately 0.1″. Image
cubes were obtained at the start and end of three successive nights
to monitor the temporal development of discrete clouds both at short
timescales (i.e. during a single night) as well as over the longer
period of the three-day observing run. These observations were compared
with similar H-band observations obtained in September 2009 with the
NIFS Integral Field Unit spectrometer on the Gemini-North telescope
in Hawaii, previously reported by Irwin et al. (2011) [Icarus, 216,
141-158], and previously unreported Gemini/NIFS observations at lower
spatial resolution made in 2011. <P />We find both similarities and
differences between these observations, spaced over four years. The
same overall cloud structure is seen with high, bright clouds visible
at mid-latitudes (30-40°N,S), with slightly lower clouds observed
at lower latitudes, together with small discrete clouds seen circling
the pole at a latitude of approximately 60°S. However, while discrete
clouds were visible at this latitude at both the main cloud deck level
(at 2-3 bar) and in the upper troposphere (100-500 mb) in 2009, no
distinct deep (2-3 bar), discrete circumpolar clouds were visible
in 2013, although some deep clouds were seen at the southern edge
of the main cloud belt at 30-40°S, which have not been observed
before. The nature of the deep sub-polar discrete clouds observed in
2009 is intriguing. While it is possible that in 2013 these deeper
clouds were masked by faster moving, overlying features, we consider
that it is unlikely that this should have happened in 2013, but not in
2009 when the upper-cloud activity was generally similar. Meanwhile,
the deep clouds seen at the southern edge of the main cloud belt at
30-40°S in 2013, should also have been detectable in 2009, but were
not seen. Hence, these observations may have detected a real temporal
variation in the occurrence of Neptune's deep clouds, pointing to
underlying variability in the convective activity at the pressure of
the main cloud deck at 2-3 bar near Neptune's south pole and also in
the main observable cloud belt at 30-40°S.
---------------------------------------------------------
Title: First evidence of non-Gaussian solar flare EUV spectral line
profiles and accelerated non-thermal ion motion
Authors: Jeffrey, Natasha L. S.; Fletcher, Lyndsay; Labrosse, Nicolas
2016A&A...590A..99J Altcode: 2016arXiv160107308J
Context. The properties of solar flare plasma can be determined from
the observation of optically thin lines. The emitting ion distribution
determines the shape of the spectral line profile, with an isothermal
Maxwellian ion distribution producing a Gaussian profile. Non-Gaussian
line profiles may indicate more complex ion distributions. <BR />
Aims: We investigate the possibility of determining flare-accelerated
non-thermal ion and/or plasma velocity distributions. <BR /> Methods:
We study EUV spectral lines produced during a flare SOL2013-05-15T01:45
using the Hinode EUV Imaging Spectrometer (EIS). The flare is located
close to the eastern solar limb with an extended loop structure,
allowing the different flare features: ribbons, hard X-ray (HXR)
footpoints and the loop-top source to be clearly observed in UV, EUV and
X-rays. EUV line spectroscopy is performed in seven different regions
covering the flare. We study the line profiles of the isolated and
unblended Fe XVI lines (λ262.9760 Å ) mainly formed at temperatures
of ~2 to 4 MK. Suitable Fe XVI line profiles at one time close to
the peak soft X-ray emission and free of directed mass motions are
examined using: 1. a higher moments analysis, 2. Gaussian fitting,
and 3. by fitting a kappa distribution line profile convolved with a
Gaussian to account for the EIS instrumental profile. <BR /> Results:
Fe XVI line profiles in the flaring loop-top, HXR footpoint and ribbon
regions can be confidently fitted with a kappa line profile with an
extra variable κ, giving low, non-thermal κ values between 2 and
3.3. An independent higher moments analysis also finds that many of the
spectral line kurtosis values are higher than the Gaussian value of 3,
even with the presence of a broad Gaussian instrumental profile. <BR
/> Conclusions: A flare-accelerated non-thermal ion population could
account for both the observed non-Gaussian line profiles, and for the
Fe XVI "excess" broadening found from Gaussian fitting, if the emitting
ions are interacting with a thermalised ~4 MK electron population,
and the instrumental profile is well-approximated by a Gaussian profile.
---------------------------------------------------------
Title: Detection of H<SUB>3</SUB><SUP>+</SUP> auroral emission in
Jupiter's 5-micron window
Authors: Giles, R. S.; Fletcher, L. N.; Irwin, P. G. J.; Melin, H.;
Stallard, T. S.
2016A&A...589A..67G Altcode: 2016arXiv160303646G
We use high-resolution ground-based observations from the VLT
CRIRES instrument in November 2012 to identify sixteen previously
undetected H<SUB>3</SUB><SUP>+</SUP> emission lines from Jupiter's
ionosphere. These emission lines are located in Jupiter's 5-micron
window (4.5-5.2 μm), an optically-thin region of the planet's spectrum
where the radiation mostly originates from the deep troposphere. The
H<SUB>3</SUB><SUP>+</SUP> emission lines are so strong that they are
visible even against this bright background. We measure the Doppler
broadening of the H<SUB>3</SUB><SUP>+</SUP> emission lines in order to
evaluate the kinetic temperature of the molecules, and we obtain a value
of 1390 ± 160 K. We also measure the relative intensities of lines in
the ν<SUB>2</SUB> fundamental in order to calculate the rotational
temperature, obtaining a value of 960 ± 40 K. Finally, we use the
detection of an emission line from the 2ν<SUB>2</SUB>(2)-ν<SUB>2</SUB>
overtone to measure a vibrational temperature of 925 ± 25 K. We
use these three independent temperature estimates to discuss the
thermodynamic equilibrium of Jupiter's ionosphere.
---------------------------------------------------------
Title: Telling twins apart: exo-Earths and Venuses with transit
spectroscopy
Authors: Barstow, J. K.; Aigrain, S.; Irwin, P. G. J.; Kendrew, S.;
Fletcher, L. N.
2016MNRAS.458.2657B Altcode: 2016arXiv160208277B; 2016MNRAS.tmp..271B
The planned launch of the James Webb Space Telescope (JWST) in
2018 will herald a new era of exoplanet spectroscopy. JWST will be
the first telescope sensitive enough to potentially characterize
terrestrial planets from their transmission spectra. In this work,
we explore the possibility that terrestrial planets with Venus-type
and Earth-type atmospheres could be distinguished from each other
using spectra obtained by JWST. If we find a terrestrial planet close
to the liquid water habitable zone of an M5 star within a distance
of 10 parsec, it would be possible to detect atmospheric ozone if
present in large enough quantities, which would enable an oxygen-rich
atmosphere to be identified. However, the cloudiness of a Venus-type
atmosphere would inhibit our ability to draw firm conclusions about
the atmospheric composition, making any result ambiguous. Observing
small, temperate planets with JWST requires significant investment of
resources, with single targets requiring of the order of 100 transits
to achieve sufficient signal to noise. The possibility of detecting a
crucial feature such as the ozone signature would need to be carefully
weighed against the likelihood of clouds obscuring gas absorption in
the spectrum.
---------------------------------------------------------
Title: Observations and Modelling of Helium Lines in Solar Flares
Authors: Simões, P. J. A.; Fletcher, L.; Labrosse, N.; Kerr, G. S.
2016ASPC..504..197S Altcode: 2015arXiv151203477S
We explore the response of the He <small>II</small> 304
Å and He <small>I</small> 584 Å line intensities to
electron beam heating in solar flares using radiative hydrodynamic
simulations. Comparing different electron beams parameters, we found
that the intensities of both He lines are very sensitive to the energy
flux deposited in the chromosphere, or more specifically to the heating
rate, with He <font size=2>II 304 Å being more sensitive to the
heating than He <small>I</small> 584 Å. Therefore, the He
line ratio increases for larger heating rates in the chromosphere. A
similar trend is found in observations, using SDO/EVE He irradiance
ratios and estimates of the electron beam energy rate obtained from
hard X-ray data. From the simulations, we also found that spectral
index of the electrons can affect the He ratio but a similar effect
was not found in the observations.
---------------------------------------------------------
Title: Division E Commission 10: Solar Activity
Authors: Schrijver, Carolus J.; Fletcher, Lyndsay; van Driel-Gesztelyi,
Lidia; Asai, Ayumi; Cally, Paul S.; Charbonneau, Paul; Gibson, Sarah
E.; Gomez, Daniel; Hasan, Siraj S.; Veronig, Astrid M.; Yan, Yihua
2016IAUTA..29..245S Altcode: 2015arXiv151003348S
After more than half a century of community support related to the
science of “solar activity”, IAU's Commission 10 was formally
discontinued in 2015, to be succeeded by C.E2 with the same area
of responsibility. On this occasion, we look back at the growth of
the scientific disciplines involved around the world over almost a
full century. Solar activity and fields of research looking into the
related physics of the heliosphere continue to be vibrant and growing,
with currently over 2,000 refereed publications appearing per year from
over 4,000 unique authors, publishing in dozens of distinct journals
and meeting in dozens of workshops and conferences each year. The
size of the rapidly growing community and of the observational and
computational data volumes, along with the multitude of connections
into other branches of astrophysics, pose significant challenges;
aspects of these challenges are beginning to be addressed through,
among others, the development of new systems of literature reviews,
machine-searchable archives for data and publications, and virtual
observatories. As customary in these reports, we highlight some
of the research topics that have seen particular interest over the
most recent triennium, specifically active-region magnetic fields,
coronal thermal structure, coronal seismology, flares and eruptions,
and the variability of solar activity on long time scales. We close
with a collection of developments, discoveries, and surprises that
illustrate the range and dynamics of the discipline.
---------------------------------------------------------
Title: The Europa Imaging System (EIS): High-Resolution Imaging and
Topography to Investigate Europa's Geology, Ice Shell, and Potential
for Current Activity
Authors: Turtle, E. P.; McEwen, A. S.; Collins, G. C.; Fletcher, L.;
Hansen, C. J.; Hayes, A. G.; Hurford, T. A.; Kirk, R. L.; Barr Mlinar,
A. C.; Nimmo, F.; Patterson, G. W.; Quick, L. C.; Soderblom, J. M.;
Thomas, N.; Ernst, C. M.
2016LPI....47.1626T Altcode:
Cameras to reveal / Europa's fractured landscapes / Ice shell mysteries.
---------------------------------------------------------
Title: Structures in the Outer Solar Atmosphere
Authors: Fletcher, L.; Cargill, P. J.; Antiochos, S. K.; Gudiksen,
B. V.
2016mssf.book..231F Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Spectral analysis of Uranus' 2014 bright storm with VLT/SINFONI
Authors: Irwin, P. G. J.; Fletcher, L. N.; Read, P. L.; Tice, D.;
de Pater, I.; Orton, G. S.; Teanby, N. A.; Davis, G. R.
2016Icar..264...72I Altcode: 2015arXiv151002274I
An extremely bright storm system observed in Uranus' atmosphere
by amateur observers in September 2014 triggered an international
campaign to observe this feature with many telescopes across the
world. Observations of the storm system in the near infrared were
acquired in October and November 2014 with SINFONI on ESO's Very
Large Telescope (VLT) in Chile. SINFONI is an Integral Field Unit
spectrometer returning 64 × 64 pixel images with 2048 wavelengths
and uses adaptive optics. Image cubes in the H-band (1.43-1.87 μm)
were obtained at spatial resolutions of ∼ 0.1″ per pixel. <P
/>The observations show that the centre of the storm feature shifts
markedly with increasing altitude, moving in the retrograde direction
and slightly poleward with increasing altitude. We also see a faint
'tail' of more reflective material to the immediate south of the
storm, which again trails in the retrograde direction. The observed
spectra were analysed with the radiative transfer and retrieval code,
NEMESIS (Irwin et al. [2008]. J. Quant. Spec. Radiat. Transfer, 109,
1136-1150). We find that the storm is well-modelled using either two
main cloud layers of a 5-layer aerosol model based on Sromovsky et
al. (Sromovsky et al. [2011]. Icarus, 215, 292-312) or by the simpler
two-cloud-layer model of Tice et al. (Tice et al. [2013]. Icarus,
223, 684-698). The deep component appears to be due to a brightening
(i.e. an increase in reflectivity) and increase in altitude of the
main tropospheric cloud deck at 2-3 bars for both models, while the
upper component of the feature was modelled as being due to either a
thickening of the tropospheric haze of the 2-layer model or a vertical
extension of the upper tropospheric cloud of the 5-layer model, assumed
to be composed of methane ice and based at the methane condensation
level of our assumed vertical temperature and abundance profile at
1.23 bar. We also found this methane ice cloud to be responsible for
the faint 'tail' seen to the feature's south and the brighter polar
'hood' seen in all observations polewards of ∼45°N for the 5-layer
model. <P />During the twelve days between our sets of observations
the higher-altitude component of the feature was observed to have
brightened significantly and extended to even higher altitudes, while
the deeper component faded.
---------------------------------------------------------
Title: Electric Current Circuits in Astrophysics
Authors: Kuijpers, Jan; Frey, Harald U.; Fletcher, Lyndsay
2016mssf.book....3K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Properties of Discrete and Axisymmetric Features in Jupiter's
Atmosphere from Observations of Thermal Emission: Recent Updates on
the Eve of the Juno Mission Arrival at Jupiter
Authors: Orton, G. S.; Fletcher, L. N.; Giles, R.; Sinclair, J.;
Greathouse, T. K.; Momary, T.; Yanamandra-Fisher, P. A.; Fujiyoshi,
T.; Fisher, B.; Payne, A.; Seede, R.; Simon, J.; Lai, M.; Nguyen,
M.; Fernandez, J.; Baines, K. H.
2015AGUFM.P41B2067O Altcode:
We have derived the spatial distribution and evolution of key properties
of Jupiter's atmosphere through the analysis of imaging and spatially
resolved spectroscopy of its thermal emission. These observations
and their analysis represent a source of data we plan to acquire
as a key component of support for the Juno mission's atmospheric
investigation. From thermal imaging and spectroscopy in the 7-25 µm
region, we can derive temperatures between 10 and 500 mbar atmospheric
pressure, cloud opacities between 500 mbar and 5 bars, the para-H2
fraction near 300 mbar, the 100-400 mbar distributions of ammonia and
phosphine, and the distribution of hydrocarbons in the stratosphere
(~1 µbar - 10 mbar). Earlier work determined atmospheric properties
of Jupiter's Great Red Spot (Fletcher et al. 2010, Icarus 208, 306)
and the evolution of the South Equatorial Belt (SEB) fade (whitening)
in 2009-2010 (Fletcher et al. 2011 Icarus, 213, 564). We will illustrate
recent results from an examination of (1) the revival (re-darkening)
of the SEB in 2010-2011, (2) discovery of uniquely dry regions of the
atmosphere that are identified with visible "brown barges" typically
located at the northern edge of Jupiter's North Equatorial Belt
(NEB), (3) vertical structure of stratospheric waves constituting
Jupiter's Quadrennial Oscillation (QQO) (Leovy et al. 1991, Nature
354, 380), and (4) previously unsuspected long-term tropospheric
thermal waves uncovered in our multi-year program covering well over
a Jovian year. Efforts are underway to provide mission-supporting
observations using mid-infrared facility and guest instruments at
several observatories during the 14-day orbits of the Juno mission,
particularly - but not exclusively - the early orbits dedicated to
remote sensing observations.
---------------------------------------------------------
Title: The Europa Imaging System (EIS): High-Resolution, 3-D Insight
into Europa's Geology, Ice Shell, and Potential for Current Activity
Authors: Turtle, E. P.; McEwen, A. S.; Collins, G. C.; Fletcher, L. N.;
Hansen, C. J.; Hayes, A.; Hurford, T., Jr.; Kirk, R. L.; Barr, A.;
Nimmo, F.; Patterson, G.; Quick, L. C.; Soderblom, J. M.; Thomas, N.
2015AGUFM.P13E..03T Altcode:
The Europa Imaging System will transform our understanding of Europa
through global decameter-scale coverage, three-dimensional maps,
and unprecedented meter-scale imaging. EIS combines narrow-angle and
wide-angle cameras (NAC and WAC) designed to address high-priority
Europa science and reconnaissance goals. It will: (A) Characterize
the ice shell by constraining its thickness and correlating surface
features with subsurface structures detected by ice penetrating
radar; (B) Constrain formation processes of surface features and
the potential for current activity by characterizing endogenic
structures, surface units, global cross-cutting relationships, and
relationships to Europa's subsurface structure, and by searching
for evidence of recent activity, including potential plumes; and (C)
Characterize scientifically compelling landing sites and hazards by
determining the nature of the surface at scales relevant to a potential
lander. The NAC provides very high-resolution, stereo reconnaissance,
generating 2-km-wide swaths at 0.5-m pixel scale from 50-km altitude,
and uses a gimbal to enable independent targeting. NAC observations
also include: near-global (>95%) mapping of Europa at ≤50-m
pixel scale (to date, only ~14% of Europa has been imaged at ≤500
m/pixel, with best pixel scale 6 m); regional and high-resolution
stereo imaging at <1-m/pixel; and high-phase-angle observations
for plume searches. The WAC is designed to acquire pushbroom stereo
swaths along flyby ground-tracks, generating digital topographic
models with 32-m spatial scale and 4-m vertical precision from 50-km
altitude. These data support characterization of cross-track clutter
for radar sounding. The WAC also performs pushbroom color imaging
with 6 broadband filters (350-1050 nm) to map surface units and
correlations with geologic features and topography. EIS will provide
comprehensive data sets essential to fulfilling the goal of exploring
Europa to investigate its habitability and perform collaborative science
with other investigations, including cartographic and geologic maps,
regional and high-resolution digital topography, GIS products, color
and photometric data products, a geodetic control network tied to
radar altimetry, and a database of plume-search observations.
---------------------------------------------------------
Title: Preface
Authors: Fletcher, L.; Heinzel, P.; van Driel-Gesztelyi, L.; Mandrini,
C. H.; Fárník, F.
2015SoPh..290.3379F Altcode: 2015SoPh..tmp..168F
No abstract at ADS
---------------------------------------------------------
Title: Impulsive Heating of Solar Flare Ribbons Above 10 MK
Authors: Simões, P. J. A.; Graham, D. R.; Fletcher, L.
2015SoPh..290.3573S Altcode: 2015arXiv150503384S; 2015SoPh..tmp...62S
The chromospheric response to the input of flare energy is marked
by extended extreme ultraviolet (EUV) ribbons and hard X-ray (HXR)
footpoints. These are usually explained as the result of heating and
bremsstrahlung emission from accelerated electrons colliding in the
dense chromospheric plasma. We present evidence of impulsive heating
of flare ribbons above 10 MK in a two-ribbon flare. We analyse the
impulsive phase of SOL2013-11-09T06:38, a C2.6 class event using
data from Atmospheric Imaging Assembly (AIA) on board of the Solar
Dynamics Observatory (SDO) and the Reuven Ramaty High Energy Solar
Spectroscopic Imager (RHESSI) to derive the temperature, emission
measure and differential emission measure of the flaring regions and
investigate the evolution of the plasma in the flaring ribbons. The
ribbons were visible at all SDO/AIA EUV/UV wavelengths, in particular,
at 94 and 131 Å filters, sensitive to temperatures of 8 MK and 12
MK. The time evolution of the emission measure of the plasma above 10
MK at the ribbons has a peak near the HXR peak time. The presence of
hot plasma in the lower atmosphere is further confirmed by a RHESSI
imaging spectroscopy analysis, which shows resolved sources at 11 -
13 MK that are associated with at least one ribbon. We found that
collisional beam-heating can only marginally explain the power necessary
to heat the 10 MK plasma at the ribbons.
---------------------------------------------------------
Title: The EChO science case
Authors: Tinetti, Giovanna; Drossart, Pierre; Eccleston, Paul; Hartogh,
Paul; Isaak, Kate; Linder, Martin; Lovis, Christophe; Micela, Giusi;
Ollivier, Marc; Puig, Ludovic; Ribas, Ignasi; Snellen, Ignas; Swinyard,
Bruce; Allard, France; Barstow, Joanna; Cho, James; Coustenis, Athena;
Cockell, Charles; Correia, Alexandre; Decin, Leen; de Kok, Remco;
Deroo, Pieter; Encrenaz, Therese; Forget, Francois; Glasse, Alistair;
Griffith, Caitlin; Guillot, Tristan; Koskinen, Tommi; Lammer, Helmut;
Leconte, Jeremy; Maxted, Pierre; Mueller-Wodarg, Ingo; Nelson, Richard;
North, Chris; Pallé, Enric; Pagano, Isabella; Piccioni, Guseppe;
Pinfield, David; Selsis, Franck; Sozzetti, Alessandro; Stixrude,
Lars; Tennyson, Jonathan; Turrini, Diego; Zapatero-Osorio, Mariarosa;
Beaulieu, Jean-Philippe; Grodent, Denis; Guedel, Manuel; Luz, David;
Nørgaard-Nielsen, Hans Ulrik; Ray, Tom; Rickman, Hans; Selig,
Avri; Swain, Mark; Banaszkiewicz, Marek; Barlow, Mike; Bowles, Neil;
Branduardi-Raymont, Graziella; du Foresto, Vincent Coudé; Gerard,
Jean-Claude; Gizon, Laurent; Hornstrup, Allan; Jarchow, Christopher;
Kerschbaum, Franz; Kovacs, Géza; Lagage, Pierre-Olivier; Lim, Tanya;
Lopez-Morales, Mercedes; Malaguti, Giuseppe; Pace, Emanuele; Pascale,
Enzo; Vandenbussche, Bart; Wright, Gillian; Ramos Zapata, Gonzalo;
Adriani, Alberto; Azzollini, Ruymán; Balado, Ana; Bryson, Ian;
Burston, Raymond; Colomé, Josep; Crook, Martin; Di Giorgio, Anna;
Griffin, Matt; Hoogeveen, Ruud; Ottensamer, Roland; Irshad, Ranah;
Middleton, Kevin; Morgante, Gianluca; Pinsard, Frederic; Rataj, Mirek;
Reess, Jean-Michel; Savini, Giorgio; Schrader, Jan-Rutger; Stamper,
Richard; Winter, Berend; Abe, L.; Abreu, M.; Achilleos, N.; Ade, P.;
Adybekian, V.; Affer, L.; Agnor, C.; Agundez, M.; Alard, C.; Alcala,
J.; Allende Prieto, C.; Alonso Floriano, F. J.; Altieri, F.; Alvarez
Iglesias, C. A.; Amado, P.; Andersen, A.; Aylward, A.; Baffa, C.;
Bakos, G.; Ballerini, P.; Banaszkiewicz, M.; Barber, R. J.; Barrado,
D.; Barton, E. J.; Batista, V.; Bellucci, G.; Belmonte Avilés,
J. A.; Berry, D.; Bézard, B.; Biondi, D.; Błęcka, M.; Boisse, I.;
Bonfond, B.; Bordé, P.; Börner, P.; Bouy, H.; Brown, L.; Buchhave,
L.; Budaj, J.; Bulgarelli, A.; Burleigh, M.; Cabral, A.; Capria,
M. T.; Cassan, A.; Cavarroc, C.; Cecchi-Pestellini, C.; Cerulli,
R.; Chadney, J.; Chamberlain, S.; Charnoz, S.; Christian Jessen,
N.; Ciaravella, A.; Claret, A.; Claudi, R.; Coates, A.; Cole, R.;
Collura, A.; Cordier, D.; Covino, E.; Danielski, C.; Damasso, M.;
Deeg, H. J.; Delgado-Mena, E.; Del Vecchio, C.; Demangeon, O.; De Sio,
A.; De Wit, J.; Dobrijévic, M.; Doel, P.; Dominic, C.; Dorfi, E.;
Eales, S.; Eiroa, C.; Espinoza Contreras, M.; Esposito, M.; Eymet,
V.; Fabrizio, N.; Fernández, M.; Femenía Castella, B.; Figueira,
P.; Filacchione, G.; Fletcher, L.; Focardi, M.; Fossey, S.; Fouqué,
P.; Frith, J.; Galand, M.; Gambicorti, L.; Gaulme, P.; García López,
R. J.; Garcia-Piquer, A.; Gear, W.; Gerard, J. -C.; Gesa, L.; Giani,
E.; Gianotti, F.; Gillon, M.; Giro, E.; Giuranna, M.; Gomez, H.;
Gomez-Leal, I.; Gonzalez Hernandez, J.; González Merino, B.; Graczyk,
R.; Grassi, D.; Guardia, J.; Guio, P.; Gustin, J.; Hargrave, P.; Haigh,
J.; Hébrard, E.; Heiter, U.; Heredero, R. L.; Herrero, E.; Hersant,
F.; Heyrovsky, D.; Hollis, M.; Hubert, B.; Hueso, R.; Israelian, G.;
Iro, N.; Irwin, P.; Jacquemoud, S.; Jones, G.; Jones, H.; Justtanont,
K.; Kehoe, T.; Kerschbaum, F.; Kerins, E.; Kervella, P.; Kipping, D.;
Koskinen, T.; Krupp, N.; Lahav, O.; Laken, B.; Lanza, N.; Lellouch,
E.; Leto, G.; Licandro Goldaracena, J.; Lithgow-Bertelloni, C.; Liu,
S. J.; Lo Cicero, U.; Lodieu, N.; Lognonné, P.; Lopez-Puertas,
M.; Lopez-Valverde, M. A.; Lundgaard Rasmussen, I.; Luntzer, A.;
Machado, P.; MacTavish, C.; Maggio, A.; Maillard, J. -P.; Magnes, W.;
Maldonado, J.; Mall, U.; Marquette, J. -B.; Mauskopf, P.; Massi, F.;
Maurin, A. -S.; Medvedev, A.; Michaut, C.; Miles-Paez, P.; Montalto,
M.; Montañés Rodríguez, P.; Monteiro, M.; Montes, D.; Morais, H.;
Morales, J. C.; Morales-Calderón, M.; Morello, G.; Moro Martín,
A.; Moses, J.; Moya Bedon, A.; Murgas Alcaino, F.; Oliva, E.; Orton,
G.; Palla, F.; Pancrazzi, M.; Pantin, E.; Parmentier, V.; Parviainen,
H.; Peña Ramírez, K. Y.; Peralta, J.; Perez-Hoyos, S.; Petrov, R.;
Pezzuto, S.; Pietrzak, R.; Pilat-Lohinger, E.; Piskunov, N.; Prinja,
R.; Prisinzano, L.; Polichtchouk, I.; Poretti, E.; Radioti, A.; Ramos,
A. A.; Rank-Lüftinger, T.; Read, P.; Readorn, K.; Rebolo López,
R.; Rebordão, J.; Rengel, M.; Rezac, L.; Rocchetto, M.; Rodler, F.;
Sánchez Béjar, V. J.; Sanchez Lavega, A.; Sanromá, E.; Santos,
N.; Sanz Forcada, J.; Scandariato, G.; Schmider, F. -X.; Scholz,
A.; Scuderi, S.; Sethenadh, J.; Shore, S.; Showman, A.; Sicardy, B.;
Sitek, P.; Smith, A.; Soret, L.; Sousa, S.; Stiepen, A.; Stolarski,
M.; Strazzulla, G.; Tabernero, H. M.; Tanga, P.; Tecsa, M.; Temple,
J.; Terenzi, L.; Tessenyi, M.; Testi, L.; Thompson, S.; Thrastarson,
H.; Tingley, B. W.; Trifoglio, M.; Martín Torres, J.; Tozzi, A.;
Turrini, D.; Varley, R.; Vakili, F.; de Val-Borro, M.; Valdivieso,
M. L.; Venot, O.; Villaver, E.; Vinatier, S.; Viti, S.; Waldmann,
I.; Waltham, D.; Ward-Thompson, D.; Waters, R.; Watkins, C.; Watson,
D.; Wawer, P.; Wawrzaszk, A.; White, G.; Widemann, T.; Winek, W.;
Wiśniowski, T.; Yelle, R.; Yung, Y.; Yurchenko, S. N.
2015ExA....40..329T Altcode: 2015ExA...tmp...67T; 2015arXiv150205747T
The discovery of almost two thousand exoplanets has revealed an
unexpectedly diverse planet population. We see gas giants in few-day
orbits, whole multi-planet systems within the orbit of Mercury,
and new populations of planets with masses between that of the Earth
and Neptune—all unknown in the Solar System. Observations to date
have shown that our Solar System is certainly not representative of
the general population of planets in our Milky Way. The key science
questions that urgently need addressing are therefore: What are
exoplanets made of? Why are planets as they are? How do planetary
systems work and what causes the exceptional diversity observed as
compared to the Solar System? The EChO (Exoplanet Characterisation
Observatory) space mission was conceived to take up the challenge to
explain this diversity in terms of formation, evolution, internal
structure and planet and atmospheric composition. This requires
in-depth spectroscopic knowledge of the atmospheres of a large and
well-defined planet sample for which precise physical, chemical and
dynamical information can be obtained. In order to fulfil this ambitious
scientific program, EChO was designed as a dedicated survey mission
for transit and eclipse spectroscopy capable of observing a large,
diverse and well-defined planet sample within its 4-year mission
lifetime. The transit and eclipse spectroscopy method, whereby the
signal from the star and planet are differentiated using knowledge of
the planetary ephemerides, allows us to measure atmospheric signals
from the planet at levels of at least 10<SUP>-4</SUP> relative to
the star. This can only be achieved in conjunction with a carefully
designed stable payload and satellite platform. It is also necessary
to provide broad instantaneous wavelength coverage to detect as many
molecular species as possible, to probe the thermal structure of the
planetary atmospheres and to correct for the contaminating effects of
the stellar photosphere. This requires wavelength coverage of at least
0.55 to 11 μm with a goal of covering from 0.4 to 16 μm. Only modest
spectral resolving power is needed, with R ~ 300 for wavelengths less
than 5 μm and R ~ 30 for wavelengths greater than this. The transit
spectroscopy technique means that no spatial resolution is required. A
telescope collecting area of about 1 m<SUP>2</SUP> is sufficiently
large to achieve the necessary spectro-photometric precision: for the
Phase A study a 1.13 m<SUP>2</SUP> telescope, diffraction limited at 3
μm has been adopted. Placing the satellite at L2 provides a cold and
stable thermal environment as well as a large field of regard to allow
efficient time-critical observation of targets randomly distributed over
the sky. EChO has been conceived to achieve a single goal: exoplanet
spectroscopy. The spectral coverage and signal-to-noise to be achieved
by EChO, thanks to its high stability and dedicated design, would be
a game changer by allowing atmospheric composition to be measured
with unparalleled exactness: at least a factor 10 more precise and
a factor 10 to 1000 more accurate than current observations. This
would enable the detection of molecular abundances three orders of
magnitude lower than currently possible and a fourfold increase from
the handful of molecules detected to date. Combining these data with
estimates of planetary bulk compositions from accurate measurements
of their radii and masses would allow degeneracies associated with
planetary interior modelling to be broken, giving unique insight
into the interior structure and elemental abundances of these alien
worlds. EChO would allow scientists to study exoplanets both as a
population and as individuals. The mission can target super-Earths,
Neptune-like, and Jupiter-like planets, in the very hot to temperate
zones (planet temperatures of 300-3000 K) of F to M-type host stars. The
EChO core science would be delivered by a three-tier survey. The EChO
Chemical Census: This is a broad survey of a few-hundred exoplanets,
which allows us to explore the spectroscopic and chemical diversity of
the exoplanet population as a whole. The EChO Origin: This is a deep
survey of a subsample of tens of exoplanets for which significantly
higher signal to noise and spectral resolution spectra can be obtained
to explain the origin of the exoplanet diversity (such as formation
mechanisms, chemical processes, atmospheric escape). The EChO Rosetta
Stones: This is an ultra-high accuracy survey targeting a subsample
of select exoplanets. These will be the bright "benchmark" cases
for which a large number of measurements would be taken to explore
temporal variations, and to obtain two and three dimensional spatial
information on the atmospheric conditions through eclipse-mapping
techniques. If EChO were launched today, the exoplanets currently
observed are sufficient to provide a large and diverse sample. The
Chemical Census survey would consist of > 160 exoplanets with a range
of planetary sizes, temperatures, orbital parameters and stellar host
properties. Additionally, over the next 10 years, several new ground-
and space-based transit photometric surveys and missions will come
on-line (e.g. NGTS, CHEOPS, TESS, PLATO), which will specifically focus
on finding bright, nearby systems. The current rapid rate of discovery
would allow the target list to be further optimised in the years prior
to EChO's launch and enable the atmospheric characterisation of hundreds
of planets.
---------------------------------------------------------
Title: Determining energy balance in the flaring chromosphere from
oxygen V line ratios
Authors: Graham, D. R.; Fletcher, L.; Labrosse, N.
2015A&A...584A...6G Altcode: 2014arXiv1411.4603G
Context. The impulsive phase of solar flares is a time of rapid
energy deposition and heating in the lower solar atmosphere,
leading to changes in the temperature and density structure of the
region. <BR /> Aims: We use an O v density diagnostic formed from
the λ192 /λ248 line ratio, provided by the Hinode/EIS instrument,
to determine the density of flare footpoint plasma at O v formation
temperatures of ~2.5 × 10<SUP>5</SUP> K, giving a constraint on the
properties of the heated transition region. <BR /> Methods: Hinode/EIS
rasters from 2 small flare events in December 2007 were used. Raster
images were co-aligned to identify and establish the footpoint pixels,
multiple-component Gaussian line fitting of the spectra was carried out
to isolate the density diagnostic pair, and the density was calculated
for several footpoint areas. The assumptions of equilibrium ionisation
and optically-thin radiation for the O v lines used were assessed
and found to be acceptable. For one of the events, properties of the
electron distribution were deduced from earlier RHESSI hard X-ray
observations. These were used to calculate the plasma heating rate
delivered by an electron beam for 2 semi-empirical atmospheres under
collisional thick-target assumptions. The radiative loss rate for
this plasma was also calculated for comparison with possible energy
input mechanisms. <BR /> Results: Electron number densities of up
to 10<SUP>11.9</SUP> cm<SUP>-3</SUP> were measured during the flare
impulsive phase using the O v λ192 /λ248 diagnostic ratio. The heating
rate delivered by an electron beam was found to exceed the radiative
losses at this density, corresponding to a height of 450 km, and when
assuming a completely ionised target atmosphere far exceed the losses
but at a height of 1450-1600 km. A chromospheric thickness of 70-700
km was found to be required to balance a conductive input to the O
v-emitting region with radiative losses. <BR /> Conclusions: Electron
densities have been observed in footpoint sources at transition region
temperatures, comparable to previous results but with improved spatial
information. The observed densities can be explained by heating of
the chromosphere by collisional electrons, with O v formed at heights
of 450-1600 km above the photosphere, depending on the atmospheric
ionisation fraction.
---------------------------------------------------------
Title: Photochemistry in Saturn's Ring-Shadowed Atmosphere: Modulation
of Hydrocarbons and Observations of Dust Content
Authors: Edgington, S. G.; Atreya, S. K.; Wilson, E. H.; Baines,
K. H.; West, R. A.; Bjoraker, G. L.; Fletcher, L. N.; Momary, T.
2015AGUFM.P41B2056E Altcode:
Cassini has been orbiting Saturn for over eleven years now. During this
epoch, the ring shadow has moved from covering much of the northern
hemisphere (the solar inclination was 24 degrees) to covering a large
swath south of the equator and it continues to move southward. At
Saturn Orbit Insertion in 2004, the projection of the A-ring onto
Saturn reached as far as 40N along the central meridian (52N at the
terminator). At its maximum extent, the ring shadow can reach as
far as 48N/S (58N/S at the terminator). The net effect is that the
intensity of both ultraviolet and visible sunlight penetrating through
the rings to any particular latitude will vary depending on both
Saturn's axis relative to the Sun and the optical thickness of each
ring system. In essence, the rings act like semi-transparent venetian
blinds. Our previous work examined the variation of the solar flux
as a function of solar inclination, i.e. for each 7.25-year season at
Saturn. Here, we report on the impact of the oscillating ring shadow
on the photolysis and production rates of hydrocarbons (acetylene,
ethane, propane, and benzene) and phosphine in Saturn's stratosphere
and upper troposphere. The impact of these production and loss rates
on the abundance of long-lived photochemical products leading to
haze formation are explored. Similarly, we assess their impact on
phosphine abundance, a disequilibrium species whose presence in the
upper troposphere can be used as a tracer of convective processes in
the deeper atmosphere. We will also present our ongoing analysis of
Cassini's CIRS, UVIS, and VIMS datasets that provide an estimate of the
evolving haze content of the northern hemisphere and we will begin to
assess the implications for dynamical mixing. In particular, we will
examine how the now famous hexagonal jet stream acts like a barrier to
transport, isolating Saturn's north polar region from outside transport
of photochemically-generated molecules and haze. The research described
in this paper was carried out in part at the Jet Propulsion Laboratory,
California Institute of Technology, under a contract with the National
Aeronautics and Space Administration. Copyright 2015 California
Institute of Technology. Government sponsorship is acknowledged.
---------------------------------------------------------
Title: The Long wave (11-16 μm) spectrograph for the EChO M3 Mission
Candidate study
Authors: Bowles, N. E.; Tecza, M.; Barstow, J. K.; Temple, J. M.;
Irwin, P. G. J.; Fletcher, L. N.; Calcutt, S.; Hurley, J.; Ferlet,
M.; Freeman, D.
2015ExA....40..801B Altcode: 2015ExA...tmp...58B
The results for the design study of the Long Wave Infrared Module
(LWIR), a goal spectroscopic channel for the EChO ESA medium class
candidate mission, are presented. The requirements for the LWIR
module were to provide coverage of the 11-16 μm spectral range at a
moderate resolving power of at least R = 30, whilst minimising noise
contributions above photon due to the thermal background of the EChO
instrument and telescope, and astrophysical sources such as the zodiacal
light. The study output module design is a KRS-6 prism spectrograph
with aluminium mirror beam expander and coated germanium lenses
for the final focusing elements. Thermal background considerations
led to enclosing the beam in a baffle cooled to approximately 25-29
K. To minimise diffuse astrophysical background contributions due to
the zodiacal light, anamorphic designs were considered in addition
to the elliptical input beam provided by the EChO telescope. Given
the requirement that measurements in this waveband place on the
performance of the infrared detector array, an additional study on
the likely scientific return with lower resolving power ( R < 30)
is included. If specific high priority molecules on moderately warm
giant planets (e.g. CO<SUB>2</SUB>, H<SUB>2</SUB>O) are targeted,
the LWIR channel can still provide improvements in determining the
atmospheric temperature structure and molecular abundances. Thus,
the inclusion of even a coarse-resolution (R≈10) LWIR module would
still make an important contribution to measurements of exoplanet
atmospheres made by EChO.
---------------------------------------------------------
Title: Soft X-Ray Pulsations in Solar Flares
Authors: Simões, P. J. A.; Hudson, H. S.; Fletcher, L.
2015SoPh..290.3625S Altcode: 2014arXiv1412.3045S; 2015SoPh..tmp...50S
The soft X-ray emissions (hν>1.5 keV) of solar flares mainly come
from the bright coronal loops at the highest temperatures normally
achieved in the flare process. Their ubiquity has led to their use
as a standard measure of flare occurrence and energy, although the
overwhelming bulk of the total flare energy goes elsewhere. Recently
Dolla et al. (Astrophys. J. Lett.749, L16, 2012) noted quasi-periodic
pulsations (QPP) in the soft X-ray signature of the X-class flare
SOL2011-02-15, as observed by the standard photometric data from the
GOES (Geostationary Operational Environmental Satellite) spacecraft. In
this article we analyse the suitability of the GOES data for this type
of analysis and find them to be generally valuable after September,
2010 (GOES-15). We then extend the result of Dolla et al. to a complete
list of X-class flares from Cycle 24 and show that most of them (80 %)
display QPPs in the impulsive phase. The pulsations show up cleanly in
both channels of the GOES data, making use of time-series of irradiance
differences (the digital time derivative on the 2-s sampling). We deploy
different techniques to characterise the periodicity of GOES pulsations,
considering the red-noise properties of the flare signals, finding
a range of characteristic time scales of the QPPs for each event,
but usually with no strong signature of a single period dominating
in the power spectrum. The QPP may also appear on somewhat longer
time scales during the later gradual phase, possibly with a greater
tendency towards coherence, but the sampling noise in GOES difference
data for high irradiance values (X-class flares) makes these more
uncertain. We show that there is minimal phase difference between
the differenced GOES energy channels, or between them and the hard
X-ray variations on short time scales. During the impulsive phase,
the footpoints of the newly forming flare loops may also contribute
to the observed soft X-ray variations.
---------------------------------------------------------
Title: Hα Line Profile Asymmetries and the Chromospheric Flare
Velocity Field
Authors: Kuridze, D.; Mathioudakis, M.; Simões, P. J. A.; Rouppe van
der Voort, L.; Carlsson, M.; Jafarzadeh, S.; Allred, J. C.; Kowalski,
A. F.; Kennedy, M.; Fletcher, L.; Graham, D.; Keenan, F. P.
2015ApJ...813..125K Altcode: 2015arXiv151001877K
The asymmetries observed in the line profiles of solar flares can
provide important diagnostics of the properties and dynamics of the
flaring atmosphere. In this paper the evolution of the Hα and Ca ii
λ8542 lines are studied using high spatial, temporal, and spectral
resolution ground-based observations of an M1.1 flare obtained with
the Swedish 1 m Solar Telescope. The temporal evolution of the Hα
line profiles from the flare kernel shows excess emission in the red
wing (red asymmetry) before flare maximum and excess in the blue wing
(blue asymmetry) after maximum. However, the Ca ii λ8542 line does
not follow the same pattern, showing only a weak red asymmetry during
the flare. RADYN simulations are used to synthesize spectral line
profiles for the flaring atmosphere, and good agreement is found
with the observations. We show that the red asymmetry observed in
Hα is not necessarily associated with plasma downflows, and the blue
asymmetry may not be related to plasma upflows. Indeed, we conclude
that the steep velocity gradients in the flaring chromosphere modify
the wavelength of the central reversal in the Hα line profile. The
shift in the wavelength of maximum opacity to shorter and longer
wavelengths generates the red and blue asymmetries, respectively.
---------------------------------------------------------
Title: Photochemistry in Saturn's Ring-Shadowed Atmosphere:
Hydrocarbon Modulation & Observations of Dust Content
Authors: Edgington, S. G.; Atreya, S. K.; Wilson, E. H.; West, R. A.;
Bjoraker, G. L.; Fletcher, L. N.; Baines, K. H.; Momary, T.
2015EPSC...10..399E Altcode:
Cassini has been orbiting Saturn for eleven years. During this epoch,
the ring shadow has moved from covering a relatively large portion of
the northern hemisphere (Figure 1) to covering a large swath south of
the equator and continues to move southward. At Saturn Orbit Insertion
on July 1, 2004, the ring plane was inclined by ~24 degrees relative
to the Sun -Saturn vector. At this time, the projection of the B-ring
onto Saturn reached as far as 40ºN along the central meridian (~52ºN
at the terminator). At its maximum extent, the ring shadow can reach
as far as 48ºN (~58ºN at the terminator). The net effect is that the
intensity of both ultraviolet and visible sunlight penetrating into any
particular latitude will vary depending on both Saturn's axis relative
to the Sun and the optical thickness of each ring system. In essence,
the rings act like venetian blinds.
---------------------------------------------------------
Title: A solar tornado observed by EIS. Plasma diagnostics
Authors: Levens, P. J.; Labrosse, N.; Fletcher, L.; Schmieder, B.
2015A&A...582A..27L Altcode: 2015arXiv150801377L
Context. The term "solar tornadoes" has been used to describe apparently
rotating magnetic structures above the solar limb, as seen in high
resolution images and movies from the Atmospheric Imaging Assembly
(AIA) aboard the Solar Dynamics Observatory (SDO). These often form
part of the larger magnetic structure of a prominence, however the
links between them remain unclear. Here we present plasma diagnostics
on a tornado-like structure and its surroundings, seen above the
limb by the Extreme-ultraviolet Imaging Spectrometer (EIS) aboard
the Hinode satellite. <BR /> Aims: We aim to extend our view of the
velocity patterns seen in tornado-like structures with EIS to a wider
range of temperatures and to use density diagnostics, non-thermal
line widths, and differential emission measures to provide insight
into the physical characteristics of the plasma. <BR /> Methods:
Using Gaussian fitting to fit and de-blend the spectral lines seen
by EIS, we calculated line-of-sight velocities and non-thermal line
widths. Along with information from the CHIANTI database, we used line
intensity ratios to calculate electron densities at each pixel. Using
a regularised inversion code we also calculated the differential
emission measure (DEM) at different locations in the prominence. <BR
/> Results: The split Doppler-shift pattern is found to be visible
down to a temperature of around log T = 6.0. At temperatures lower
than this, the pattern is unclear in this data set. We obtain an
electron density of log n<SUB>e</SUB> = 8.5 when looking towards the
centre of the tornado structure at a plasma temperature of log T =
6.2, as compared to the surroundings of the tornado structure where
we find log n<SUB>e</SUB> to be nearer 9. Non-thermal line widths
show broader profiles at the tornado location when compared to the
surrounding corona. We discuss the differential emission measure in
both the tornado and the prominence body, which suggests that there is
more contribution in the tornado at temperatures below log T = 6.0 than
in the prominence. <P />A movie is available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201425586/olm">http://www.aanda.org</A>
---------------------------------------------------------
Title: IRIS observations of the Mg ii h and k lines during a solar
flare
Authors: Kerr, G. S.; Simões, P. J. A.; Qiu, J.; Fletcher, L.
2015A&A...582A..50K Altcode: 2015arXiv150803813K
The bulk of the radiative output of a solar flare is emitted from
the chromosphere, which produces enhancements in the optical and UV
continuum, and in many lines, both optically thick and thin. We have,
until very recently, lacked observations of two of the strongest of
these lines: the Mg ii h and k resonance lines. We present a detailed
study of the response of these lines to a solar flare. The spatial and
temporal behaviour of the integrated intensities, k/h line ratios,
line of sight velocities, line widths and line asymmetries were
investigated during an M class flare (SOL2014-02-13T01:40). Very
intense, spatially localised energy input at the outer edge of the
ribbon is observed, resulting in redshifts equivalent to velocities of
~15-26 km s<SUP>-1</SUP>, line broadenings, and a blue asymmetry in the
most intense sources. The characteristic central reversal feature that
is ubiquitous in quiet Sun observations is absent in flaring profiles,
indicating that the source function increases with height during the
flare. Despite the absence of the central reversal feature, the k/h
line ratio indicates that the lines remain optically thick during
the flare. Subordinate lines in the Mg ii passband are observed to be
in emission in flaring sources, brightening and cooling with similar
timescales to the resonance lines. This work represents a first analysis
of potential diagnostic information of the flaring atmosphere using
these lines, and provides observations to which synthetic spectra from
advanced radiative transfer codes can be compared.
---------------------------------------------------------
Title: Observations of Jupiter at 5 micron from IRTF/TEXES :
latitudinal variability of disequilibrium species
Authors: Drossart, P.; Encrenaz, T.; Greathouse, T. K.; DeWitt, C.;
Fouchet, T.; Janssen, M.; Gulkis, S.; Orton, G. S.; Fletcher, L.;
Giles, R.; Atreya, S. K.; Boudon, V.
2015EPSC...10..194D Altcode:
Observations of Jupiter in the 5 μm spectral window,obtained in
March/April 2015 at IRTF are presented, in preparation of the arrival of
the NASA/JUNO mission in 2016. Sounding of the troposphere of Jupiter
below 2 bars is obtained from the observations, to search for the
variability of disequilibrium species, related to deep atmospheric
circulation.
---------------------------------------------------------
Title: Stratospheric temperature and composition of Jupiter's polar
aurora from IRTF-TEXES
Authors: Sinclair, J.; Orton, G. S.; Greathouse, T. K.; Fletcher,
L. N.; Irwin, P. G. J.
2015EPSC...10..374S Altcode:
We perform an analysis of TEXES (Texas Echelon Cross Echelle
Spectrograph, 5- to 25- μm,[1]) spectra of Jupiter's high latitudes
observed in December 2014 in order to study the jovian polar
aurora. The high resolving power (R∼85000) of TEXES allows a large
altitude range (10 mbar to 0.01 mbar) in Jupiter's stratosphere to
be sounded. Retrievals of temperature and stratospheric composition
of these measurements therefore: 1) allow the vertical deposition
of auroral energy to be determined and 2) quantify how the auro-ral
processes modify the thermal structure and composition of the jovian
stratosphere.
---------------------------------------------------------
Title: JUICE: A European Mission to Jupiter and its Icy Moons
Authors: Witasse, O.; Altobelli, N.; Barabash, S.; Bruzzone, L.;
Dougherty, M.; Erd, C.; Fletcher, L.; Gladstone, R.; Grasset, O.;
Gurvits, L.; Hartogh, P.; Hussmann, H.; Iess, I.; Langevin, Y.;
Palumbo, P.; Piccioni, G.; Sarri, G.; Titov, D.; Wahlund, J. -E.
2015EPSC...10..564W Altcode:
JUICE -JUpiter ICy moons Explorer -is the first large mission in the
ESA Cosmic Vision 2015-2025 programme[1]. The mission was selected
in May 2012 and adopted in November 2014. The implementation phase
starts in July 2015, following the selection of the prime industrial
contractor. Planned for launch in June 2022 and arrival at Jupiter
in October 2029, it will spend at least three years making detailed
observations of Jupiter and three of its largest moons, Ganymede,
Callisto and Europa.
---------------------------------------------------------
Title: A unified view of coronal loop contraction and oscillation
in flares
Authors: Russell, A. J. B.; Simões, P. J. A.; Fletcher, L.
2015A&A...581A...8R Altcode: 2015arXiv150607716R
Context. Transverse loop oscillations and loop contractions are
commonly associated with solar flares, but the two types of motion
have traditionally been regarded as separate phenomena. <BR /> Aims:
We present an observation of coronal loops that contract and oscillate
following the onset of a flare. We aim to explain why both behaviours
are seen together and why only some of the loops oscillate. <BR />
Methods: A time sequence of SDO/AIA 171 Å images is analysed to
identify the positions of coronal loops following the onset of the
M6.4 flare SOL2012-03-09T03:53. We focus on five loops in particular,
all of which contract during the flare, with three of them oscillating
as well. A simple model is then developed for the contraction and
oscillation of a coronal loop. <BR /> Results: We propose that coronal
loop contractions and oscillations can occur in a single response to
removal of magnetic energy from the corona. Our model reproduces the
various types of loop motion observed and explains why the highest loops
oscillate during their contraction, while no oscillation is detected for
the shortest contracting loops. The proposed framework suggests that
loop motions can be used as a diagnostic for the removal of coronal
magnetic energy by flares, while rapid decrease in coronal magnetic
energy is a newly identified excitation mechanism for transverse loop
oscillations. <P />Appendices are available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201525746/olm">http://www.aanda.org</A>
---------------------------------------------------------
Title: Cloud structure and composition of Jupiter's troposphere from
5- μ m Cassini VIMS spectroscopy
Authors: Giles, R. S.; Fletcher, L. N.; Irwin, P. G. J.
2015Icar..257..457G Altcode: 2015arXiv150601608G
Jupiter's tropospheric composition and cloud structure are studied
using Cassini VIMS 4.5-5.1 μ m thermal emission spectra from
the 2000-2001 flyby. We make use of both nadir and limb darkening
observations on the planet's nightside, and compare these with dayside
observations. Although there is significant spatial variability
in the 5- μ m brightness temperatures, the shape of the spectra
remain very similar across the planet, suggesting the presence of a
spectrally-flat, spatially inhomogeneous cloud deck. We find that a
simple cloud model consisting of a single, compact cloud is able to
reproduce both nightside and dayside spectra, subject to the following
constraints: (i) the cloud base is located at pressures of 1.2 bar
or lower; (ii) the cloud particles are highly scattering; and (iii)
the cloud is sufficiently spectrally flat. Using this cloud model, we
search for global variability in the cloud opacity and the phosphine
deep volume mixing ratio. We find that the vast majority of the 5- μ
m inhomogeneity can be accounted for by variations in the thickness
of the cloud decks, with huge differences between the cloudy zones
and the relatively cloud-free belts. The relatively low spectral
resolution of VIMS limits reliable retrievals of gaseous species,
but some evidence is found for an enhancement in the abundance of
phosphine at high latitudes.
---------------------------------------------------------
Title: Photochemical response to the variation of temperature in
the 2011-2012 stratospheric vortex of Saturn
Authors: Cavalié, T.; Dobrijevic, M.; Fletcher, L. N.; Loison,
J. -C.; Hickson, K. M.; Hue, V.; Hartogh, P.
2015A&A...580A..55C Altcode:
Context. A hot vortex formed in the stratosphere of Saturn following
the 2010-2011 Northern Storm. Huge temperature increases have been
measured in the vortex around the millibar level. Enhancements in
hydrocarbon abundances have been observed at the millibar level in
2011-2012 inside this vortex. <BR /> Aims: We model the time-dependent
photochemistry inside the vortex by accounting for the temperature
variability over the period from January 2011 to March 2012 to assess
whether photochemistry alone can explain the enhancements seen in the
hydrocarbon abundances. <BR /> Methods: We used a 1D time-dependent
photochemical model of Saturn and adapted it to the perturbed conditions
of the vortex after validating it in quiescent conditions. <BR
/> Results: Our model predicts non-variability for ethane
(C<SUB>2</SUB>H<SUB>6</SUB>) and acetylene (C<SUB>2</SUB>H<SUB>2</SUB>)
and an increase in ethylene (C<SUB>2</SUB>H<SUB>4</SUB>) by a factor of
3 in the mbar region. Heavier hydrocarbons show a stronger variability
than the lighter ones. We are unable to reproduce the increase seen
in C<SUB>2</SUB>H<SUB>2</SUB> , and we significantly underestimate the
increase seen in C<SUB>2</SUB>H<SUB>4</SUB>. <BR /> Conclusions: Pure
photochemistry does not explain the variability seen in the abundance
of most hydrocarbons. This means that dynamics (eddy diffusion and/or
advection) must have played a significant role in shaping the vertical
profiles of the main hydrocarbons.
---------------------------------------------------------
Title: Erratum: Transit spectroscopy with JWST: systematics,
star-spots and stitching
Authors: Barstow, J. K.; Aigrain, S.; Irwin, P. G. J.; Kendrew, S.;
Fletcher, L. N.
2015MNRAS.451.1306B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Division II: Commission 10: Solar Activity
Authors: van Driel-Gesztelyi, Lidia; Scrijver, Karel J.; Klimchuk,
James A.; Charbonneau, Paul; Fletcher, Lyndsay; Hasan, S. Sirajul;
Hudson, Hugh S.; Kusano, Kanya; Mandrini, Cristina H.; Peter, Hardi;
Vršnak, Bojan; Yan, Yihua
2015IAUTB..28..106V Altcode:
The Business Meeting of Commission 10 was held as part of the Business
Meeting of Division II (Sun and Heliosphere), chaired by Valentin
Martínez-Pillet, the President of the Division. The President of
Commission 10 (C10; Solar activity), Lidia van Driel-Gesztelyi, took
the chair for the business meeting of C10. She summarised the activities
of C10 over the triennium and the election of the incoming OC.
---------------------------------------------------------
Title: Solar Flares and the Chromosphere
Authors: Fletcher, Lyndsay
2015IAUGA..2286134F Altcode:
During a solar flare, the chromosphere emits across a large fraction
of the electromagnetic spectrum, providing diagnostic information
on heating, dynamics and flare energy transport by both thermal and
non-thermal means. The evolution of chromospheric ribbons and footpoints
also traces the progress of coronal reconnection, and links radiation
output with magnetic evolution. Since the chromosphere emits the
majority of a flare's radiation, the current emphasis on chromospheric
observations by missions such as IRIS, and future large facilities
such as the DKIST, is very beneficial to flare research. In this
talk I will overview recent developments in observations and theory
of flaring chromospheres and make some suggestions about profitable
future avenues for research.
---------------------------------------------------------
Title: Meandering Shallow Atmospheric Jet as a Model of Saturn's
North-polar Hexagon
Authors: Morales-Juberías, R.; Sayanagi, K. M.; Simon, A. A.;
Fletcher, L. N.; Cosentino, R. G.
2015ApJ...806L..18M Altcode:
The Voyager flybys of Saturn in 1980-1981 revealed a circumpolar
Hexagon at ∼78° north planetographic latitude that has persisted
for over 30 Earth years, more than one Saturn year, and has been
observed by ground-based telescopes, Hubble Space Telescope and
multiple instruments on board the Cassini orbiter. Its average phase
speed is very slow with respect to the System III rotation rate,
defined by the primary periodicity in the Saturn Kilometric Radiation
during the Voyager era. Cloud tracking wind measurements reveal the
presence of a prograde jet-stream whose path traces the Hexagon’s
shape. Previous numerical models have produced large-amplitude, n = 6,
wavy structures with westward intrinsic phase propagation (relative to
the jet). However, the observed net phase speed has proven to be more
difficult to achieve. Here we present numerical simulations showing
that instabilities in shallow jets can equilibrate as meanders closely
resembling the observed morphology and phase speed of Saturn’s
northern Hexagon. We also find that the winds at the bottom of the
model are as important as the winds at the cloud level in matching
the observed Hexagon’s characteristics.
---------------------------------------------------------
Title: Structures in the Outer Solar Atmosphere
Authors: Fletcher, L.; Cargill, P. J.; Antiochos, S. K.; Gudiksen,
B. V.
2015SSRv..188..211F Altcode: 2014SSRv..tmp...52F; 2014arXiv1412.7378F
The structure and dynamics of the outer solar atmosphere are reviewed
with emphasis on the role played by the magnetic field. Contemporary
observations that focus on high resolution imaging over a range
of temperatures, as well as UV, EUV and hard X-ray spectroscopy,
demonstrate the presence of a vast range of temporal and spatial scales,
mass motions, and particle energies present. By focusing on recent
developments in the chromosphere, corona and solar wind, it is shown
that small scale processes, in particular magnetic reconnection, play
a central role in determining the large-scale structure and properties
of all regions. This coupling of scales is central to understanding
the atmosphere, yet poses formidable challenges for theoretical models.
---------------------------------------------------------
Title: VizieR Online Data Catalog: Bayesian method for detecting
stellar flares (Pitkin+, 2014)
Authors: Pitkin, M.; Williams, D.; Fletcher, L.; Grant, S. D. T.
2015yCat..74452268P Altcode:
We present a Bayesian-odds-ratio-based algorithm for detecting stellar
flares in light-curve data. We assume flares are described by a
model in which there is a rapid rise with a half-Gaussian profile,
followed by an exponential decay. Our signal model also contains a
polynomial background model required to fit underlying light-curve
variations in the data, which could otherwise partially mimic a
flare. We characterize the false alarm probability and efficiency of
this method under the assumption that any unmodelled noise in the data
is Gaussian, and compare it with a simpler thresholding method based
on that used in Walkowicz et al. We find our method has a significant
increase in detection efficiency for low signal-to-noise ratio (S/N)
flares. For a conservative false alarm probability our method can
detect 95 per cent of flares with S/N less than 20, as compared to S/N
of 25 for the simpler method. We also test how well the assumption of
Gaussian noise holds by applying the method to a selection of 'quiet'
Kepler stars. As an example we have applied our method to a selection
of stars in Kepler Quarter 1 data. The method finds 687 flaring stars
with a total of 1873 flares after vetos have been applied. For these
flares we have made preliminary characterizations of their durations
and and S/N. <P />(1 data file).
---------------------------------------------------------
Title: Direct observation of the energy release site in a solar
flare by SDO/AIA, Hinode/EIS, and RHESSI
Authors: Simões, P. J. A.; Graham, D. R.; Fletcher, L.
2015A&A...577A..68S Altcode: 2015arXiv150301491S
<BR /> Aims: We present direct evidence of the detection of the main
energy release site in a non-eruptive solar flare, SOL2013-11-09T06:38
UT. This GOES class C2.6 event was characterised by two flaring ribbons
and a compact, bright coronal source located between them, which is
the focus of our study. <BR /> Methods: We use imaging from SDO/AIA,
and imaging spectroscopy from RHESSI to characterise the thermal and
non-thermal emission from the coronal source, and EUV spectroscopy
from the Hinode/Extreme ultraviolet Imaging Spectrometer, which
scanned the coronal source during the impulsive peak, to analyse
Doppler shifts in Fe xii (log T = 6.2) and Fe xxiv (log T = 7.2)
emission lines, and determine the source density. <BR /> Results:
The coronal source exhibited an impulsive emission lightcurve in all
SDO/AIA filters during the impulsive phase. RHESSI hard X-ray images
indicate both thermal and non-thermal emission at the coronal source,
and its plasma temperature derived from RHESSI imaging spectroscopy
shows an impulsive rise, reaching a maximum at 12-13 MK about 10 s
prior to the hard X-ray peak. High red-shifts associated with this
bright source indicate downflows of 40-250 km s<SUP>-1</SUP> at a broad
range of temperatures, interpreted as loop shrinkage and/or outflows
along the magnetic field. Outflows from the coronal source towards
each ribbon are also observed by SDO/AIA images at 171, 193, 211, 304,
and 1600 Å. The electron density of the source obtained from a Fe xiv
line pair is 10<SUP>11.50</SUP> cm<SUP>-3</SUP> which is collisionally
thick to electrons with energy up to 45-65 keV, responsible for the
source's non-thermal X-ray emission. <BR /> Conclusions: Given the
rich observational evidence, we conclude that the bright coronal source
is the location of the main release of magnetic energy in this flare,
with a geometry consistent with component reconnection between crossing,
current-carrying loops. We argue that the energy that can be released
via reconnection, based on observational estimates, can plausibly
account for the non-thermal energetics of the flare.
---------------------------------------------------------
Title: Electric Current Circuits in Astrophysics
Authors: Kuijpers, Jan; Frey, Harald U.; Fletcher, Lyndsay
2015SSRv..188....3K Altcode: 2014arXiv1403.0795K; 2014SSRv..tmp...19K
Cosmic magnetic structures have in common that they are anchored in a
dynamo, that an external driver converts kinetic energy into internal
magnetic energy, that this magnetic energy is transported as Poynting
flux across the magnetically dominated structure, and that the magnetic
energy is released in the form of particle acceleration, heating, bulk
motion, MHD waves, and radiation. The investigation of the electric
current system is particularly illuminating as to the course of events
and the physics involved. We demonstrate this for the radio pulsar wind,
the solar flare, and terrestrial magnetic storms.
---------------------------------------------------------
Title: Reanalysis of Uranus' cloud scattering properties from
IRTF/SpeX observations using a self-consistent scattering cloud
retrieval scheme
Authors: Irwin, P. G. J.; Tice, D. S.; Fletcher, L. N.; Barstow,
J. K.; Teanby, N. A.; Orton, G. S.; Davis, G. R.
2015Icar..250..462I Altcode: 2016arXiv160102814I
We have developed a new retrieval approach to modelling near-infrared
spectra of Uranus that represents a significant improvement over
previous modelling methods. We reanalysed IRTF/SpeX observations of
Uranus observed in 2009 covering the wavelength range 0.8-1.8 μm and
reported by Tice et al. (Tice, D.S., Irwin, P.G.J., Fletcher, L.N.,
Teanby, N.A., Hurley, J., Orton, G.S., Davis, G.R. [2013]. Icarus
223, 684-698). By retrieving the imaginary refractive index spectra
of cloud particles we are able to consistently define the real part
of the refractive index spectra, through a Kramers-Kronig analysis,
and thus determine self-consistent extinction cross-section,
single-scattering and phase-function spectra for the clouds and
hazes in Uranus' atmosphere. We tested two different cloud-modelling
schemes used in conjunction with the temperature/methane profile of
Baines et al. (Baines, K.H., Mickelson, M.E., Larson, L.E., Ferguson,
D.W. [1995]. Icarus 114, 328-340), a reanalysis of the Voyager-2
radio-occultation observations performed by Sromovsky, Fry and Kim
(Sromovsky, L.A., Fry, P.M., Kim, J.H. [2011]. Icarus 215, 292-312),
and a recent determination from Spitzer (Orton, G.S., Fletcher, L.N.,
Moses, J.I., Mainzer, A.K., Hines, D., Hammel, H.B., Martin-Torres,
F.J., Burgdorf, M., Merlet, C., Line, M.R. [2014]. Icarus 243,
494-513). We find that both cloud-modelling schemes represent the
observed centre-of-disc spectrum of Uranus well, and both require
similar cloud scattering properties of the main cloud residing at ∼2
bars. However, a modified version of the Sromovsky, Fry and Kim (2011)
model, with revised spectral properties of the lowest cloud layer,
fits slightly better at shorter wavelengths and is more consistent
with the expected vertical position of Uranus' methane cloud. <P />We
find that the bulk of the reflected radiance from Uranus arises from
a thick cloud at approximately the 2 bar level, composed of particles
that are significantly more absorbing at wavelengths λ > 1.0 μm
than they are at shorter wavelengths λ < 1.0 μm. This spectral
information provides a possible constraint on the identity of the
main particle type, although we find that the scattering properties
required are not consistent with any of the available laboratory data
for pure NH<SUB>3</SUB>, NH<SUB>4</SUB>SH, or CH<SUB>4</SUB> ice (all
suspected of condensing in the upper troposphere). It is possible that
the observed clouds are mixtures of tropospheric condensate mixed with
photochemical products diffusing down from above, which masks their
pure scattering features. Because there is no available laboratory
data for pure H<SUB>2</SUB>S or PH<SUB>3</SUB> ice (both of which
might be present as well), they cannot be excluded as the cloud-forming
species. We note, however, that their absorptive properties would have
to be two orders of magnitude greater than the other measured ices at
wavelengths greater than 1 μm to be consistent with our retrieval,
which suggests that mixing with photochemical products may still
be important.
---------------------------------------------------------
Title: IRIS Observations of the Mg II h & k Lines During a
Solar Flare
Authors: Kerr, Graham Stewart; Simões, Paulo J. A.; Qiu, Jiong;
Fletcher, Lyndsay
2015TESS....130702K Altcode:
The bulk of the radiative output of a solar flare is radiated from the
chromosphere. We have, until very recently, lacked routine observations
of one of the strongest chromospheric lines: the MgII h&k resonance
lines. These optically thick lines sample the atmosphere from the
upper photosphere to the upper chromosphere and have been shown to be
important diagnostics of the atmosphere in the non flaring features
(quiet Sun, plage, network, sunspots, and prominences). However,
only one flare observation of these lines has been reported (Lemaire
et al 1984). With the launch of the IRIS solar telescope we are in a
position to routinely observe the MgII h&k lines during flares,
and we present a detailed study of the response of these lines to
a solar flare. The spatial and temporal behaviour of the integrated
intensities, k/h line ratios, line of sight velocities, line widths
and line asymmetries were investigated during an M class flare, using
a nonparametric quartiles approach. Redshifts of ~20km/s and line
broadenings are observed at times of significant intensity enhancements,
at the outer edge of the flare ribbons. The lines show blue asymmetry
in only the most intense sources. Interestingly the characteristic
central reversal feature that is ubiquitous in quiet Sun observations
is absent in flaring profiles. Subordinate lines in the MgII passband
are observed to be in emission within flaring sources, brightening and
cooling in sync with the resonance lines. Additionally, we present the
results of initial experiments with advanced numerical models to aid
in the physical interpretation of these observed properties. This was
achieved using the radiation hydrodynamic code RADYN that simulates
the response of the solar atmosphere to flare energy input (we used
a range of beam parameters to investigate energy injection to the
atmosphere). RADYN provides both the hydrodynamic response of the
atmosphere and the radiative response in energetically important lines
and continua. The hydrodynamic output from RADYN was used as input to
the radiative transfer code RH that solves the MgII resonance lines
using partial redistributon.
---------------------------------------------------------
Title: The Radiated Energy Budget Of Chromospheric Plasma In A Major
Solar Flare Deduced From Multi-Wavelength Observations
Authors: Milligan, Ryan; Kerr, Graham Stewart; Dennis, Brian; Hudson,
Hugh; Fletcher, Lyndsay; Allred, Joel; Chamberlin, Phillip; Ireland,
Jack; Mathioudakis, Mihalis; Keenan, Francis
2015TESS....130209M Altcode:
The response of the lower solar atmosphere is an important diagnostic
tool for understanding energy transport during solar flares. The 15
February 2011 X-class flare was fortuitously observed by a host of
space-based instruments that sampled the chromospheric response over
a range of lines and continua at <20s cadence. These include the
free-bound EUV continua of H I (Lyman), He I, and He II, plus the
emission lines of He II at 304Å and H I (Lyα) at 1216Å by SDO/EVE,
the UV continua at 1600Å and 1700Å by SDO/AIA, and the white light
continuum at 4504Å, 5550Å, and 6684Å, along with the Ca II H line
at 3968Å using Hinode/SOT. RHESSI also observed the entire event at
energies up to ~100keV, making it possible to determine the properties
of the nonthermal electrons deemed to be responsible for driving the
enhanced chromospheric emission under the assumption of thick-target
collisions. Integrating over the duration of the impulsive phase,
the total energy contained in the nonthermal electrons was found to be
>2×10<SUP>31</SUP> erg. By comparison, the summed energy detected by
instruments onboard SDO and Hinode amounted to ~3×10<SUP>30</SUP> erg;
about 15% of the total nonthermal energy. The Lyα line was found to
dominate the measured radiative losses in contrast to the predictions
of numerical simulations. Parameters of both the driving electron
distribution and the resulting chromospheric response are presented
in detail to encourage the numerical modeling of flare heating for
this event to determine the depth of the solar atmosphere at which
these line and continuum processes originate, and the mechanism(s)
responsible for their generation.
---------------------------------------------------------
Title: Transit spectroscopy with James Webb Space Telescope:
systematics, starspots and stitching
Authors: Barstow, J. K.; Aigrain, S.; Irwin, P. G. J.; Kendrew, S.;
Fletcher, L. N.
2015MNRAS.448.2546B Altcode: 2015arXiv150106349B
The James Webb Space Telescope (JWST) is predicted to make great
advances in the field of exoplanet atmospheres. Its 25 m<SUP>2</SUP>
mirror means that it can reach unprecedented levels of precision
in observations of transit spectra, and can thus characterize the
atmospheres of planets orbiting stars several hundred pc away. Its
coverage of the infrared spectral region between 0.6 and 28 μm allows
the abundances of key molecules to be probed during the transit of a
planet in front of the host star, and when the same planet is eclipsed
constraints can be placed on its temperature structure. In this work,
we explore the possibility of using low-spectral-resolution observations
by JWST/Near-Infrared Spectrograph and JWST/Mid-Infrared Instrumen-Low
Resolution Spectrometer together to optimize wavelength coverage
and break degeneracies in the atmospheric retrieval problem for a
range of exoplanets from hot Jupiters to super-Earths. This approach
involves stitching together non-simultaneous observations in different
wavelength regions, rendering it necessary to consider the effect of
time-varying instrumental and astrophysical systematics. We present
the results of a series of retrieval feasibility tests examining the
effects of instrument systematics and starspots on the recoverability
of the true atmospheric state, and demonstrate that correcting for
these systematics is key for successful exoplanet science with JWST.
---------------------------------------------------------
Title: Microflares to megaflares: Solar observations and modeling
Authors: Fletcher, Lyndsay
2015HiA....16...97F Altcode:
The observationally determined properties of solar flares such as
overall energy budget and distribution in space, time and energy of
flare radiation, have improved enormously over the last cycle. This
has enabled precision diagnostics of flare plasmas and nonthermal
particles in large and small events, informing and driving new
theoretical models. The theoretical challenges in understanding flare
are considerable, involving MHD and kinetic processes operating in an
environment far from equilibrium. New observations have also provided
some challenges to long-standing models of flare energy release and
transport. This talk overviewed recent observational and theoretical
developments, and highlighted some important questions for the future
---------------------------------------------------------
Title: Stratospheric Chemistry in Saturn's Atmosphere During the
Beacon Storm
Authors: Armstrong, E. S.; Moses, J. L.; Fletcher, L. N.; Irwin,
P. G. J.; Hesman, B. E.; Romani, P. N.
2015LPI....46.1188A Altcode: 2015LPICo1832.1188A
Stratospheric chemistry is investigated to try to reconcile
photochemical model outputs with Cassini/CIRS observations during the
Beacon Storm (2010-12).
---------------------------------------------------------
Title: Optical Spectral Observations of a Flickering White-light
Kernel in a C1 Solar Flare
Authors: Kowalski, Adam F.; Cauzzi, Gianna; Fletcher, Lyndsay
2015ApJ...798..107K Altcode: 2014arXiv1411.0770K
We analyze optical spectra of a two-ribbon, long-duration
C1.1 flare that occurred on 2011 August 18 within AR 11271
(SOL2011-08-18T15:15). The impulsive phase of the flare was observed
with a comprehensive set of space-borne and ground-based instruments,
which provide a range of unique diagnostics of the lower flaring
atmosphere. Here we report the detection of enhanced continuum emission,
observed in low-resolution spectra from 3600 Å to 4550 Å acquired
with the Horizontal Spectrograph at the Dunn Solar Telescope. A small,
<=0.”5 (10<SUP>15</SUP> cm<SUP>2</SUP>) penumbral/umbral kernel
brightens repeatedly in the optical continuum and chromospheric
emission lines, similar to the temporal characteristics of the hard
X-ray variation as detected by the Gamma-ray Burst Monitor on the Fermi
spacecraft. Radiative-hydrodynamic flare models that employ a nonthermal
electron beam energy flux high enough to produce the optical contrast
in our flare spectra would predict a large Balmer jump in emission,
indicative of hydrogen recombination radiation from the upper flare
chromosphere. However, we find no evidence of such a Balmer jump in
the bluemost spectral region of the continuum excess. Just redward of
the expected Balmer jump, we find evidence of a "blue continuum bump"
in the excess emission which may be indicative of the merging of the
higher order Balmer lines. The large number of observational constraints
provides a springboard for modeling the blue/optical emission for this
particular flare with radiative-hydrodynamic codes, which are necessary
to understand the opacity effects for the continuum and emission line
radiation at these wavelengths.
---------------------------------------------------------
Title: A Bayesian method for detecting stellar flares
Authors: Pitkin, M.; Williams, D.; Fletcher, L.; Grant, S. D. T.
2014MNRAS.445.2268P Altcode: 2014arXiv1406.1712P
We present a Bayesian-odds-ratio-based algorithm for detecting stellar
flares in light-curve data. We assume flares are described by a
model in which there is a rapid rise with a half-Gaussian profile,
followed by an exponential decay. Our signal model also contains a
polynomial background model required to fit underlying light-curve
variations in the data, which could otherwise partially mimic a
flare. We characterize the false alarm probability and efficiency of
this method under the assumption that any unmodelled noise in the data
is Gaussian, and compare it with a simpler thresholding method based
on that used in Walkowicz et al. We find our method has a significant
increase in detection efficiency for low signal-to-noise ratio (S/N)
flares. For a conservative false alarm probability our method can
detect 95 per cent of flares with S/N less than 20, as compared to S/N
of 25 for the simpler method. We also test how well the assumption of
Gaussian noise holds by applying the method to a selection of `quiet'
Kepler stars. As an example we have applied our method to a selection
of stars in Kepler Quarter 1 data. The method finds 687 flaring stars
with a total of 1873 flares after vetos have been applied. For these
flares we have made preliminary characterizations of their durations
and and S/N.
---------------------------------------------------------
Title: Neptune and Triton: Essential pieces of the Solar System puzzle
Authors: Masters, A.; Achilleos, N.; Agnor, C. B.; Campagnola, S.;
Charnoz, S.; Christophe, B.; Coates, A. J.; Fletcher, L. N.; Jones,
G. H.; Lamy, L.; Marzari, F.; Nettelmann, N.; Ruiz, J.; Ambrosi, R.;
Andre, N.; Bhardwaj, A.; Fortney, J. J.; Hansen, C. J.; Helled, R.;
Moragas-Klostermeyer, G.; Orton, G.; Ray, L.; Reynaud, S.; Sergis,
N.; Srama, R.; Volwerk, M.
2014P&SS..104..108M Altcode:
The planet Neptune and its largest moon Triton hold the keys to major
advances across multiple fields of Solar System science. The ice giant
Neptune played a unique and important role in the process of Solar
System formation, has the most meteorologically active atmosphere in the
Solar System (despite its great distance from the Sun), and may be the
best Solar System analogue of the dominant class of exoplanets detected
to date. Neptune's moon Triton is very likely a captured Kuiper Belt
object, holding the answers to questions about the icy dwarf planets
that formed in the outer Solar System. Triton is geologically active,
has a tenuous nitrogen atmosphere, and is predicted to have a subsurface
ocean. However, our exploration of the Neptune system remains limited to
a single spacecraft flyby, made by Voyager 2 in 1989. Here, we present
the high-level science case for further exploration of this outermost
planetary system, based on a white paper submitted to the European Space
Agency (ESA) for the definition of the second and third large missions
in the ESA Cosmic Vision Programme 2015-2025. We discuss all the major
science themes that are relevant for further spacecraft exploration
of the Neptune system, and identify key scientific questions in each
area. We present an overview of the results of a European-led Neptune
orbiter mission analysis. Such a mission has significant scope for
international collaboration, and is essential to achieve our aim of
understanding how the Solar System formed, and how it works today.
---------------------------------------------------------
Title: The science case for an orbital mission to Uranus: Exploring
the origins and evolution of ice giant planets
Authors: Arridge, C. S.; Achilleos, N.; Agarwal, J.; Agnor, C. B.;
Ambrosi, R.; André, N.; Badman, S. V.; Baines, K.; Banfield, D.;
Barthélémy, M.; Bisi, M. M.; Blum, J.; Bocanegra-Bahamon, T.;
Bonfond, B.; Bracken, C.; Brandt, P.; Briand, C.; Briois, C.; Brooks,
S.; Castillo-Rogez, J.; Cavalié, T.; Christophe, B.; Coates, A. J.;
Collinson, G.; Cooper, J. F.; Costa-Sitja, M.; Courtin, R.; Daglis,
I. A.; de Pater, I.; Desai, M.; Dirkx, D.; Dougherty, M. K.; Ebert,
R. W.; Filacchione, G.; Fletcher, L. N.; Fortney, J.; Gerth, I.;
Grassi, D.; Grodent, D.; Grün, E.; Gustin, J.; Hedman, M.; Helled,
R.; Henri, P.; Hess, S.; Hillier, J. K.; Hofstadter, M. H.; Holme,
R.; Horanyi, M.; Hospodarsky, G.; Hsu, S.; Irwin, P.; Jackman, C. M.;
Karatekin, O.; Kempf, S.; Khalisi, E.; Konstantinidis, K.; Krüger,
H.; Kurth, W. S.; Labrianidis, C.; Lainey, V.; Lamy, L. L.; Laneuville,
M.; Lucchesi, D.; Luntzer, A.; MacArthur, J.; Maier, A.; Masters, A.;
McKenna-Lawlor, S.; Melin, H.; Milillo, A.; Moragas-Klostermeyer,
G.; Morschhauser, A.; Moses, J. I.; Mousis, O.; Nettelmann, N.;
Neubauer, F. M.; Nordheim, T.; Noyelles, B.; Orton, G. S.; Owens, M.;
Peron, R.; Plainaki, C.; Postberg, F.; Rambaux, N.; Retherford, K.;
Reynaud, S.; Roussos, E.; Russell, C. T.; Rymer, A. M.; Sallantin, R.;
Sánchez-Lavega, A.; Santolik, O.; Saur, J.; Sayanagi, K. M.; Schenk,
P.; Schubert, J.; Sergis, N.; Sittler, E. C.; Smith, A.; Spahn, F.;
Srama, R.; Stallard, T.; Sterken, V.; Sternovsky, Z.; Tiscareno,
M.; Tobie, G.; Tosi, F.; Trieloff, M.; Turrini, D.; Turtle, E. P.;
Vinatier, S.; Wilson, R.; Zarka, P.
2014P&SS..104..122A Altcode:
Giant planets helped to shape the conditions we see in the Solar System
today and they account for more than 99% of the mass of the Sun's
planetary system. They can be subdivided into the Ice Giants (Uranus
and Neptune) and the Gas Giants (Jupiter and Saturn), which differ
from each other in a number of fundamental ways. Uranus, in particular
is the most challenging to our understanding of planetary formation
and evolution, with its large obliquity, low self-luminosity, highly
asymmetrical internal field, and puzzling internal structure. Uranus
also has a rich planetary system consisting of a system of inner natural
satellites and complex ring system, five major natural icy satellites,
a system of irregular moons with varied dynamical histories, and a
highly asymmetrical magnetosphere. Voyager 2 is the only spacecraft to
have explored Uranus, with a flyby in 1986, and no mission is currently
planned to this enigmatic system. However, a mission to the uranian
system would open a new window on the origin and evolution of the
Solar System and would provide crucial information on a wide variety
of physicochemical processes in our Solar System. These have clear
implications for understanding exoplanetary systems. In this paper
we describe the science case for an orbital mission to Uranus with
an atmospheric entry probe to sample the composition and atmospheric
physics in Uranus' atmosphere. The characteristics of such an orbiter
and a strawman scientific payload are described and we discuss the
technical challenges for such a mission. This paper is based on a white
paper submitted to the European Space Agency's call for science themes
for its large-class mission programme in 2013.
---------------------------------------------------------
Title: Scientific rationale for Saturn's in situ exploration
Authors: Mousis, O.; Fletcher, L. N.; Lebreton, J. -P.; Wurz, P.;
Cavalié, T.; Coustenis, A.; Courtin, R.; Gautier, D.; Helled, R.;
Irwin, P. G. J.; Morse, A. D.; Nettelmann, N.; Marty, B.; Rousselot,
P.; Venot, O.; Atkinson, D. H.; Waite, J. H.; Reh, K. R.; Simon, A. A.;
Atreya, S.; André, N.; Blanc, M.; Daglis, I. A.; Fischer, G.; Geppert,
W. D.; Guillot, T.; Hedman, M. M.; Hueso, R.; Lellouch, E.; Lunine,
J. I.; Murray, C. D.; O`Donoghue, J.; Rengel, M.; Sánchez-Lavega, A.;
Schmider, F. -X.; Spiga, A.; Spilker, T.; Petit, J. -M.; Tiscareno,
M. S.; Ali-Dib, M.; Altwegg, K.; Bolton, S. J.; Bouquet, A.; Briois,
C.; Fouchet, T.; Guerlet, S.; Kostiuk, T.; Lebleu, D.; Moreno, R.;
Orton, G. S.; Poncy, J.
2014P&SS..104...29M Altcode: 2014arXiv1404.4811M
Remote sensing observations meet some limitations when used to study
the bulk atmospheric composition of the giant planets of our solar
system. A remarkable example of the superiority of in situ probe
measurements is illustrated by the exploration of Jupiter, where key
measurements such as the determination of the noble gases' abundances
and the precise measurement of the helium mixing ratio have only been
made available through in situ measurements by the Galileo probe. This
paper describes the main scientific goals to be addressed by the future
in situ exploration of Saturn placing the Galileo probe exploration of
Jupiter in a broader context and before the future probe exploration of
the more remote ice giants. In situ exploration of Saturn's atmosphere
addresses two broad themes that are discussed throughout this paper:
first, the formation history of our solar system and second, the
processes at play in planetary atmospheres. In this context, we detail
the reasons why measurements of Saturn's bulk elemental and isotopic
composition would place important constraints on the volatile reservoirs
in the protosolar nebula. We also show that the in situ measurement of
CO (or any other disequilibrium species that is depleted by reaction
with water) in Saturn's upper troposphere may help constraining its
bulk O/H ratio. We compare predictions of Jupiter and Saturn's bulk
compositions from different formation scenarios, and highlight the key
measurements required to distinguish competing theories to shed light
on giant planet formation as a common process in planetary systems with
potential applications to most extrasolar systems. In situ measurements
of Saturn's stratospheric and tropospheric dynamics, chemistry and
cloud-forming processes will provide access to phenomena unreachable to
remote sensing studies. Different mission architectures are envisaged,
which would benefit from strong international collaborations, all based
on an entry probe that would descend through Saturn's stratosphere and
troposphere under parachute down to a minimum of 10 bar of atmospheric
pressure. We finally discuss the science payload required on a Saturn
probe to match the measurement requirements.
---------------------------------------------------------
Title: Long-Term Time Variability of Temperature, Gas Abundance and
Cloud Fields in Jupiter from Thermal Emission Observations
Authors: Orton, G. S.; Fletcher, L. N.; Yanamandra-Fisher, P. A.;
Fisher, B.; Greathouse, T. K.; Liu, J.; Schneider, T.; Kim, S.
2014AGUFM.P23A3973O Altcode:
Mid-infrared raster-scans and 2D images of Jupiter's thermal emission in
discrete filters between 4.8 and 24.5 μm have been have covered nearly
2 Jovian years, enabling time-domain studies of its temperature field,
minor-constituent distribution and cloud properties. The behavior of
stratospheric (~10-mbar) and tropospheric (~100-400 mbar) temperatures
is generally consistent with predictions of seasonal variability. These
also appear to be long-term periodicities of tropospheric temperatures,
with meridionally dependent amplitudes, phases and periods. Temperatures
near and south of the equator vary least. There were no variations of
zonal mean temperatures associated with any of the "global upheaval"
or the corresponding "revival" events that have produced dramatic
changes of Jupiter's visible appearance and cloud cover, although
there are colder discrete regions associated with the updraft events
that marked the early stages of revivals. Changes visible albedo
are accompanied by increases in cloudiness at 700 mbar and higher
pressures, together with the mixing ratio of NH3 gas. In contrast to
all these changes, the meridional distribution of the 240-mbar para-H2
fraction appears to be time-invariant. Jupiter also exhibits prominent
temperature waves in both the upper troposphere and stratosphere that
move slowly retrograde in System III. Unlike Saturn's slowly moving
waves, these waves are ubiquitous at certain latitudes and at all
longitudes therein. The time scale for coherence of these waves is
somewhere between a few days and 4 weeks. These waves are consistent
with convectively generated Rossby waves.
---------------------------------------------------------
Title: The Europa Imaging System (EIS): High-Resolution, 3-D Insight
into Europa's Geology, Ice Shell, and Potential for Current Activity
Authors: Turtle, E. P.; McEwen, A. S.; Collins, G. C.; Fletcher, L. N.;
Hansen, C. J.; Hayes, A.; Hurford, T., Jr.; Kirk, R. L.; Barr, A.;
Nimmo, F.; Patterson, G.; Quick, L. C.; Soderblom, J. M.; Thomas, N.
2014AGUFM.P13E..03T Altcode:
The Europa Imaging System will transform our understanding of Europa
through global decameter-scale coverage, three-dimensional maps,
and unprecedented meter-scale imaging. EIS combines narrow-angle and
wide-angle cameras (NAC and WAC) designed to address high-priority
Europa science and reconnaissance goals. It will: (A) Characterize
the ice shell by constraining its thickness and correlating surface
features with subsurface structures detected by ice penetrating
radar; (B) Constrain formation processes of surface features and
the potential for current activity by characterizing endogenic
structures, surface units, global cross-cutting relationships, and
relationships to Europa's subsurface structure, and by searching
for evidence of recent activity, including potential plumes; and (C)
Characterize scientifically compelling landing sites and hazards by
determining the nature of the surface at scales relevant to a potential
lander. The NAC provides very high-resolution, stereo reconnaissance,
generating 2-km-wide swaths at 0.5-m pixel scale from 50-km altitude,
and uses a gimbal to enable independent targeting. NAC observations
also include: near-global (>95%) mapping of Europa at ≤50-m
pixel scale (to date, only ~14% of Europa has been imaged at ≤500
m/pixel, with best pixel scale 6 m); regional and high-resolution
stereo imaging at <1-m/pixel; and high-phase-angle observations
for plume searches. The WAC is designed to acquire pushbroom stereo
swaths along flyby ground-tracks, generating digital topographic
models with 32-m spatial scale and 4-m vertical precision from 50-km
altitude. These data support characterization of cross-track clutter
for radar sounding. The WAC also performs pushbroom color imaging
with 6 broadband filters (350-1050 nm) to map surface units and
correlations with geologic features and topography. EIS will provide
comprehensive data sets essential to fulfilling the goal of exploring
Europa to investigate its habitability and perform collaborative science
with other investigations, including cartographic and geologic maps,
regional and high-resolution digital topography, GIS products, color
and photometric data products, a geodetic control network tied to
radar altimetry, and a database of plume-search observations.
---------------------------------------------------------
Title: Photochemistry in Saturn's Ring-Shadowed Atmosphere: Modeling
of Key Molecules and Observations of Dust Content
Authors: Edgington, S. G.; Atreya, S. K.; Wilson, E. H.; West, R. A.;
Fletcher, L. N.; Baines, K. H.; Bjoraker, G. L.; Momary, T.
2014AGUFM.P23A3975E Altcode:
Cassini has been orbiting Saturn for over ten years now. During this
epoch, the ring shadow has moved from covering a large portion of the
northern hemisphere to covering a large swath south of the equator
and continues to move southward. At Saturn Orbit Insertion in 2004,
the ring plane was inclined by ~24 degrees relative to the Sun-Saturn
vector. The projection of the B-ring onto Saturn reached as far as 40N
along the central meridian (~52N at the terminator). At its maximum
extent, the ring shadow can reach as far as 48N/S (~58N/S at the
terminator). The net effect is that the intensity of both ultraviolet
and visible sunlight penetrating into any particular latitude will vary
depending on both Saturn's axis relative to the Sun and the optical
thickness of each ring system. In essence, the rings act like venetian
blinds. Our previous work [1] examined the variation of the solar
flux as a function of solar inclination, i.e. ~7.25 year season at
Saturn. Here, we report on the impact of the oscillating ring shadow
on the photolysis and production rates of hydrocarbons in Saturn's
stratosphere and upper troposphere, including acetylene, ethane,
propane, and benzene. Beginning with methane, we investigate the impact
on production and loss rates of the long-lived photochemical products
leading to haze formation are examined at several latitudes over a
Saturn year. Similarly, we assess its impact on phosphine abundance,
a disequilibrium species whose presence in the upper troposphere is
a tracer of convective processes in the deep atmosphere. We will also
present our ongoing analysis of Cassini's CIRS, UVIS, and VIMS datasets
that provide an estimate of the evolving haze content of the northern
hemisphere and we will begin to assess the implications for dynamical
mixing. In particular, we will examine how the now famous hexagonal
jet stream acts like a barrier to transport, isolating Saturn's north
polar region from outside transport of photochemically-generated
molecules and haze. [1] Edgington, S.G., et al., 2012. Photochemistry
in Saturn's Ring Shadowed Atmosphere: Modeling, Observations, and
Preliminary Analysis. Bull. American. Astron. Soc., 38, 499 (#11.23).
---------------------------------------------------------
Title: On the Origin of a Sunquake during the 2014 March 29 X1 Flare
Authors: Judge, Philip G.; Kleint, Lucia; Donea, Alina; Sainz Dalda,
Alberto; Fletcher, Lyndsay
2014ApJ...796...85J Altcode: 2014arXiv1409.6268J
Helioseismic data from the Helioseismic Magnetic Imager instrument have
revealed a sunquake associated with the X1 flare SOL2014-03-29T17:48
in active region NOAA 12017. We try to discover if acoustic-like
impulses or actions of the Lorentz force caused the sunquake. We
analyze spectropolarimetric data obtained with the Facility Infrared
Spectrometer (FIRS) at the Dunn Solar Telescope (DST). Fortunately,
the FIRS slit crossed the flare kernel close to the acoustic source
during the impulsive phase. The infrared FIRS data remain unsaturated
throughout the flare. Stokes profiles of lines of Si I 1082.7 nm and He
I 1083.0 nm are analyzed. At the flare footpoint, the Si I 1082.7 nm
core intensity increases by a factor of several, and the IR continuum
increases by 4% ± 1%. Remarkably, the Si I core resembles the classical
Ca II K line's self-reversed profile. With nLTE radiative models of
H, C, Si, and Fe, these properties set the penetration depth of flare
heating to 100 ± 100 km (i.e., photospheric layers). Estimates of the
non-magnetic energy flux are at least a factor of two less than the
sunquake energy flux. Milne-Eddington inversions of the Si I line show
that the local magnetic energy changes are also too small to drive the
acoustic pulse. Our work raises several questions. Have we missed the
signature of downward energy propagation? Is it intermittent in time
and/or non-local? Does the 1-2 s photospheric radiative damping time
discount compressive modes? <P />The National Center for Atmospheric
Research is sponsored by the National Science Foundation.
---------------------------------------------------------
Title: Constraints on Jupiter's stratospheric HCl abundance and
chlorine cycle from Herschel/HIFI
Authors: Teanby, N. A.; Showman, A. P.; Fletcher, L. N.; Irwin,
P. G. J.
2014P&SS..103..250T Altcode:
Detection of HCl on Jupiter would provide insight into the chlorine
cycle and external elemental fluxes on giant planets, yet so far
has not been possible. Here we present the most sensitive search for
Jupiter's stratospheric HCl to date using observations of the 625.907
and 1876.221 GHz spectral lines with Herschel's HIFI instrument. HCl
was not detected, but we determined the most stringent upper limits so
far, improving on previous studies by two orders of magnitude. If HCl is
assumed to be uniformly mixed, with a constant volume mixing ratio above
the 1 mbar pressure level and has zero abundance below, we obtain a
3-σ upper limit of 0.061 ppb; in contrast, if we assume uniform mixing
above the 1 mbar level and allow a non-zero but downward-decreasing
abundance from 1 mbar to the troposphere based on eddy diffusion, we
obtain a 3-σ upper limit of 0.027 ppb. This is below the abundance
expected for a solar composition cometary source and implies that
upper stratospheric HCl loss processes are required for consistency
with observations of the external oxygen flux. We investigated loss
via aerosol scavenging using a simple diffusion model and conclude
that it could be a very effective mechanism for HCl removal. Transient
scavenging by stratospheric NH<SUB>3</SUB> from impacts is another
potentially important loss mechanism. This suggests that it is
extremely unlikely that HCl is present in sufficient quantities to
be detectable in the near future. An alternative explanation for our
very low upper limits could be that HCl is sub-solar in comets or that
cometary chlorine exists in inactive reservoirs that are not readily
converted to HCl during the impact process.
---------------------------------------------------------
Title: The transit spectra of Earth and Jupiter
Authors: Irwin, P. G. J.; Barstow, J. K.; Bowles, N. E.; Fletcher,
L. N.; Aigrain, S.; Lee, J. -M.
2014Icar..242..172I Altcode: 2014arXiv1408.3914I
In recent years, an increasing number of observations have been made
of the transits of 'Hot Jupiters', such as HD 189733b, about their
parent stars from the visible through to mid-infrared wavelengths,
which have been modelled to derive the likely atmospheric structure
and composition of these planets. As measurement techniques improve,
the measured transit spectra of 'Super-Earths' such as GJ 1214b are
becoming better constrained, allowing model atmospheric states to be
fitted for this class of planet also. While it is not yet possible to
constrain the atmospheric states of small planets such as the Earth or
cold planets like Jupiter, it is hoped that this might become practical
in the coming decades and if so, it is of interest to determine what we
might infer from such measurements. In this work we have constructed
atmospheric models of the Solar System planets from 0.4 to 15.5 μm
that are consistent with ground-based and satellite observations and
from these calculate the primary transit and secondary eclipse spectra
(with respect to the Sun and typical M-dwarfs) that would be observed
by a 'remote observer', many light years away. From these spectra we
test what current retrieval models might infer about their atmospheric
states and compare these with the 'ground truths' in order to assess:
(a) the inherent uncertainties in transit spectra observations; (b)
the relative merits of primary transit and secondary eclipse spectra;
and (c) the advantages of acquiring directly imaged spectra of these
planets. We find that observing secondary eclipses of the Solar System
would not give sufficient information for determining atmospheric
properties with 10 m-diameter telescopes from a distance of 10 light
years, but that primary transits give much better information. We find
that a single transit of Jupiter in front of the Sun could potentially
be used to determine temperature and stratospheric composition, but
for the Earth the mean atmospheric composition could only be determined
if it were orbiting a much smaller M-dwarf. For both Jupiter and Earth
we note that direct imaging with sufficient nulling of the light from
the parent star theoretically provides the best method of determining
the atmospheric properties of such planets.
---------------------------------------------------------
Title: Instrumental methods for professional and amateur
collaborations in planetary astronomy
Authors: Mousis, O.; Hueso, R.; Beaulieu, J. -P.; Bouley, S.; Carry,
B.; Colas, F.; Klotz, A.; Pellier, C.; Petit, J. -M.; Rousselot,
P.; Ali-Dib, M.; Beisker, W.; Birlan, M.; Buil, C.; Delsanti, A.;
Frappa, E.; Hammel, H. B.; Levasseur-Regourd, A. C.; Orton, G. S.;
Sánchez-Lavega, A.; Santerne, A.; Tanga, P.; Vaubaillon, J.; Zanda,
B.; Baratoux, D.; Böhm, T.; Boudon, V.; Bouquet, A.; Buzzi, L.;
Dauvergne, J. -L.; Decock, A.; Delcroix, M.; Drossart, P.; Esseiva,
N.; Fischer, G.; Fletcher, L. N.; Foglia, S.; Gómez-Forrellad, J. M.;
Guarro-Fló, J.; Herald, D.; Jehin, E.; Kugel, F.; Lebreton, J. -P.;
Lecacheux, J.; Leroy, A.; Maquet, L.; Masi, G.; Maury, A.; Meyer,
F.; Pérez-Hoyos, S.; Rajpurohit, A. S.; Rinner, C.; Rogers, J. H.;
Roques, F.; Schmude, R. W.; Sicardy, B.; Tregon, B.; Vanhuysse, M.;
Wesley, A.; Widemann, T.
2014ExA....38...91M Altcode: 2013arXiv1305.3647M; 2014ExA...tmp...35M
Amateur contributions to professional publications have increased
exponentially over the last decades in the field of planetary
astronomy. Here we review the different domains of the field in
which collaborations between professional and amateur astronomers are
effective and regularly lead to scientific publications.We discuss
the instruments, detectors, software and methodologies typically used
by amateur astronomers to collect the scientific data in the different
domains of interest. Amateur contributions to the monitoring of planets
and interplanetary matter, characterization of asteroids and comets,
as well as the determination of the physical properties of Kuiper Belt
Objects and exoplanets are discussed.
---------------------------------------------------------
Title: The Radiated Energy Budget of Chromospheric Plasma in a Major
Solar Flare Deduced from Multi-wavelength Observations
Authors: Milligan, Ryan O.; Kerr, Graham S.; Dennis, Brian R.; Hudson,
Hugh S.; Fletcher, Lyndsay; Allred, Joel C.; Chamberlin, Phillip C.;
Ireland, Jack; Mathioudakis, Mihalis; Keenan, Francis P.
2014ApJ...793...70M Altcode: 2014arXiv1406.7657M
This paper presents measurements of the energy radiated by the lower
solar atmosphere, at optical, UV, and EUV wavelengths, during an
X-class solar flare (SOL2011-02-15T01:56) in response to an injection
of energy assumed to be in the form of nonthermal electrons. Hard
X-ray observations from RHESSI were used to track the evolution of
the parameters of the nonthermal electron distribution to reveal the
total power contained in flare accelerated electrons. By integrating
over the duration of the impulsive phase, the total energy contained
in the nonthermal electrons was found to be >2 × 10<SUP>31</SUP>
erg. The response of the lower solar atmosphere was measured in
the free-bound EUV continua of H I (Lyman), He I, and He II, plus
the emission lines of He II at 304 Å and H I (Lyα) at 1216 Å by
SDO/EVE, the UV continua at 1600 Å and 1700 Å by SDO/AIA, and the
white light continuum at 4504 Å, 5550 Å, and 6684 Å, along with the
Ca II H line at 3968 Å using Hinode/SOT. The summed energy detected
by these instruments amounted to ~3 × 10<SUP>30</SUP> erg about 15%
of the total nonthermal energy. The Lyα line was found to dominate
the measured radiative losses. Parameters of both the driving electron
distribution and the resulting chromospheric response are presented
in detail to encourage the numerical modeling of flare heating for
this event, to determine the depth of the solar atmosphere at which
these line and continuum processes originate, and the mechanism(s)
responsible for their generation.
---------------------------------------------------------
Title: Onset of Electron Acceleration in a Flare Loop
Authors: Sharykin, Ivan; Liu, Siming; Fletcher, Lyndsay
2014ApJ...793...25S Altcode: 2014arXiv1408.1413S
We carried out a detailed analysis of X-ray and radio observations of a
simple flare loop that occurred on 2002 August 12, with the impulsive
hard X-ray (HXR) light curves dominated by a single pulse. The
emission spectra of the early impulsive phase are consistent with
an isothermal model in the coronal loop with a temperature reaching
several keV. A power-law high-energy spectral tail is evident near the
HXR peak time, in accordance with the appearance of footpoints at high
energies, and is well correlated with the radio emission. The energy
content of the thermal component keeps increasing gradually after
the disappearance of this nonthermal component. These results suggest
that electron acceleration only covers the central period of a longer
and more gradual energy dissipation process and that the electron
transport within the loop plays a crucial role in the formation of
the inferred power-law electron distribution. The spectral index of
power-law photons shows a very gradual evolution, indicating that the
electron accelerator is in a quasi-steady state, which is confirmed by
radio observations. These results are consistent with the theory of
stochastic electron acceleration from a thermal background. Advanced
modeling with coupled electron acceleration and spatial transport
processes is needed to explain these observations more quantitatively,
which may reveal the dependence of the electron acceleration on the
spatial structure of the acceleration region.
---------------------------------------------------------
Title: BayesFlare: Bayesian method for detecting stellar flares
Authors: Pitkin, M.; Williams, D.; Fletcher, L.; Grant, S. D. T.
2014ascl.soft07015P Altcode:
BayesFlare identifies flaring events in light curves released by
the Kepler mission; it identifies even weak events by making use of
the flare signal shape. The package contains functions to perform
Bayesian hypothesis testing comparing the probability of light curves
containing flares to that of them containing noise (or non-flare-like)
artifacts. BayesFlare includes functions in its amplitude-marginalizer
suite to account for underlying sinusoidal variations in light curve
data; it includes such variations in the signal model, and then
analytically marginalizes over them.
---------------------------------------------------------
Title: Thermal Emission Constraints on the Atmospheres of Uranus
and Neptune
Authors: Orton, G. S.; Fletcher, L. N.; Moses, J. I.; Lellouch, E.;
Moreno, R.; Swinyard, B. M.; Hofstadter, M. D.; Greathouse, T. K.
2014LPICo1798.2002O Altcode:
Photometric and spectroscopic observations of Uranus and Neptune have
been analyzed from both spacecraft and Earth-based platforms, in order
to create self-consistent models of their temperature fields and the
distribution of trace gases.
---------------------------------------------------------
Title: Where is the Chromospheric Response to Conductive Energy
Input from a Hot Pre-flare Coronal Loop?
Authors: Battaglia, Marina; Fletcher, Lyndsay; Simões, Paulo J. A.
2014ApJ...789...47B Altcode: 2014arXiv1405.4621B
Before the onset of a flare is observed in hard X-rays, there is often
a prolonged pre-flare or pre-heating phase with no detectable hard X-ray
emission but pronounced soft X-ray emission, which suggests that energy
is already being released and deposited into the corona and chromosphere
at this stage. This work analyzes the temporal evolution of coronal
source heating and the chromospheric response during this pre-heating
phase to investigate the origin and nature of early energy release and
transport during a solar flare. Simultaneous X-ray, EUV, and microwave
observations of a well-observed flare with a prolonged pre-heating phase
are analyzed to study the time evolution of the thermal emission and
to determine the onset of particle acceleration. During the 20 minute
duration of the pre-heating phase we find no hint of accelerated
electrons in either hard X-rays or microwave emission. However,
the total energy budget during the pre-heating phase suggests that
energy must be supplied to the flaring loop to sustain the observed
temperature and emission measure. Under the assumption of this energy
being transported toward the chromosphere via thermal conduction,
significant energy deposition at the chromosphere is expected. However,
no detectable increase of the emission in the AIA wavelength channels
sensitive to chromospheric temperatures is observed. The observations
suggest energy release and deposition in the flaring loop before the
onset of particle acceleration, yet a model in which energy is conducted
to the chromosphere and subsequent heating of the chromosphere is not
supported by the observations.
---------------------------------------------------------
Title: Scientific Rationale and Concepts for an In Situ Saturn Probe
Authors: Mousis, O.; Coustenis, A.; Lebreton, J. -P.; Atkinson,
D. H.; Lunine, J. I.; Rey, K.; Fletcher, L. N.; Simon-Miller, A.;
Atreya, S.; Brinckerhoff, W.; Cavalié, T.; Colaprete, A.; Gautier,
D.; Guillot, T.; Hueso, R.; Mahaffy, P.; Marty, B.; Morse, A. D.;
Sims, J.; Spilker, T.; Spilker, L.; Webster, C.; Waite, J. H.; Wurz, P.
2014LPICo1795.8094M Altcode:
We summarize the science case for in situ measurements at Saturn and
discuss the possible mission concepts that would be consistent with
the constraints of ESA M-class missions.
---------------------------------------------------------
Title: F-CHROMA.Flare Chromospheres: Observations, Models and Archives
Authors: Cauzzi, Gianna; Fletcher, Lyndsay; Mathioudakis, Mihalis;
Carlsson, Mats; Heinzel, Petr; Berlicki, Arek; Zuccarello, Francesca
2014AAS...22412339C Altcode:
F-CHROMA is a collaborative project newly funded under the EU-Framework
Programme 7 "FP7-SPACE-2013-1", involving seven different European
research Institutes and Universities. The goal of F-CHROMA is to
substantially advance our understanding of the physics of energy
dissipation and radiation in the flaring solar atmosphere, with a
particular focus on the flares' chromosphere. A major outcome of the
F-CHROMA project will be the creation of an archive of chromospheric
flare observations and models to be made available to the community
for further research.In this poster we describe the structure and
milestones of the project, the different activities planned, as well
as early results. Emphasis will be given to the dissemination efforts
of the project to make results of these activities available to and
usable by the community.
---------------------------------------------------------
Title: In Situ Probe Science at Saturn
Authors: Atkinson, D. H.; Lunine, J. I.; Simon-Miller, A. A.; Atreya,
S. K.; Brinckerhoff, W.; Colaprete, A.; Coustenis, A.; Fletcher, L. N.;
Guillot, T.; Lebreton, J. -P.; Mahaffy, P.; Mousis, O.; Orton, G. S.;
Reh, K.; Spilker, L. J.; Spilker, T. R.; Webster, C.
2014LPICo1795.8005A Altcode:
Key to understanding solar system formation and evolution is the origin
and evolution of the giant planets. A small shallow Saturn probe can
serve to test competing theories of solar system and giant planet
origin, chemical, and dynamical evolution.
---------------------------------------------------------
Title: From Voyager-IRIS to Cassini-CIRS: Interannual variability
in Saturn’s stratosphere?
Authors: Sinclair, J. A.; Irwin, P. G. J.; Fletcher, L. N.; Greathouse,
T.; Guerlet, S.; Hurley, J.; Merlet, C.
2014Icar..233..281S Altcode:
We present an intercomparison of Saturn’s stratosphere between
Voyager 1-IRIS observations in 1980 and Cassini-CIRS observations in
2009 and 2010. Over a saturnian year (∼29.5 years) has now passed
since the Voyager flybys of Saturn in 1980/1981. Cassini observations
in 2009/2010 capture Saturn in the same season as Voyager observations
(just after the vernal equinox) but one year later. Any differences
in Saturn’s atmospheric properties implied by a comparison of
these two datasets could therefore reveal the extent of interannual
variability. We retrieve temperature and stratospheric acetylene and
ethane concentrations from Voyager 1-IRIS (Δν∼=4.3 cm<SUP>-1</SUP>)
observations in 1980 and Cassini-CIRS (Δν∼=15.5 cm<SUP>-1</SUP>)
‘FIRMAP’ observations in 2009 and 2010. We observe a difference
in temperature at the equator of 7.1 ± 1.2 K at the 2.1-mbar level
that implies that the two datasets have captured Saturn’s semiannual
oscillation (SSAO) in a slightly different phase suggesting that its
period is more quasi-semiannual. Elevated concentrations of acetylene
at 25°S in 1980 with respect to 2010 imply stronger downwelling
at the former date which may also be explained by a difference in
the phase of the SSAO and its dynamical forcing at low latitudes. At
high-southern and high-northern latitudes, stratospheric temperatures
and hydrocarbon concentrations appear elevated in 1980 with respect
to 2009/2010. This could be an artefact of the low signal-to-noise
ratio of the corresponding observations but might also be explained
by increased auroral activity during solar maximum in 1980.
---------------------------------------------------------
Title: Changes to Saturn's Zonal-mean Tropospheric Thermal Structure
after the 2010-2011 Northern Hemisphere Storm
Authors: Achterberg, R. K.; Gierasch, P. J.; Conrath, B. J.; Fletcher,
L. N.; Hesman, B. E.; Bjoraker, G. L.; Flasar, F. M.
2014ApJ...786...92A Altcode:
We use far-infrared (20-200 μm) data from the Composite Infrared
Spectrometer on the Cassini spacecraft to determine the zonal-mean
temperature and hydrogen para-fraction in Saturn's upper troposphere
from observations taken before and after the large northern hemisphere
storm in 2010-2011. During the storm, zonal mean temperatures in the
latitude band between approximately 25°N and 45°N (planetographic
latitude) increased by about 3 K, while the zonal mean hydrogen
para-fraction decreased by about 0.04 over the same latitudes, at
pressures greater than about 300 mbar. These changes occurred over
the same latitude range as the disturbed cloud band seen in visible
images. The observations are consistent with low para-fraction gas being
brought up from the level of the water cloud by the strong convective
plume associated with the storm, while being heated by condensation
of water vapor, and then advected zonally by the winds near the plume
tops in the upper troposphere.
---------------------------------------------------------
Title: Clouds on the Hot Jupiter HD189733b: Constraints from the
Reflection Spectrum
Authors: Barstow, J. K.; Aigrain, S.; Irwin, P. G. J.; Hackler, T.;
Fletcher, L. N.; Lee, J. M.; Gibson, N. P.
2014ApJ...786..154B Altcode: 2014arXiv1403.6664B
The hot Jupiter HD 189733b is probably the best studied of the known
extrasolar planets, with published transit and eclipse spectra covering
the near UV to mid-IR range. Recent work on the transmission spectrum
has shown clear evidence for the presence of clouds in its atmosphere,
which significantly increases the model atmosphere parameter space
that must be explored in order to fully characterize this planet. In
this work, we apply the NEMESIS atmospheric retrieval code to the
recently published HST/STIS reflection spectrum, and also to the dayside
thermal emission spectrum in light of new Spitzer/IRAC measurements,
as well as our own re-analysis of the HST/NICMOS data. We first use
the STIS data to place some constraints on the nature of clouds on
HD 189733b and explore solution degeneracy between different cloud
properties and the abundance of Na in the atmosphere; as already
noted in previous work, absorption due to Na plays a significant
role in determining the shape of the reflection spectrum. We then
perform a new retrieval of the temperature profile and abundances
of H<SUB>2</SUB>O, CO<SUB>2</SUB>, CO, and CH<SUB>4</SUB> from the
dayside thermal emission spectrum. Finally, we investigate the effect
of including cloud in the model on this retrieval process. We find
that the current quality of data does not warrant the extra complexity
introduced by including cloud in the model; however, future data are
likely to be of sufficient resolution and signal-to-noise that a more
complete model, including scattering particles, will be required.
---------------------------------------------------------
Title: In situ Probe Science at Saturn
Authors: Atkinson, D. H.; Mousis, O.; Lunine, J. I.; Simon-Miller,
A. A.; Atreya, S. K.; Brinckerhoff, W.; Colaprete, A.; Coustenis, A.;
Fletcher, L. N.; Guillot, T.; Lebreton, J. -P.; Mahaffy, P.; Orton,
G. S.; Reh, K.; Spilker, L. J.; Spilker, T. R.; Webster, C.
2014EPSC....9...12A Altcode:
A fundamental goal of solar system exploration is to understand
the origin of the solar system, the initial stages, conditions, and
processes by which the solar system formed, how the formation process
was initiated, and the nature of the interstellar seed material from
which the solar system was born. Key to understanding solar system
formation and subsequent dynamical and chemical evolution is the origin
and evolution of the giant planets and their atmospheres. Several
theories have been put forward to explain the process of solar system
formation, and the origin and evolution of the giant planets and
their atmospheres. Each theory offers quantifiable predictions of the
abundances of noble gases He, Ne, Ar, Kr, and Xe, and abundances of key
isotopic ratios 4He/3He, D/H, 15N/14N, 18O/16O, and 13C/12C. Detection
of certain disequilibrium species, diagnostic of deeper internal
processes and dynamics of the atmosphere, would also help discriminate
between competing theories. Measurements of the critical abundance
profiles of these key constituents into the deeper well-mixed atmosphere
must be complemented by measurements of the profiles of atmospheric
structure and dynamics at high vertical resolution and also require in
situ exploration. The atmospheres of the giant planets can also serve
as laboratories to better understand the atmospheric chemistries,
dynamics, processes, and climates on all planets including Earth,
and offer a context and provide a ground truth for exoplanets and
exoplanetary systems. Additionally, Giant planets have long been
thought to play a critical role in the development of potentially
habitable planetary systems. In the context of giant planet science
provided by the Galileo, Juno, and Cassini missions to Jupiter and
Saturn, a small, relatively shallow Saturn probe capable of measuring
abundances and isotopic ratios of key atmospheric constituents, and
atmospheric structure including pressures, temperatures, dynamics,
and cloud locations and properties not accessible by remote sensing
can serve to test competing theories of solar system and giant planet
origin, chemical, and dynamical evolution.
---------------------------------------------------------
Title: Cycle 23 Variation in Solar Flare Productivity
Authors: Hudson, Hugh; Fletcher, Lyndsay; McTiernan, Jim
2014SoPh..289.1341H Altcode: 2014arXiv1401.6474H
The NOAA listings of solar flares in cycles 21 - 24, including the GOES
soft X-ray magnitudes, enable a simple determination of the number of
flares each flaring active region produces over its lifetime. We have
studied this measure of flare productivity over the interval 1975 -
2012. The annual averages of flare productivity remained approximately
constant during cycles 21 and 22, at about two reported M- or X-flares
per region, but then increased significantly in the declining phase
of cycle 23 (the years 2004 - 2005). We have confirmed this by using
the independent RHESSI flare catalog to check the NOAA events listings
where possible. We note that this measure of solar activity does not
correlate with the solar cycle. The anomalous peak in flare productivity
immediately preceded the long solar minimum between cycles 23 and 24.
---------------------------------------------------------
Title: Monitoring Jovian Dynamics Using Maps of NH3 and PH3
Authors: Encrenaz, T.; Greathouse, T.; Drossart, P.; Fouchet, T.;
Janssen, M.; Gulkis, S.; Orton, G.; Fletcher, L.; Giles, R.
2014EPSC....9..240E Altcode:
Phosphine and ammonia are important tracers of Jovian tropospheric
dynamics, but their vertical distributions are still poorly known. This
information will be needed for the analysis of the radio and infrared
data of the JUNO mission in 2016. We have started an observing campaign
to obtain 3D maps of NH3 and PH3 in the 0.1-5 bar pressure range,
by using TEXES/IRTF and selecting 3 spectral ranges (at 4.65, 8.9 and
10.5 microns) that probe 3 different pressure levels. The first data
(Feb. 2014) allow us to map NH3 and PH3 at low latitudes. We plan to
continue this campaign to obtain a full latitude and longitude coverage
and to improve the sensitivity.
---------------------------------------------------------
Title: Seasonal Evolution of Saturn's Polar Atmosphere from a Decade
of Cassini/CIRS Observations
Authors: Fletcher, L. N.; Sinclair, J. A.; Irwin, P. G. J.; Giles,
R. S.; Orton, G. S.; Hesman, B. E.; Hurley, J.; Bjoraker, G. L.;
Simon, A. A.
2014EPSC....9...62F Altcode:
Saturn's polar regions are subjected to extreme insolation variations
over its 29.5 year orbit due to the gas giant's 26-degree axial
tilt, causing seasonal changes to the thermal structure, chemistry,
dynamics and cloud properties of the polar environments. Cassini's
high inclination orbits permit detailed scrutiny of Saturn's high
latitudes in a dataset that now spans a decade (a third of a Saturn
year, 2004-2014), five years either side of the northern spring
equinox in 2009. Thermal infrared Cassini/CIRS spectra (7-16 μm)
from all mission phases are inverted to determine the rate of change
of polar temperatures, wind shears, tropospheric phosphine (as a
tracer of vertical mixing) and stratospheric hydrocarbons (tracers of
middle atmospheric circulation and chemistry). Cassini's unique vantage
point allows us to track these parameters as the summer southern pole
receded into autumn and the winter northern pole emerged into spring
sunlight. Results show the most rapid changes to temperature and
composition occurring poleward of 70o in each hemisphere, in excess
of expectations from simple radiative climate models. Small cyclonic
vortices persist at both poles throughout theCassini mission, while the
broad stratospheric vortices are seasonally variable. The signature
of the northern hexagon is still present in the tropospheric thermal
structure. At the time of writing, an infraredbright polar vortex is
beginning to emerge at the northern spring pole, consistent with the
historical record of Saturn observations from the 1980s (previous
northern spring, [4]).
---------------------------------------------------------
Title: Long-term variability of temperatures and clouds in Saturn
from ground-based observations of thermal emission
Authors: Orton, G.; Fletcher, L.; Sinclair, J.; Yanamandra-Fisher,
P.; Greathouse, T.; Momary, T.; Fujiyoshi, T.; Aguilar, I.
2014EPSC....9..681O Altcode:
We report the results of long-term studies of thermal emission from
the atmosphere of Saturn using ground-based imaging covering 1990 to
the present. Both seasonal and non-seasonal effects have been detected
in its atmosphere. Seasonal effects are most pronounced and indicate
a variance from radiative climate model results that is consistent
with an additional source of stratospheric heating other than gaseous
absorption of sunlight. Associated with the seasonal variations is
the establishment of warm polar vortices in the stratosphere toward
late spring and early summer, with the anticipation of such a vortex
appearing imminently in Saturn's north polar region. Non-seasonal
effects include a variation of low-latitude thermal waves, initially
identified as consistent with a semi-annual oscillation, although
recent observations indicate a variation from that behavior. Slowly
moving zonal thermal waves have been detected irregularly; they have
been most prominent in Saturn's southern mid-latitudes. Deep atmospheric
cloud structure has shown consistent zonal-mean structure from 1995 to
the present; however it has been marked by substantial discrete opaque
("cold") features. The great springtime storm of 2010-2011 produced
substantial perturbations of both atmospheric temperatures and deep
cloud structure.
---------------------------------------------------------
Title: Interpretation of the 14N/15N ratio measured in Saturn's
ammonia
Authors: Mousis, O.; Lunine, J. I.; Fletcher, L. N.; Mandt, K. E.;
Gautier, D.; Atreya, S.
2014EPSC....9..425M Altcode:
The recent derivation of a 1-sigma lower limit for the 14N/15N ratio in
Saturn's ammonia, which is found to be ~500 [1], prompts us to revise
models of Saturn's formation using as constraints the abundances of
heavy elements inferred in its atmosphere. This lower limit is found
consistent with the 14N/15N ratio (~435) measured by the Galileo probe
at Jupiter and implies that the two giant planets were essentially
formed from the same nitrogen reservoir in the nebula, which is N2
[1]. However, in contrast with Jupiter whose C and N enrichments are
uniform, carbon is more than twice enriched in Saturn's atmosphere
compared to nitrogen. This non-uniform enrichment at Saturn, considered
with the recent derivation of a lower limit for the 14N/15N ratio,
challenges the formation models elaborated so far. Here we propose an
alternative formation scenario that may explain all these properties
together
---------------------------------------------------------
Title: Scientific Rationale and Concepts for an In Situ Saturn Probe
Authors: Mousis, O.; Atkinson, D.; Atreya, S.; Coustenis, A.; Fletcher,
L. N.; Gautier, D.; Guillot, T.; Hueso, R.; Lebreton, J. -P.; Lunine,
J. I.; Marty, B.; Reh, K.; Venkatapathy, E.; Waite, J. H.; Wurz, P.
2014EPSC....9..437M Altcode:
We summarize the science case for in situ measurements at Saturn and
discuss the possible mission concepts that would be consistent with
the constraints of ESA M-class missions.
---------------------------------------------------------
Title: Possible Concepts for an In Situ Saturn Probe Mission
Authors: Coustenis, A.; Lebreton, J. -P.; Mousis, O.; Atkinson, D. H.;
Lunine, J. I.; Reh, K.; Fletcher, L.; Simon-Miller, A.; Atreya, S. K.;
Brinckerhoff, W.; Cavalié, T.; Colaprete, A.; Gautier, D.; Guillot,
T.; Mahaffy, P.; Marty, B.; Morse, A. D.; Sims, J.; Spilker, T.;
Spilker, L.; Webster, C.; Waite, J. H.; Wurz, P.
2014LPI....45.1244C Altcode:
We present Saturn entry probe concepts for in situ exploration
informing us on the formation history of our solar system and the
planet's atmosphere processes.
---------------------------------------------------------
Title: Europa's Water Vapor Plumes: Discovery with HST and Plans
for JUICE-UVS Observations
Authors: Retherford, K. D.; Roth, L.; Saur, J.; Gladstone, G. R.;
Nimmo, F.; McGrath, M. A.; Feldman, P. D.; Strobel, D. F.; Greathouse,
T. K.; Davis, M. W.; Steffl, A. J.; Spencer, J. R.; Bagenal, F.;
Fletcher, L.; Juice-UVS Team
2014LPI....45.1639R Altcode:
Discovery of water vapor plumes on Europa obtained with HST, and
updated plans for JUICE Ultraviolet Spectrograph (UVS) observations.
---------------------------------------------------------
Title: Physical Properties of White-light Sources in the 2011 February
15 Solar Flare
Authors: Kerr, G. S.; Fletcher, L.
2014ApJ...783...98K Altcode: 2014arXiv1401.4877K
White-light flares (WLFs) are observational rarities, making them
understudied events. However, optical emission is a significant
contribution to flare energy budgets and the emission mechanisms
responsible could have important implications for flare models. Using
Hinode SOT optical continuum data taken in broadband red, green,
and blue filters, we investigate WL emission from the X2.2 flare
SOL2011-02-15T01:56:00. We develop a technique to robustly identify
enhanced flare pixels and, using a knowledge of the RGB filter
transmissions, determined the source color temperature and effective
temperature. We investigated two idealized models of WL emission—an
optically thick photospheric source, and an optically thin chromospheric
slab. Under the optically thick assumption, the color temperature and
effective temperature of flare sources in sunspot umbra and penumbra
were determined as a function of time and position. Values in the range
of 5000-6000 K were found, corresponding to a blackbody temperature
increase of a few hundred kelvin. The power emitted in the optical
was estimated at ~10<SUP>26</SUP> erg s<SUP>-1</SUP>. In some of the
WL sources the color and blackbody temperatures are the same within
uncertainties, consistent with a blackbody emitter. In other regions
this is not the case, suggesting that some other continuum emission
process is contributing. An optically thin slab model producing hydrogen
recombination radiation is also discussed as a potential source of
WL emission; it requires temperatures in the range 5500-25,000 K,
and total energies of ~10<SUP>27</SUP> erg s<SUP>-1</SUP>.
---------------------------------------------------------
Title: Exploring the diversity of Jupiter-class planets
Authors: Fletcher, L. N.; Irwin, P. G. J.; Barstow, J. K.; de Kok,
R. J.; Lee, J. -M.; Aigrain, S.
2014RSPTA.37230064F Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Scientific Rationale of a Saturn Probe Mission
Authors: Mousis, O.; Fletcher, L. N.; Lebreton, J. -P.; Wurz, P.;
Cavalié, T.; Coustenis, A.; Atkinson, D. H.; Atreya, S.; Gautier,
D.; Guillot, T.; Lunine, J. I.; Marty, B.; Morse, A. D.; Rey, K. R.;
Simon-Miller, A.; Spilker, T.; Waite, J. H.
2014LPI....45.1261M Altcode:
We describe the main scientific goals to be addressed by future in
situ exploration of Saturn.
---------------------------------------------------------
Title: Jupiter Icy Moons Explorer (JUICE): Science Objectives,
Mission and Instruments
Authors: Plaut, J. J.; Barabash, S.; Bruzzone, L.; Dougherty, M.; Erd,
C.; Fletcher, L.; Gladstone, R.; Grasset, O.; Gurvits, L.; Hartogh,
P.; Hussmann, H.; Iess, L.; Jaumann, R.; Langevin, Y.; Palumbo, P.;
Piccioni, G.; Titov, D.; Wahlund, J. -E.
2014LPI....45.2717P Altcode:
The JUpiter ICy Moons Explorer (JUICE) is an ESA mission that will
fly by and observe the icy moons Europa, Ganymede, and Callisto,
and finally orbit Ganymede.
---------------------------------------------------------
Title: In Situ Probe Science at Saturn
Authors: Atkinson, D. H.; Lunine, J. I.; Simon-Miller, A. A.; Atreya,
S. K.; Brinckerhoff, W.; Colaprete, A.; Coustenis, A.; Fletcher, L. N.;
Guillot, T.; Lebreton, J. -P.; Mahaffy, P.; Mousis, O.; Orton, G. S.;
Reh, K.; Spilker, L. J.; Spilker, T. R.; Webster, C.
2014LPI....45.1377A Altcode:
A shallow Saturn probe measuring key atmospheric abundances and isotope
ratios can test competing theories of solar system and giant planet
formation.
---------------------------------------------------------
Title: Europa's Water Vapor Plumes: The Potential for Discovery with
JUICE-UVS Observations
Authors: Retherford, K. D.; Roth, L.; Saur, J.; Gladstone, G. R.;
Nimmo, F.; McGrath, M. A.; Feldman, P. D.; Strobel, D. F.; Steffl,
A. J.; Greathouse, T. K.; Spencer, J. R.; Bagenal, F.; Fletcher, L. N.
2014LPICo1774.4033R Altcode:
Far-UV auroral imaging and stellar occultation techniques are able
to identify whether water vapor plumes exist on Europa. Detailed
observation plans for the JUICE Ultraviolet Spectrograph (UVS) are
reported along with recent HST auroral imaging.
---------------------------------------------------------
Title: The first submillimeter observation of CO in the stratosphere
of Uranus
Authors: Cavalié, T.; Moreno, R.; Lellouch, E.; Hartogh, P.; Venot,
O.; Orton, G. S.; Jarchow, C.; Encrenaz, T.; Selsis, F.; Hersant,
F.; Fletcher, L. N.
2014A&A...562A..33C Altcode: 2013arXiv1311.2458C
Context. Carbon monoxide (CO) has been detected in all giant planets and
its origin is both internal and external in Jupiter and Neptune. Despite
its first detection in Uranus a decade ago, the magnitude of its
internal and external sources remains unconstrained. <BR /> Aims: We
targeted CO lines in Uranus in the submillimeter range to constrain its
origin. <BR /> Methods: We recorded the disk-averaged spectrum of Uranus
with very high spectral resolution at the frequencies of CO rotational
lines in the submillimeter range in 2011-2012. We used empirical and
diffusion models of the atmosphere of Uranus to constrain the origin of
CO. We also used a thermochemical model of its troposphere to derive an
upper limit on the oxygen-to-hydrogen (O/H) ratio in the deep atmosphere
of Uranus. <BR /> Results: We have detected the CO(8-7) rotational line
for the first time with Herschel-HIFI. Both empirical and diffusion
models results show that CO has an external origin. An empirical profile
in which CO is constant above the 100 mbar level with a mole fraction
of 7.1-9.0 × 10<SUP>-9</SUP>, depending on the adopted stratospheric
thermal structure, reproduces the data. Sporadic and steady source
models cannot be differentiated with our data. Taking the internal
source model upper limit of a mole fraction of 2.1 × 10<SUP>-9</SUP>
we find, based on our thermochemical computations, that the deep O/H
ratio of Uranus is less than 500 times solar. <BR /> Conclusions:
Our work shows that the average mole fraction of CO decreases from
the stratosphere to the troposphere and thus strongly advocates for
an external source of CO in Uranus. Photochemical modeling of oxygen
species in the atmosphere of Uranus and more sensitive observations
are needed to reveal the nature of the external source. <P />Herschel
is an ESA space observatory with science instruments provided by
European-led Principal Investigator consortia and with important
participation from NASA.
---------------------------------------------------------
Title: JUICE: The ESA Mission to Study Habitability of the Jovian
Icy Moons
Authors: Titov, D.; Barabash, S.; Bruzzone, L.; Dougherty, M.; Duvet,
L.; Erd, C.; Fletcher, L.; Gladstone, R.; Grasset, O.; Gurvits,
L.; Hartogh, P.; Hussmann, H.; Iess, L.; Jaumann, R.; Langevin, Y.;
Palumbo, P.; Piccioni, G.; Wahlund, J. -E.
2014LPICo1774.4035T Altcode:
The presentation will give an overview of the ESA's JUICE (JUpiter ICy
moons Explorer) mission to the Jovian system, its science scenario,
observation strategy, and the newly selected payload.
---------------------------------------------------------
Title: Line-by-line analysis of Neptune's near-IR spectrum observed
with Gemini/NIFS and VLT/CRIRES
Authors: Irwin, P. G. J.; Lellouch, E.; de Bergh, C.; Courtin, R.;
Bézard, B.; Fletcher, L. N.; Orton, G. S.; Teanby, N. A.; Calcutt,
S. B.; Tice, D.; Hurley, J.; Davis, G. R.
2014Icar..227...37I Altcode:
New line data describing the absorption of CH<SUB>4</SUB> and
CH<SUB>3</SUB>D from 1.26 to 1.71 μm (WKMC-80K, Campargue, A.,
Wang, L., Mondelain, D., Kassi, S., Bézard, B., Lellouch, E.,
Coustenis, A., de Bergh, C., Hirtzig, M., Drossart, P. [2012]. Icarus
219, 110-128) have been applied to the analysis of Gemini-N/NIFS
observations of Neptune made in 2009 and VLT/CRIRES observations
made in 2010. The new line data are found to greatly improve the
fit to the observed spectra and present a considerable advance over
previous methane datasets. The improved fits lead to an empirically
derived wavelength-dependent correction to the scattering properties
of the main observable cloud deck at 2-3 bars that is very similar
to the correction determined for Uranus' lower cloud using the same
line dataset by Irwin et al. (Irwin, P.G.J., de Bergh, C., Courtin,
R., Bézard, B., Teanby, N.A., Davis, G.R., Fletcher, L.N., Orton,
G.S., Calcutt, S.B., Tice, D., Hurley, J. [2012]. Icarus 220,
369-382). By varying the abundance of CH<SUB>3</SUB>D in our
simulations, analysis of the Gemini/NIFS observations leads to
a new determination of the CH<SUB>3</SUB>D/CH<SUB>4</SUB> ratio
for Neptune of 3.0-0.9+1.0×10<SUP>-4</SUP>, which is smaller than
previous determinations, but is identical (to within error) with the
CH<SUB>3</SUB>D/CH<SUB>4</SUB> ratio of 2.9-0.5+0.9×10<SUP>-4</SUP>
derived by a similar analysis of Gemini/NIFS observations of Uranus
made in the same year. Thus it appears that the atmospheres of Uranus
and Neptune have an almost identical D/H ratio, which suggests that
the icy planetisimals forming these planets came from the same source
reservoir, or a reservoir that was well-mixed at the locations of ice
giant formation, assuming complete mixing between the atmosphere and
interior of both these planets. VLT/CRIRES observations of Neptune
have also been analysed with the WKMC-80K methane line database,
yielding very good fits, with little evidence for missing absorption
features. The CRIRES spectra indicate that the mole fraction of CO
at the 2-3 bar level must be substantially less than its estimated
stratospheric value of 1 × 10<SUP>-6</SUP>, which suggests that the
predominant source of CO in Neptune's atmosphere is external, through
the influx of micrometeorites and comets, although these data cannot
rule out an additional internal source.
---------------------------------------------------------
Title: Colors of Jupiter's large anticyclones and the interaction
of a Tropical Red Oval with the Great Red Spot in 2008
Authors: Sánchez-Lavega, A.; Legarreta, J.; García-Melendo, E.;
Hueso, R.; Pérez-Hoyos, S.; Gómez-Forrellad, J. M.; Fletcher, L. N.;
Orton, G. S.; Simon-Miller, A.; Chanover, N.; Irwin, P.; Tanga, P.;
Cecconi, M.
2013JGRE..118.2537S Altcode:
nature and mechanisms producing the chromophore agents that provide
color to the upper clouds and hazes of the atmospheres of the giant
planets are largely unknown. In recent times, the changes in red
coloration that have occurred in large- and medium-scale Jovian
anticyclones have been particularly interesting. In late June and
early July 2008, a particularly color intense tropical red oval
interacted with the Great Red Spot (GRS) leading to the destruction
of the tropical red oval and cloud dispersion. We present a detailed
study of the tropical vortices, usually white but sometimes red, and a
characterization of their color spectral signatures and dynamics. From
the spectral reflectivity in methane bands we study their vertical
cloud structure compared to that of the GRS and BA. Using two spectral
indices we found a near correlation between anticyclones cloud top
altitudes and red color. We present detailed observations of the
interaction of the red oval with the GRS and model simulations of the
phenomena that allow us to constrain the relative vertical extent of
the vortices. We conclude that the vertical cloud structure, vertical
extent, and dynamics of Jovian anticyclones are not the causes of
their coloration. We propose that the red chromophore forms when
background material (a compound or particles) is entrained by the
vortex, transforming into red once inside the vortex due to internal
conditions, exposure to ultraviolet radiation, or to the mixing of
two chemical compounds that react inside the vortex, confined by a
potential vorticity ring barrier.
---------------------------------------------------------
Title: Variation of solar oscillation frequencies in solar cycle 23
and their relation to sunspot area and number (Corrigendum)
Authors: Jain, R.; Tripathy, S. C.; Watson, F. T.; Fletcher, L.;
Jain, K.; Hill, F.
2013A&A...560C...1J Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Constraining the Depth of Saturn's Zonal Winds by Measuring
Thermal and Gravitational Signals
Authors: Liu, J.; Schneider, T.; Fletcher, L. N.
2013AGUFM.P21C1748L Altcode:
In 2016, NASA's Cassini spacecraft will orbit Saturn in highly
elliptical orbits and will measure Saturn's gravitational and thermal
signals at the end of its mission. This provides an opportunity to
constrain the structure of the zonal winds on the planet. Here we make
predictions of what Cassini will measure based on dynamical arguments
that constrain the flow and on already available observations. There
are strong dynamical constraints on the zonal winds and the associated
entropy and density distributions on Saturn. Due to Saturn's strong
internal heat flux, rapid rotation and negligible atmospheric viscosity,
convective motions are constrained to be primarily along surfaces of
constant angular momentum; they approximately homogenize entropy along
the spin axis. Using the assumption that in the interior, entropy is
homogenized in the direction of the spin axis, but not perpendicular
to it, we determine the zonal winds and the associated thermal
and gravitational signals by combing the equation of state of the
atmosphere, the observed zonal winds at the cloud level, and plausible
assumptions about the strength of the magnetohydrodynamic (MHD) drag
that zonal winds experience in the deep interior. A difficulty arises
because Saturn's observed zonal winds are not well defined because
the planetary rotation rate is uncertain. Using a range of plausible
estimates of the rotation rate, we find the observed zonal winds on
Saturn likely extend deeply into Saturn (to a depth between about
0.65 RS and 0.85 RS, with Saturn's radius RS, corresponding to 1 Mbar
and 0.2 Mbar). Material properties of Saturn (the equation of state)
constrain zonal winds with strengths similar to the cloud levels
winds to be confined only within the outer few percent of Saturn's
radius, irrespective of Saturn's rotation rate and the depth of MHD
drag. The theoretically derived meridional equator-to-pole temperature
contrasts in thermal wind balance with the zonal winds increase with
depth and reach 1~2 K at 1 bar and 2~4 K at 5 bar. They would be much
larger if the zonal winds were shallow, but already available thermal
observations by Cassini CIRS rule out very shallow flows: zonal winds
relative to System III rotation rate have to extend deeper than 5000 bar
(0.97 RS). Otherwise the associated equator-to-pole contrast (O(10K)
at 1 bar) would exceed the observed values. The gravitational signal
corresponding to deeply penetrating zonal winds are much larger than
those that would be associated with shallow zonal winds. Combining the
thermal signals with the gravitational signals of the zonal winds, the
penetration depths of the zonal winds relative to different rotation
rates can be determined by Cassini at the end of its mission.
---------------------------------------------------------
Title: Impact flux on Jupiter: From superbolides to large-scale
collisions
Authors: Hueso, R.; Pérez-Hoyos, S.; Sánchez-Lavega, A.; Wesley,
A.; Hall, G.; Go, C.; Tachikawa, M.; Aoki, K.; Ichimaru, M.; Pond,
J. W. T.; Korycansky, D. G.; Palotai, C.; Chappell, G.; Rebeli, N.;
Harrington, J.; Delcroix, M.; Wong, M.; de Pater, I.; Fletcher, L. N.;
Hammel, H.; Orton, G. S.; Tabe, I.; Watanabe, J.; Moreno, J. C.
2013A&A...560A..55H Altcode:
Context. Regular observations of Jupiter by a large number of amateur
astronomers have resulted in the serendipitous discovery of short
bright flashes in its atmosphere, which have been proposed as being
caused by impacts of small objects. Three flashes were detected:
one on June 3, 2010, one on August 20, 2010, and one on September 10,
2012. <BR /> Aims: We show that the flashes are caused by impacting
objects that we characterize in terms of their size, and we study the
flux of small impacts on Jupiter. <BR /> Methods: We measured the light
curves of these atmospheric airbursts to extract their luminous energy
and computed the masses and sizes of the objects. We ran simulations
of impacts and compared them with the light curves. We analyzed the
statistical significance of these events in the large pool of Jupiter
observations. <BR /> Results: All three objects are in the 5-20 m size
category depending on their density, and they released energy comparable
to the recent Chelyabinsk airburst. Model simulations approximately
agree with the interpretation of the limited observations. Biases in
observations of Jupiter suggest a rate of 12-60 similar impacts per
year and we provide software tools for amateurs to examine the faint
signature of impacts in their data to increase the number of detected
collisions. <BR /> Conclusions: The impact rate agrees with dynamical
models of comets. More massive objects (a few 100 m) should impact
with Jupiter every few years leaving atmospheric dark debris features
that could be detectable about once per decade.
---------------------------------------------------------
Title: Models for Temperature and Composition in Uranus from Spitzer,
Herschel and Ground-Based Infrared through Millimeter Observations
Authors: Orton, G. S.; Fletcher, L. N.; Feuchtgruber, H.; Lellouch,
E.; Moreno, R.; Encrenaz, T.; Hartogh, P.; Jarchow, C.; Swinyard, B.;
Moses, J. I.; Burgdorf, M. J.; Hammel, H. B.; Line, M. R.; Sandell,
G.; Dowell, C. D.
2013AGUFM.P21B1729O Altcode:
Photometric and spectroscopic observations of Uranus were combined to
create self-consistent models of its global-mean temperature profile,
bulk composition, and vertical distribution of gases. These were
derived from a suite of spacecraft and ground-based observations
that includes the Spitzer IRS, and the Herschel HIFI, PACS and SPIRE
instruments, together with ground-based observations from UKIRT and
CSO. Observations of the collision-induced absorption of H2 have
constrained the temperature structure in the troposphere; this was
possible up to atmospheric pressures of ~2 bars. Temperatures in
the stratosphere were constrained by H2 quadrupole line emission. We
coupled the vertical distribution of CH4 in the stratosphere of Uranus
with models for the vertical mixing in a way that is consistent with
the mixing ratios of hydrocarbons whose abundances are influenced
primarily by mixing rather than chemistry. Spitzer and Herschel data
constrain the abundances of CH3, CH4, C2H2, C2H6, C3H4, C4H2, H2O and
CO2. At millimeter wavelengths, there is evidence that an additional
opacity source is required besides the H2 collision-induced absorption
and the NH3 absorption needed to match the microwave spectrum; this
can reasonably (but not uniquely) be attributed to H2S. These models
will be made more mature by consideration of spatial variability from
Voyager IRIS and more recent spatially resolved imaging and mapping
from ground-based observatories. The model is of ';programmatic'
interest because it serves as a calibration source for Herschel
instruments, and it provides a starting point for planning future
spacecraft investigations of the atmosphere of Uranus.
---------------------------------------------------------
Title: The Evolution of Hydrocarbon Compounds in Saturn's Stratosphere
During the 2010 Northern Storm
Authors: Hesman, B. E.; Bjoraker, G. L.; Achterberg, R. K.; Sada,
P. V.; Jennings, D. E.; Lunsford, A. W.; Sinclair, J.; Romani, P. N.;
Boyle, R.; Fletcher, L. N.; Irwin, P.
2013AGUFMSM21C2205H Altcode:
The massive eruption at 40N (planetographic latitude) in December
2010 has produced significant and long-lived changes in temperature
and species abundances in Saturn's northern hemisphere (Hesman et
al. 2012a, Fletcher et al. 2012). The northern storm region has been
observed on many occasions between January 2011 and June of 2012 by
Cassini's Composite Infrared Spectrometer (CIRS). In this time period,
temperatures in regions referred to as 'beacons' (warm regions in
the stratosphere at certain longitudes in the storm latitude) became
significantly warmer than pre-storm values of 140K. In this period
hydrocarbon emission greatly increased; however, this increased
emission could not be attributed due to the temperature changes
alone for many of these species (Hesman et al. 2012b, Bjoraker
et al 2012). The unique nature of the stratospheric beacons also
resulted in the detection of ethylene (C<SUB>2</SUB>H<SUB>4</SUB>)
using CIRS. These beacon regions have also led to the identification
of rare hydrocarbon species such as C<SUB>4</SUB>H<SUB>2</SUB>
and C<SUB>3</SUB>H<SUB>4</SUB> in the stratosphere. These species
are all expected from photochemical processes in the stratosphere,
however high temperatures, unusual chemistry, or dynamics are
enhancing these species. The exact cause of these enhancements is
still under investigation. Ground-based observations were performed
using the high-resolution spectrometer Celeste in May 2011 to
confirm the CIRS detection of C<SUB>2</SUB>H<SUB>4</SUB> and to
study its spectral signatures at higher spectral resolution. In
order to follow the evolution of its emission further observations
were performed in July 2011 and March 2012. These observations are
being used in conjunction with the CIRS observations to investigate
the source of the approximately 100-fold increase of ethylene in the
stratospheric beacon. The time evolution of hydrocarbon emission
from C<SUB>2</SUB>H<SUB>2</SUB>, C<SUB>2</SUB>H<SUB>4</SUB>,
C<SUB>2</SUB>H<SUB>6</SUB>, C<SUB>3</SUB>H<SUB>4</SUB>, and
C<SUB>4</SUB>H<SUB>2</SUB> in Saturn's Northern Storm beacon
regions will be discussed. References: Bjoraker, G., B.E. Hesman,
R.K. Achterberg, P.N. Romani. 2012, 'The Evolution of Hydrocarbons
in Saturn's Northern Storm Region,' AAS DPS Conference, Vol. 44,
#403.05. Fletcher, L.N. et al. 2012, 'The Origin and Evolution of
Saturn's 2011-2012 Stratospheric Vortex,' Icarus, 221, 560-586. Hesman,
B.E. et al. 2012a, 'Elusive Ethylene Detected in Saturn's Northern
Storm Region,' The Astrophysical Journal, 760, 24-30. Hesman, B.E. et
al. 2012b, 'Ethylene Emission in the Aftermath of Saturn's 2010 Northern
Storm,' AAS DPS Conference, Vol. 44, #403.06.
---------------------------------------------------------
Title: The optical transmission spectrum of the hot Jupiter HAT-P-32b:
clouds explain the absence of broad spectral features?
Authors: Gibson, N. P.; Aigrain, S.; Barstow, J. K.; Evans, T. M.;
Fletcher, L. N.; Irwin, P. G. J.
2013MNRAS.436.2974G Altcode: 2013MNRAS.tmp.2486G; 2013arXiv1309.6998G
We report Gemini-North Gemini Multi-Object Spectrograph observations
of the inflated hot Jupiter HAT-P-32b during two primary transits. We
simultaneously observed two comparison stars and used differential
spectrophotometry to produce multiwavelength light curves. `White'
light curves and 29 `spectral' light curves were extracted for each
transit and analysed to refine the system parameters and produce
transmission spectra from 520 to 930 nm in ≈14 nm bins. The light
curves contain time-varying white noise as well as time-correlated
noise, and we used a Gaussian process model to fit this complex noise
model. Common mode corrections derived from the white light-curve fits
were applied to the spectral light curves which significantly improved
our precision, reaching typical uncertainties in the transit depth of
∼2 × 10<SUP>-4</SUP>, corresponding to about half a pressure scale
height. The low-resolution transmission spectra are consistent with a
featureless model, and we can confidently rule out broad features larger
than about one scale height. The absence of Na/K wings or prominent
TiO/VO features is most easily explained by grey absorption from clouds
in the upper atmosphere, masking the spectral features. However, we
cannot confidently rule out clear atmosphere models with low abundances
(∼10<SUP>-3</SUP> solar) of TiO, VO or even metal hydrides masking
the Na and K wings. A smaller scale height or ionization could also
contribute to muted spectral features, but alone are unable to account
for the absence of features reported here.
---------------------------------------------------------
Title: Europa's Atmosphere and Aurora: Recent Advances from HST-STIS
and Plans for Plume Searches with JUICE-UVS
Authors: Retherford, K. D.; Gladstone, R.; Roth, L.; McGrath, M. A.;
Saur, J.; Feldman, P. D.; Steffl, A. J.; Strobel, D. F.; Greathouse,
T. K.; Spencer, J. R.; Bagenal, F.; Fletcher, L. N.; Eterno, J. S.
2013AGUFM.P53A1838R Altcode:
Space Telescope Imaging System (STIS) images of Europa's neutral oxygen
130.4 nm and 135.6 nm emissions contain a wealth of information about
the molecular oxygen atmosphere, discovered using previous Hubble far-UV
observations. Europa's magnetospheric plasma interaction generates
auroral emissions, which exhibit a morphology that has been difficult
to interpret. Recent observations in Nov. & Dec. 2012 allow a new
understanding of how Jupiter's magnetic field orientation and relation
to the plasma sheet control the emission variability, yet explanations
for this general behavior, including the likely role of ocean-induced
magnetic fields and possible local atmospheric density enhancements,
remain incomplete (cf. Roth et al. this meeting). NASA's Ultraviolet
Spectrograph (UVS) instrument contribution to the ESA-led Jupiter
Icy Moons Explorer (JUICE) mission will obtain excellent imaging of
these atmospheric and auroral emissions from Europa during two flybys
currently planned, with the objective of investigating these and other
unanswered questions. UVS's stellar occultation technique will be used
to characterize Europa's atmosphere structure and composition and to
also search for local enhancements created by plumes. This stellar
occultation technique, demonstrated by Cassini-UVIS at Enceladus, has
the benefit of being useful at relatively large distances (several 10's
of Jupiter radii) as well as during the Europa flyby sequences (several
10's of Europa radii). A robust search for plumes is planned in JUICE's
first year at Jupiter to provide a roughly 30-degree grid of global
coverage, followed by focused targeting of likely plumes/active-regions
during early and late stages of the flyby sequences. High spatial
resolution limb imaging is also planned near closest approaches, which
could directly image plume gases in a manner analogous with plume
aurora imaging of Io. A UV spectrograph on the planned Europa Clipper
mission could perform an even more robust search for such currently
active geological sites with connectivity to subsurface liquid water.
---------------------------------------------------------
Title: Photochemistry in Saturn's Ring-Shadowed Atmosphere: Of
Venetian Blinds, Atmospheric Molecules and Observations
Authors: Edgington, S. G.; Atreya, S. K.; Wilson, E. H.; Baines,
K. H.; West, R. A.; Bjoraker, G. L.; Fletcher, L. N.; Momary, T.
2013AGUFMSM21C2204E Altcode:
Cassini has been orbiting Saturn for over nine years. During this epoch,
the ring shadow has moved from covering a relatively large portion of
the northern hemisphere to covering a large swath south of the equator
and continues to move southward. At Saturn Orbit Insertion in 2004,
the ring plane was inclined by ~24 degrees relative to the Sun-Saturn
vector. The projection of the B-ring onto Saturn reached as far as 40N
along the central meridian (~52N at the terminator). At its maximum
extent, the ring shadow can reach as far as 48N/S (~58N/S at the
terminator). The net effect is that the intensity of both ultraviolet
and visible sunlight penetrating into any particular latitude will
vary depending on both Saturn's axis relative to the Sun and the
optical thickness of each ring system. In essence, the rings act like
venetian blinds. Our previous work [1] examined the variation of the
solar flux as a function of solar inclination, i.e. ~8 year season at
Saturn. Here, we report on the impact of the oscillating ring shadow
on the photolysis and production rates of hydrocarbons in Saturn's
stratosphere and upper troposphere, including acetylene, ethane,
propane, and benzene. Beginning with methane, we investigate the impact
on production and loss rates of the long-lived photochemical products
leading to haze formation are examined at several latitudes over a
Saturn year. Similarly, we assess its impact on phosphine abundance,
a disequilibrium species whose presence in the upper troposphere is a
tracer of convection processes in the deep atmosphere. Comparison to
the corresponding rates for the clear atmosphere and for the case of
Jupiter, where the variation of solar insolation due to tilt is known
to be insignificant (~3 degree inclination), will be presented. We
will present our ongoing analysis of Cassini's CIRS, UVIS, and VIMS
datasets that provide an estimate of the evolving haze content of the
northern hemisphere and we will begin to assess the implications for
dynamical mixing. [1] Edgington, S.G., et al., 2012. Photochemistry
in Saturn's Ring Shadowed Atmosphere: Modeling, Observations, and
Preliminary Analysis. Bull. American. Astron. Soc., 38, 499 (#11.23).
---------------------------------------------------------
Title: Changes in Saturn's Zonal-Mean Tropospheric Structure After
the 2010-2011 Northern Storm
Authors: Achterberg, R. K.; Gierasch, P. J.; Conrath, B. J.; Fletcher,
L. N.; Hesman, B. E.; Bjoraker, G. L.; Flasar, F.
2013AGUFMSM21C2203A Altcode:
In early December 2010, a large convective storm erupted at
approximately 40°N planetographic latitude on Saturn, lasting
until early July 2011 (Sánchez-Lavega et al. 2012, Icarus,
220, 561-576). We use far-infrared (20μm - 200μm) data from the
Composite Infrared Spectrometer (CIRS) on the Cassini spacecraft to
determine the zonal-mean temperature and hydrogen para-fraction in
Saturn's upper troposphere between approximately 200 and 800 mbar from
observations taken before and after the large northern hemisphere storm
in 2010-2011. During the storm, the latitude band between approximately
25°N and 45°N (planetographic latitude) warmed by about 3 K, while the
hydrogen para-fraction decreased by about 0.04 over the same latitudes,
at pressures greater than about 300 mbar. These changes occurred over
the same latitude range as the disturbed cloud band seen in visible
images. The decrease in hydrogen para-fraction is consistent with a
strong convective plume advecting low para-fraction hydrogen upward
from the several bar level, where the equilibrium para-fraction is
0.25, and the subsequent mixing of the low para-fraction hydrogen with
the ambient atmosphere. Heat released from water condensation in the
plume, or the conversion of ortho-hydrogen to para-hydrogen may then
explain the observed temperature increase. The changes observed in
the zonal-mean temperatures are roughly consistent with the changes
in zonal winds seen by Sayanagi et al. (2013, Icarus, 223, 460-478)
assuming geostrophic balance.
---------------------------------------------------------
Title: Oxygen Compounds in Saturn's Stratosphere During the 2010
Northern Storm
Authors: Bjoraker, G. L.; Hesman, B. E.; Achterberg, R. K.; Jennings,
D. E.; Romani, P. N.; Fletcher, L. N.; Irwin, P.
2013AGUFMSM21C2206B Altcode:
The massive storm at 40N on Saturn that began in December 2010 has
produced significant and long-lived changes in temperature and species
abundances in the stratosphere throughout the northern hemisphere
(Hesman et al. 2012a, Fletcher et al. 2012). The northern storm
region has been observed on many occasions between January 2011 and
January 2013 by Cassini's Composite Infrared Spectrometer (CIRS). In
this time period, temperatures in regions referred to as 'beacons'
(warm regions in the stratosphere at certain longitudes in the storm
latitude) became significantly warmer than pre-storm values of 140K,
peaking at 220K in May 2011 followed by gradual cooling. Hydrocarbon
emission greatly increased over pre-storm values and then slowly decayed
as the beacon cooled. Radiative transfer modeling has revealed that
this increased emission is due to enhanced gas abundances for many
of these species, rather than simply due to the temperature changes
alone (Hesman et al. 2012b, Bjoraker et al 2012). In order to build a
comprehensive picture of the changes to the stratosphere due to the
2010 northern storm we are now investigating the oxygen compounds
in Saturn's stratosphere to determine if similar changes in these
species were measured. The time evolution of stratospheric CO2 and
H2O abundances in the beacon regions throughout 2011 and 2012 will be
presented and compared with pre-storm measurements made in 2010.
---------------------------------------------------------
Title: Ground-Based Observations of the Aftermath of the 2010-2011
Great Northern Springtime Storm in Saturn (Invited)
Authors: Orton, G. S.; Fletcher, L. N.; Fouchet, T.; Fujiyoshi, T.;
Greathouse, T. K.; Momary, T.; Yanamandra-Fisher, P. A.
2013AGUFMSM14A..06O Altcode:
For the first time, a suite of ground-based and spacecraft instruments
were available to detect and characterize one of the rare giant
convective storms erupting in Saturn's atmosphere. The storm that
erupted on 2010 December 5 created an immense thermal and chemical
perturbation of the atmosphere. Most of the perturbation of the visible
cloud system had abated within a year of the initial eruption, but
changes to the atmosphere were evident at thermal infrared wavelengths,
and they continue to the present. Here we review the observations from
ground-based stations that include NASA's Infrared Telescope Facility
(IRTF) and the Subaru Telescope, both at the summit of Mauna Kea, as
well as observations from ESO's Very Large Telescope. Evident in the
5-μm spectral window was the clearing of nearly all clouds around and
above the 3-bar level of the atmosphere at the latitude of the primary
storm. In the intervening two years, imaging in the same window by
the IRTF NSFCam2 instrument shows that the cleared region remains
prominent and is filling in with a pre-storm cloud cover only very
slowly. Most unexpected was the generation of a stratospheric vortex
of high temperatures, 'the beacon' (Fletcher et al. 2011 Science 332,
1413). This phenomenon also continues more than two years later and has
been tracked using several mid-infrared imaging instruments: VISIR at
the VLT, COMICS at Subaru, and MIRSI at the IRTF using moderate-band
filters. More precise determination of its vertical distribution was
made using the University of Texas Echelon Cross Echelle Spectrograph
(TEXES) at the IRTF, targeting specific lines of CH4 and the H2
quadrupole. All of these measurements, taken in concert, show that
the heated region of the stratosphere is diminishing in amplitude,
expanding in longitude and slowly sinking in altitude.
---------------------------------------------------------
Title: The Impulsive Phase in Solar Flares: Recent Multi-wavelength
Results and their Implications for Microwave Modeling and Observations
Authors: Fletcher, Lyndsay; Simoes, Paulo J. A.
2013arXiv1311.7175F Altcode:
This short paper reviews several recent key observations of the
processes occurring in the lower atmosphere (chromosphere and
photosphere) during flares. These are: evidence for compact and
fragmentary structure in the flare chromosphere, the conditions in
optical flare footpoints, step-like variations in the magnetic field
during the flare impulsive phase, and hot, dense 'chromospheric'
footpoints. The implications of these observations for microwaves are
also discussed.
---------------------------------------------------------
Title: Implosion of Coronal Loops during the Impulsive Phase of a
Solar Flare
Authors: Simões, P. J. A.; Fletcher, L.; Hudson, H. S.; Russell,
A. J. B.
2013ApJ...777..152S Altcode: 2013arXiv1309.7090S
We study the relationship between implosive motions in a solar
flare, and the energy redistribution in the form of oscillatory
structures and particle acceleration. The flare SOL2012-03-09T03:53
(M6.4) shows clear evidence for an irreversible (stepwise) coronal
implosion. Extreme-ultraviolet (EUV) images show at least four
groups of coronal loops at different heights overlying the flaring
core undergoing fast contraction during the impulsive phase of the
flare. These contractions start around a minute after the flare onset,
and the rate of contraction is closely associated with the intensity
of the hard X-ray and microwave emissions. They also seem to have
a close relationship with the dimming associated with the formation
of the coronal mass ejection and a global EUV wave. Several studies
now have detected contracting motions in the corona during solar
flares that can be interpreted as the implosion necessary to release
energy. Our results confirm this, and tighten the association with
the flare impulsive phase. We add to the phenomenology by noting
the presence of oscillatory variations revealed by Geostationary
Operational Environmental Satellite soft X-rays (SXR) and spatially
integrated EUV emission at 94 and 335 Å. We identify pulsations
of ≈60 s in SXR and EUV data, which we interpret as persistent,
semi-regular compressions of the flaring core region which modulate
the plasma temperature and emission measure. The loop oscillations,
observed over a large region, also allow us to provide rough estimates
of the energy temporarily stored in the eigenmodes of the active-region
structure as it approaches its new equilibrium.
---------------------------------------------------------
Title: Science goals and concepts of a Saturn probe for the future
L2/L3 ESA call
Authors: Schmider, F. -X.; Mousis, O.; Fletcher, L. N.; Altwegg, K.;
André, N.; Blanc, M.; Coustenis, A.; Gautier, D.; Geppert, W. D.;
Guillot, T.; Irwin, P.; Lebreton, J. -P.; Marty, B.; Sánchez-Lavega,
A.; Waite, J. H.; Wurz, P.
2013sf2a.conf...65S Altcode:
Comparative studies of the elemental enrichments and isotopic abundances
measured on Saturn can provide unique insights into the processes
at work within our planetary system and are related to the time and
location of giant planet formation. In situ measurements via entry
probes remain the only reliable, unambiguous method for determining
the atmospheric composition from the thermosphere to the deep
cloud-forming regions of their complex weather layers. Furthermore,
in situ experiments can reveal the meteorological properties of
planetary atmospheres to provide “ground truth” for orbital remote
sensing. Following the orbital reconnaissance of the Galileo and Cassini
spacecraft, and the single-point in situ measurement of the Galileo
probe to Jupiter, we believe that an in situ measurement of Saturn's
atmospheric composition should be an essential element of ESA's future
cornerstone missions, providing the much-needed comparative planetology
to reveal the origins of our outer planets. This quest for understanding
the origins of our solar system and the nature of planetary atmospheres
is in the heart of ESA's Cosmic Vision, and has vast implications for
the origins of planetary systems around other stars.
---------------------------------------------------------
Title: The Ultraviolet Spectrograph (UVS) on ESA’s JUICE Mission
Authors: Gladstone, Randy; Retherford, K.; Steffl, A.; Eterno, J.;
Davis, M.; Versteeg, M.; Greathouse, T.; Araujo, M.; Walther, B.;
Persson, K.; Persyn, S.; Dirks, G.; McGrath, M.; Feldman, P.; Bagenal,
F.; Spencer, J.; Schindhelm, R.; Fletcher, L.
2013DPS....4521104G Altcode:
The Jupiter Icy Moons Explorer (JUICE) was selected in May 2012 as
the first L-class mission of ESA’s Cosmic Vision Program. JUICE will
launch in 2022 on a 7.6-year journey to the Jovian system, including
a Venus and multiple Earth gravity assists, before entering Jupiter
orbit in January 2030. JUICE will study the entire Jovian system for
3.5 years, concentrating on Europa, Ganymede, and Callisto, with the
last 10 months spent in Ganymede orbit. The Ultraviolet Spectrograph
(UVS) on JUICE was jointly selected by NASA and ESA as part of its
~130 kg payload of 11 scientific instruments. UVS is the fifth in a
series of successful ultraviolet imaging spectrographs (Rosetta-Alice,
New Horizons Pluto-Alice, LRO-LAMP) and is largely based on the
most recent of these, Juno-UVS. It observes photons in the 55-210
nm wavelength range, at moderate spectral and spatial resolution
along a 7.5-degree slit. A main entrance “airglow port” (AP) is
used for most observations (e.g., airglow, aurora, surface mapping,
and stellar occultations), while a separate “solar port” (SP)
allows for solar occultations. Another aperture door, with a small
hole through the centre, is used as a “high-spatial-resolution
port” (HP) for detailed observations of bright targets. Time-tagging
(pixel list mode) and programmable spectral imaging (histogram mode)
allow for observational flexibility and optimal data management. As on
Juno-UVS, the effects of penetrating electron radiation on electronic
parts and data quality are substantially mitigated through contiguous
shielding, filtering of pulse height amplitudes, management of high
voltage settings, and careful use of radiation-hard, flight-tested
parts. The science goals of UVS are to: 1) explore the atmospheres,
plasma interactions, and surfaces of the Galilean satellites; 2)
determine the dynamics, chemistry, and vertical structure of Jupiter’s
upper atmosphere from equator to pole; and 3) investigate the Jupiter-Io
connection by quantifying energy and mass flow in the Io atmosphere,
neutral clouds, and torus. Here we present the salient features of
the UVS instrument and describe the science we plan to address.
---------------------------------------------------------
Title: Properties of Slowly Moving Thermal Waves in Saturn from
Cassini CIRS and Ground-Based Thermal Observations from 2003 to 2009
Authors: Orton, Glenn S.; Fletcher, L. N.; Flasar, F.; Achterberg,
R. K.; Yanamandra-Fisher, P. A.; Lewis, M.; Fujiyoshi, T.; Bell, J.;
Christian, J.; Brown, S. K.
2013DPS....4531207O Altcode:
Hemispherical maps of Saturn’s atmosphere made both by Cassini’s
Composite Infrared Spectrometer (CIRS, 7-1000 µm) and ground-based
mid-infrared observations (7-25 µm) were surveyed for the presence and
properties of zonal thermal waves and their variability in time. The
most inclusive CIRS surveys, FIRMAPs (15 cm-1 spectral resolution),
covered the planet from the equator to either north or south pole,
sweeping through the latitude range while the planet rotated beneath
over its ~10-hour rotation. Ground-based observations were made at
the Infrared Telescope Facility using the MIRSI instrument, the Very
Large Telescope using VISIR and the Subaru Telescope using COMICS. We
sampled spectral ranges dominated both by upper-tropospheric emission
(80-200 mbar) and by stratospheric emission (0.5-3 mbar). We examined
data that were taken between 2003 and Saturn’s spring equinox
in 2009. During this time, the strongest waves were found between
planetographic latitudes of 30° - 45°S and 0° - 30°N. Some
low-wavelength components cover all 360° in longitude, similar to
the slowly moving thermal waves in Jupiter’s atmosphere, but the
strongest waves were found in “trains” that covered less than
180°. In 2005, tropospheric waves had a mean peak-to-peak variance
that was the equivalent of temperature variability of about 1 K. Between
2005 and 2007, they had subsided to about 0.5 K. During and after 2008,
they soared to over 3 K. During this entire period, similar waves in the
northern hemisphere were never larger than 0.8 K. In the stratosphere,
waves followed a similar time sequence, with southern hemisphere
waves in 2005 reaching amplitudes as high as 3.5 K in brightness
temperature, subsequently decreasing, then growing in 2008-2009 to
over 5 K. Stratospheric waves in the northern hemisphere were nearly
constant ~2 K, but with an instance of 6 K at one epoch in 2008. We
were able to track the phase of some of the waves in the southern
hemisphere, which moved about 0.5° of longitude per day retrograde
with respect to System III. The phase of tropospheric and stratospheric
waves appeared to be highly correlated with one another with little
offset in longitudes but not with positions of atmospheric storms.
---------------------------------------------------------
Title: IRTF/TEXES observations of Saturn’s stratospheric beacon
Authors: Fouchet, Thierry; Greathouse, T. K.; Richter, M. J.; Lacy,
J.; Fletcher, L.; Spiga, A.
2013DPS....4550907F Altcode:
On December 5th, 2010, a giant convective storm erupted in Saturn’s
Northern Hemisphere as each Saturnian year at least since 1876. For
the first time, a huge thermal and chemical stratospheric disturbance
associated with this large convective event was detected from
ground-based and Cassini observations (Fletcher et al. 2011). This
stratospheric disturbance is named the beacon. Here, we present
high spectral resolution observations of the beacon obtained by the
Texas Echelon Cross Echelle Spectrograph (TEXES) mounted on the
IRTF during 6 nights from July 15th, 2011 to July 20th, 2011. We
targeted several different CH4 lines between 1230 and 1280 cm-1,
probing the stratospheric temperature between 5 hPa and 0.05 hPa,
and the H2 S(1) quadrupolar and collision-induced lines at 587 cm-1,
probing the stratospheric temperature between 150 hPa and 5 hPa. The
stratospheric temperatures are retrieved from the dataset using a
forward radiative model coupled with a constrained linear inverse
method. Within the core of the beacon the maximum temperature inferred
from the data is 178K at 40°N, hence about 50K warmer than the mean
temperature measured before the occurrence of the storm. However,
the TEXES data unambiguously demonstrate that this warming is not
vertically homogeneous but rather confined in a specific pressure
range between 1-5 hPa, overhung by a cold layer between 0.1 and 1
hPa. This vertical behavior is evident from the CH4 line spectral
profiles with the core of the lines in absorption and the wings in
emission. Moreover, our data demonstrate that the altitude of the
local temperature maximum increases northwards. We will present how
this thermal structure can help deciphering the stratospheric heating
sources. On the western side of the beacon, the stratospheric heating
is concentrated at lower pressures, hence higher altitudes, than within
the beacon, between 0.1 and 0.01 hPa. We interpret this structure as
being caused by convective motions within the beacon, and westward
advection associated with a vertical shear of stratospheric zonal winds.
---------------------------------------------------------
Title: Multi-wavelength Observations of Neptune’s Atmosphere
Authors: de Pater, Imke; Fletcher, L.; Luszcz-Cook, S.; deBoer, D.;
Butler, B.; Orton, G.; Sitko, M.; Hammel, H.
2013DPS....4531220D Altcode:
We conducted a multi-wavelength observing campaign on Neptune between
June and October, 2003. We used the 10-m Keck telescope at near- and
mid-infrared wavelengths and the VLA at radio wavelengths. Near infrared
images were taken in October 2003 in broad- and narrow-band filters
between 1 and 2.5 micron, using the infrared camera NIRC2 coupled to
the Keck Adaptive Optics system. At these wavelengths we detect sunlight
reflected off clouds in the upper troposphere and lower stratosphere. As
shown by various authors before, bright bands of discrete cloud
features are visible between 20°S and 50°S and near 30°N, as well
as several distinct bright cloud features near 70°S, and the south
polar “dot”. Mid-infrared images were taken on September 5 and 6
(2003) using the Keck LWS system in atmospheric windows at 8, 8.9, 10.7,
11.7, 12.5, 17.65, 18.75 and 22 micron. At these wavelengths we detect
thermal emission from Neptune’s stratosphere due to the presence of
hydrocarbons, and from near the tropopause due to collision induced
opacity by hydrogen. At all wavelengths the South polar region stands
out as a bright spot. At 17 - 22 micron also the equatorial region is
slightly enhanced in intensity. These characteristics are consistent
with later imaging at similar wavelengths (Hammel et al. 2007; Orton et
al. 2007). Microwave images were constructed from NRAO VLA data between
0.7 and 6.0 cm. At these wavelengths depths of several up to >50
bar are probed. An increase in brightness indicates decreased opacity
of absorbers (e.g., NH3, H2S), since under such circumstances deep,
and hence warm levels (adiabatic temperature-pressure profile), will
be probed. The multi-wavelength observing campaign in 2003 was focused
on obtaining images that probe different altitudes in Neptune’s
atmosphere. Indeed, this set of data probes altitudes from about 0.1
mbar down to ~50 bar, and hence can be used to constrain the global
atmospheric circulation in Neptune’s atmosphere. At the meeting we
will show our results and interpretation of the findings.
---------------------------------------------------------
Title: Hydrocarbon and oxygen photochemistry on Uranus as revealed
from Spitzer/IRS observations
Authors: Moses, Julianne I.; Orton, G. S.; Fletcher, L. N.; Mainzer,
A. K.; Hines, D. C.; Hammel, H. B.; Martin-Torres, J.; Burgdorf, M.;
Merlet, C.; Line, M. R.; Poppe, A.
2013DPS....4531213M Altcode:
Due to the very low atmospheric temperatures and hydrocarbon column
abundances on Uranus, the planet appears very faint at mid-infrared
wavelengths, making determinations of atmospheric composition
difficult. The Spitzer Space Telescope Infrared Spectrometer (IRS)
is two orders of magnitude more sensitive than previous space-based
instruments, favoring the detection of faint molecular emission
features from Uranus’ atmosphere (e.g., Burgdorf et al. 2006,
Icarus 184, 634). Global-average Spitzer/IRS spectra acquired just
days after the planet’s 2007 northern vernal equinox (Orton et
al. 2013, manuscript submitted to Icarus) exhibit molecular emission
features from CH4, C2H2, C2H6, C3H4, C4H2, and CO2 in Uranus’
stratosphere. We use these Spitzer/IRS observations to constrain new
1-D photochemical models for Uranus. Although the upper-stratospheric
methane abundance is well determined from the observations, there is a
range of model parameter space in terms of eddy diffusion coefficients
Kzz and tropopause methane relative humidities that can reproduce
the observed methane emission. However, all such models possess Kzz
values that are considerably smaller than those on the other giant
planets; the observations show no convincing evidence for significant
changes in low-latitude Kzz values with time since the Voyager era. We
highlight the differences in atmospheric chemistry and mixing between
Uranus and the other giant planets (including the reasons behind the
lower C2H6/C2H2 ratio on Uranus), discuss the implications of the
observed C4H2 emission with respect to the vapor pressure of C4H2 over
diacetylene ice at low temperatures, and summarize the implications
with respect to the influx of external oxygen compounds and their
corresponding upper-atmospheric haze components. This research was
supported by the NASA Planetary Atmospheres program.
---------------------------------------------------------
Title: The origin of CO in the stratosphere of Uranus
Authors: Cavalié, Thibault; Moreno, R.; Lellouch, E.; Hartogh,
P.; Venot, O.; Orton, G. S.; Jarchow, C.; Encrenaz, T.; Selsis, F.;
Hersant, F.; Fletcher, L. N.
2013DPS....4531214C Altcode:
Oxygen-rich deep interiors of the Giant Planets cannot explain the
discovery of H2O and CO2 in the stratospheres of the Giant Planets
by Feuchtgruber et al. (1997) because these species are trapped by
condensation around their tropopause levels (except CO2 in Jupiter and
Saturn). Therefore, several sources in the direct or far environment
of the Giant Planets have been proposed: icy rings and/or satellites,
interplanetary dust particles and large comet impacts. CO does not
condense at the tropopauses of Giant Planets, so that oxygen-rich
interiors are a valid source. An internal component has indeed been
observed in the vertical profile of CO in Jupiter (Bézard et al., 2002)
and in Neptune (Lellouch et al., 2005), while an upper limit has been
set on its magnitude by for Saturn (Cavalié et al., 2009). In addition
to interiors, large comets seem to be the dominant external source, as
shown by various studies: Bézard et al. (2002) for Jupiter, Cavalié et
al. (2010) for Saturn and Lellouch et al. (2005) for Neptune. The first
detection of CO in Uranus was obtained by Encrenaz et al. (2004) from
fluorescent emission at 4.7 microns. Assuming a uniform distribution,
a mixing ratio of 2x10-8 was derived. Despite this first detection
almost a decade ago, the situation has remained unclear ever since. In
this paper, we will present the first submillimeter detection of
CO in Uranus, carried out with Herschel in 2011-2012. Using a simple
diffusion model, we review the various possible sources of CO (internal
and external). We show that CO is mostly external. We also derive
an upper limit for the internal source. And with the thermochemical
model of Venot et al. (2012), adapted to the interior of Uranus, we
derive an upper limit on its deep O/H ratio from it. Acknowledgments
T. Cavalié acknowledges support from CNES and the European Research
Council (Starting Grant 209622: E3ARTHs). References Bézard et
al., 2002. Icarus, 159, 95-111. Cavalié et al., 2009. Icarus, 203,
531-540. Cavalié et al., 2010. A&A, 510, A88. Encrenaz et al.,
2004. A&A, 413, L5-L9. Feuchtgruber et al., 1997. Nature, 389,
159-162. Lellouch et al., 2005. A&A, 430, L37-L40. Venot et al.,
2012. A&A, 546, A43.
---------------------------------------------------------
Title: Oxygen Compounds in Saturn’s Stratosphere During the 2010
Northern Storm
Authors: Hesman, Brigette E.; Bjoraker, G. L.; Achterberg, R. K.;
Jennings, D. E.; Romani, P. N.; Fletcher, L. N.; Irwin, P. G.
2013DPS....4531212H Altcode:
The massive eruption at 40N (planetographic latitude) in December
2010 has produced significant and long-lived changes in temperature
and species abundances in Saturn’s northern hemisphere (Hesman et
al. 2012a, Fletcher et al. 2012). The northern storm region has been
observed on many occasions between January 2011 and June of 2012 by
Cassini’s Composite Infrared Spectrometer (CIRS). In this time period,
temperatures in regions referred to as “beacons” (warm regions in
the stratosphere at certain longitudes in the storm latitude) became
significantly warmer than pre-storm values of 140K. In this period
hydrocarbon emission greatly increased however this increased emission
could not be attributed due to the temperature changes alone for many
of these species (Hesman et al. 2012b, Bjoraker et al 2012). In order
to build a comprehensive picture of the changes to the stratosphere
due to the 2010 northern storm we are now investigating the oxygen
compounds in Saturn’s stratosphere to determine if similar changes
in these species were measured. The time evolution of stratospheric
CO2 and H2O abundances in the beacon regions throughout 2011 and
2012 will be presented. References: Bjoraker, G., B.E. Hesman,
R.K. Achterberg, P.N. Romani. 2012, “The Evolution of Hydrocarbons
in Saturn’s Northern Storm Region,” AAS DPS Conference, Vol. 44,
#403.05. Fletcher, L.N. et al. 2012, “The Origin and Evolution
of Saturn’s 2011-2012 Stratospheric Vortex,” Icarus, 221,
560-586. Hesman, B.E. et al. 2012a, “Elusive Ethylene Detected
in Saturn’s Northern Storm Region,” The Astrophysical Journal,
760, 24-30. Hesman, B.E. et al. 2012b, “Ethylene Emission in the
Aftermath of Saturn’s 2010 Northern Storm,” AAS DPS Conference,
Vol. 44, #403.06.
---------------------------------------------------------
Title: Photochemistry in Saturn’s Ring-Shadowed Atmosphere:
Venetian Blinds, Atmospheric Molecules and Observations
Authors: Edgington, Scott G.; Atreya, S. K.; Wilson, E. H.; Baines,
K. H.; West, R. A.; Bjoraker, G. L.; Fletcher, L. N.; Momary, T.
2013DPS....4531215E Altcode:
Cassini has been orbiting Saturn for over nine years. During this
epoch, the ring shadow has moved from covering a relatively large
portion of the northern hemisphere to covering a large swath south of
the equator and continues to move southward. At Saturn Orbit Insertion
in 2004, the ring plane was inclined by ~24 degrees relative to the
Sun-Saturn vector. The projection of the B-ring onto Saturn reached as
far as 40N along the central meridian 52N at the terminator). At its
maximum extent, the ring shadow can reach as far as 48N/S 58N/S at the
terminator). The net effect is that the intensity of both ultraviolet
and visible sunlight penetrating into any particular latitude will
vary depending on both Saturn’s axis relative to the Sun and the
optical thickness of each ring system. In essence, the rings act like
venetian blinds. Our previous work [1] examined the variation of the
solar flux as a function of solar inclination, i.e. ~8 year season at
Saturn. Here, we report on the impact of the oscillating ring shadow
on the photolysis and production rates of hydrocarbons in Saturn’s
stratosphere and upper troposphere, including acetylene, ethane,
propane, and benzene. Beginning with methane, we investigate the impact
on production and loss rates of the long-lived photochemical products
leading to haze formation are examined at several latitudes over a
Saturn year. Similarly, we assess its impact on phosphine abundance,
a disequilibrium species whose presence in the upper troposphere is
a tracer of convection processes in the deep atmosphere. Comparison
to the corresponding rates for the clear atmosphere and for the case
of Jupiter, where the variation of solar insolation due to tilt is
known to be insignificant 3 degree inclination), will be presented. We
will present our ongoing analysis of Cassini’s CIRS, UVIS, and VIMS
datasets that provide an estimate of the evolving haze content of the
northern hemisphere and we will begin to assess the implications for
dynamical mixing. [1] Edgington, S.G., et al., 2012. Photochemistry
in Saturn’s Ring Shadowed Atmosphere: Modeling, Observations, and
Preliminary Analysis. Bull. American. Astron. Soc., 38, 499 (#11.23).
---------------------------------------------------------
Title: Neptune Clouds and Methane, from Ground-Based Visible and
Near-Infrared Spectroscopy with Adaptive Optics
Authors: Tice, D. S.; Irwin, P. G. J.; Houghton, R. W. C.; Fletcher,
L. N.; Clarke, F.; Hurley, J.; Thatte, N.; Tecza, M.
2013EPSC....8..549T Altcode:
Observations of Neptune were made in June/July 2012 with the SWIFT
integral field spectrometer at the Palomar Observatory's 200-inch
Hale Telescope. Spectral resolutions for observations between 0.65
μm and 1.0 μm were R ≥ 3250. Palomar's PALM-3000 adaptive optics
system enabled images of the full Neptunian disc to be recorded at a
spatial scale of 0.08"·pixel^-1 with a seeing of approximately 0.30"
- 0.40". Retrievals of cloud properties and methane abundance in
the highly dynamic atmosphere were obtained with the general-purpose
retrieval tool, NEMESIS. The short wavelengths of the observations
allowed for good characterisation of the scattering particles' optical
properties in the many cloud and haze layers of the upper Neptunian
atmosphere. A region of relatively low methane absorption and high
collision-induced hydrogen quadrupole absorption at 825 nm further
constrains spectral properties of clouds as distinguished from those
of methane absorption.
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Title: The thermal structure of the 2011 Saturn's stratospheric
beacon mapped with TEXES/IRTF
Authors: Fouchet, T.; Greathouse, T.; Richter, M.; Lacy, J.; Fletcher,
L.; Guerlet, S.; Spiga, A.
2013EPSC....8..381F Altcode:
We present spectral observations of Saturn's stratosphere obtained
in 2011 by the TEXES imaging spectrometer mounted on the IRTF. These
observations allowed us to determine the thermal structure of the
stratospheric disturbance induced by the 2010 Great White Storm.
---------------------------------------------------------
Title: Saturn northern hemisphere's atmosphere and polar hexagon
in 2013
Authors: Delcroix, M.; Yanamandra-Fisher, P.; Fischer, G.; Fletcher,
L. N.; Sayanagi, K. M.; Barry, T.
2013EPSC....8.1067D Altcode:
In 2013, two years after the dramatic events of the Great White Spot
(GWS), amateur astronomers continued to follow the evolution of the
"GWS zone" centered around 41° planetographic on Saturn. They could
also detect the hexagonal wave surrounding Saturn's north pole with
a spot at its edge.
---------------------------------------------------------
Title: TEXES Spectral Mapping of Jupiter and Saturn and the Origins
of Giant Planet Nitrogen
Authors: Fletcher, L. N.; Greathouse, T. K.; Orton, G. S.; Irwin,
P. G. J.; Sinclair, J. A.
2013EPSC....8...28F Altcode:
We report spectral mapping of the atmospheres of Jupiter and Saturn
in February 2013 using the Texas Echelon cross Echelle Spectrograph
(TEXES, [1]) mounted on NASA's Infrared Telescope Facility (IRTF). The
purpose of these observations was (i) to study jovian meteorology
via measurements of temperature, wind shear, humidity (i.e., ammonia
content) and cloud coverage; (ii) to assess the aftermath of Saturn's
northern 2010-2011 storm, including the continued existence of the
stratospheric anticyclonic vortex [2]; and (iii) to determine precise
estimates of the 15N/14N ratio on both planets to constrain the
origins of nitrogen to the gas giants. Mid-infrared observations of
this nature complement spacecraft observations from Cassini, Juno and,
ultimately, JUICE.
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Title: Cassini Returns to Saturn's Poles: Seasonal Change in the
Polar Vortices
Authors: Fletcher, L. N.; Orton, G. S.; Irwin, P. G. J.; Sinclair,
J. A.; Hesman, B. E.; Hurley, J.; Bjoraker, G. L.; Simon-Miller, A. A.
2013EPSC....8...29F Altcode:
High inclination orbits during Cassini's solstice mission (2012-2013)
are providing us with our first observations of Saturn's high
latitudes since the previous high inclination phase in 2007 (during
the prime mission). Since that time, the northern spring pole has
emerged into sunlight and the southern autumn pole has disappeared
into winter darkness, allowing us to study the seasonal changes
occurring within the polar vortices in response to these dramatic
insolation changes. Observations from the Cassini Composite Infrared
Spectrometer [1] have revealed (i) the continued presence of small,
cyclonic polar hotspots at both spring and autumn poles [2]; and (ii)
the emergence of an infrared-bright polar vortex at the north pole,
consistent with the historical record of Saturn observations from the
1980s (previous northern spring, [3]).
---------------------------------------------------------
Title: First submillimeter observation of CO in the stratosphere of
Uranus with Herschel-HIFI
Authors: Cavalié, T.; Moreno, R.; Lellouch, E.; Hartogh, P.; Jarchow,
C.; Venot, O.; Hersant, F.; Selsis, F.; Orton, G.; Encrenaz, T.;
Fletcher, L.
2013EPSC....8...72C Altcode:
Oxygen-rich deep interiors of the Giant Planets [1] cannot explain
the discovery of water vapor and carbon dioxide in the stratospheres
of the Giant Planets by [2] because these species are trapped by
condensation around their tropopause levels (except CO2 in Jupiter and
Saturn). Therefore, several sources in the direct or far environment of
the Giant Planets have been proposed: icy rings and/or satellites [3],
interplanetary dust particles [4] and large comet impacts [5]. Infrared
Space Observatory (ISO), Cassini, Odin and Herschel observations
have proven that the Jovian stratospheric water and carbon dioxide
originate from the Shoemaker-Levy 9 comet impacts in July 1994 [6, 7],
while Herschel has recently shown the external flux of water at Saturn
and Titan is most likely due to the Enceladus geysers and the water
torus they feed [8, 9]. <P />As for carbon monoxide (CO), the emerging
picture seems to show more uniformity for its sources. Because CO does
not condense at the tropopauses of Giant Planets, oxygen-rich interiors
are a valid source. An internal component has indeed been observed
in the vertical profile of CO in Jupiter by [10] and in Neptune by
[11], while an upper limit has been set on its magnitude by [12] for
Saturn. In addition to interiors, large comets seem to be the dominant
external source of CO in the Giant Planets, as shown by various studies:
[10] and [13] for Jupiter, [14] for Saturn and [15] for Neptune. <P
/>Despite its first detection almost a decade ago by [16], the situation
has remained unclear for Uranus ever since. The (sub)millimeter domain
with the use of heterodyne spectroscopy has long been considered as
promising to determine the vertical profile of CO, and thus its origin,
in Uranus (e.g., [17]). However, attempts made to detect the molecule
have failed so far in this spectral range, leading only to upper limits
[18]. In this paper, we present the first submillimeter detection of CO
in Uranus carried out with the HIFI instrument [19] onboard the Herschel
Space Observatory [20] in 2011-2012. Using a simple transport model,
we review the various possible sources of CO (internal and external)
and constrain their magnitude. For instance, we derive an upper limit
for the internal source of CO. And with the thermochemical model of
[21], adapted to the interior of Uranus, we derive an upper limit on
its deep O/H ratio from it.
---------------------------------------------------------
Title: Constraining the atmosphere of GJ 1214b using an optimal
estimation technique
Authors: Barstow, J. K.; Aigrain, S.; Irwin, P. G. J.; Fletcher,
L. N.; Lee, J. -M.
2013MNRAS.434.2616B Altcode: 2013MNRAS.tmp.1887B; 2013arXiv1306.6567B
We explore cloudy, extended H<SUB>2</SUB>-He atmosphere scenarios for
the warm super-Earth GJ 1214b using an optimal estimation retrieval
technique. This planet, orbiting an M4.5 star only 13 pc from the Earth,
is of particular interest because it lies between the Earth and Neptune
in size and may be a member of a new class of planet that is neither
terrestrial nor gas giant. Its relatively flat transmission spectrum
has so far made atmospheric characterization difficult. The Non-linear
optimal Estimator for MultivariateE spectral analySIS (NEMESIS)
algorithm is used to explore the degenerate model parameter space for
a cloudy, H<SUB>2</SUB>-He-dominated atmosphere scenario. Optimal
estimation is a data-led approach that allows solutions beyond the
range permitted by ab initio equilibrium model atmosphere calculations,
and as such prevents restriction from prior expectations. We show that
optimal estimation retrieval is a powerful tool for this kind of study,
and present an exploration of the degenerate atmospheric scenarios for
GJ 1214b. Whilst we find a family of solutions that provide a very good
fit to the data, the quality and coverage of these data are insufficient
for us to more precisely determine the abundances of cloud and trace
gases given an H<SUB>2</SUB>-He atmosphere, and we also cannot rule out
the possibility of a high molecular weight atmosphere. Future ground-
and space-based observations will provide the opportunity to confirm
or rule out an extended H<SUB>2</SUB>-He atmosphere, but more precise
constraints will be limited by intrinsic degeneracies in the retrieval
problem, such as variations in cloud top pressure and temperature.
---------------------------------------------------------
Title: The 2010-2011 revival of Jupiter's South Equatorial Belt
Authors: Giles, R. S.; Fletcher, L. N.; Irwin, P. G. J.; Orton, G. S.;
Rogers, J. H.
2013EPSC....8...33G Altcode:
In 2009-2010, Jupiter's South Equatorial Belt (SEB) faded to a very pale
colour before the 2010-2011 revival restored the belt to its ordinary
dark appearance. Mid-infrared images of the revival were taken using
VISIR (VLT) across a range of wavelengths from 7 to 25 μm. These were
used to retrieve changes in temperature and aerosol optical depth as
the revival proceeded between November 2010 and September 2011.
---------------------------------------------------------
Title: Science goals and concepts of a Saturn probe for the future
L2/L3 ESA call
Authors: Mousis, O.; Fletcher, L. N.; André, N.; Blanc, M.;
Coustenis, A.; Gautier, D.; Geppert, W. D.; Guillot, T.; Irwin, P.;
Lebreton, J. -P.; Marty, B.; Morse, A.; Murray, C.; Petit, J. -M.;
Sanchez-Lavega, A.; Schmider, F. -X.; Waite, J. H.; Wurz, P.
2013EPSC....8..232M Altcode:
A Saturn probe is the next natural step beyond Galileo's in
situ exploration of Jupiter, and the Cassini spacecraft's orbital
reconnaissance of Saturn in order to understand the origin of giant
planets. Here we describe the science goals and concepts of a Saturn
probe that could be submitted to the future L2/L3 ESA call.
---------------------------------------------------------
Title: From Voyager-IRIS to Cassini-CIRS: Interannual Variability
in Saturn's Stratosphere
Authors: Sinclair, J. A.; Irwin, P. G. J.; Fletcher, L. N.; Hurley,
J.; Merlet, C.
2013EPSC....8...35S Altcode:
We present an intercomparison of Saturn's atmosphere from Voyager-IRIS
observations in 1980 with Cassini-CIRS observations in 2009/2010. Over
a Saturn year (∼29.5 years) has now passed since the Voyager flyby of
Saturn in 1980/1981. Cassini observations in 2009/2010 and those from
Voyager therefore capture Saturn in the same season (at approximately
the vernal equinox, solar longitude, Ls~∼0°). Any differences in
Saturn's stratospheric properties implied by a comparison of these two
datasets will therefore highlight interannual variability. We retrieve
temperature and stratospheric acetylene and ethane concentrations from
Voyager 1-IRIS (FWHM = 4.3 cm-1) in 1980 and Cassini-CIRS 'FIRMAP'
(FWHM = 15.5 cm-1) observations in 2009/2010. Preliminary results show
the equator to be warmer by 7.3 ± 1.6 K at ∼2.1 mbar in 2009 than
in 1980 implying a differing phase of the SSAO (Saturn's semi-annual
oscillation). Ethane's meridional distribution at 2.1 mbar appears
consistent between 1980 and 2009/2010. However, the concentrations
of acetylene at the same altitude appear enhanced at ∼25°S and
∼25°N in 1980 when compared to 2009/2010. A global-circulation
model shows cells of downwelling at these latitudes [3]: the richer
concentrations of acetylene at these latitudes in 1980 suggests that
there was stronger downwelling at this time than in 2009.
---------------------------------------------------------
Title: The flux of impacts in Jupiter: From superbolides to
large-scale collisions
Authors: Hueso, R.; Pérez-Hoyos, S.; Sánchez-Lavega, A.; . Wesley,
A.; Hall, G.; Go, C.; Tachikawa, M.; Aoki, K.; Ichimaru, M.; Delcroix,
M.; Wong, M.; Pond, J. W. T.; Korycansky, D. G.; Palotai, C.; Rebeli,
N.; Harrington, J.; de Pater, I.; Fletcher, L. N.; Hammel, H.; Orton,
G. S.; Tabe, I.; Watanabe, J.; Moreno, J. C.
2013EPSC....8..228H Altcode:
Observations of Jupiter by a large number of amateurs have resulted
in the discovery of three fireballs in its atmosphere produced by
the impacts of small objects. The fireballs were detected on June 3,
2010, August 20, 2010 and September 10, 2012. The light-curves of these
atmospheric airbursts provide a measure of the masses and sizes of the
impacting objects and the statistical significance of the three events
can be examined from knowledge of the large pool of Jupiter observations
by the global community of amateur astronomers. These objects are in
the category of 5-20 m sizes depending on their density and release
energies comparable to the recent Chelyabinsk airburst. Current biases
in observations of Jupiter suggest a rate of similar impacts of 18-160
per year.
---------------------------------------------------------
Title: Clouds on hot Jupiters: implications for transit spectroscopy
Authors: Barstow, J. K.; Aigrain, S.; Irwin, P. G. J.; Fletcher,
L. N.; Lee, J. -M.
2013EPSC....8..255B Altcode:
Since the first detection of a planet orbiting another main sequence
star, hundreds of extrasolar planets have been confirmed and more than
2000 candidates have been identified. To date, the best-characterised
class of planets using this method are the 'hot Jupiters', and evidence
is now emerging that these hot planets have cloudy atmospheres. Clouds
and aerosols have a large impact on the spectroscopic signatures
and radiation balance of the planets in our own solar system; this
is also true for brown dwarfs, which exist at similar temperatures
to the hottest of the giant exoplanets. We investigate the effect of
different types of cloud on the transmission and eclipse spectra of
hot Jupiters, and will thereby explore ways of breaking degeneracies
between different model atmosphere scenarios.
---------------------------------------------------------
Title: The Ultraviolet Spectrograph on the JUICE Mission (JUICE-UVS)
Authors: Gladstone, R.; Retherford, K.; Eterno, J.; Persyn, S.; Davis,
M.; Versteeg, M.; Greathouse, T.; Persson, K.; Dirks, G.; Walther,
B.; Araujo, M.; Steffl, A.; Schindhelm, R.; Spencer, J.; McGrath,
M.; Bagenal, F.; Feldman, P.; Fletcher, L.
2013EPSC....8..394G Altcode:
The ultraviolet spectrograph instrument for the JUICE mission
(JUICE-UVS) has been selected to provide a variety of ultraviolet
science observations during the mission's survey of the Jovian
system. The goals of our investigation are to explore the atmospheres,
plasma interactions, and surfaces of the Galilean satellites; to
determine the dynamics, chemistry, and vertical structure of Jupiter's
upper atmosphere, from equator to pole, as a template for giant planets
everywhere; and to investigate the Jupiter-Io connection by quantifying
energy and mass flow in the Io atmosphere, neutral clouds, and torus. In
this talk we describe the science objectives for JUICE-UVS, along with
an overview of its design and expected performance.
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Title: The transit spectra of the Solar System planets
Authors: Irwin, P. G. J.; Fletcher, L. N.; Barstow, J.; Aigrain, S.;
Lee, J. -M.
2013EPSC....8...92I Altcode:
In recent years, an increasing number of observations have been made
of the transits of 'Hot Jupiters', such as HD 189733b, from the visible
through to midinfrared wavelengths, which have been modelled to derive
the likely atmospheric structure and composition of these planets. As
measurement techniques improve, the measured transit spectra of
'Super-Earths' such as GJ 1214b are becoming better constrained,
allowing model atmospheric states to be fitted for this class of
planet also. While it is not yet possible to constrain the atmospheric
states of small planets like the Earth or cold planets like Jupiter,
it is hoped that this might become practical in the coming decades and
if so, it is of interest to determine what we might infer from such
measurements. In this work we have constructed atmospheric models of
the Solar System planets from 0.2 - 15 μm that are consistent with
groundbased and satellite observations and from these calculate the
primary and secondary transit spectra (with respect to the Sun) that
would be observed by a 'remote observer', many light years away. From
these spectra we test what current retrieval models might infer about
their atmospheric states and compare these with the 'ground truths'
in order to assess: a) the inherent uncertainties in transit spectra
observations; b) the relative merits of primary versus secondary
transit spectra; and c) assess the optimal wavelength coverage and
sensitivities required to retrieve atmospheric states that reasonably
match the Solar System planet atmospheres.
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Title: Hot ribbon plasma during the rise phase of a flare
Authors: Fletcher, Lyndsay; Hannah, I.
2013SPD....44...66F Altcode:
Strong heating of the chromosphere and transition region during
flares results in ribbons containing plasma at temperatures ranging
from a few thousand K to 10 million K. We have used SDO to construct
emission measure maps in the extended rise phase of the M1.0 event
SOL2010-08-07T17:55 using the method of Hannah & Kontar (2012),
allowing a pixel-by-pixel examination of the development of thermal
plasma in the ribbons, and detailed comparison with the ribbons'
magnetic environment. Using RHESSI hard X-ray observations we set
limits on the non-thermal emission from the ribbons, and examine the
contribution of energy loss by non-thermal electrons to the ribbon
heating in this phase.
---------------------------------------------------------
Title: Seasonal variations of temperature, acetylene and ethane in
Saturn's atmosphere from 2005 to 2010, as observed by Cassini-CIRS
Authors: Sinclair, J. A.; Irwin, P. G. J.; Fletcher, L. N.; Moses,
J. I.; Greathouse, T. K.; Friedson, A. J.; Hesman, B.; Hurley, J.;
Merlet, C.
2013Icar..225..257S Altcode:
Acetylene (C<SUB>2</SUB>H<SUB>2</SUB>) and ethane
(C<SUB>2</SUB>H<SUB>6</SUB>) are by-products of complex photochemistry
in the stratosphere of Saturn. Both hydrocarbons are important to
the thermal balance of Saturn's stratosphere and serve as tracers
of vertical motion in the lower stratosphere. Earlier studies of
Saturn's hydrocarbons using Cassini-CIRS observations have provided
only a snapshot of their behaviour. Following the vernal equinox in
August 2009, Saturn's northern and southern hemispheres have entered
spring and autumn, respectively, however the response of Saturn's
hydrocarbons to this seasonal shift remains to be determined. In this
paper, we investigate how the thermal structure and concentrations of
acetylene and ethane have evolved with the changing season on Saturn. We
retrieve the vertical temperature profiles and acetylene and ethane
volume mixing ratios from Δν∼=15.5cm<SUP>-1</SUP> Cassini-CIRS
observations. In comparing 2005 (solar longitude, L<SUB>s</SUB>
∼ 308°), 2009 (L<SUB>s</SUB> ∼ 3°) and 2010 (L<SUB>s</SUB>
∼ 15°) results, we observe the disappearance of Saturn's warm
southern polar hood with cooling of up to 17.1 K ± 0.8 K at 1.1 mbar
at high-southern latitudes. Comparison of the derived temperature
trend in this region with a radiative climate model (Section 4 of
Fletcher et al., 2010 and Greathouse et al. (2013, in preparation))
indicates that this cooling is radiative although dynamical changes
in this region cannot be ruled out. We observe a 21 ± 12% enrichment
of acetylene and a 29 ± 11% enrichment of ethane at 25°N from 2005
to 2009, suggesting downwelling at this latitude. At 15°S, both
acetylene and ethane exhibit a decrease in concentration of 6 ± 11%
and 17 ± 9% from 2005 to 2010, respectively, which suggests upwelling
at this latitude (though a statistically significant change is only
exhibited by ethane). These implied vertical motions at 15°S and
25°N are consistent with a recently-developed global circulation
model of Saturn's tropopause and stratosphere(Friedson and Moses,
2012), which predicts this pattern of upwelling and downwelling as a
result of a seasonally-reversing Hadley circulation. Ethane exhibits
a general enrichment at mid-northern latitudes from 2005 to 2009. As
the northern hemisphere approaches summer solstice in 2017, this
feature might indicate an onset of a meridional enrichment of ethane,
as has been observed in the southern hemisphere during/after southern
summer solstice.
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Title: Flare Science with the ATST
Authors: Fletcher, Lyndsay
2013SPD....4440102F Altcode:
A flare's radiation appears mostly in the near-UV, optical and
near infrared, emitted by the dense chromosphere where most of the
flare energy is ultimately dissipated. Catching flares with a small
field-of-view imager or a slit-rastering spectrometer is challenging,
but observations with the ATST will lead to tremendous advances in
our knowledge of a flare's magnetic environment and its variations,
the structure and evolution of the flare chromosphere, and the temporal
and spatial scales of energy transport and dissipation. This talk will
review in brief our understanding of flares in the ATST's wavelength
range, and describe some observational goals for flare science with
the ATST first light instruments.
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Title: Flare Ribbon Energetics in the Early Phase of an SDO Flare
Authors: Fletcher, L.; Hannah, I. G.; Hudson, H. S.; Innes, D. E.
2013ApJ...771..104F Altcode: 2014arXiv1401.6538F
The sites of chromospheric excitation during solar flares are
marked by extended extreme ultraviolet ribbons and hard X-ray
(HXR) footpoints. The standard interpretation is that these are
the result of heating and bremsstrahlung emission from non-thermal
electrons precipitating from the corona. We examine this picture using
multi-wavelength observations of the early phase of an M-class flare
SOL2010-08-07T18:24. We aim to determine the properties of the heated
plasma in the flare ribbons, and to understand the partition of the
power input into radiative and conductive losses. Using GOES, SDO/EVE,
SDO/AIA, and RHESSI, we measure the temperature, emission measure (EM),
and differential emission measure of the flare ribbons, and deduce
approximate density values. The non-thermal EM, and the collisional
thick target energy input to the ribbons are obtained from RHESSI using
standard methods. We deduce the existence of a substantial amount
of plasma at 10 MK in the flare ribbons, during the pre-impulsive
and early-impulsive phase of the flare. The average column EM of
this hot component is a few times 10<SUP>28</SUP> cm<SUP>-5</SUP>,
and we can calculate that its predicted conductive losses dominate
its measured radiative losses. If the power input to the hot ribbon
plasma is due to collisional energy deposition by an electron beam
from the corona then a low-energy cutoff of ~5 keV is necessary to
balance the conductive losses, implying a very large electron energy
content. Independent of the standard collisional thick-target electron
beam interpretation, the observed non-thermal X-rays can be provided
if one electron in 10<SUP>3</SUP>-10<SUP>4</SUP> in the 10 MK (1 keV)
ribbon plasma has an energy above 10 keV. We speculate that this could
arise if a non-thermal tail is generated in the ribbon plasma which
is being heated by other means, for example, by waves or turbulence.
---------------------------------------------------------
Title: Stochastic Simulations of the Pitch-angle Scattering of High
Energy Electrons
Authors: Dickson, Ewan C.; Kontar, E.; Fletcher, L.
2013SPD....44...56D Altcode:
The angular variation of high energy electrons during a solar flare is
key to understanding the acceleration mechanism. Regularised inversion
of RHESSI X-ray spectra, using the effect of photospheric albedo, allows
us to estimate the angular distributions of the emitting electrons. The
results for all flares studied are consistent with an isotropic
pitch-angle distribution, and inconsistent with a ratio of downward to
upward going electron flux greater than 3:1. To attempt to understand
these results, I have performed stochastic simulations of electron
pitch-angle scattering by Coulomb collisions, including the effects
of collisional energy loss, and of magnetic field convergence. This
allows us to estimate what constraints these observations put on the
parameters of the electron beam, such as initial directionality, and of
the characteristics of the loop itself. These simulations suggest that
Coulomb collisions cannot sufficiently isotropise the distribution to
be consistent with the observations, even for an initially isotropic
injected distribution.
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Title: The properties of flare kernels observed by the Dunn Solar
Telescope
Authors: Fletcher, Lyndsay; Kowalski, A.; Cauzzi, G.; Hawley, S. L.;
Hudson, H. S.
2013SPD....44...67F Altcode:
We report on a campaign at the Dunn Solar Telescope which resulted in
successful imaging and spectroscopic observations of a C1.1 solar flare
on 18th August 2011. This flare exhibited ribbons with complicated
fine structure at the resolution of the DST/IBIS instrument, and a
number of bright kernels with sizes comparable to the smallest scales
sampled by IBIS, around 2-4 pixels (0."3-0."6) FWHM. We focus on these
bright kernels, describing their spatial characteristics in the core
and wing of H alpha and Ca II 8542, and in the UV and EUV with SDO. We
also show preliminary broad-band spectroscopy of the kernels which may
demonstrate the presence of an optical continuum in this small flare.
---------------------------------------------------------
Title: A new approach to model particle acceleration and energy
transfer in solar flares
Authors: Rubio Da Costa, Fatima; Zuccarello, F.; Fletcher, L.;
Labrosse, N.; Kasparova, J.; Prosecký, T.; Carlsson, M.; Petrosian,
V.; Liu, W.
2013SPD....4440401R Altcode:
Motivated by available observations of two different flares in Lyα and
Hα, we model the conditions of the solar atmosphere using a radiation
hydrodynamics code (RADYN, Carlsson & Stein, 1992) and analyze the
energy transport carried by a beam of non-thermal electrons injected
at the top of a 1D coronal loop. The numerical Lyα and Hα intensities
match with the observations. The electron energy distribution is assumed
to follow a power law of the form (E/E<SUP>c</SUP> )<SUB>-δ</SUB> for
energies greater than a cutoff value of E<SUP>c</SUP>. Abbett &
Hawley (1999) and Allred et al. (2005) assumed that the non-thermal
electrons flux injected at the top of a flaring loop, the cut-off energy
and the power law index are constant over time. An improvement was
achieved by Allred & Hawley (2006), who modified the RADYN code
in such a way that the input parameters were time dependent. Their
inputs were based on observations of a flare obtained with RHESSI. By
combining RADYN with the “flare” code from Stanford University
which models the acceleration and transport of particles and radiation
of solar flares in non-LTE regime, we can calculate the non-thermal
electrons flux, the cut-off energy and the power law index at every
simulated time step. The atmospheric parameters calculated by RADYN
could in turn be used as updated inputs for "flare", providing several
advantages over the results from Liu et al. (2009), who combined the
particle acceleration code with a 1-D hydrodynamic code, improving
the atmospheric conditions.
---------------------------------------------------------
Title: Impulsive Thermal X-Ray Emission from a Low-lying Coronal Loop
Authors: Liu, Siming; Li, Youping; Fletcher, Lyndsay
2013ApJ...769..135L Altcode: 2013arXiv1304.5584L
Understanding the relationship among different emission components plays
an essential role in the study of particle acceleration and energy
conversion in solar flares. In flares where gradual and impulsive
emission components can be readily identified, the impulsive emission
has been attributed to non-thermal particles. We carry out detailed
analysis of Hα and X-ray observations of a GOES class B microflare
loop on the solar disk. The impulsive hard X-ray emission, however,
is found to be consistent with a hot, quasi-thermal origin, and
there is little evidence of emission from chromospheric footpoints,
which challenges conventional models of flares and reveals a class of
microflares associated with dense loops. Hα observations indicate that
the loop lies very low in the solar corona or even in the chromosphere
and both emission and absorption materials evolve during the flare. The
enhanced Hα emission may very well originate from the photosphere
when the low-lying flare loop heats up the underlying chromosphere
and reduces the corresponding Hα opacity. These observations may be
compared with detailed modeling of flare loops with the internal kink
instability, where the mode remains confined in space without apparent
change in the global field shape, to uncover the underlying physical
processes and to probe the structure of solar atmosphere.
---------------------------------------------------------
Title: JUpiter ICy moons Explorer (JUICE): An ESA mission to orbit
Ganymede and to characterise the Jupiter system
Authors: Grasset, O.; Dougherty, M. K.; Coustenis, A.; Bunce, E. J.;
Erd, C.; Titov, D.; Blanc, M.; Coates, A.; Drossart, P.; Fletcher,
L. N.; Hussmann, H.; Jaumann, R.; Krupp, N.; Lebreton, J. -P.;
Prieto-Ballesteros, O.; Tortora, P.; Tosi, F.; Van Hoolst, T.
2013P&SS...78....1G Altcode:
Past exploration of Jupiter's diverse satellite system has forever
changed our understanding of the unique environments to be found
around gas giants, both in our solar system and beyond. The detailed
investigation of three of Jupiter's Galilean satellites (Ganymede,
Europa, and Callisto), which are believed to harbour subsurface water
oceans, is central to elucidating the conditions for habitability of
icy worlds in planetary systems in general. The study of the Jupiter
system and the possible existence of habitable environments offer
the best opportunity for understanding the origins and formation of
the gas giants and their satellite systems. The JUpiter ICy moons
Explorer (JUICE) mission, selected by ESA in May 2012 to be the
first large mission within the Cosmic Vision Program 2015-2025, will
perform detailed investigations of Jupiter and its system in all their
inter-relations and complexity with particular emphasis on Ganymede
as a planetary body and potential habitat. The investigations of the
neighbouring moons, Europa and Callisto, will complete a comparative
picture of the Galilean moons and their potential habitability. Here we
describe the scientific motivation for this exciting new European-led
exploration of the Jupiter system in the context of our current
knowledge and future aspirations for exploration, and the paradigm it
will bring in the study of giant (exo) planets in general.
---------------------------------------------------------
Title: On the potential of the EChO mission to characterize gas
giant atmospheres
Authors: Barstow, J. K.; Aigrain, S.; Irwin, P. G. J.; Bowles, N.;
Fletcher, L. N.; Lee, J. -M.
2013MNRAS.430.1188B Altcode: 2013MNRAS.tmp..637B; 2013MNRAS.tmp..679B
Space telescopes such as Exoplanet Characterisation Observatory (EChO)
and James Webb Space Telescope (JWST) will be important for the future
study of extrasolar planet atmospheres. Both of these missions are
capable of performing high sensitivity spectroscopic measurements
at moderate resolutions in the visible and infrared, which will
allow the characterization of atmospheric properties using primary
and secondary transit spectroscopy. We use the Non-linear optimal
Estimator for MultivariateE spectral analysis (NEMESIS) radiative
transfer and retrieval tool, as developed by Irwin et al. and Lee
et al., to explore the potential of the proposed EChO mission to
solve the retrieval problem for a range of H<SUB>2</SUB>-He planets
orbiting different stars. We find that EChO should be capable of
retrieving temperature structure to ∼200 K precision and detecting
H<SUB>2</SUB>O, CO<SUB>2</SUB> and CH<SUB>4</SUB> from a single
eclipse measurement for a hot Jupiter orbiting a Sun-like star and a
hot Neptune orbiting an M star, also providing upper limits on CO and
NH<SUB>3</SUB>. We provide a table of retrieval precisions for these
quantities in each test case. We expect around 30 Jupiter-sized planets
to be observable by EChO; hot Neptunes orbiting M dwarfs are rarer,
but we anticipate observations of at least one similar planet.
---------------------------------------------------------
Title: The Emission Measure Distribution of Impulsive Phase Flare
Footpoints
Authors: Graham, D. R.; Hannah, I. G.; Fletcher, L.; Milligan, R. O.
2013ApJ...767...83G Altcode: 2013arXiv1302.2514G
The temperature distribution of the emitting plasma is a crucial
constraint when studying the heating of solar flare footpoints. However,
determining this for impulsive phase footpoints has been difficult
in the past due to insufficient spatial resolution to resolve the
footpoints from the loop structures, and a lack of spectral and temporal
coverage. We use the capabilities of Hinode/Extreme Ultraviolet Imaging
Spectrometer to obtain the first emission measure distributions (EMDs)
from impulsive phase footpoints in six flares. Observations with good
spectral coverage were analyzed using a regularized inversion method to
recover the EMDs. We find that the EMDs all share a peak temperature of
around 8 MK, with lines formed around this temperature having emission
measures (EMs) peaking between 10<SUP>28</SUP> and 10<SUP>29</SUP>
cm<SUP>-5</SUP>, indicating a substantial presence of plasma at very
high temperatures within the footpoints. An EMD gradient of EM(T) ~
T is found in all events. Previous theoretical work on EM gradients
shows this to be consistent with a scenario in which the deposited flare
energy directly heats only the top layer of the flare chromosphere,
while deeper layers are heated by conduction.
---------------------------------------------------------
Title: Propagation of Alfvénic Waves from Corona to Chromosphere
and Consequences for Solar Flares
Authors: Russell, A. J. B.; Fletcher, L.
2013ApJ...765...81R Altcode: 2013arXiv1302.2458R
How do magnetohydrodynamic waves travel from the fully ionized corona,
into and through the underlying partially ionized chromosphere, and
what are the consequences for solar flares? To address these questions,
we have developed a two-fluid model (of plasma and neutrals) and used
it to perform one-dimensional simulations of Alfvén waves in a solar
atmosphere with realistic density and temperature structure. Studies of
a range of solar features (faculae, plage, penumbra, and umbra) show
that energy transmission from corona to chromosphere can exceed 20%
of incident energy for wave periods of 1 s or less. Damping of waves
in the chromosphere depends strongly on wave frequency: waves with
periods 10 s or longer pass through the chromosphere with relatively
little damping, however, for periods of 1 s or less, a substantial
fraction (37%-100%) of wave energy entering the chromosphere is
damped by ion-neutral friction in the mid- and upper chromosphere,
with electron resistivity playing some role in the lower chromosphere
and in umbras. We therefore conclude that Alfvénic waves with periods
of a few seconds or less are capable of heating the chromosphere during
solar flares, and speculate that they could also contribute to electron
acceleration or exciting sunquakes.
---------------------------------------------------------
Title: A Gemini ground-based transmission spectrum of WASP-29b:
a featureless spectrum from 515 to 720 nm
Authors: Gibson, N. P.; Aigrain, S.; Barstow, J. K.; Evans, T. M.;
Fletcher, L. N.; Irwin, P. G. J.
2013MNRAS.428.3680G Altcode: 2012arXiv1210.7798G
We report Gemini-South Gemini Multi-Object Spectrograph observations of
the exoplanet system WASP-29 during primary transit as a test case for
differential spectrophotometry. We use the multi-object spectrograph
to observe the target star and a comparison star simultaneously to
produce multiple light curves at varying wavelengths. The `white'
light curve and 15 `spectral' light curves are analysed to refine the
system parameters and produce a transmission spectrum from ∼515 to
720 nm. All light curves exhibit time-correlated noise, which we model
using a variety of techniques. These include a simple noise rescaling,
a Gaussian process model and a wavelet-based method. These methods all
produce consistent results, although with different uncertainties. The
precision of the transmission spectrum is improved by subtracting a
common signal from all the spectral light curves, reaching a typical
precision of ∼1 × 10<SUP>-4</SUP> in transit depth. The transmission
spectrum is free of spectral features, and given the non-detection
of a pressure broadened Na feature, we can rule out the presence
of a Na-rich atmosphere free of clouds or hazes, although we cannot
rule out a narrow Na core. This indicates that Na is not present in
the atmosphere, and/or that clouds/hazes play a significant role in
the atmosphere and mask the broad wings of the Na feature, although
the former is a more likely explanation given WASP-29b's equilibrium
temperature of ∼970 K, at which Na can form various compounds. We
also briefly discuss the use of Gaussian process and wavelet methods
to account for time-correlated noise in transit light curves.
---------------------------------------------------------
Title: Particle acceleration and dynamical heating in Cycle 24 flares
Authors: Hannah, I. G.; Fletcher, L.; Kontar, E. P.
2012AGUFMSH51C..07H Altcode:
The current wealth of solar observations presents a unique opportunity
to study energy release in solar flares, particularly particle
acceleration and plasma heating. The spatial and temporal resolution
of SDO/AIA EUV data give an unprecedented view of dynamical heating
in solar flares yet to fully exploit this resource the underlying
thermal properties of the emitting plasma needs to be recovered. This
is difficult as it is an ill-posed inverse problem and there is
copious data. Our recently implemented regularized inversion method
(Hannah & Kontar A&A 2012a,b) can quickly and robustly find the
Differential Emission Measure (DEM) solution (and its uncertainties),
with the resulting EM maps allowing the temperature and density
evolution to be studied both spatially and temporally. Combing this with
the hard X-ray imaging and spectroscopy of RHESSI, we present a study of
the non-thermal energy input and thermal response in some flares of the
rising phase of cycle 24. We also look at the relationship between the
energetics of flares and the underlying magnetic field configurations.
---------------------------------------------------------
Title: Latitudinal variation of upper tropospheric NH<SUB>3</SUB>
on Saturn derived from Cassini/CIRS far-infrared measurements
Authors: Hurley, J.; Fletcher, L. N.; Irwin, P. G. J.; Calcutt, S. B.;
Sinclair, J. A.; Merlet, C.
2012P&SS...73..347H Altcode:
Ammonia (NH<SUB>3</SUB>) has been detected both on Saturn and Jupiter,
and although its concentration and distribution has been well-studied
on Jupiter, it has proven more difficult to do so on Saturn due
to higher sensitivity requirements resulting from Saturn's lower
atmospheric temperatures and the dominance of Saturn's phosphine
which masks the ammonia signal. Using far-infrared measurements of
Saturn taken by Cassini/CIRS between February 2005 and December 2010,
the latitudinal variations of upper tropospheric ammonia on Saturn
are studied. Sensitivity to NH<SUB>3</SUB> in the far-infrared is
explored to provide estimates of temperature, para-H<SUB>2</SUB>
and PH<SUB>3</SUB>, from 2.5 cm<SUP>-1</SUP> spectral resolution
measurements alone, 0.5 cm<SUP>-1</SUP> spectral-resolution
measurements alone, and 0.5 cm<SUP>-1</SUP> measurements degraded
to 2.5 cm<SUP>-1</SUP> spectral resolution. The estimates of
NH<SUB>3</SUB> from these three different datasets largely agree,
although there are notable differences using the high emission angle
0.5 cm<SUP>-1</SUP> data, which are asserted to result from a reduction
in sensitivity at higher emission angles. For low emission angles,
the 0.5 cm<SUP>-1</SUP>-retrieved values of NH<SUB>3</SUB> can be used
to reproduce the 2.5 cm<SUP>-1</SUP> spectra with similar efficacy as
those derived directly from the 2.5 cm<SUP>-1</SUP> resolution data
itself, and vice versa. Using low emission angle data, NH<SUB>3</SUB>
is observed to have broad peak abundances at ±25° latitude, attributed
to result from condensation and/or photolytic processes. Lack of data
coverage at equatorial latitudes precludes analysis of NH<SUB>3</SUB>
abundance at less than about 10° latitude. Noise levels are not
sufficient to distinguish fine zonal features, although it seems that
NH<SUB>3</SUB> cannot trace the zonal belt/zone structure in the upper
troposphere of Saturn.
---------------------------------------------------------
Title: Photochemistry in Saturn's Ring Shadowed Atmosphere: Production
Rates of Key Atmospheric Molecules and Preliminary Analysis of
Observations
Authors: Edgington, S. G.; Atreya, S. K.; Wilson, E. H.; West, R. A.;
Baines, K. H.; Bjoraker, G. L.; Fletcher, L. N.; Momary, T.
2012AGUFM.P13B1946E Altcode:
Cassini has been orbiting Saturn for over eight years. During this
epoch, the ring shadow has moved from shading a large portion of
the northern hemisphere (the ring plane was inclined by ~24 degrees
relative to the Sun-Saturn vector) to shading mid-latitudes south
of the equator and continues southward. At its maximum extent,
the projection of the ring plane shadow onto Saturn can reach as
far as 48N (~58N at the terminator). The net result, is that the
intensity of both ultraviolet and visible sunlight penetrating onto
any particular northern/southern latitude will vary depending on
Saturn's tilt relative to the Sun and the optical thickness of each
ring system. Our previous work has examined the variation of the solar
flux as a function of solar inclination, i.e. season on Saturn. Here we
report on the impact of the oscillating ring shadow on the photolysis
and production rates of key hydrocarbons in Saturn's stratosphere and
upper troposphere, including ethane, acetylene, propane, benzene. We
investigate the impact on production and loss rates of the long-lived,
photochemical hydrocarbons leading to haze formation at several
latitudes over one Saturn year. Similarly, we assess the impact on
the abundance of phosphine, a disequilibrium species whose presence
in the upper troposphere is a tracer of convection processes in the
deep atmosphere. Along with the above, we present preliminary analysis
of Cassini's UVIS and VIMS datasets that provide an estimate of the
evolving haze content of the northern hemisphere. We will also compare
our model results to abundances determined from previously released
CIRS observations. The research described in this paper was carried out
at the Jet Propulsion Laboratory, California Institute of Technology,
under a contract with the National Aeronautics and Space Administration.
---------------------------------------------------------
Title: Properties of Slowly Moving Thermal Waves in Saturn from
Cassini CIRS Observations from 2004 to 2009
Authors: Orton, G. S.; Fletcher, L. N.; Flasar, F. M.; Achterberg,
R. K.; Brown, S. K.
2012AGUFM.P13B1928O Altcode:
Hemispherical maps of Saturn's atmosphere made by the Cassini
Composite Infrared Spectrometer (CIRS) were surveyed for the presence
and properties of zonal thermal waves and their variability in
time. The most inclusive surveys in latitude, FIRMAPs (15 cm-1 spectral
resolution), covered the planet from the equator to either the north or
south pole, sweeping through the latitude range while the planet rotated
beneath over its ~10-hour rotation. Four spectral ranges were sampled:
two in a region dominated by upper-tropospheric emission (80-200 mbar)
from collision-induced H2 opacity and two in regions dominated by
stratospheric emission (0.5-3 mbar) from ethane (12.3 μm) and methane
(7.7 μm), respectively. We examined maps that were taken between 2004
and Saturn's spring equinox in 2009. During this time, the strongest
waves were found between planetographic latitudes of 30° and 45° S;
in the northern hemisphere, they were found between the equator and
30°N. Some low-wavenumber components cover all 360° in longitude,
similar to the slowly moving thermal waves in Jupiter's atmosphere,
but the strongest waves were found in "trains" that covered only one
hemisphere or less. In 2005, tropospheric waves had a mean peak-to-peak
variance that was the equivalent of temperature variability of about 1
K. Between 2005 and 2007, they had subsided to about 0.5 K. During and
after 2008 they soared to over 3 K. During this entire period, similar
waves in the northern hemisphere were never larger than 0.8 K. In the
stratosphere, waves followed a similar time sequence, with southern
hemisphere waves in 2005 reaching as much as 3.5 K in brightness
temperature, subsequently decreasing, then growing in 2008-2009 to
over 5 K. Stratospheric waves in the northern hemisphere were nearly
constant around 2 K, but with an instance of 6 K at one epoch in
2008. The phase of the waves moved about 0.5° of longitude per day
retrograde with respect to System III. The phase of tropospheric and
stratospheric waves appeared to be highly correlated with one another,
with little offset in longitude.
---------------------------------------------------------
Title: Elusive Ethylene Detected in Saturn's Northern Storm Region
Authors: Hesman, B. E.; Bjoraker, G. L.; Sada, P. V.; Achterberg,
R. K.; Jennings, D. E.; Romani, P. N.; Lunsford, A. W.; Fletcher,
L. N.; Boyle, R. J.; Simon-Miller, A. A.; Nixon, C. A.; Irwin, P. G. J.
2012ApJ...760...24H Altcode:
The massive eruption at 40°N (planetographic latitude) on Saturn
in 2010 December has produced significant and lasting effects in
the northern hemisphere on temperature and species abundances. The
northern storm region was observed on many occasions in 2011 by
Cassini's Composite Infrared Spectrometer (CIRS). In 2011 May,
temperatures in the stratosphere greater than 200 K were derived from
CIRS spectra in the regions referred to as "beacons" (warm regions in
the stratosphere). Ethylene has been detected in the beacon region in
Saturn's northern storm region using CIRS. Ground-based observations
using the high-resolution spectrometer Celeste on the McMath-Pierce
Telescope on 2011 May 15 were used to confirm the detection and improve
the altitude resolution in the retrieved profile. The derived ethylene
profile from the CIRS data gives a C<SUB>2</SUB>H<SUB>4</SUB> mole
fraction of 5.9 ± 4.5 × 10<SUP>-7</SUP> at 0.5 mbar, and from Celeste
data it gives 2.7 ± 0.45 × 10<SUP>-6</SUP> at 0.1 mbar. This is two
orders of magnitude higher than the amount measured in the ultraviolet
at other latitudes prior to the storm. It is also much higher than
predicted by photochemical models, indicating that perhaps another
production mechanism is required or a loss mechanism is being inhibited.
---------------------------------------------------------
Title: Unusual Stokes V profiles during flaring activity of a
delta sunspot
Authors: Fischer, C. E.; Keller, C. U.; Snik, F.; Fletcher, L.;
Socas-Navarro, H.
2012A&A...547A..34F Altcode: 2012arXiv1209.0983F
<BR /> Aims: We analyze a set of full Stokes profile observations of
the flaring active region NOAA 10808. The region was recorded with
the Vector-Spectromagnetograph of the Synoptic Optical Long-term
Investigations of the Sun facility. The active region produced
several successive X-class flares between 19:00 UT and 24:00 UT on
September 13, 2005 and we aim to quantify transient and permanent
changes in the magnetic field and velocity field during one of the
flares, which has been fully captured. <BR /> Methods: The Stokes
profiles were inverted using the height-dependent inversion code
LILIA to analyze magnetic field vector changes at the flaring site. We
report multilobed asymmetric Stokes V profiles found in the δ-sunspot
umbra. We fit the asymmetric Stokes V profiles assuming an atmosphere
consisting of two components (SIR inversions) to interpret the profile
shape. The results are put in context with Michelson Doppler Imager
(MDI) magnetograms and reconstructed X-ray images from the Reuven
Ramaty High Energy Solar Spectroscopic Imager. <BR /> Results: We
obtain the magnetic field vector and find signs of restructuring
of the photospheric magnetic field during the flare close to the
polarity inversion line at the flaring site. At two locations in the
umbra we encounter strong fields (~3 kG), as inferred from the Stokes
I profiles, which, however, exhibit a low polarization signal. During
the flare we observe in addition asymmetric Stokes V profiles at one
of these sites. The asymmetric Stokes V profiles appear co-spatial
and co-temporal with a strong apparent polarity reversal observed
in MDI-magnetograms and a chromospheric hard X-ray source. The
two-component atmosphere fits of the asymmetric Stokes profiles
result in line-of-sight velocity differences in the range of ~12 km
s<SUP>-1</SUP> to 14 km s<SUP>-1</SUP> between the two components in
the photosphere. Another possibility is that local atmospheric heating
is causing the observed asymmetric Stokes V profile shape. In either
case our analysis shows that a very localized patch of ~5″ in the
photospheric umbra, co-spatial with a flare footpoint, exhibits a
subresolution fine structure.
---------------------------------------------------------
Title: Ethylene Emission in the Aftermath of Saturn’s 2010
Northern Storm
Authors: Hesman, Brigette E.; Bjoraker, G. L.; Sada, P. V.; Achterberg,
R. K.; Jennings, D. E.; Lunsford, A. W.; Romani, P. N.; Fletcher,
L. N.; Boyle, R. J.; Kerr, T.; Sinclair, J. A.; Nixon, C. A.; Davis,
G. R.; Irwin, P. G. J.
2012DPS....4440306H Altcode:
The massive eruption at 40N (planetographic latitude) in December
2010 has produced significant and long-lived changes in temperature
and species abundances in Saturn’s northern hemisphere (Fletcher
et al. 2011). The northern storm region has been observed on many
occasions between January 2011 and June of 2012 by Cassini’s Composite
Infrared Spectrometer (CIRS). In this time period, temperatures in
regions referred to as “beacons” (warm regions in the stratosphere
at certain longitudes in the storm latitude) became significantly
warmer than pre-storm values of 140K. A significant finding in the
beacon region has been ethylene emission; a molecule that has been
challenging to detect on Saturn but is an important species in
Saturn’s photochemistry. The derived ethylene profile from the
CIRS data gives a C<SUB>2</SUB>H<SUB>4</SUB> mole fraction of 5.9
± 4.5x10<SUP>-7</SUP> at 0.5 mbar. Ground-based observations were
performed using the high-resolution spectrometer Celeste to study
ethylene’s spectral signatures at higher spectral resolution than
available with CIRS. Analysis of the May 2011 Celeste data finds a
C<SUB>2</SUB>H<SUB>4</SUB> mole fraction of 2.7 ± 0.45x10<SUP>-6</SUP>
at 0.1 mbar. The ethylene abundances derived from CIRS and Celeste
observations are two orders of magnitude higher than predicted by
photochemical models, indicating that perhaps another production
mechanism is required or a loss mechanism is being inhibited. To
investigate the source of ethylene in the beacon region the temporal
evolution of this molecule will be presented based on data collected by
CIRS, between January 2011 and June 2012, together with ground-based
Celeste observations from the McMath-Pierce Telescope (May 2011), the
United Kingdom Infrared Telescope (July 2011), and the NASA Infrared
Telescope Facility (April 2012). References: Fletcher, L. N. et al.,
2011. Thermal Structure and Dynamics of Saturn’s Northern Springtime
Disturbance. Science 332, 1413-1417.
---------------------------------------------------------
Title: OSS (Outer Solar System): a fundamental and planetary physics
mission to Neptune, Triton and the Kuiper Belt
Authors: Christophe, B.; Spilker, L. J.; Anderson, J. D.; André,
N.; Asmar, S. W.; Aurnou, J.; Banfield, D.; Barucci, A.; Bertolami,
O.; Bingham, R.; Brown, P.; Cecconi, B.; Courty, J. -M.; Dittus, H.;
Fletcher, L. N.; Foulon, B.; Francisco, F.; Gil, P. J. S.; Glassmeier,
K. H.; Grundy, W.; Hansen, C.; Helbert, J.; Helled, R.; Hussmann, H.;
Lamine, B.; Lämmerzahl, C.; Lamy, L.; Lehoucq, R.; Lenoir, B.; Levy,
A.; Orton, G.; Páramos, J.; Poncy, J.; Postberg, F.; Progrebenko,
S. V.; Reh, K. R.; Reynaud, S.; Robert, C.; Samain, E.; Saur, J.;
Sayanagi, K. M.; Schmitz, N.; Selig, H.; Sohl, F.; Spilker, T. R.;
Srama, R.; Stephan, K.; Touboul, P.; Wolf, P.
2012ExA....34..203C Altcode: 2011arXiv1106.0132C; 2012ExA...tmp...32C
The present OSS (Outer Solar System) mission continues a long and
bright tradition by associating the communities of fundamental physics
and planetary sciences in a single mission with ambitious goals in both
domains. OSS is an M-class mission to explore the Neptune system almost
half a century after the flyby of the Voyager 2 spacecraft. Several
discoveries were made by Voyager 2, including the Great Dark Spot
(which has now disappeared) and Triton's geysers. Voyager 2 revealed
the dynamics of Neptune's atmosphere and found four rings and evidence
of ring arcs above Neptune. Benefiting from a greatly improved
instrumentation, a mission as OSS would result in a striking advance
in the study of the farthest planet of the solar system. Furthermore,
OSS would provide a unique opportunity to visit a selected Kuiper Belt
object subsequent to the passage of the Neptunian system. OSS would
help consolidate the hypothesis of the origin of Triton as a Kuiper
Belt object captured by Neptune, and to improve our knowledge on the
formation of the solar system. The OSS probe would carry instruments
allowing precise tracking of the spacecraft during the cruise. It
would facilitate the best possible tests of the laws of gravity in
deep space. These objectives are important for fundamental physics,
as they test General Relativity, our current theoretical description
of gravitation, but also for cosmology, astrophysics and planetary
science, as General Relativity is used as a tool in all these
domains. In particular, the models of solar system formation uses
General Relativity to describe the crucial role of gravity. OSS is
proposed as an international cooperation between ESA and NASA, giving
the capability for ESA to launch an M-class mission towards the farthest
planet of the solar system, and to a Kuiper Belt object. The proposed
mission profile would allow to deliver a 500 kg class spacecraft. The
design of the probe is mainly constrained by the deep space gravity test
in order to minimize the perturbation of the accelerometer measurement.
---------------------------------------------------------
Title: EChO. Exoplanet characterisation observatory
Authors: Tinetti, G.; Beaulieu, J. P.; Henning, T.; Meyer, M.;
Micela, G.; Ribas, I.; Stam, D.; Swain, M.; Krause, O.; Ollivier,
M.; Pace, E.; Swinyard, B.; Aylward, A.; van Boekel, R.; Coradini,
A.; Encrenaz, T.; Snellen, I.; Zapatero-Osorio, M. R.; Bouwman, J.;
Cho, J. Y. -K.; Coudé de Foresto, V.; Guillot, T.; Lopez-Morales, M.;
Mueller-Wodarg, I.; Palle, E.; Selsis, F.; Sozzetti, A.; Ade, P. A. R.;
Achilleos, N.; Adriani, A.; Agnor, C. B.; Afonso, C.; Allende Prieto,
C.; Bakos, G.; Barber, R. J.; Barlow, M.; Batista, V.; Bernath, P.;
Bézard, B.; Bordé, P.; Brown, L. R.; Cassan, A.; Cavarroc, C.;
Ciaravella, A.; Cockell, C.; Coustenis, A.; Danielski, C.; Decin,
L.; De Kok, R.; Demangeon, O.; Deroo, P.; Doel, P.; Drossart, P.;
Fletcher, L. N.; Focardi, M.; Forget, F.; Fossey, S.; Fouqué, P.;
Frith, J.; Galand, M.; Gaulme, P.; González Hernández, J. I.;
Grasset, O.; Grassi, D.; Grenfell, J. L.; Griffin, M. J.; Griffith,
C. A.; Grözinger, U.; Guedel, M.; Guio, P.; Hainaut, O.; Hargreaves,
R.; Hauschildt, P. H.; Heng, K.; Heyrovsky, D.; Hueso, R.; Irwin, P.;
Kaltenegger, L.; Kervella, P.; Kipping, D.; Koskinen, T. T.; Kovács,
G.; La Barbera, A.; Lammer, H.; Lellouch, E.; Leto, G.; Lopez Morales,
M.; Lopez Valverde, M. A.; Lopez-Puertas, M.; Lovis, C.; Maggio, A.;
Maillard, J. P.; Maldonado Prado, J.; Marquette, J. B.; Martin-Torres,
F. J.; Maxted, P.; Miller, S.; Molinari, S.; Montes, D.; Moro-Martin,
A.; Moses, J. I.; Mousis, O.; Nguyen Tuong, N.; Nelson, R.; Orton,
G. S.; Pantin, E.; Pascale, E.; Pezzuto, S.; Pinfield, D.; Poretti,
E.; Prinja, R.; Prisinzano, L.; Rees, J. M.; Reiners, A.; Samuel,
B.; Sánchez-Lavega, A.; Forcada, J. Sanz; Sasselov, D.; Savini, G.;
Sicardy, B.; Smith, A.; Stixrude, L.; Strazzulla, G.; Tennyson, J.;
Tessenyi, M.; Vasisht, G.; Vinatier, S.; Viti, S.; Waldmann, I.;
White, G. J.; Widemann, T.; Wordsworth, R.; Yelle, R.; Yung, Y.;
Yurchenko, S. N.
2012ExA....34..311T Altcode: 2012ExA...tmp...35T; 2011arXiv1112.2728T
A dedicated mission to investigate exoplanetary atmospheres represents
a major milestone in our quest to understand our place in the
universe by placing our Solar System in context and by addressing the
suitability of planets for the presence of life. EChO—the Exoplanet
Characterisation Observatory—is a mission concept specifically geared
for this purpose. EChO will provide simultaneous, multi-wavelength
spectroscopic observations on a stable platform that will allow very
long exposures. The use of passive cooling, few moving parts and well
established technology gives a low-risk and potentially long-lived
mission. EChO will build on observations by Hubble, Spitzer and
ground-based telescopes, which discovered the first molecules and
atoms in exoplanetary atmospheres. However, EChO's configuration
and specifications are designed to study a number of systems in a
consistent manner that will eliminate the ambiguities affecting prior
observations. EChO will simultaneously observe a broad enough spectral
region—from the visible to the mid-infrared—to constrain from
one single spectrum the temperature structure of the atmosphere, the
abundances of the major carbon and oxygen bearing species, the expected
photochemically-produced species and magnetospheric signatures. The
spectral range and resolution are tailored to separate bands belonging
to up to 30 molecules and retrieve the composition and temperature
structure of planetary atmospheres. The target list for EChO includes
planets ranging from Jupiter-sized with equilibrium temperatures T
<SUB>eq</SUB> up to 2,000 K, to those of a few Earth masses, with
T <SUB>eq</SUB> u223c 300 K. The list will include planets with no
Solar System analog, such as the recently discovered planets GJ1214b,
whose density lies between that of terrestrial and gaseous planets,
or the rocky-iron planet 55 Cnc e, with day-side temperature close to
3,000 K. As the number of detected exoplanets is growing rapidly each
year, and the mass and radius of those detected steadily decreases, the
target list will be constantly adjusted to include the most interesting
systems. We have baselined a dispersive spectrograph design covering
continuously the 0.4-16 μm spectral range in 6 channels (1 in the
visible, 5 in the InfraRed), which allows the spectral resolution to
be adapted from several tens to several hundreds, depending on the
target brightness. The instrument will be mounted behind a 1.5 m class
telescope, passively cooled to 50 K, with the instrument structure and
optics passively cooled to u223c45 K. EChO will be placed in a grand
halo orbit around L2. This orbit, in combination with an optimised
thermal shield design, provides a highly stable thermal environment and
a high degree of visibility of the sky to observe repeatedly several
tens of targets over the year. Both the baseline and alternative
designs have been evaluated and no critical items with Technology
Readiness Level (TRL) less than 4-5 have been identified. We have also
undertaken a first-order cost and development plan analysis and find
that EChO is easily compatible with the ESA M-class mission framework.
---------------------------------------------------------
Title: JUpiter ICy Moons Explorer (JUICE): The ESA L1 Mission to
the Jupiter System
Authors: Dougherty, M. K.; Grasset, O.; Erd, C.; Titov, D.; Bunce,
E.; Coustenis, A.; Blanc, M.; Coates, A.; Drossart, P.; Fletcher,
L.; Hussmann, H.; Jaumann, R.; Krupp, N.; Prieto-Ballesteros, O.;
Tortora, P.; Tosi, F.; Van Hoolst, T.
2012LPICo1683.1039D Altcode:
The Jupiter Icy Moons Explorer (JUICE) mission has recently been
selected by ESA as the first large mission within the Cosmic Visions
2015-2025 plan. We will introduce the mission that is being developed
to thoroughly explore the Jupiter system with focus on the largest
satellite, Ganymede.
---------------------------------------------------------
Title: Clouds and Hazes in Saturn's Troposphere and Stratosphere
Authors: Merlet, Cecile; Irwin, P.; Fletcher, L.
2012DPS....4441215M Altcode:
We present new results from the analysis of Saturn's near-infrared
spectra measured with the Visual and Infrared Mapping Spectrometer
(VIMS) instrument on the Cassini orbiter. VIMS near-infrared data
are particularly relevant for the study of clouds and hazes in the
troposphere and stratosphere of Saturn. Thermal emission in the 4.5-5.1
wavelength range is absorbed and scattered mainly by tropospheric clouds
and radiatively active gases. The vertical structure as well as the
optical and physical properties of tropospheric aerosols are obtained
from Saturn's thermal emission spectra by using the retrieval algorithm
Nemesis. The distribution of tropospheric phosphine and ammonia in gas
phase will also be presented here. We managed to break the degeneracies
inherent to the retrieval problem by analysing Saturn's thermal emission
simultaneously at various viewing geometries. By using this method,
we found that VIMS spectra at 4.5-5.1 microns are also sensitive to
the hazes formed above the cloud layers. Saturn's reflected sunlight
spectra at 0.8-3.5 microns measured with VIMS were also analysed in
order to constrain the haze properties in the upper troposphere and
lower stratosphere of the planet. Results from both the 0.8-3.5 and
4.5-5.1 wavelength ranges were combined to determine the cloud and
haze model most consistent with VIMS spectroscopy over a wide range of
viewing geometries and lighting conditions. An increase of temperature
below the tropopause, often referred to as the temperature knee,
was retrieved from Cassini/CIRS spectra. Seasonal variations of the
knee and haze structure are compared, and as a result the assumption
of local heating by the hazes to explain this feature will be discussed.
---------------------------------------------------------
Title: Analysis Of Irtf Spex Near-infrared Observations Of Uranus:
Aerosol Optical Properties And Latitudinally Variable Methane
Authors: Tice, Dane; Irwin, P. G. J.; Fletcher, L. N.; Teanby, N. A.;
Hurley, J.; Orton, G. S.; Davis, G. R.
2012DPS....4441219T Altcode:
We present results from the analysis of near-infrared spectra of
Uranus observed in August 2009 with the SpeX spectrograph at the NASA
Infrared Telescope Facility (IRTF). Spectra range from 0.8 to 1.8
μm at a spatial resolution of 0.5” and a spectral resolution of
R = 1,200. This data is particularly well-suited to characterize the
optical properties of aerosols in the Uranian stratosphere and upper
troposphere. This is in part due to its coverage shortward of 1.0 μm
where methane absorption, which dominates the features in the Uranian
near-infrared spectrum, weakens slightly. Another particularly useful
aspect of the data is it’s specific, highly spectrally resolved
(R > 4,000) coverage of the collision-induced hydrogen quadrupole
absorption band at 825 nm, enabling us to differentiate between methane
abundance and cloud opacity. An optimal-estimation retrieval code,
NEMESIS, is used to analyze the spectra, and atmospheric models are
developed that represent good agreement with data in the full spectral
range analyzed. Aerosol single-scattering albedos that reveal a strong
wavelength dependence will be discussed. Additionally, an analysis of
latitudinal methane variability is undertaken, utilizing two methods
of analysis. First, a reflectance study from locations along the
central meridian is undertaken. The spectra from these locations
are centered around 825 nm, where the collision-induced absorption
feature of hydrogen is utilized to distinguish between latitudinal
changes in the spectrum due to aerosol opacity and those due to
methane variability. Secondly, high resolution retrievals from 0.8 -
0.9 μm portion of the spectrum and spectral resolutions between R =
4,000 and 4,500 are used to make the same distinction. Both methods
will be compared and discussed, as will their indications supporting
a methane enrichment in the equatorial region of the planet.
---------------------------------------------------------
Title: Seasonal Variations of Temperature, Acetylene and Ethane in
Saturn's Stratosphere from 2005 to 2010
Authors: Sinclair, James; Irwin, P. G. J.; Fletcher, L. N.; Moses,
J. I.; Greathouse, T. K.; Friedson, A. J.; Hesman, B.; Hurley, J.;
Merlet, C.
2012DPS....4450003S Altcode:
Acetylene (C<SUB>2</SUB>H<SUB>2</SUB>) and ethane
(C<SUB>2</SUB>H<SUB>6</SUB>) exemplify by-products of complex
photochemistry in Saturn’s stratosphere. Their relative stability
together with their strong vertical gradients in concentration allow
for their use as tracers of vertical motion in Saturn’s lower
stratosphere. Earlier studies of Saturn's hydrocarbons have provided
only a snapshot of their behaviour with temporal variations remaining to
be determined. In this study, we investigate how the thermal structure
and concentrations of acetylene and ethane have evolved on Saturn
with the changing season. We use FIRMAP (15.5 cm<SUP>-1</SUP> spectral
resolution) Cassini-CIRS observations, initially retrieve temperature
and subsequently retrieve the abundances of acetylene and ethane. In
comparing 2005, 2009 and 2010 results, we observe the disappearance of
Saturn's southern warm polar hood with cooling of up to 18.6 K ± 0.9 K
at 1.1 mbar south of 75°S (planetographic). This suggests dissipation
of Saturn's south polar vortex in addition to an autumnal cooling. We
observe a 20% ± 9% enrichment of acetylene and a 30% ± 10% enrichment
of ethane at 2.1 mbar at 25°N, together with a 14% ± 9% depletion of
acetylene and an 18% ± 7% depletion of ethane at the same altitude at
15°S. This suggests the presence of localised downwelling and upwelling
at these latitudes, respectively. These vertical motions are consistent
with a recently-developed GCM (global circulation model) of Saturn's
tropopause and stratosphere, which predicts this pattern of upwelling
and downwelling as a result of seasonally-reversing Hadley circulation.
---------------------------------------------------------
Title: Saturn’s Equatorial Plumes At Depth Observed By Cassini/VIMS
and Radar: Some Ammonia-wet, Some Dry
Authors: Baines, Kevin H.; Momary, T. W.; Janssen, M. A.; Ingersoll,
A. P.; Fletcher, L. N.; Brown, R. H.; Buratti, B. J.; Clark, R. N.;
Nicholson, P. D.; Sotin, C.
2012DPS....4450004B Altcode:
Large (> 3000 km), discrete clouds and ammonia vapor features
buried under Saturn’s ubiquotous equatorial haze have been
mapped contemporaneously in Cassini/VIMS 5-micron spectra and 2-cm
raster-scan imagery by the Cassini/RADAR used in passive mode. Since
2008 these features have been clearly observed on four occasions -
October 14-15, 2009, December 8-10, 2009, July 24-25, 2010, and
March 19-21, 2011 - from a vantage point close to the knife-edge of
the rings, which reduced the ring obscuration to just ± 3 degrees of
latitude about the equator. Spectral modeling indicates that the cloud
features are primarily located in the 2-3 bar region, and thus are
likely to be comprised of ammonia hydrosulfide (NH4SH) with perhaps
an admixture of water, but not of pure ammonia condensate. RADAR
imagery reveals variations of the local ammonia humidity in the same
2-3 bar region, assuming constant temperatures at depth to within
a few degrees. Observations acquired March 19-21, 2011 clearly show
correlations of ammonia-humid air with NH4SH cloud features, consistent
with the idea that NH4SH clouds form from updrafts of ammonia-humid air,
akin to the formation of convective water clouds on Earth in regions of
high humidity. However, observations acquired December 8-10, 2009 show
the opposite behavior, with localized cloud features largely coinciding
with regions of low ammonia humidity. One possible explanation is
that in the case of weaker updrafts, the rising NH3 is significantly
depleted as it creates the NH4SH clouds, leaving ammonia-depleted holes
in the background ammonia vapor. Alternatively, the supply of H2S in
updrafts may vary relative to NH3, thus regulating the formation of
both NH4SH aerosols and the left-over NH3 vapor. Finally, clouds in
ammonia-dry regions may just indicate mature clouds no longer undergoing
formation, as observed in the downwind “comet tail” clouds of the
major northern storm of 2010-2011.
---------------------------------------------------------
Title: Line Positions, Intensities And Line Shape Parameters Of
PH<SUB>3</SUB> Near 4.4 µm
Authors: Venkataraman, Malathy; Benner, D. C.; Kleiner, I.; Brown,
L. R.; Sams, R. L.; Fletcher, L. N.
2012DPS....4441227V Altcode:
Accurate knowledge of spectral line parameters in the 2000 to
2400 cm<SUP>-1</SUP> region of PH<SUB>3</SUB> is important for the
CASSINI/VIMS exploration of dynamics and chemistry of Saturn and for the
correct interpretation of future Jovian observations by JUNO and ESA’s
newly-selected mission JUICE. Since the available intensity information
for phosphine is inconsistent, we measured line positions and
intensities for over 4000 individual transitions in the 2ν<SUB>2</SUB>,
ν<SUB>2</SUB>+ν<SUB>4</SUB>, 2ν<SUB>4</SUB>, ν<SUB>1</SUB> and the
ν<SUB>3</SUB> bands from analyzing high-resolution, high S/N spectra
recorded at room temperature using two Fourier transform spectrometers
(FTS); the Bruker IFS 125 HR FTS at PNNL and the Kitt Peak FTS at the
National Solar Observatory in Arizona. In addition to line positions and
intensities, self-broadened half width and self-induced pressure-shift
coefficients were also measured for about 800 transitions for the
various bands. The strong Coriolis and other types of interactions
occurring among the various vibrational levels result in a large number
of forbidden transitions as well as cause A+A- splittings in transitions
with K″ that are multiples of 3. Line mixing was detected between
several A+A- pairs of transitions; and self- line mixing coefficients
were measured for several such pairs of transitions by applying the
off-diagonal relaxation matrix formalism of Levy et al.<SUP>1</SUP> A
multispectrum nonlinear least squares technique<SUP>2</SUP> employing a
non-Voigt line shape including line mixing and speed dependence was used
in fitting all the spectra simultaneously. Present results are compared
with other reported values. This research is supported by NASA’s
Outer Planets Research Program. References [1] A. Lévy et al., In
“Spectroscopy of the Earth’s Atmosphere and Interstellar Medium”,
Ed. K, Narahari Rao and A. Weber, Boston, Academic Press; p, 261-337
(1992). [2] D. C. Benner et al., J Quant. Spectrosc. Radiat. Transfer
53, 705, 1995.
---------------------------------------------------------
Title: Latitudinal Variation Of Upper Tropospheric NH3 On Saturn
Derived From Cassini/cirs Far-infrared Measurements
Authors: Hurley, Jane; Fletcher, L. N.; Irwin, P. G. J.; Calcutt,
S. B.; Sinclair, J. A.; Merlet, C.
2012DPS....4441212H Altcode:
Ammonia (NH3) has been detected both on Saturn and Jupiter, and although
its concentration and distribution has been well-studied on Jupiter, it
has proven more difficult to do so on Saturn due to higher sensitivity
requirements resulting from Saturn’s lower atmospheric temperatures
and the dominance of Saturn’s phosphine (PH3) which masks the NH3
signal. Using far-infrared measurements of Saturn taken by Cassini/CIRS
between February 2005 and December 2010, the latitudinal variations
of upper tropospheric NH3 on Saturn are studied. Sensitivity to NH3
in the far-infrared is explored to provide estimates of temperature,
para-H2 and PH3, from 2.5 cm-1 spectral resolution measurements
alone, 0.5 cm-1 spectral-resolution measurements alone, and 0.5 cm-1
measurements degraded to 2.5 cm-1 spectral resolution. The estimates of
NH3 from these three different datasets largely agree, although there
are notable differences using the high emission angle 0.5 cm-1 data,
which are asserted to result from a reduction in sensitivity at higher
emission angles. For low emission angles, the 0.5 cm-1-retrieved values
of NH3 can be used to reproduce the 2.5 cm-1 spectra with similar
efficacy as those derived directly from the 2.5 cm-1 resolution data
itself, and vice versa. Using low emission angle data, NH3 is observed
to have broad peak abundances at ±25° latitude, attributed to result
from condensation and/or photolytic processes. Lack of data coverage at
equatorial latitudes precludes analysis of NH3 abundance at less than
about 10° latitude. Noise levels are not sufficient to distinguish
fine zonal features, although it seems that NH3 cannot trace the zonal
belt/zone structure in the upper troposphere of Saturn.
---------------------------------------------------------
Title: Photochemistry in Saturn’s Ring Shadowed Atmosphere:
Production Rates of Key Atmospheric Molecules and Haze Observations
Authors: Edgington, Scott G.; Atreya, S. K.; Wilson, E. H.; West,
R. A.; Baines, K. H.; Bjoracker, G. L.; Fletcher, L. N.; Momary, T. W.
2012DPS....4441214E Altcode:
Cassini has been orbiting Saturn for over eight years. During this
epoch, the ring shadow has moved from shading a large portion of
the northern hemisphere (the ring plane was inclined by 24 degrees
relative to the Sun-Saturn vector) to shading mid-latitudes south
of the equator and continues southward. At its maximum extent,
the projection of the ring plane shadow onto Saturn can reach as
far as 48N ( 58N at the terminator). The net result, is that the
intensity of both ultraviolet and visible sunlight penetrating onto
any particular northern/southern latitude will vary depending on
Saturn’s tilt relative to the Sun and the optical thickness of
each ring system. Our previous work has examined the variation of
the solar flux as a function of solar inclination, i.e. season on
Saturn. Here we report on the impact of the oscillating ring shadow on
the photolysis and production rates of key hydrocarbons in Saturn’s
stratosphere and upper troposphere, including ethane, acetylene,
propane, benzene. We investigate the impact on production and loss
rates of the long-lived, photochemical hydrocarbons leading to haze
formation at several latitudes over one Saturn year. Similarly, we
assess the impact on the abundance of phosphine, a disequilibrium
species whose presence in the upper troposphere is a tracer of
convection processes in the deep atmosphere. Along with the above,
we present preliminary analysis of Cassini’s UVIS and VIMS datasets
that provide an estimate of the evolving haze content of the northern
hemisphere. The research described in this paper was carried out at
the Jet Propulsion Laboratory, California Institute of Technology,
under a contract with the National Aeronautics and Space Administration.
---------------------------------------------------------
Title: Seasonal And Non-seasonal Variations Of Jupiter’s Atmosphere
From Observations Of Thermal Emission, 1994-2011
Authors: Orton, Glenn S.; Fletcher, L.; Yanamandra-Fisher, P.;
Greathouse, T.; Fisher, B.; Greco, J.; Wakefield, L.; Snead, E.;
Boydstun, K.; Arzumanyan, G.; Christian, J.
2012DPS....4450001O Altcode:
We analyzed mid-infrared images of Jupiter’s thermal emission,
covering 1.5 Jovian years, acquired in discrete filters between 7.8 and
24.5 μm. The behavior of stratospheric ( 10-mbar) and tropospheric (
100-400 mbar) temperatures is generally consistent with predictions of
seasonal variability, with differences between 100-mbar temperatures
±50-60° from the equator on the order of ±2 K. Removing this effect,
there appear to be long-term periodicities of tropospheric temperatures,
with amplitude, phase and period dependent on latitude. Temperatures
near and south of the equator vary least (< ±1 K). At some
higher latitudes, the amplitudes vary by as much as ±2.5 K with peak
periodicities still showing a 12-year signature with other periods
ranging from 3 to 8 years. The 4-year variation of stratospheric
temperatures known as the quasi-quadrennial oscillation or “QQO”
(Leovy et al. 1991, Nature 354, 380) continued during this period. There
were no variations of zonal mean temperatures associated with any of
the “global upheaval” events that have produced dramatic changes
of Jupiter’s visible appearance and cloud cover, although there
are colder discrete regions associated with updrafts, e.g. the early
stages of the re-darkening (“revival”) of the South Equatorial Belt
(SEB) in late 2010. On the other hand increases in the visible albedos
(“fades”) of belts are accompanied by increases in cloudiness at 700
mbar (most likely an NH3 ice cloud layer) and higher pressures, together
with the mixing ratio of NH<SUB>3</SUB> gas near 400 mbar (above its
condensation level). These quantities decrease during re-darkening
(“revival”) episodes, during which we note exceptions to the
general correlation between dark albedos and minimal cloudiness. In
contrast to all these changes, the meridional distribution of the
240-mbar para-H<SUB>2</SUB> fraction appears to be time-invariant.
---------------------------------------------------------
Title: Variation of solar oscillation frequencies in solar cycle 23
and their relation to sunspot area and number
Authors: Jain, R.; Tripathy, S. C.; Watson, F. T.; Fletcher, L.;
Jain, K.; Hill, F.
2012A&A...545A..73J Altcode:
<BR /> Aims: Studying the long term evolution of the solar acoustic
oscillations is necessary for understanding how the large-scale solar
dynamo operates. In particular, an understanding of the solar cycle
variation in the frequencies of solar oscillations can provide a
powerful diagnostic tool for constraining various dynamo models. In
this work, we report the temporal evolution of solar oscillations
for the solar cycle 23, and correlate with solar magnetic activity
indices. <BR /> Methods: We use solar oscillation frequencies obtained
from the Michelson Doppler Imager on board the Solar and Heliospheric
Observatory, correlate them with the sunspot number provided by the
international sunspot number, R<SUB>I</SUB>, and compare them with the
sunspot number calculated with the Sunspot Tracking And Recognition
Algorithm (STARA). <BR /> Results: We find that the mean frequency
shifts correlate very well with the sunspot numbers obtained from
two different datasets. We also find a hysteresis-type behaviour
for the STARA sunspot area and mean magnetic field strength for the
different phases of the solar cycle. The increase in solar oscillation
frequencies precedes slightly the increase in total sunspot area and
the mean magnetic field strength for the solar cycle 23. We briefly
discuss the cyclic behaviour in the context of p-mode frequencies.
---------------------------------------------------------
Title: Habitability of the giant icy moons: current knowledge and
future insights from the JUICE mission
Authors: Grasset, O.; Prieto-Ballesteros, O.; Titov, D.; Erd, C.;
Bunce, E.; Coustenis, A.; Blanc, M.; Coates, A.; Fletcher, L.; van
Hoolst, T.; Hussmann, H.; Jaumann, R.; Krupp, N.; Tortora, P.; Tosi,
F.; Wielders, A.
2012epsc.conf..925G Altcode: 2012espc.conf..925G
Large satellites of gas giants, at orbits beyond the snow-line, such
as Jupiter or Saturn, can contain a large amount of water (almost 45%
in mass). Hydrospheres are extremely thick, ~600 km for Ganymede and
Callisto, and may possess liquid layers below the icy crust. Thus,
the Galilean satellites provide a conceptual basis within which new
theories for understanding habitability can be constructed. Measurements
from the Voyager and Galileo spacecraft revealed the potential of these
satellites in this context. The JUpiter Icy moons Explorer (JUICE) will
greatly enhance our understanding of their potential habitability. It
is known, even at Earth where life mostly depends on solar energy,
that habitats exist deep in the oceans in eternal darkness feeding on
chemical energy. Aqueous layers are suspected below the icy crusts
of the moons, which possess similar physical characteristics than
Earth's deep oceans. Since they are certainly very stable through time,
and because complex chemistry and energy sources may be available,
life may have originated within such subsurface habitats despite the
hostile surface conditions. Liquid water reservoirs have been proposed
on Ganymede, Europa and Callisto from geophysical models, based on
Galileo observations. These oceans that are covered by ice shells
exist independently of the input of stellar energy, and are located
well outside the conventional habitable zone of the Sun. Considering
the pressure range encountered within the icy moons, four different
scenarios can be defined. These result from varying thicknesses of the
water ice layers and the liquid ocean with respect to the silicate floor
(Figure 1). Case 2 in Figure 1 is highly probable for the largest moons
(Ganymede and Callisto), while case 3 is more probable for Europa
and smaller icy moons if they host liquid reservoirs such as has been
discovered at Enceladus. Europa's ocean is unique because it may be in
contact with the rock layer. This substrate may be geologically active
and affected by hydrothermal processes, similar to the terrestrial
sea floor. This may enhance habitability conditions since the rock
layer could release chemical elements and energy to the surrounding
water ocean. Differentiation of the rock could be responsible for
the presence of salts and other essential elements in the ocean, and
produce the low albedo terrains seen on the surface. An estimation of
the minimal thickness of the icy crust over the most active regions of
Europa is among the measurement goals of JUICE and this will provide
important constraints on the subsurface structure of the moon. On the
larger icy moons, Ganymede and Callisto, where internal pressures are
sufficient to allow for the formation of high pressure ice phases,
the existence of an ocean suggests that it should be enclosed between
thick ice layers. Chemical and energy exchanges between the rocky
layer and the ocean, which are so important for habitability, cannot
be ruled out but would imply efficient transport processes through the
thick high pressure icy layer. Such processes are indeed possible but
not as clearcut as the exchanges that can be envisaged for Europa. Icy
and liquid layers are probably not solely constituted of pure H2O. Many
other compounds such as salts, or CO2 have been observed on the surfaces
and may emerge from the deep interiors of the moons. Volatiles, organics
and minerals solidified from the aqueous cryo-magmas, could be detected
remotely from an orbiting spacecraft. Analysis of these materials
will give great insight to the physico-chemistry and composition
of the deep environments. But such organic matter and other surface
compounds will experience a different radiation environment at Europa
than at Ganymede (due to the difference in radial distance from Jupiter)
and thus may suffer different alteration processes, influencing their
detection on the surface. Measurements from terrains on both Europa
and Ganymede will allow a comparison of different radiation doses and
terrain ages from similar materials. JUICE will address key areas that
emerge in the study of habitable worlds around gas giants including
constraints on the volume of liquid water in the Jovian system. The
mission will also establish the inventory of biologically essential
elements on the surfaces of the icy moons, and determine the magnitude
of their transport among the moons which exchange material as a result
of volcanism, sputtering, and impacts. The mission may also allow us
to infer environmental properties such as the pH, salinity, and water
activity of the oceans and will investigate the effects of radiation
on the detectability of surface organics.
---------------------------------------------------------
Title: Temperature Structure and Composition of Uranus Derived from
Observations by ISO, Spitzer, Herschel, and Ground-Based Telescopes
Coupled with Photochemical Models
Authors: Orton, G.; Fletcher, L.; Feuchtgruber, H.; Lellouch, E.;
Moreno, R.; Encrenaz, T.; Hartogh, P.; Jarchow, C.; Moses, J.;
Burgdorg, M.; Hammel, H.; Line, M.; Mainzer, A.; Hofstadter, M.;
Sandell, G.; Dowell, D.
2012epsc.conf..289O Altcode: 2012espc.conf..289O
The combined power of absolutely calibrated photometry and spectroscopy
of Uranus has been combined to create self-consistent models of
its global-mean temperature profile, bulk composition, and vertical
distribution of gases.
---------------------------------------------------------
Title: The Evolution of Saturn's Stratospheric Beacon 2011-2012
Authors: Fletcher, L. N.; Hesman, B. E.; Achterberg, R. K.; Bjoraker,
G.; Gorius, N.; Irwin, P. G. J.; Hurley, J.; Sinclair, J.; Orton,
G. S.; Read, P. L.; Flasar, F. M.; Legarreta, J.; Garcia-Melendo,
E.; Sanchez-Lavega, A.
2012epsc.conf..313F Altcode: 2012espc.conf..313F
The slow warming of Saturn's springtime stratosphere was spectacularly
disrupted in 2010 by the eruption of a planetary-scale tropospheric
storm system [1-3]. The roiling, convective motions of the tropospheric
cloud decks had a dramatic influence on the atmospheric temperatures
and composition many hundreds of kilometers higher up, in Saturn's
stably stratified middle atmosphere. Energy transported from the
tropospheric storm was deposited in two warm stratospheric airmasses,
known as beacons B1 and B2 because of their brightness in thermal
infrared imaging. These features were observed throughout 2011 and
2012 using a combination of 7- 1000 μm spectroscopic mapping from
the Cassini Composite Infrared Spectrometer (CIRS, [1]) and filtered
7-25 μm imaging from the VLT/VISIR and IRTF/MIRSI thermal-infrared
instruments. These infrared observations are used to discuss the
motions, temperatures, composition, winds and stability of these newly
discovered phenomena in Saturn's stratosphere.
---------------------------------------------------------
Title: Examining Rotational Variability in the Upper Tropospheres
and Lower Stratospheres of Uranus and Neptune from Herschel PACS
OT1 Observations
Authors: Orton, G.; Feuchtgruber, H.; Fletcher, L.; Lellouch, E.;
Moreno, R.; Encrenaz, T.; Billebaud, F.; Cavalie, T.; Dobreijevcic,
M.; Decin, L.; Hartogh, P.; Jarchow, C.; Lara, L. M.; Liu, J.
2012epsc.conf..867O Altcode: 2012espc.conf..867O
The power of high-resolution submillimeter spectroscopy of Uranus
and Neptune was put to use to survey the rotational variability of
stratospheric and tropospheric constituents of their atmospheres.
---------------------------------------------------------
Title: Exploring the Atmospheres of the Ice Giants
Authors: Fletcher, L. N.; Orton, G. S.; Hofstadter, M.; Irwin,
P. G. J.; de Pater, I.
2012epsc.conf..862F Altcode: 2012espc.conf..862F
Of all the planets in our solar system, the two ice giants Uranus
and Neptune remain the least explored and poorly understood because
of their great distance from Earth. And yet they occupy a unique
position in the hierarchy of planetary types, being intermediate
between gas giants with their enormous hydrogen-helium envelopes, and
terrestrial-sized worlds and Super Earths. These ice giants, so-called
because their bulk compositions are dominated by heavier elements,
are a true frontier of our exploration of planetary atmospheres,
having been visited only once by Voyager 2 in 1986 and 1989, and may
be representative of a whole class of planetary objects throughout our
galaxy. Even though Earth-based observations (ISO, Spitzer, Herschel,
ground-based) have improved dramatically in the decades since Voyager 2,
many questions about this unexplored region of our Solar System remain
unanswered. Voyager revealed unexpected differences in the appearance,
composition, dynamics and chemistry between these two worlds, which
could ultimately help us to understand how planetary atmospheres form
and evolve as a function of distance from their host stars. This talk
will review our present understanding of ice giant atmospheres, and
assess the key questions to be answered by future exploration.
---------------------------------------------------------
Title: The application of new methane line absorption data to
Gemini-N/NIFS and KPNO/FTS observations of Uranus' near-infrared
spectrum
Authors: Irwin, P. G. J.; de Bergh, C.; Courtin, R.; Bézard, B.;
Teanby, N. A.; Davis, G. R.; Fletcher, L. N.; Orton, G. S.; Calcutt,
S. B.; Tice, D.; Hurley, J.
2012Icar..220..369I Altcode:
New line data describing the absorption of CH<SUB>4</SUB> and
CH<SUB>3</SUB>D from 1.26 to 1.71 μm (Campargue, A., Wang, L.,
Mondelain, D., Kassi, S., Bézard, B., Lellouch, E., Coustenis,
A., de Bergh, C., Hirtzig, M., Drossart, P. [2012]. Icarus
219, 110-128), building upon previous papers by Campargue
et al. (Campargue, A., Wang, L., Kassi, S., Masat, M.,
Votava, O. [2010]. J. Quant. Spectrosc. Radiat. Transfer
111, 1141-1151; Wang, L., Kassi, S., Campargue,
A. [2010]. J. Quant. Spectrosc. Radiat. Transfer 111,
1130-1140; Wang, L., Kassi, S., Liu, A.W., Hu, S.M., Campargue,
A. [2011]. J. Quant. Spectrosc. Radiat. Transfer 112, 937-951)) have
been applied to the analysis of Gemini-N/NIFS observations of Uranus
made in 2010 and compared with earlier disc-averaged observations
made by KPNO/FTS in 1982. The new line data are found to improve
greatly the fit to the observed spectra and present a huge advance
over previous methane absorption tables by allowing us to determine
the CH<SUB>3</SUB>D/CH<SUB>4</SUB> ratio and also start to break the
degeneracy between methane abundance and cloud top height. The best
fits are obtained if the cloud particles in the main cloud deck at
the 2-3 bar level become less scattering with wavelength across the
1.4-1.6 μm region and we have modelled this variation here by varying
the extinction cross-section and single-scattering albedo of the
particles. Applying the new line data to the NIFS spectra of Uranus,
we determine a new estimate of the CH<SUB>3</SUB>D/CH<SUB>4</SUB>
ratio of 2.9-0.5+0.9×10<SUP>-4</SUP>, which is consistent with
the estimate of de Bergh et al. (de Bergh, C., Lutz, B.L., Owen,
T., Brault, J., Chauville, J. [1986]. Astrophys. J. 311, 501-510)
of 3.6-2.8+3.6×10<SUP>-4</SUP>, made by fitting a disc-averaged
KPNO/FTS spectrum measured in 1982, but much better constrained. The
NIFS observations made in 2010 have been disc-averaged and compared with
the 1982 KPNO/FTS spectrum and found to be in excellent agreement. Using
k-tables fitted to the new line data, the central meridian observations
of Uranus' H-band spectrum (1.49-1.64 μm) made by Gemini-N/NIFS in 2010
have been reanalyzed. The use of the new methane absorption coefficients
and the modified scattering properties of the cloud particles in the
main cloud deck appears to break the degeneracy between cloud height and
methane abundance immediately above it in this spectral region and we
find that both vary with latitude across Uranus' disc. Overall, we find
that the main cloud deck becomes higher, but thinner from equator to
poles, with a local maximum in cloud top height in the circumpolar zones
at 45°N and 45°S. At the same time, using the 'D' temperature pressure
profile of Lindal et al. (Lindal, G.F., Lyons, J.R., Sweetnam, D.N.,
Eshleman, V.R., Hinson, D.P. [1987]. J. Geophys. Res. 92, 14987-15001)
and a deep methane abundance of 1.6% (Baines, K.H., Mickelson, M.E.,
Larson, L.E., Ferguson, D.W. [1995]. Icarus 144, 328-340) we find that
the relative humidity of methane is high near the equator (∼60%) and
decreases sharply towards the poles, except near the circumpolar zone
at 45°N, which has brightened steadily since 2007, and where there is
a local maximum in methane relative humidity. In tests conducted with
the warmer 'F1' profile of Sromovsky et al. (2011) we find a similar
variation of methane abundance above the main cloud, although for this
warmer temperature profile this abundance is dependent mostly on the
fitted deep methane mole fraction.
---------------------------------------------------------
Title: Charge-exchange Limits on Low-energy α-particle Fluxes in
Solar Flares
Authors: Hudson, H. S.; Fletcher, L.; MacKinnon, A. L.; Woods, T. N.
2012ApJ...752...84H Altcode: 2014arXiv1401.6477H
This paper reports on a search for flare emission via charge-exchange
radiation in the wings of the Lyα line of He II at 304 Å, as
originally suggested for hydrogen by Orrall & Zirker. Via this
mechanism a primary α particle that penetrates into the neutral
chromosphere can pick up an atomic electron and emit in the He
II bound-bound spectrum before it stops. The Extreme-ultraviolet
Variability Experiment on board the Solar Dynamics Observatory gives
us our first chance to search for this effect systematically. The
Orrall-Zirker mechanism has great importance for flare physics because
of the essential roles that particle acceleration plays; this mechanism
is one of the few proposed that would allow remote sensing of primary
accelerated particles below a few MeV nucleon<SUP>-1</SUP>. We study
10 events in total, including the γ-ray events SOL2010-06-12 (M2.0)
and SOL2011-02-24 (M3.5) (the latter a limb flare), seven X-class
flares, and one prominent M-class event that produced solar energetic
particles. The absence of charge-exchange line wings may point to a
need for more complete theoretical work. Some of the events do have
broadband signatures, which could correspond to continua from other
origins, but these do not have the spectral signatures expected from
the Orrall-Zirker mechanism.
---------------------------------------------------------
Title: Line Parameters of the PH_3 Pentad in the 4-5 μm Region
Authors: Devi, V. Malathy; Benner, D. Chris; Kleiner, I.; Sams, R. L.;
Blake, T. A.; Brown, Linda R.; Fletcher, L. N.
2012mss..confEFA08D Altcode:
Line positions, intensities and line shape parameters are reported
for four bands of phosphine between 2150 and 2400 cm<SUP>-1</SUP>
in order to improve the spectroscopic database for remote sensing
of the giant planets. Knowledge of PH_3 in this spectral region is
important for Cassini/VIMS exploration of dynamics and chemistry on
Saturn, as well as for interpreting the near-IR data from Juno and
ESA's proposed Jupiter mission. For this study, five high-resolution
(0.0023 cm<SUP>-1</SUP>), high signal-to-noise (>2000) spectra of
pure PH_3 were recorded at room temperature (298.2 K) with the Bruker
IFS 125HR Fourier transform spectrometer at Pacific Northwest National
Laboratory. Individual line parameters were retrieved by multispectrum
fitting of all five spectra simultaneously. Positions and intensities
were measured for over 3100 transitions. The rotational quantum numbers
of measured lines go as high as J”=16 and K”=15 in the ν_3 and
ν_1 bands; some lines of the weaker bands 2ν_4 and ν_2+ν_4 are
also reported. The measured positions and intensities are compared
to new theoretical calculations of the pentad. Lorentz self-broadened
width and pressure-induced shift coefficients of many transitions were
also obtained, along with speed dependence parameters. Line mixing
coefficients were determined for several A<SUP>+</SUP>A<SUP>-</SUP>
pairs of transitions for K”=3, 6, and 9. <P />Research described in
this paper was performed at the College of William and Mary and the
Jet Propulsion Laboratory, California Institute of Technology, under
contracts and cooperative agreements with the National Aeronautics and
Space Administration. L. Fletcher acknowledges support from a Glasstone
Science Fellowship. <P />D. C. Benner, C. P. Rinsland, V. Malathy Devi,
M. A. H. Smith and D. A. Atkins, JQSRT 53 (1995) 705-721.
---------------------------------------------------------
Title: Numerical Simulations of Chromospheric Hard X-Ray Source
Sizes in Solar Flares
Authors: Battaglia, M.; Kontar, E. P.; Fletcher, L.; MacKinnon, A. L.
2012ApJ...752....4B Altcode: 2012arXiv1204.1151B
X-ray observations are a powerful diagnostic tool for transport,
acceleration, and heating of electrons in solar flares. Height and
size measurements of X-ray footpoint sources can be used to determine
the chromospheric density and constrain the parameters of magnetic
field convergence and electron pitch-angle evolution. We investigate
the influence of the chromospheric density, magnetic mirroring, and
collisional pitch-angle scattering on the size of X-ray sources. The
time-independent Fokker-Planck equation for electron transport is
solved numerically and analytically to find the electron distribution
as a function of height above the photosphere. From this distribution,
the expected X-ray flux as a function of height, its peak height, and
full width at half-maximum are calculated and compared with RHESSI
observations. A purely instrumental explanation for the observed
source size was ruled out by using simulated RHESSI images. We find
that magnetic mirroring and collisional pitch-angle scattering tend
to change the electron flux such that electrons are stopped higher in
the atmosphere compared with the simple case with collisional energy
loss only. However, the resulting X-ray flux is dominated by the
density structure in the chromosphere and only marginal increases in
source width are found. Very high loop densities (>10<SUP>11</SUP>
cm<SUP>-3</SUP>) could explain the observed sizes at higher energies,
but are unrealistic and would result in no footpoint emission below
about 40 keV, contrary to observations. We conclude that within
a monolithic density model the vertical sizes are given mostly by
the density scale height and are predicted smaller than the RHESSI
results show.
---------------------------------------------------------
Title: Flare Ribbons In The Early Phase Of An SDO Flare: Emission
Measure And Energetics
Authors: Fletcher, Lyndsay; Hannah, I. G.; Hudson, H. S.; Innes, D. E.
2012AAS...22050902F Altcode:
We report on the M1.0 flare of 7th August 2010, which displayed
extended early phase chromospheric ribbons, well observed by SDO/AIA
and RHESSI. Most large flares saturate rapidly in the high-temperature
AIA channels, however this event could be followed in unsaturated AIA
images for ten minutes in the build-up to and first few minutes of the
impulsive phase. Analysis of GOES, RHESSI and SDO/AIA demonstrates
the presence of high temperature ( 10MK), compact plasma volumes in
the chromospheric flare ribbons, with a column emission measure of
on average 3-7 x 10<SUP>28</SUP> cm<SUP>-5</SUP>. We construct a
time-resolved energy budget for the ribbon plasma, including also
SDO/EVE data, and discuss the implications of the observed ribbon
properties for flare energisation. <P />This work was supported by
the UK’s Science and Technology Facilities Council (ST/1001801),
and by the European Commission through the FP7 HESPE project
(FP7-2010-SPACE-263086).
---------------------------------------------------------
Title: Solar Flare Observations of the EUV Continua
Authors: Milligan, Ryan O.; Chamberlin, P.; Hudson, H.; Woods, T.;
Mathioudakis, M.; Fletcher, L.; Kowalski, A.; Keenan, F.
2012AAS...22052105M Altcode:
Recent solar flare simulations suggest that the energy deposited in the
chromosphere by nonthermal electrons during a flare's impulsive phase
is re-emitted in the form of recombination (free-bound) continua, in
particular, the Lyman, Balmer, and Paschen continua of hydrogen, and
the He I and He II continua (Allred et al. 2005). However, definitive
observations of free-bound emission during solar flares have been scarce
in recent years as many modern, space-based instruments do not have
the required sensitivity, wavelength coverage, or duty cycle. With
the launch of SDO, these observations are now routinely available
thanks to the EUV Variability Experiment (EVE) instrument. Here we
present unambiguous, spectrally and temporally resolved detections of
enhanced free-free and free-bound continua during the first X-class
solar flare of Solar Cycle 24. While we find that the flare energy
in the EVE spectral range amounts to at most a few percent of the
total flare energy, these findings highlight the capability of EVE
in giving us the first comprehensive look at these diagnostically
important continuum components.
---------------------------------------------------------
Title: Solar Chromospheric Flares: Energy Release, Transport and
Radiation
Authors: Fletcher, L.
2012ASPC..456..183F Altcode: 2012arXiv1207.0384F
This paper presents an overview of some recent observational and
theoretical results on solar flares, with an emphasis on flare
impulsive-phase chromospheric properties, including: electron
diagnostics, optical and UV emission, and discoveries made by the
Hinode mission, especially in the EUV. A brief perspective on future
observations and theoretical requirements is also given.
---------------------------------------------------------
Title: Dynamical Heating In Flares Observed With SDO/AIA & RHESSI
Authors: Hannah, Iain; Fletcher, L.; Kontar, E. P.
2012AAS...22032202H Altcode:
The spatial and temporal resolution of SDO/AIA data presents an
unprecedented view of the dynamics of heating during solar flares. This
combined with the non-thermal energetics from RHESSI hard X-ray imaging
and spectroscopy provides constraints on the flaring energy release. The
recently implemented regularized inversion method (Hannah & Kontar
A&A 2012) robustly recovers the underlying thermal distribution (the
Differential Emission Measure, DEM) of the coronal plasma from SDO/AIA
images. Crucially it is not limited to the isothermal or Gaussian-model
approximation that some other approaches depend upon. Our method
provides the uncertainties in the DEM and is computationally quick,
producing DEMs per pixel for a series of SDO/AIA images allowing
temperature maps and movies to be created. We use the regularized
inversion method to study the temporal and spatial evolution of the
plasma heating in flares and show how the non-thermal energy relates
to this. We also investigate how the calibration errors/uncertainties
affect the inferred DEMs and errors.
---------------------------------------------------------
Title: Observations of upper tropospheric acetylene on Saturn:
No apparent correlation with 2000 km-sized thunderstorms
Authors: Hurley, J.; Irwin, P. G. J.; Fletcher, L. N.; Moses, J. I.;
Hesman, B.; Sinclair, J.; Merlet, C.
2012P&SS...65...21H Altcode:
Thunderstorm activity has been observed on Saturn via radio
emissions from lightning discharges and optical detections of the
lightning flashes on the planet's nightside. Thunderstorms provide
extreme environments in which specific atmospheric chemistry can be
induced-namely through energy release via lightning discharges, and
fast vertical transport resulting in rapid advection of tropospheric
species. It is thus theorised that certain atmospheric trace species -
such as C<SUB>2</SUB>H<SUB>2</SUB>, HCN, and CO - can be generated in
the troposphere by large bursts of energy in the form of lightning,
and transported upward towards the upper troposphere by the extreme
dynamics of thunderstorms, where they should be observable by satellite
instruments. In this work, high-spectral-resolution Cassini/CIRS
observations from October 2005 through April 2009 are used to
study whether there is an observable increase in upper tropospheric
acetylene in regions of known normal thunderstorm activity. Using both
individual measurements in which there is known thunderstorm activity,
as well as large coadditions of data to study latitudinal-dependencies
over the full disc, no systematic enhancement in upper tropospheric
(100 mbar) C<SUB>2</SUB>H<SUB>2</SUB> was detected around regions
in which there are known occurrences of normally sized (2000 km)
thunderstorms, or in normally sized thunderstorm-prone regions such as
40°S. It is likely that the magnitude of the enhancement theorised
is too generous or that enhancements are not advected into the upper
troposphere as vertical mixing rates in models would suggest, since
Cassini/CIRS can only detect C<SUB>2</SUB>H<SUB>2</SUB> above the
200 mbar level-although the massive northern hemisphere thunderstorm
of 2010/2011 seems able to decrease stratospheric concentrations
of C<SUB>2</SUB>H<SUB>2</SUB>. From this, it can be asserted that
lightning from normal thunderstorm activity cannot be the key
source for upper tropospheric C<SUB>2</SUB>H<SUB>2</SUB> on Saturn,
since the upper-tropospheric concentrations retrieved agree with the
concentrations stemming from the photolysis of CH<SUB>4</SUB> (2-3 ppbv)
from solar radiation penetrating through the Saturnian atmosphere,
with an upper limit for lightning-induced C<SUB>2</SUB>H<SUB>2</SUB>
volume mixing ratio of 10<SUP>-9</SUP>.
---------------------------------------------------------
Title: Investigating the Structure of Impulsive Phase Footpoints
Authors: Graham, David; Hannah, I.; Fletcher, L.; Milligan, R.
2012AAS...22050903G Altcode:
The location of flare heating in the solar atmosphere is imperative
to understanding the heating mechanism. The differential emission
measure is an important tool in understanding the properties of flaring
plasma. However, determining the DEM of impulsive phase footpoints
has been difficult in the past without sufficient spatial resolution
to resolve footpoints from loop structures, and a lack of spectral
and temporal coverage. We use the capabilities of Hinode/EIS to
present the first DEMs from the impulsive phase of a number of flare
footpoints. Observations were chosen from a period when EIS telemetry
was at its best and analysed using a new regularised inversion method
(Hannah & Kontar 2012). We find a peak temperature in the DEM
of around 7 MK with emission measures peaking between 10^28 and
10^29 cm-5, indicating a substantial presence of plasma at 'coronal'
temperatures within the footpoint. In addition to the DEM, we perform
a wide range of density diagnostics from transition region to coronal
temperatures, allowing us estimate where in the atmosphere the EUV
emission originates.
---------------------------------------------------------
Title: Break up of returning plasma after the 7 June 2011 filament
eruption by Rayleigh-Taylor instabilities
Authors: Innes, D. E.; Cameron, R. H.; Fletcher, L.; Inhester, B.;
Solanki, S. K.
2012A&A...540L..10I Altcode: 2012arXiv1202.4981I
Context. A prominence eruption on 7 June 2011 produced spectacular
curtains of plasma falling through the lower corona. At the solar
surface they created an incredible display of extreme ultraviolet
brightenings. <BR /> Aims: To identify and analyze some of the local
instabilities which produce structure in the falling plasma. <BR />
Methods: The structures were investigated using SDO/AIA 171 Å and
193 Å images in which the falling plasma appeared dark against
the bright coronal emission. <BR /> Results: Several instances of
the Rayleigh-Taylor instability were investigated. In two cases the
Alfvén velocity associated with the dense plasma could be estimated
from the separation of the Rayleigh-Taylor fingers. A second type of
feature, which has the appearance of self-similar branching horns was
discussed. <P />Appendix A and two movies are available in electronic
form at <A href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
Title: Commission 10: Solar Activity
Authors: van Driel-Gesztelyi, Lidia; Schrijver, Carolus J.; Klimchuk,
James A.; Charbonneau, Paul; Fletcher, Lyndsay; Hasan, S. Sirajul;
Hudson, Hugh S.; Kusano, Kanya; Mandrini, Cristina H.; Peter, Hardi;
Vršnak, Bojan; Yan, Yihua
2012IAUTA..28...69V Altcode:
Commission 10 of the International Astronomical Union has more than
650 members who study a wide range of activity phenomena produced by
our nearest star, the Sun. Solar activity is intrinsically related
to solar magnetic fields and encompasses events from the smallest
energy releases (nano- or even picoflares) to the largest eruptions
in the Solar System, coronal mass ejections (CMEs), which propagate
into the Heliosphere reaching the Earth and beyond. Solar activity is
manifested in the appearance of sunspot groups or active regions, which
are the principal sources of activity phenomena from the emergence of
their magnetic flux through their dispersion and decay. The period
2008-2009 saw an unanticipated extended solar cycle minimum and
unprecedentedly weak polar-cap and heliospheric field. Associated with
that was the 2009 historical maximum in galactic cosmic rays flux since
measurements begun in the middle of the 20th Century. Since then Cycle
24 has re-started solar activity producing some spectacular eruptions
observed with a fleet of spacecraft and ground-based facilities. In
the last triennium major advances in our knowledge and understanding
of solar activity were due to continuing success of space missions as
SOHO, Hinode, RHESSI and the twin STEREO spacecraft, further enriched
by the breathtaking images of the solar atmosphere produced by the
Solar Dynamic Observatory (SDO) launched on 11 February 2010 in the
framework of NASA's Living with a Star program. In August 2012, at the
time of the IAU General Assembly in Beijing when the mandate of this
Commission ends, we will be in the unique position to have for the
first time a full 3-D view of the Sun and solar activity phenomena
provided by the twin STEREO missions about 120 degrees behind and
ahead of Earth and other spacecraft around the Earth and ground-based
observatories. These new observational insights are continuously
posing new questions, inspiring and advancing theoretical analysis
and modelling, improving our understanding of the physics underlying
magnetic activity phenomena. Commission 10 reports on a vigorously
evolving field of research produced by a large community. The number
of refereed publications containing `Sun', `heliosphere', or a synonym
in their abstracts continued the steady growth seen over the preceding
decades, reaching about 2000 in the years 2008-2010, with a total of
close to 4000 unique authors. This report, however, has its limitations
and it is inherently incomplete, as it was prepared jointly by the
members of the Organising Committee of Commission 10 (see the names
of the primary contributors to the sections indicated in parentheses)
reflecting their fields of expertise and interest. Nevertheless, we
believe that it is a representative sample of significant new results
obtained during the last triennium in the field of solar activity.
---------------------------------------------------------
Title: Solar Particle Acceleration Radiation and Kinetics (SPARK). A
mission to understand the nature of particle acceleration
Authors: Matthews, Sarah A.; Williams, David R.; Klein, Karl-Ludwig;
Kontar, Eduard P.; Smith, David M.; Lagg, Andreas; Krucker, Sam;
Hurford, Gordon J.; Vilmer, Nicole; MacKinnon, Alexander L.; Zharkova,
Valentina V.; Fletcher, Lyndsay; Hannah, Iain G.; Browning, Philippa
K.; Innes, Davina E.; Trottet, Gerard; Foullon, Clare; Nakariakov,
Valery M.; Green, Lucie M.; Lamoureux, Herve; Forsyth, Colin; Walton,
David M.; Mathioudakis, Mihalis; Gandorfer, Achim; Martinez-Pillet,
Valentin; Limousin, Olivier; Verwichte, Erwin; Dalla, Silvia; Mann,
Gottfried; Aurass, Henri; Neukirch, Thomas
2012ExA....33..237M Altcode: 2011ExA...tmp..124M
Energetic particles are critical components of plasma populations
found throughout the universe. In many cases particles are accelerated
to relativistic energies and represent a substantial fraction of
the total energy of the system, thus requiring extremely efficient
acceleration processes. The production of accelerated particles
also appears coupled to magnetic field evolution in astrophysical
plasmas through the turbulent magnetic fields produced by diffusive
shock acceleration. Particle acceleration is thus a key component
in helping to understand the origin and evolution of magnetic
structures in, e.g. galaxies. The proximity of the Sun and the range
of high-resolution diagnostics available within the solar atmosphere
offers unique opportunities to study the processes involved in particle
acceleration through the use of a combination of remote sensing
observations of the radiative signatures of accelerated particles, and
of their plasma and magnetic environment. The SPARK concept targets the
broad range of energy, spatial and temporal scales over which particle
acceleration occurs in the solar atmosphere, in order to determine how
and where energetic particles are accelerated. SPARK combines highly
complementary imaging and spectroscopic observations of radiation from
energetic electrons, protons and ions set in their plasma and magnetic
context. The payload comprises focusing-optics X-ray imaging covering
the range from 1 to 60 keV; indirect HXR imaging and spectroscopy
from 5 to 200 keV, γ-ray spectroscopic imaging with high-resolution
LaBr<SUB>3</SUB> scintillators, and photometry and source localisation
at far-infrared wavelengths. The plasma environment of the regions
of acceleration and interaction will be probed using soft X-ray
imaging of the corona and vector magnetography of the photosphere
and chromosphere. SPARK is designed for solar research. However,
in addition it will be able to provide exciting new insights into the
origin of particle acceleration in other regimes, including terrestrial
gamma-ray flashes (TGF), the origin of γ-ray bursts, and the possible
existence of axions.
---------------------------------------------------------
Title: Examining Rotational Variability in the Upper Tropospheres
and Lower Stratospheres of Uranus and Neptune from Herschel PACS
OT1 Observations: Implications for the Stability of Temperature and
Compositional Structure
Authors: Orton, G.; Feuchtgruber, H.; Fletcher, L.; Lellouch, E.;
Moreno, R.; Billebaud, F.; Cavalie, T.; Decin, L.; Dobreijecvic, M.;
Encrenaz, T.; Hartogh, P.; Jarchow, C.; Lara, L. M.; Liu, J.
2012EGUGA..14.3434O Altcode:
The power of high-resolution submillimeter spectroscopy of Uranus
and Neptune was put to use to survey the rotational variability of
stratospheric and tropospheric constituents of their atmospheres. These
observations were motivated by the surprising discovery of as much as
12% rotational variability of emission from stratospheric constituents
in the atmosphere of Uranus by the Spitzer Infrared Spectrometer
and the detection of spatial variability in thermal images of
Neptune's stratospheric emission (Orton et al. 2007, Astron. &
Astrophys 473, L3). Our observing program consisted of three separate
sequences of observations to look at the strongest lines of H2O in the
high-resolution PACS spectra of both planets, whose upwelling radiance
emerges from the same vertical region as the Spitzer IRS observations
of Uranus and ground-based images of Neptune, and the strongest line
of CH4 in the PACS spectrum of Neptune. We omitted measurements of
CH4 lines in Uranus, which are almost non-detectable. We added the
strongest HD line in Uranus to measure variability of tropospheric
temperatures that could modulate stratospheric CH4 abundances through
local cold-trapping and the strongest two HD lines in Neptune (Lellouch
et al. 2010, Astron. & Astrophys. 518, L152) that determine both
the tropopause temperature to limit local cold-trapping efficacy and
the lower stratospheric temperature, to help differentiate between
longitudinal variability of stratospheric H2O and CH4 abundances
vs. temperatures. These were repeated over the 17-hour interval that
is common to the equatorial rotation periods of both Uranus and
Neptune. Although these lines had already been observed in Uranus
and Neptune by PACS, no repeat measurements had ever been made to
determine longitudinal variability. The observations were consistent
with previous measurements, but no significant rotational variability
was detected. It is possible that the absence of rotational variability
in the HD and CH4 lines is because variability is confined to very
low pressures, e.g. much lower than a microbar. However, the absence
of variable emission from high-altitude exogenic H2O vapor is harder
to explain, unless the variability seen in Uranus by Spitzer and in
Neptune from the VLT, is not the result of variations in temperature
by in the hydrocarbon abundances. Alternatively, the stratospheres
of both planets are variable in time. The cause of such variability
is unknown, but spatially confined outbursts have been detected in
the visible and near infrared, and they may have as much influence on
the stratosphere of Uranus as the great springtime storm in Saturn's
northern hemisphere, creating a strong, localized "beacon" of thermal
radiation (cf. Fletcher et al. 2011, Science, 332,1413) that could
dominate the emission observed over the hemisphere.
---------------------------------------------------------
Title: Observations of Enhanced Extreme Ultraviolet Continua during
an X-Class Solar Flare Using SDO/EVE
Authors: Milligan, Ryan O.; Chamberlin, Phillip C.; Hudson, Hugh S.;
Woods, Thomas N.; Mathioudakis, Mihalis; Fletcher, Lyndsay; Kowalski,
Adam F.; Keenan, Francis P.
2012ApJ...748L..14M Altcode: 2012arXiv1202.1731M
Observations of extreme ultraviolet (EUV) emission from an X-class solar
flare that occurred on 2011 February 15 at 01:44 UT are presented,
obtained using the EUV Variability Experiment (EVE) on board the
Solar Dynamics Observatory. The complete EVE spectral range covers
the free-bound continua of H I (Lyman continuum), He I, and He II,
with recombination edges at 91.2, 50.4, and 22.8 nm, respectively. By
fitting the wavelength ranges blueward of each recombination edge
with an exponential function, light curves of each of the integrated
continua were generated over the course of the flare, as was emission
from the free-free continuum (6.5-37 nm). The He II 30.4 nm and Lyα
121.6 nm lines, and soft X-ray (SXR; 0.1-0.8 nm) emission from GOES are
also included for comparison. Each free-bound continuum was found to
have a rapid rise phase at the flare onset similar to that seen in the
25-50 keV light curves from RHESSI, suggesting that they were formed
by recombination with free electrons in the chromosphere. However,
the free-free emission exhibited a slower rise phase seen also in the
SXR emission from GOES, implying a predominantly coronal origin. By
integrating over the entire flare the total energy emitted via
each process was determined. We find that the flare energy in the
EVE spectral range amounts to at most a few percent of the total
flare energy, but EVE gives us a first comprehensive look at these
diagnostically important continuum components.
---------------------------------------------------------
Title: Momentum Distribution in Solar Flare Processes
Authors: Hudson, H. S.; Fletcher, L.; Fisher, G. H.; Abbett, W. P.;
Russell, A.
2012SoPh..277...77H Altcode:
We discuss the consequences of momentum conservation in processes
related to solar flares and coronal mass ejections (CMEs), in particular
describing the relative importance of vertical impulses that could
contribute to the excitation of seismic waves ("sunquakes"). The
initial impulse associated with the primary flare energy transport
in the impulsive phase contains sufficient momentum, as do the
impulses associated with the acceleration of the evaporation flow (the
chromospheric shock) or the CME itself. We note that the deceleration
of the evaporative flow, as coronal closed fields arrest it, will tend
to produce an opposite impulse, reducing the energy coupling into
the interior. The actual mechanism of the coupling remains unclear
at present.
---------------------------------------------------------
Title: The role of filament activation in a solar eruption
Authors: Rubio da Costa, F.; Zuccarello, F.; Fletcher, L.; Romano,
P.; Labrosse, N.
2012A&A...539A..27R Altcode: 2014arXiv1412.1858R
Context. Observations show that the mutual relationship between
filament eruptions and solar flares cannot be described in terms of an
unique scenario. In some cases, the eruption of a filament appears to
trigger a flare, while in others the observations are more consistent
with magnetic reconnection that produces both the flare observational
signatures (e.g., ribbons, plasma jets, post-flare loops, etc.) and
later the destabilization and eruption of a filament. <BR /> Aims:
Contributing to a better comprehension of the role played by filament
eruptions in solar flares, we study an event which occurred in NOAA
8471, where a flare and the activation of (at least) two filaments
were observed on 28 February 1999. <BR /> Methods: By using imaging
data acquired in the 1216, 1600, 171 and 195 Å TRACE channels and by
BBSO in the continnum and in the Hα line, a morphological study of
the event is carried out. Moreover, using TRACE 1216 and 1600 Å data,
an estimate of the "pure" Lyα power is obtained. The extrapolation of
the magnetic field lines is done using the SOHO/MDI magnetograms and
assuming a potential field. <BR /> Results: Initially an area hosting a
filament located over a δ spot becomes brighter than the surroundings,
both in the chromosphere and in the corona. This area increases in
brightness and extension, eventually assuming a two-ribbon morphology,
until it reaches the eastern part of the active region. Here a second
filament becomes activated and the brightening propagates to the south,
passing over a large supergranular cell. The potential magnetic field
extrapolation indicates that the field line connectivity changes
after the flare. <BR /> Conclusions: The event is triggered by the
destabilization of a filament located between the two polarities
of a δ spot. This destabilization involves the magnetic arcades
of the active region and causes the eruption of a second filament,
that gives rise to a CME and to plasma motions over a supergranular
cell. We conclude that in this event the two filaments play an active
and decisive role, albeit in different stages of the phenomenon,
in fact the destabilization of one filament causes brightenings,
reconnection and ribbons, while the second one, whose eruption is caused
by the field reconfiguration resulting from the previous reconnection,
undergoes the greatest changes and causes the CME.
---------------------------------------------------------
Title: JUpiter ICy moons Explorer (JUICE): An ESA L-Class Mission
Candidate to the Jupiter System
Authors: Dougherty, M.; Grasset, O.; Erd, C.; Titov, D.; Bunce,
E.; Coustenis, A.; Blanc, M.; Coates, A.; Drossart, P.; Fletcher,
L.; Hussmann, H.; Jaumann, R.; Krupp, N.; Prieto-Ballesteros, O.;
Tortora, P.; Tosi, F.; van Hoolst, T.
2012LPI....43.1806D Altcode:
JUICE is the next step for an in-depth exploration of the geophysical
and environmental characteristics of Ganymede and exploration of
Callisto and Europa, and will provide an in-depth understanding of
Jupiter’s atmosphere and magnetosphere.
---------------------------------------------------------
Title: Further seasonal changes in Uranus’ cloud structure observed
by Gemini-North and UKIRT
Authors: Irwin, P. G. J.; Teanby, N. A.; Davis, G. R.; Fletcher,
L. N.; Orton, G. S.; Calcutt, S. B.; Tice, D. S.; Hurley, J.
2012Icar..218...47I Altcode:
Near-infrared observations of Uranus were made in October/November 2010
with the Gemini-North telescope in Hawaii, using NIFS, an integral field
spectrograph, and the NIRI instrument in imaging mode. Observations
were acquired using adaptive optics and have a spatial resolution of
approximately 0.1-0.2″. <P />The observed spectra along Uranus’
central meridian were analysed using a multiple-scattering retrieval
algorithm to infer the vertical/latitudinal variation in cloud
optical depth, which we compare with previous observations made by
Gemini-North/NIFS in 2009 and UKIRT/UIST observations made between 2006
and 2008. Assuming a continuous distribution of small particles (r ∼
1 μm, and refractive index of 1.4 + 0i) with the single scattering
albedo set to 0.75 and using a Henyey-Greenstein phase function with
asymmetry parameter set to 0.7 at all wavelengths and latitudes, the
retrieved cloud density profiles show that the north polar zone at
45°N has continued to steadily brighten while the south polar zone at
45°S has continued to fade. As with our previous analyses we find that,
assuming that the methane vertical profile is the same at all latitudes,
the clouds forming these polar zones at 45°N and 45°S lie at slightly
lower pressures than the clouds at more equatorial latitudes. However,
we also find that the Gemini data can be reproduced by assuming that
the main cloud remains fixed at ∼2 bar at all latitudes and adjusting
the relative humidity of methane instead. In this case we find that
the deep cloud is still more opaque at the equator and at the zones at
45°N and 45°S and shows the same seasonal trends as when the methane
humidity remain fixed. However, with this approach the relative humidity
of methane is seen to rise sharply from approximately 20% at polar
latitudes to values closer to 80% for latitudes equatorward of 45°S
and 45°N, consistent with the analysis of 2002 HST observations by
Karkoschka and Tomasko (Karkoschka, E., Tomasko, M. [2009]. Icarus 202,
287-302), with a possible indication of seasonal variability. Overall,
Uranus appeared to be less convectively active in 2010 than in the
previous 4 years, supporting the conclusion that now the northern
spring equinox (which occurred in 2007) has passed, the atmosphere is
settling back into the more quiescent state seen by Voyager 2 in 1986.
---------------------------------------------------------
Title: Sub-millimetre spectroscopy of Saturn's trace gases from
Herschel/SPIRE
Authors: Fletcher, L. N.; Swinyard, B.; Salji, C.; Polehampton, E.;
Fulton, T.; Sidher, S.; Lellouch, E.; Moreno, R.; Orton, G.; Cavalié,
T.; Courtin, R.; Rengel, M.; Sagawa, H.; Davis, G. R.; Hartogh, P.;
Naylor, D.; Walker, H.; Lim, T.
2012A&A...539A..44F Altcode:
<BR /> Aims: We provide an extensive new sub-millimetre survey of
the trace gas composition of Saturn's atmosphere using the broad
spectral range (15-51 cm<SUP>-1</SUP>) and high spectral resolution
(0.048 cm<SUP>-1</SUP>) offered by Fourier transform spectroscopy
by the Herschel/SPIRE instrument (Spectral and Photometric Imaging
REceiver). Observations were acquired in June 2010, shortly after
equinox, with negligible contribution from Saturn's ring emission. <BR
/> Methods: Tropospheric temperatures and the vertical distributions
of phosphine and ammonia are derived using an optimal estimation
retrieval algorithm to reproduce the sub-millimetre data. The abundance
of methane, water and upper limits on a range of different species are
estimated using a line-by-line forward model. <BR /> Results: Saturn's
disc-averaged temperature profile is found to be quasi-isothermal
between 60 and 300 mbar, with uncertainties of 7 K due to the absolute
calibration of SPIRE. Modelling of PH<SUB>3</SUB> rotational lines
confirms the vertical profile derived in previous studies and shows
that negligible PH<SUB>3</SUB> is present above the 10- to 20-mbar
level. The upper tropospheric abundance of NH<SUB>3</SUB> appears
to follow a vapour pressure distribution throughout the region of
sensitivity in the SPIRE data, but the degree of saturation is highly
uncertain. The tropospheric CH<SUB>4</SUB> abundance and Saturn's bulk
C/H ratio are consistent with Cassini studies. We improve the upper
limits on several species (H<SUB>2</SUB>S, HCN, HCP and HI); provide
the first observational constraints on others (SO<SUB>2</SUB>, CS,
methanol, formaldehyde, CH<SUB>3</SUB>Cl); and confirm previous upper
limits on HF, HCl and HBr. Stratospheric emission from H<SUB>2</SUB>O
is suggested at 36.6 and 38.8 cm<SUP>-1</SUP> with a 1σ significance
level, and these lines are used to derive mole fractions and column
abundances consistent with ISO and SWAS estimations a decade earlier.
---------------------------------------------------------
Title: Optimal estimation retrievals of the atmospheric structure
and composition of HD 189733b from secondary eclipse spectroscopy
Authors: Lee, J. -M.; Fletcher, L. N.; Irwin, P. G. J.
2012MNRAS.420..170L Altcode: 2011arXiv1110.2934L; 2011MNRAS.tmp.1983L
Recent spectroscopic observations of transiting hot Jupiters have
permitted the derivation of the thermal structure and molecular
abundances of H<SUB>2</SUB>O, CO<SUB>2</SUB>, CO and CH<SUB>4</SUB>
in these extreme atmospheres. Here, for the first time, we apply the
technique of optimal estimation to determine the thermal structure
and composition of an exoplanet by solving the inverse problem. The
development of a suite of radiative transfer and retrieval tools
for exoplanet atmospheres is described, building upon a retrieval
algorithm which is extensively used in the study of our own Solar
system. First, we discuss the plausibility of detection of different
molecules in the dayside atmosphere of HD 189733b and the best-fitting
spectrum retrieved from all publicly available sets of secondary
eclipse observations between 1.45 and 24 μm. Additionally, we use
contribution functions to assess the vertical sensitivity of the
emission spectrum to temperatures and molecular composition. Over
the altitudes probed by the contribution functions, the retrieved
thermal structure shows an isothermal upper atmosphere overlying a
deeper adiabatic layer (temperature decreasing with altitude), which
is consistent with previously reported dynamical and observational
results. The formal uncertainties on retrieved parameters are estimated
conservatively using an analysis of the cross-correlation functions and
the degeneracy between different atmospheric properties. The formal
solution of the inverse problem suggests that the uncertainties on
retrieved parameters are larger than suggested in previous studies,
and that the presence of CO and CH<SUB>4</SUB> is only marginally
supported by the available data. Nevertheless, by including as broad
a wavelength range as possible in the retrieval, we demonstrate that
available spectra of HD 189733b can constrain a family of potential
solutions for the atmospheric structure.
---------------------------------------------------------
Title: Retrieval of Atmosphere Structure and Composition of Exoplanets
from Transit Spectroscopy
Authors: Lee, Jae-Min; Fletcher, L. N.; Irwin, P. G. J.
2012AAS...21940502L Altcode:
Recent spectroscopic observations of transiting exoplanets of HD
189733b, HD 209458b, GJ 436b and GJ 1214b provide the best chance
of characterizing the thermal structure and composition of their
atmospheres. Here we have applied an optimal estimation retrieval
architecture to fit exoplanet spectra to determine the thermal
structure and composition by solving the inverse problem. The
development of a suite of radiative transfer and retrieval tools for
exoplanet atmospheres is explained, building upon a rapid correlated-k
approximation and a retrieval algorithm extensively used in our own
solar system. With these tools we discuss the best-fitting spectrum to
the measurements with the best-estimated solution (i.e. the maximum
a posteriori solution) for the vertical temperature structure and
molecular abundances. Additionally, the contribution functions and
the vertical sensitivity to the molecules are fully utilized to
interpret transmission and emission spectra, probing the structure
and composition of the atmosphere. Furthermore, the analysis of the
cross-correlation functions permits us to quantify the uncertainties
in the degeneracy between the retrieved atmospheric properties based
on the current quality of the data. This sheds light on the range
of diverse interpretations offered by other studies so far. It also
allows us to scrutinize further atmospheric features by maximizing
the capability of the current retrieval algorithm and to demonstrate
the benefit of using as broad a spectral range as possible, with clear
implications for the next generation of exoplanetary missions.
---------------------------------------------------------
Title: Relationship between an M6.6 solar flare and subsequent
filament activations.
Authors: Rubio da Costa, F.; Zuccarello, F.; Romano, P.; Fletcher,
L.; Labrosse, N.
2012MSAIS..19..113R Altcode:
We study an event which occurred in NOAA 8471, where an M6.6 flare
and the activation of two filaments were observed on 28 February
1999. A multi-wavelength study allows us to investigate the behavior
of the several features observed at different atmospheric levels, that
might be used to answer to the question whether and in what conditions
the eruption of filaments can play an active or a passive role in the
flare occurrence. Imaging data were acquired by BBSO in the Halpha line
and by TRACE in the 1216, 1600, 171 and 195 Å channels, allowing us
to deduce the morphology and temporal evolution of the event and to
estimate the Ly-alpha power. Moreover, in order to study the magnetic
topology, the extrapolation of the photospheric magnetic field lines
was done assuming potential field and using SOHO/MDI magnetograms.
---------------------------------------------------------
Title: Solar flares in Halpha and Ly-alpha : observations vs
simulations.
Authors: Rubio da Costa, F.; Zuccarello, F.; Fletcher, L.; Labrosse,
N.; Prosecký, T.; Kašparová, J.
2012MSAIS..19..117R Altcode:
In order to study the properties of faint, moderate and bright flares,
we simulate the conditions of the solar atmosphere using a radiative
hydrodynamic model \citep{2005ApJ...630..573A}. A constant beam of
non-thermal electrons is injected at the apex of a 1D coronal loop
and heating from thermal soft X-ray and UV emission is included. We
study the contribution of different processes to the total intensity of
different lines at different atmospheric layers. We obtain the total
integrated intensity of different lines and we compare those of the
Ly-alpha and Halpha lines with the observational values for Ly-alpha
(using TRACE 1216 and 1600 Å data and estimating the “pure” Ly-alpha
emission) and Halpha (using data from the Ondřejov Observatory). We
inferred from the analysis of the values obtained by simulation that
the X-ray energy of the different kind of flares does not strongly
affect the Ly-alpha results; the Halpha results are comparable to the
observed ones, concluding that the simulated solar atmosphere fits
better at lower layers of the chromosphere than at upper layers.
---------------------------------------------------------
Title: Saturn's Great White Storm (2010): Correlations between Clouds
and Thermal Fields?
Authors: Momary, T.; Yanamandra-Fisher, P. A.; Orton, G. S.; Baines,
K. H.; Fletcher, L.; Trinh, S.; Delcroix, M.
2011AGUFM.P13C1683M Altcode:
It is well known that convective storms occur regularly in Saturn's
atmosphere, but giant storm outbreaks, known as Great White Spot
(GWS) outbreaks, occur approximately every 29 years or once per
Saturnian year, just past northern solstice. Including the recent
GWS outbreak of December 2010, a total of six have occurred, and are
considered to be related to the changing seasonal insolation, though
their triggers are not yet known or what occurs below the clouds on
smaller temporal and spatial timelines. Although not predictable, as
evidenced by the current Northern Storm and observed by Cassini, the
great storms start out with a violent outbreak, dredging up material
from the deep atmosphere, which then is dispersed by the prevailing
winds. The recent 2010 December GWS outbreak is an outlier, occurring
at northern latitudes of approximately 35°N (the northern "Tornado
Alley"), just past vernal equinox, almost a season early. It has rapidly
encircled the planet in two months and is now in its mature phase, with
discrete structure obvious at all longitudes at both mid-infrared and
deep atmosphere (or 5-microns). Recent amateur observations indicate a
link between lightning strikes, convective storm activity, GWS and spoke
activity in the morning ansa (Delacroix et al., 2011). We shall explore
correlations between the many visible/CCD observations from the amateur
community, the albedo and thermal maps produced with data acquired from
NASA/InfraRed Telescope Facility (IRTF)/NSFCAM2, a 1 - 5-micron imager,
during the various phases of the 2010 - 2011 GWS. We will characterize
changes in the local environs of the outbreak site at various epochs and
compare with other locations on the planet. Delacroix, M., E. Kraaikamp
and P. Yanamandra-Fisher,2011. First Ground Observations of Saturn's
Spokes Around 2009 Equinox. EPSC/DPS, Nantes, France.
---------------------------------------------------------
Title: A Sensitive Search for Traces of Stratospheric NH3, PH3,
C2H5D, and CH2C2H2 within Saturn's Beacon
Authors: Greathouse, T. K.; Irons, W.; Fouchet, T.; Fletcher, L.;
Orton, G. S.; Bézard, B.; Tokunaga, A. T.; Lacy, J. H.
2011AGUFM.P13C1682G Altcode:
The development of a hot region in Saturn's stratosphere, the
Beacon, coincided with observations of a massive storm outbreak in
Saturn's deeper atmosphere. It is thought that these disturbances
in the troposphere and stratosphere are related. The severity
and size of the deep convective storm along with the increased
stratospheric temperatures of the Beacon suggested the possibility
that the tropospheric convection was strong enough to inject chemical
constituents from the troposphere into the stratosphere by convective
overshoot. Using the high spectral resolution capabilities of TEXES,
the Texas Echelon cross Echelle Spectrograph, mounted on the NASA
Infrared Telescope Facility, IRTF, we performed a sensitive search for
NH3 and PH3 emission lines that would indicate the presence of NH3 and
PH3 in the stratospheric region of the Beacon. We will present upper
limits to the NH3 and PH3 abundances as initial reductions of the data
retrieved between July 14th and 19th, 2011 showed no obvious emission
features from either gas. The high temperatures within the Beacon
also allowed for a detailed search for molecules as yet undetected in
the stratospheres of the Outer Planets, but predicted to exist at low
abundance levels. Observations centered at 800 cm-1 and 845 cm-1 were
retrieved to search for C2H5D and CH2C2H2 emission, respectively. Like
the search for NH3 and PH3, initial reductions show no trace of these
molecules. We will present a more thorough analysis with an upper
limit to the CH2C2H2 abundance within the Beacon. Only a model to data
comparison will be made for the C2H5D spectral setting, since a full
set of line parameters for this molecule have yet to be recorded.
---------------------------------------------------------
Title: High Energy Solar Physics Data in Europe (HESPE): a European
project for the exploitation of hard X-ray data in solar flare physics
Authors: Piana, M.; Csillaghy, A.; Kontar, E. P.; Fletcher, L.;
Veronig, A. M.; Vilmer, N.; Hurford, G. J.; Dennis, B. R.; Schwartz,
R. A.; Massone, A.; Krucker, S.; Benvenuto, F.; Etesi, L. I.; Guo,
J.; Hochmuth, N.; Reid, H.
2011AGUFMSH33B2068P Altcode:
It has been recognized since the early days of the space program that
high-energy observations play a crucial role in understanding the basic
mechanisms of solar eruptions. Unfortunately, the peculiar nature of
this radiation makes it so difficult to extract useful information
from it that non-conventional observational techniques together with
complex data analysis procedures must be adopted. HESPE is a European
project funded within the seventh Framework Program, with the aim of
realizing computational methods for solar high-energy data analysis and
technological tools for the intelligent exploitation of science-ready
products. Such products and methods are put at disposal of the solar,
heliospheric and space weather communities, who will exploit them in
order to build flare prediction models and to integrate the information
extracted from hard X-rays and gamma rays data, with the one extracted
from other wavelengths data.
---------------------------------------------------------
Title: Non-Observation of the He II 304 A Charge-Exchange Continuum
in Major Solar Flares
Authors: Hudson, H. S.; Fletcher, L.; MacKinnon, A.; Woods, T. N.
2011AGUFMSH41A1909H Altcode:
We report on a search for flare emission via charge-exchange continuum
radiation in the wings of the Lyman-alpha line of He ii at 304 A, as
originally suggested for hydrogen by Orrall and Zirker (1976). Via this
mechanism a primary alpha particle that penetrates into the neutral
chromosphere can pick up an atomic electron and radiate recombination
continuum before it stops. The Extreme-ultraviolet Variability
Experiment (EVE) on board the Solar Dynamics Observatory (SDO) gives
us our first chance to search for this effect systematically. The
Orrall-Zirker charge-exchange mechanism has great importance for flare
physics because of the essential roles that particle acceleration plays;
this mechanism is one of the few proposed that would allow remote
sensing of primary accelerated particles below a few MeV/nucleon. We
study four EVE events: the gamma-ray events SOL2010-06-12 (M2.0) and
SOL20 11-02-24 (M3.5), the latter a limb flare, and the X-class flares
SOL2010-02-15 (X2.2) and SOL2011-03-09 (X1.2). No clear signature of
the charge-exchange continuum appears, but SOL2010-02-15 (X2.2) does
reveal a gradual broad-band signature that we tentatively interpret
as due to unresolved emission lines or instrumental scattering.
---------------------------------------------------------
Title: Splinter Session "Solar and Stellar Flares"
Authors: Fletcher, L.; Hudson, H.; Cauzzi, G.; Getman, K. V.; Giampapa,
M.; Hawley, S. L.; Heinzel, P.; Johnstone, C.; Kowalski, A. F.; Osten,
R. A.; Pye, J.
2011ASPC..448..441F Altcode: 2011csss...16..441F; 2012arXiv1206.3997F
This summary reports on papers presented at the Cool Stars-16 meeting in
the splinter session "Solar and Stellar flares." Although many topics
were discussed, the main themes were the commonality of interests,
and of physics, between the solar and stellar flare communities,
and the opportunities for important new observations in the near future.
---------------------------------------------------------
Title: Investigation of the Photochemistry in Saturn's Ring Shadowed
Atmosphere: Production Rates of Key Atmospheric Molecules
Authors: Edgington, S. G.; Atreya, S. K.; Wilson, E. H.; Baines,
K. H.; West, R. A.; Bjoraker, G. L.; Fletcher, L.
2011AGUFM.P13C1685E Altcode:
Cassini has been orbiting Saturn for well over seven years. During
this epoch, the ring shadow has changed from shading a large portion
of the northern hemisphere to shading a small region just south of the
equator and is continuing southward. At Saturn Orbit Insertion (July
1, 2004), the ring plane was inclined by ~24 degrees relative to the
Sun-Saturn vector. The projection of the B-ring onto Saturn reached as
far as 40N along the central meridian (~52N at the terminator). At its
maximum extent, the ring shadow can reach as far as 48N (~58N at the
terminator). The net result, is that the intensity of both ultraviolet
and visible sunlight penetrating into any particular northern/southern
latitude will vary depending on Saturn's tilt relative to the Sun
and the optical thickness of each ring system. Previous work [1]
looked at the variation of the solar flux as a function of solar
inclination, i.e. season (see Figure 1). The current work looks at
the impact of the oscillating ring shadow on the photodissociation
and production rates of key molecules in Saturn's stratosphere and
upper troposphere over time. Beginning with methane, the impact on
production and loss rates of the long-lived photochemical hydrocarbons
leading to haze formation are examined at several latitudes over a
Saturn year. We also look at the impacts on phosphine abundance, a
disequilibrium species whose presence in the upper troposphere is a
tracer of convection processes in the deep atmosphere. Comparison to
the corresponding photodissociation rates for a clear atmosphere and
the effect of dynamical mixing will be presented. [1] Edgington,S.G.,
et al., 2006. Adaptation of a 2-D Photochemical Model to Improve Our
Understanding of Saturn's Atmosphere. B.A.A.S., 38, 499 (#11.23). The
research described in this paper was carried out at the Jet Propulsion
Laboratory, California Institute of Technology, under a contract with
the National Aeronautics and Space Administration.
---------------------------------------------------------
Title: The Evolution of Trace Species and Temperature in Saturn's
Northern Storm Region
Authors: Hesman, B. E.; Fletcher, L.; Bjoraker, G. L.; Sada, P. V.;
Achterberg, R. K.; Jennings, D. E.; Lunsford, A. W.; Boyle, R. J.;
Kerr, T.; Romani, P. N.; Simon-Miller, A. A.; Nixon, C. A.; Davis,
G. R.; Irwin, P. G.
2011AGUFM.P11H..04H Altcode:
The massive eruption at 40°N (planetographic latitude) in December
2010 has produced significant and long-lived changes in temperature and
species abundances in Saturn's northern hemisphere (Fletcher et al.,
2011). The northern storm region has been observed on many occasions
in between January and August of 2011 by Cassini's Composite Infrared
Spectrometer (CIRS). In this time period, temperatures in regions
referred to as "beacons" (warm regions in the stratosphere at certain
longitudes in the storm latitude) became significantly warmer than
pre-storm values of 140K. These temperatures reached a peak of 220K near
the 2-mbar region in May 2011 following the merger of two beacons. These
are the highest temperatures ever observed at this altitude on
Saturn. The temperatures in the storm region vary longitudinally
by ~70K which is the largest variation in temperature ever seen on
Saturn. These warm temperatures resulted in the detection of ethylene
(C<SUB>2</SUB>H<SUB>4</SUB>) using CIRS. Early analysis of the May
data indicates ethylene volume mixing ratios of 3x10<SUP>-8</SUP>
at 2 mbar. These beacon regions have also led to the identification
of rare species such as diacetylene (C<SUB>4</SUB>H<SUB>2</SUB>),
methylacetylene (CH<SUB>3</SUB>C<SUB>2</SUB>H), and carbon dioxide
(CO<SUB>2</SUB>) in the stratosphere. These species were previously
measured by the Infrared Space Observatory (de Graauw et al.,
1997) and CIRS (Guerlet et al., 2010). However, mapping these
species in longitude and latitude over the storm region using CIRS
provides insight into the changes in the photochemistry induced
by the storm. Ground-based observations were performed using the
high-resolution spectrometer Celeste in May and July to confirm the
CIRS detection of ethylene and to study its spectral signatures at
higher spectral resolution than available with CIRS, and investigate
the evolution of its abundance profile as the storm progresses. The
time evolution of ethylene abundance in Saturn's northern storm region
using CIRS and ground-based data from the McMath-Pierce Telescope
(May 2011) and the United Kingdom Infrared Telescope (July 2011)
will be presented. In addition, the abundance profiles, as measured
by CIRS, of C<SUB>4</SUB>H<SUB>2</SUB>, CH<SUB>3</SUB>C<SUB>2</SUB>H,
and CO<SUB>2</SUB> will also be discussed including how their abundance
profiles have changed throughout the storm period.
---------------------------------------------------------
Title: TEXES observations of Saturn's stratospheric thermal structure
after the 2010 convective event
Authors: Fouchet, T.; Greathouse, T. K.; Fletcher, L. N.; Richter,
M. J.; Lacy, J. H.; Irons, W.; Guerlet, S.; Bézard, B.; Lellouch,
E.; Hesman, B. E.; Achterberg, R. K.; Tokunaga, A. T.
2011AGUFM.P13C1681F Altcode:
In December 2010, a huge convective event distorted the cloud layer
at 40 N in Saturn's springtime hemisphere. These large convective
events are observed regularly in Saturn's atmosphere, about one event
per saturnian year, and may play a central role in the transport of
the internal heat flux to the radiative layer. However, this event
occured at a season (Ls=16) different from that of the previous
events (Ls= 110-170). Another unexpected aspect of the 2010 event
was its stratospheric signature. As shown by Fletcher et al. (2011)
from Cassini/CIRS and VLT/VISIR, in the 40N latitude band, the 1-mbar
pressure level warmed by several tens of K at some longitudes and
cooled by several K at other longitudes. In order to assess the vertical
thermal structure in the disturbed latitudinal band, we performed five
half-nights of observations with TEXES mounted on the NASA Infrared
Telescope Facility (IRTF) from July 14th, 2011 to July 19th, 2011. The
high spectral resolution (R=100,000) provided by TEXES allowed us to
resolve several lines of methane in the range 1245-1250 cm-1, and the
H<SUB>2</SUB> S(1) quadrupole line and collision-induced continuum to
measure the temperature structure between 100~mbar and 0.01~mbar. We
will present the results of the observations in terms of stratospheric
temperature structure.
---------------------------------------------------------
Title: Cassini/CIRS Observations of Temperatures in Saturn's Northern
Storm Region
Authors: Achterberg, R. K.; Hesman, B. E.; Bjoraker, G. L.; Fletcher,
L.; Conrath, B. J.; Gierasch, P. J.; Flasar, F. M.
2011AGUFM.P13C1680A Altcode:
In early December 2010, a large convective storm appeared in Saturn's
northern hemisphere, centered near 40°N planetographic at the center of
a westward jet (Sanchez-Lavega et al., 2011; Fisher et al. 2011). Storms
of the observed magnitude, referred to as Great White Spots (GWS),
are rare on Saturn, historically occurring once per Saturn year (30
Earth years), at equatorial or mid-northern latitudes during northern
summer; the current storm is unusual in occurring during northern
spring, roughly one season earlier than previous GWS outbursts. Thermal
infrared observations, both groundbased and from the Cassini Composite
Infrared Spectrometer (CIRS) orbiting Saturn, taken six weeks after the
appearance of the storm, revealed significant changes to the thermal
structure of Saturn's northern hemisphere (Fletcher et al., 2011). Cold
temperatures were measured at the location of the disturbance in both
the upper troposphere and stratosphere, and, surprisingly, hot spots
to the east and west of the disturbance longitude with temperature
contrasts of 16K, much larger than usual zonal temperature contrasts
on Saturn. CIRS has continued to observe the latitude of the storm
at one to two month intervals. These observations typically cover an
approximately 10° wide latitude strip over one or two rotations of
Saturn at a spatial resolution of 2° of arc in the CIRS mid-IR focal
planes (600-1400 cm<SUP>-1</SUP>, 7-16μm). From these observations,
we can retrieve temperatures in the upper troposphere between 50
and 200 mbar, and in the middle stratosphere between ~0.2 and 10
mbar. These observations show that temperatures in the stratospheric
hot spots continued to increase through May 2011, when temperatures
reached a peak of over 220 K, following the merger of two hot spots
into one, with zonal temperature contrasts of 70 K. By mid-July,
the maximum temperature in the hot spot had decreased to just under
200K. Furthermore, in May and July, the peak temperatures were at a
pressure roughly two scale heights larger (lower in altitude) than
in earlier observations - 2 mbar compared to 0.4 mbar. In the upper
troposphere, temperature perturbations associated with the storm are
around 5 to 10 K, larger than seen on Saturn prior to the storm, but
much smaller than the temperature variations seen in the stratosphere.
---------------------------------------------------------
Title: Thermal Evolution of Saturn's 2010-2011 Disturbance
Authors: Orton, G. S.; Fletcher, L.; Yanamandra-Fisher, P.; Mason,
C.; Greco, J.; Valkov, S.; Baines, K. H.; Nanu, R.; Villar, G.; Trinh,
S.; Pacheco, J.; Sola, M.; Momary, T.; Greathouse, T. K.; Fouchet, T.
2011AGUFM.P13C1679O Altcode:
The remarkable disturbance that began in Saturn's northern hemisphere
late in 2010 was initiated by a single discrete outburst of bright
white cloud material, which spread with the prevailing zonal winds
to completely encircle the planet within a matter of weeks. We report
here the results of studies of the influence of the storm on thermal
emission. These were obtained from thermal imaging observations
between 5 and 25 μm, combining high-resolution imaging from ESO's
Very Large Telescope (VLT) using the VISIR instrument and more
frequent imaging from NASA's Infrared Telescope Facility (IRTF) using
the MIRSI and NSFCam2 instruments. These observations were used to
document the evolution of the spatial distributions of temperatures,
gas composition and cloud opacity to trace the atmospheric circulation
associated with the storm, which is consistent with a single convective
plume in the deep clouds, sheared by the zonal winds and triggering
widespread planetary wave activity. The disturbance generated the
largest stratospheric thermal anomalies ever detected on Saturn
(infrared 'beacons' that dominate the planetary emission), revealing
dynamical coupling over hundreds of kilometers from the troposphere
to the stratosphere. Observations made between January and March of
2011 revealed the presence of two stratospheric 'beacons' and only
tropospheric cooling associated with the upwelling regions of the
disturbance. Observations in April and thereafter showed that these
'beacons' had merged into a single feature, and that temperatures
in the upper troposphere were increasing with time around the
disturbance. Coincident with the disturbance, there appeared a major
increase in the amplitude of zonal thermal waves in the northern
hemisphere at longitudes distant from the disturbance. We note that
the amplitude of zonal thermal waves in the southern hemisphere also
increased. We will continue to track the evolution of this phenomenon,
providing support for ground-based and Cassini spectroscopic
observations.
---------------------------------------------------------
Title: The Evolution of Saturn's Northern Storm of 2010-2011 and
Environs as Viewed by Cassini/VIMS
Authors: Baines, K. H.; Momary, T.; Fletcher, L.; Showman, A. P.;
Delitsky, M.; Brown, R. H.; Buratti, B. J.; Clark, R. N.; Nicholson,
P. D.; Sotin, C.
2011AGUFM.P11H..06B Altcode:
Images and spectra acquired by the Visual Infrared Mapping Spectrometer
on board the Cassini Orbiter reveal that the current northern storm
on Saturn is remarkable for (1) its location - the first significant
storm seen in northern mid-latitudes since 1906, (2) its duration -
presently approaching 8 months, and (3) its power, as indicated by
the relatively massive ammonia-laden clouds it produces that reveal
significant, persistent transport of materials over at least one
bar of depth (> 30 km of altitude). Situated near 35 degrees
north latitude (planetocentric) near the maximum of a westward jet,
the storm head moves westward at ~ 2.7 degrees per day, or ~ 27
m/s. Multi-spectral images of the feature and its environs in 352 colors
spanning nearly all longitudes were acquired by VIMS on February 24,
May 11 and July 12, 2011. In all imagery, the head of the storm appears
atypically dark in ammonia-ice sensitive wavelengths 2.73-3.1 micron,
indicating significant amounts of ammonia ice. Simultaneously, the
feature appears bright at pseudo-continuum near-infrared wavelengths,
particularly at 4.08 micron, indicating an atypically massive cloud of
large particles. Some 3-5 degree of latitude to the north and south of
the cloudhead, streamers of such large-particle ammonia clouds extend
more than 150 degrees of longitude to the east. While these streamers
appear nearly equivalent in brightness in diagnostic wavelengths in
the February 24, 2011 observations, the northern streamer clearly
dominates in the May 11, 2011 map. As well, a new dark spot, the first
observed associated with this storm, appears more than 250 degrees
of longitude downstream of the cloudhead in the May 11, 2011 images
and persists through the July 12, 2011 observations. Its appearance
may be associated with the dissipation of overlying cloud features as
the dark spot wandered eastward, Similar in size (> 3000 km) and
spectral appearance to the dark spots associated with the 2008 southern
storm (Baines et al, Planetary and Space Sci., 57, 1650-1658,2009),
this feature suggests upwelling of materials from the ~10-bar level,
as previously proposed for the southern storm. New imagery expected in
August 2011 as well as additional analysis of the July, 2011 images will
be discussed and dynamical implications presented, including possible
relationships of the northern storm with the String of Pearls feature
observed for 5 years in the same latitude and longitude range but which
has not been observed since the advent of the storm in December 2010.
---------------------------------------------------------
Title: Multispectral imaging observations of Neptune's cloud structure
with Gemini-North
Authors: Irwin, P. G. J.; Teanby, N. A.; Davis, G. R.; Fletcher,
L. N.; Orton, G. S.; Tice, D.; Hurley, J.; Calcutt, S. B.
2011Icar..216..141I Altcode:
Observations of Neptune were made in September 2009 with the
Gemini-North Telescope in Hawaii, using the NIFS instrument in the
H-band covering the wavelength range 1.477-1.803 μm. Observations
were acquired in adaptive optics mode and have a spatial resolution
of approximately 0.15-0.25″. The observations were analysed with a
multiple-scattering retrieval algorithm to determine the opacity of
clouds at different levels in Neptune's atmosphere. We find that the
observed spectra at all locations are very well fit with a model that
has two thin cloud layers, one at a pressure level of ∼2 bar all over
the planet and an upper cloud whose pressure level varies from 0.02 to
0.08 bar in the bright mid-latitude region at 20-40°S to as deep as 0.2
bar near the equator. The opacity of the upper cloud is found to vary
greatly with position, but the opacity of the lower cloud deck appears
remarkably uniform, except for localised bright spots near 60°S and a
possible slight clearing near the equator. A limb-darkening analysis of
the observations suggests that the single-scattering albedo of the upper
cloud particles varies from ∼0.4 in regions of low overall albedo
to close to 1.0 in bright regions, while the lower cloud is consistent
with particles that have a single-scattering albedo of ∼0.75 at this
wavelength, similar to the value determined for the main cloud deck in
Uranus' atmosphere. The Henyey-Greenstein scattering particle asymmetry
of particles in the upper cloud deck are found to be in the range g
∼ 0.6-0.7 (i.e. reasonably strongly forward scattering). Numerous
bright clouds are seen near Neptune's south pole at a range of pressure
levels and at latitudes between 60 and 70°S. Discrete clouds were seen
at the pressure level of the main cloud deck (∼2 bar) at 60°S on
three of the six nights observed. Assuming they are the same feature
we estimate the rotation rate at this latitude and pressure to be 13.2
± 0.1 h. However, the observations are not entirely consistent with
a single non-evolving cloud feature, which suggests that the cloud
opacity or albedo may vary very rapidly at this level at a rate not
seen in any other giant-planet atmosphere.
---------------------------------------------------------
Title: Thermal Evolution of Saturn's Springtime Disturbance
Authors: Fletcher, L. N.; Orton, G. S.; Irwin, P. G. J.;
Sanchez-Lavega, A.; Baines, K. H.; Hesman, B. E.; Read, P. L.; Flasar,
F. M.; Momary, T. W.; Simon-Miller, A. A.; Hueso, R.; Bjoraker, G. L.;
Yanamandra-Fisher, P.
2011epsc.conf..713F Altcode: 2011DPS....43..713F
Saturn's slow seasonal warming was spectacularly disrupted in
December 2010 by the eruption of an enormous storm system in its
springtime hemisphere. This storm, which is still evolving at the
time of writing, is only the sixth known example of a planetwide
storm system on Saturn, and the first to occur at this latitude
(near 40oN) in over a century [1,2]. A combined analysis of thermal
infrared imaging from ESO's Very Large Telescope VISIR instrument and
5-200 μm spectroscopy from instruments onboard Cassini revealed the
substantial atmospheric perturbations related to the storm complex over
a wide range of altitudes [1]. Since that time the storm complex has
continued to evolve through the mature phase. In particular Saturn's
newly-identified stratospheric beacons (a high-altitude response to
mechanical forcing from the troposphere) have been observed to move in
the stratospheric wind field, merge and strengthen to generate thermal
differences considerably larger than those reported in our initial study
(Fig. 1, from IRTF/MIRSI, May 22 2011).
---------------------------------------------------------
Title: The December 2010 outbreak of a major storm in Saturn's
atmosphere: Observations and models
Authors: Sanchez-Lavega, A.; Del Río-Gaztelurrutia, T.; Hueso,
R.; Gómez-Forrellad, J. M.; Sanz-Requena, J. F.; Legarreta, J.;
García-Melendo, E.; Colas, F.; Lecacheux, J.; Fletcher, L. N.;
Barrado-Navascués, D.; Parker, D.
2011epsc.conf..400S Altcode: 2011DPS....43..400S
On December 5, 2010, a major storm erupted in Saturn's northern
hemisphere at a planetographic latitude of 37.7 deg [1]. These phenomena
are known as "Great White Spots" (GWS) and they have been observed
once per Saturn year since the first case confidently reported in
1876. The last event occurred at Saturn's Equator in 1990 [2]. A
GWS differs from similar smaller-scale storms in that it generates a
planetary-scale disturbance that spreads zonally spanning the whole
latitude band. Studies of the 1990 case indicated that the storm
produced a long-term substantial change in the cloud and haze structure
around the tropopause level, and in the equatorial winds. We report on
the evolution and motions of the new GWS and its associated disturbance
during the months following the outbreak, based mainly on high quality
images obtained in the visual range submitted to the International Outer
Planet Watch PVOL database [3], with the 1m telescope at Pic-du-Midi
Observatory and 2.2 m telescope at Calar Alto Observatory. The high
temporal sampling and coverage allowed us to study the dynamics of the
GWS in detail and the multi-wavelength observations provide information
on its cloud top structure. We present non-linear simulations using the
EPIC code of the evolution of the potential vorticity generated by an
impulsive and localized Gaussian heat pulse that compare extraordinary
well to the observed cloud field evolution.
---------------------------------------------------------
Title: Uranus' cloud structure and scattering particle properties
from IRTF SpeX observations
Authors: Tice, D. S.; Irwin, P. G. J.; Fletcher, L. N.; Teanby, N. A.;
Orton, G. S.; Davis, G. R.
2011epsc.conf..143T Altcode: 2011DPS....43..143T
Observations of Uranus were made in August 2009 with the SpeX
spectrograph at the NASA Infrared Telescope Facility (IRTF). Analysed
spectra range from 0.8 to 1.8 μm at a spatial resolution of 0.5" and
a spectral resolution of R = 1,200. Spectra from 0.818 to 0.834 μm,
a region characterised by both strong hydrogen quadrupole and methane
absorptions are considered to determine methane content. Evidence
indicates that methane abundance varies with latitude. NEMESIS, an
optimal estimation retrieval code with full-scattering capability, is
employed to analyse the full range of data. Cloud and haze properties
in the upper troposphere and stratosphere are characterised, and are
consistent with other current literature. New information on single
scattering albedos and particle size distributions are inferred.
---------------------------------------------------------
Title: The EVE Doppler Sensitivity and Flare Observations
Authors: Hudson, H. S.; Woods, T. N.; Chamberlin, P. C.; Fletcher,
L.; Del Zanna, G.; Didkovsky, L.; Labrosse, N.; Graham, D.
2011SoPh..273...69H Altcode: 2011SoPh..tmp..362H
The Extreme-ultraviolet Variability Experiment (EVE; see Woods et al.,
2009) obtains continuous EUV spectra of the Sun viewed as a star. Its
primary objective is the characterization of solar spectral irradiance,
but its sensitivity and stability make it extremely interesting for
observations of variability on time scales down to the limit imposed
by its basic 10 s sample interval. In this paper we characterize the
Doppler sensitivity of the EVE data. We find that the 30.4 nm line of
He II has a random Doppler error below 0.001 nm (1 pm, better than 10
km s<SUP>−1</SUP> as a redshift), with ample stability to detect
the orbital motion of its satellite, the Solar Dynamics Observatory
(SDO). Solar flares also displace the spectrum, both because of Doppler
shifts and because of EVE's optical layout, which (as with a slitless
spectrograph) confuses position and wavelength. As a flare develops,
the centroid of the line displays variations that reflect Doppler shifts
and therefore flare dynamics. For the impulsive phase of the flare
SOL2010-06-12, we find the line centroid to have a redshift of 16.8 ±
5.9 km s<SUP>−1</SUP> relative to that of the flare gradual phase
(statistical errors only). We find also that high-temperature lines,
such as Fe XXIV 19.2 nm, have well-determined Doppler components for
major flares, with decreasing apparent blueshifts as expected from
chromospheric evaporation flows.
---------------------------------------------------------
Title: Elusive Ethylene Detected in Saturn's Northern Storm Region
Authors: Hesman, B. E.; Bjoraker, G. L.; Sada, P. V.; Achterberg,
R. K.; Jennings, D. E.; Lunsford, A. W.; Boyle, R. J.; Romani, P. N.;
Simon-Miller, A. A.; Nixon, C. A.; Fletcher, L. N.; Irwin, P. G. J.
2011epsc.conf.1222H Altcode: 2011DPS....43.1222H
The massive eruption at 40°N (planetographic latitude) in December 2010
has produced significant and lasting effects in the northern hemisphere
on temperature and species abundances [1]. The northern storm region
has been observed on many occasions in between January and May of
2011 by Cassini's Composite Infrared Spectrometer (CIRS). In May 2011
temperatures in the stratosphere greater than 220K were derived from
CIRS spectra in the regions referred to as "beacons" (warm regions in
the stratosphere). Ethylene (C2H4) has been detected in a beacon in
Saturn's northern storm region using CIRS. Ground-based observations
using the high-resolution spectrometer Celeste on the McMath-Pierce
Telescope on May 15, 2011 were used to confirm the detection. Early
analysis indicate ethylene volume mixing ratios of 3x10-8 at 2 mbar.
---------------------------------------------------------
Title: JUICE (JUpiter ICy moon Explorer): a European-led mission to
the Jupiter system
Authors: Dougherty, M. K.; Grasset, O.; Bunce, E.; Coustenis,
A.; Titov, D. V.; Erd, C.; Blanc, M.; Coates, A. J.; Coradini,
A.; Drossart, P.; Fletcher, L.; Hussmann, H.; Jaumann, R.; Krupp,
N.; Prieto-Ballesteros, O.; Tortora, P.; Tosi, F.; van Hoolst, T.;
Lebreton, J. -P.
2011epsc.conf.1343D Altcode: 2011DPS....43.1343D
The former ESA-NASA EJSM-Laplace mission is being reformulated by ESA
as a European-led single spacecraft mission to the Jovian system. The
concept has been recently renamed JUICE (JUpiter ICy moon Explorer). The
new mission is based on the design of the Jupiter Ganymede Orbiter
(JGO) - the ESA flight element of EJSM-Laplace.
---------------------------------------------------------
Title: Seasonal Variations of Hydrocarbons in Saturn's Stratosphere
Authors: Sinclair, J. A.; Irwin, P. G. J.; Fletcher, L. N.; Hurley,
J.; Merlet, C.
2011epsc.conf..511S Altcode: 2011DPS....43..511S
We present a study of the seasonal variations of hydrocarbons in
the stratosphere of Saturn. Meridional variations of the abundances
of hydrocarbons such as acetylene (C2H2) and ethane (C2H6) have
previously been determined, in particular using observations from
the Cassini/CIRS (Composite Infrared Spectrometer) instrument. Such
studies have used Cassini data obtained during the prime mission (2004 -
2008) therefore studying Saturn from shortly after summer solstice to
'autumn' in the Southern Hemisphere. With the occurence of the vernal
equinox in August 2009, Saturn's northern hemisphere is now approaching
summer solstice. We aim to determine the response of the hydrocarbon
photochemistry as a result of seasonal changes.
---------------------------------------------------------
Title: Saturn's Enigmatic "String of Pearls" and Northern Storm of
2010-2011: Manifestations of a Common Dynamical Mechanism?
Authors: Baines, K.; Momary, T.; Fletcher, L.; Showman, A.; Brown,
R.; Buratti, B.; Clark, R.; Nicholson, P.; Go, C.; Wesley, A.
2011epsc.conf.1658B Altcode: 2011DPS....43.1658B
The "String of Pearls" (SoP) and the Northern Storm on Saturn near 34o
north latitude may both be manifestations of convective processes at
depth. As one possibility, the SoP may be a set of von Kármán vortex
street features with convectively-driven updrafts as the driving
obstacles. VIMS observations show marked increases in the size and
latitudinal separation of the pearls (vortices) during the year prior
to storm eruption, indicative of a growing convective system that
may have subsequently erupted as a major thunderstorm. Other common
convective mechanisms (uplift-driven Rossby waves, vortex-shedding
from rising updrafts) may be possible. New VIMS images and spectra of
the thunderstorm and SoP are presented.
---------------------------------------------------------
Title: The 2010-2011 Revival of Jupiter's South Equatorial Belt:
Perturbations of Temperatures, Clouds and Composition from Infrared
Observations
Authors: Orton, G.; Fletcher, L.; Yanamandra-Fisher, P.;
Sanchez-Lavega, A.; Perez-Hoyos, S.; de Pater, I.; Wong, M.; Goetz,
R.; Valkov, S.; Greco, J.; Edwards, M.; Rogers, J.; Baines, K.
2011epsc.conf..673O Altcode: 2011DPS....43..673O
On 2010 November 9, a perturbation appeared in Jupiter's South
Equatorial Belt (SEB), which began a classical "revival" of the
SEB, returning the entire axisymmetric region to its normal dark
color from its anomalous, light, "faded" state. The early revival is
marked by strong upwelling gas at the outbreak location, to the west
of which appear alternating clear and cloudy regions. Clear regions
are correlated with dark clouds near the outbreak and in a southern
retrograding branch but less so in a northern prograding branch. A
5-μm image from 2010 March 1 shows much of the SEB closer to a
pre-faded state.
---------------------------------------------------------
Title: Investigation of the Photochemistry in Saturn's Ring Shadowed
Atmosphere: Production Rates of Key Atmospheric Molecules
Authors: Edgington, S. G.; Atreya, S. K.; Wilson, E. H.; Baines,
K. H.; West, R. A.; Bjoraker, G. L.; Fletcher, L. N.
2011epsc.conf.1710E Altcode: 2011DPS....43.1710E
Cassini has been orbiting Saturn for well over six years. During
this epoch, the ring shadow has moved from covering a relatively large
portion of the northern hemisphere to covering a small region just south
of the equator (see Figure 1). For example, at Saturn Orbit Insertion
(SOI; July 1, 2004), the ring plane was inclined by ~24 degrees relative
to the Sun-Saturn vector. At this time, the projection of the B-ring
onto Saturn reached as far as 40ºN along the central meridian (~52ºN
at the terminator). At its maximum extent, the ring shadow can reach
as far as 48ºN (~58ºN at the terminator). The net result, is that the
intensity of both ultraviolet and visible sunlight penetrating into any
particular northern/southern latitude will vary depending on Saturn's
tilt relative to the Sun and the optical thickness of each ring system
(see Figure 2). Previous work [1] looked at the variation of the solar
flux as a function of solar inclination, i.e. season (see Figure 3). The
current work looks at the impact of the oscillating ring shadow on the
photodissociation and production rates of key molecules in Saturn's
stratosphere and upper troposphere over time. Beginning with methane,
the impact on production and loss rates of the long-lived photochemical
products leading to haze formation are examined at several latitudes
over a Saturn year. We also look at the impacts on phosphine abundance,
a disequilibrium species whose presence in the upper troposphere is
a tracer of convection processes in the deep atmosphere. Comparison
to the corresponding rates for the clear atmosphere and the effect of
dynamical mixing will be presented.
---------------------------------------------------------
Title: An Observational Overview of Solar Flares
Authors: Fletcher, L.; Dennis, B. R.; Hudson, H. S.; Krucker, S.;
Phillips, K.; Veronig, A.; Battaglia, M.; Bone, L.; Caspi, A.; Chen,
Q.; Gallagher, P.; Grigis, P. T.; Ji, H.; Liu, W.; Milligan, R. O.;
Temmer, M.
2011SSRv..159...19F Altcode: 2011SSRv..tmp..261F; 2011arXiv1109.5932F
We present an overview of solar flares and associated phenomena,
drawing upon a wide range of observational data primarily from the
RHESSI era. Following an introductory discussion and overview of
the status of observational capabilities, the article is split into
topical sections which deal with different areas of flare phenomena
(footpoints and ribbons, coronal sources, relationship to coronal mass
ejections) and their interconnections. We also discuss flare soft X-ray
spectroscopy and the energetics of the process. The emphasis is to
describe the observations from multiple points of view, while bearing
in mind the models that link them to each other and to theory. The
present theoretical and observational understanding of solar flares is
far from complete, so we conclude with a brief discussion of models,
and a list of missing but important observations.
---------------------------------------------------------
Title: Evolution of sunspot properties during solar cycle 23
Authors: Watson, F. T.; Fletcher, L.; Marshall, S.
2011A&A...533A..14W Altcode: 2011arXiv1108.4285W
Context. The long term study of the Sun is necessary if we are to
determine the evolution of sunspot properties and thereby inform
modeling of the solar dynamo, particularly on scales of a solar
cycle. <BR /> Aims: We aim to determine a number of sunspot properties
over cycle 23 using the uniform database provided by the SOHO Michelson
Doppler Imager data. We focus in particular on their distribution on
the solar disk, maximum magnetic field and umbral/penumbral areas. We
investigate whether the secular decrease in sunspot maximum magnetic
field reported in Kitt Peak data is present also in MDI data. <BR />
Methods: We have used the Sunspot Tracking And Recognition Algorithm
(STARA) to detect all sunspots present in the SOHO Michelson Doppler
Imager continuum data giving us 30 084 separate detections. We record
information on the sunspot locations, area and magnetic field properties
as well as corresponding information for the umbral areas detected
within the sunspots, and track them through their evolution. <BR />
Results: We find that the total visible umbral area is 20-40% of
the total visible sunspot area regardless of the stage of the solar
cycle. We also find that the number of sunspots observed follows
the Solar Influences Data Centre international sunspot number with
some interesting deviations. Finally, we use the magnetic information
in our catalogue to study the long term variation of magnetic field
strength within sunspot umbrae and find that it increases and decreases
along with the sunspot number. However, if we were to assume a secular
decrease as was reported in the Kitt Peak data and take into account
sunspots throughout the whole solar cycle we would find the maximum
umbral magnetic fields to be decreasing by 23.6 ± 3.9 Gauss per year,
which is far less than has previously been observed by other studies
(although measurements are only available for solar cycle 23). If we
only look at the declining phase of cycle 23 we find the decrease in
sunspot magnetic fields to be 70 Gauss per year.
---------------------------------------------------------
Title: Recent Advances in Understanding Particle Acceleration
Processes in Solar Flares
Authors: Zharkova, V. V.; Arzner, K.; Benz, A. O.; Browning, P.;
Dauphin, C.; Emslie, A. G.; Fletcher, L.; Kontar, E. P.; Mann, G.;
Onofri, M.; Petrosian, V.; Turkmani, R.; Vilmer, N.; Vlahos, L.
2011SSRv..159..357Z Altcode: 2011SSRv..tmp..156Z; 2011SSRv..tmp..249Z; 2011SSRv..tmp..232Z;
2011arXiv1110.2359Z; 2011SSRv..tmp..278Z
We review basic theoretical concepts in particle acceleration,
with particular emphasis on processes likely to occur in regions of
magnetic reconnection. Several new developments are discussed, including
detailed studies of reconnection in three-dimensional magnetic field
configurations (e.g., current sheets, collapsing traps, separatrix
regions) and stochastic acceleration in a turbulent environment. Fluid,
test-particle, and particle-in-cell approaches are used and results
compared. While these studies show considerable promise in accounting
for the various observational manifestations of solar flares, they
are limited by a number of factors, mostly relating to available
computational power. Not the least of these issues is the need to
explicitly incorporate the electrodynamic feedback of the accelerated
particles themselves on the environment in which they are accelerated. A
brief prognosis for future advancement is offered.
---------------------------------------------------------
Title: Long-term evolution of the aerosol debris cloud produced by
the 2009 impact on Jupiter
Authors: Sánchez-Lavega, A.; Orton, G. S.; Hueso, R.; Pérez-Hoyos,
S.; Fletcher, L. N.; García-Melendo, E.; Gomez-Forrellad, J. M.;
de Pater, I.; Wong, M.; Hammel, H. B.; Yanamandra-Fisher, P.;
Simon-Miller, A.; Barrado-Izagirre, N.; Marchis, F.; Mousis, O.;
Ortiz, J. L.; García-Rojas, J.; Cecconi, M.; Clarke, J. T.; Noll,
K.; Pedraz, S.; Wesley, A.; Kalas, P.; McConnell, N.; Golisch, W.;
Griep, D.; Sears, P.; Volquardsen, E.; Reddy, V.; Shara, M.; Binzel,
R.; Grundy, W.; Emery, J.; Rivkin, A.; Thomas, C.; Trilling, D.;
Bjorkman, K.; Burgasser, A. J.; Campins, H.; Sato, T. M.; Kasaba,
Y.; Ziffer, J.; Mirzoyan, R.; Fitzgerald, M.; Bouy, H.; International
Outer Planet Watch Team (IOPW-PVOL)
2011Icar..214..462S Altcode: 2011Icar..214..462I
We present a study of the long-term evolution of the cloud of aerosols
produced in the atmosphere of Jupiter by the impact of an object on
19 July 2009 (Sánchez-Lavega, A. et al. [2010]. Astrophys. J. 715,
L155-L159). The work is based on images obtained during 5 months from
the impact to 31 December 2009 taken in visible continuum wavelengths
and from 20 July 2009 to 28 May 2010 taken in near-infrared deep
hydrogen-methane absorption bands at 2.1-2.3 μm. The impact cloud
expanded zonally from ∼5000 km (July 19) to 225,000 km (29 October,
about 180° in longitude), remaining meridionally localized within a
latitude band from 53.5°S to 61.5°S planetographic latitude. During
the first two months after its formation the site showed heterogeneous
structure with 500-1000 km sized embedded spots. Later the reflectivity
of the debris field became more homogeneous due to clump mergers. The
cloud was mainly dispersed in longitude by the dominant zonal winds and
their meridional shear, during the initial stages, localized motions
may have been induced by thermal perturbation caused by the impact's
energy deposition. The tracking of individual spots within the impact
cloud shows that the westward jet at 56.5°S latitude increases its
eastward velocity with altitude above the tropopause by 5-10 m s
<SUP>-1</SUP>. The corresponding vertical wind shear is low, about 1
m s <SUP>-1</SUP> per scale height in agreement with previous thermal
wind estimations. We found evidence for discrete localized meridional
motions with speeds of 1-2 m s <SUP>-1</SUP>. Two numerical models
are used to simulate the observed cloud dispersion. One is a pure
advection of the aerosols by the winds and their shears. The other
uses the EPIC code, a nonlinear calculation of the evolution of the
potential vorticity field generated by a heat pulse that simulates
the impact. Both models reproduce the observed global structure of the
cloud and the dominant zonal dispersion of the aerosols, but not the
details of the cloud morphology. The reflectivity of the impact cloud
decreased exponentially with a characteristic timescale of 15 days; we
can explain this behavior with a radiative transfer model of the cloud
optical depth coupled to an advection model of the cloud dispersion by
the wind shears. The expected sedimentation time in the stratosphere
(altitude levels 5-100 mbar) for the small aerosol particles forming
the cloud is 45-200 days, thus aerosols were removed vertically over
the long term following their zonal dispersion. No evidence of the
cloud was detected 10 months after the impact.
---------------------------------------------------------
Title: Hinode/EIS plasma diagnostics in the flaring solar chromosphere
Authors: Graham, D. R.; Fletcher, L.; Hannah, I. G.
2011A&A...532A..27G Altcode:
Context. The impulsive phase of solar flares is a time of rapid energy
deposition and heating in the lower solar atmosphere, leading to changes
in the temperature, density, ionisation and velocity structure of
this region. <BR /> Aims: We aim to study the lower atmosphere during
the impulsive phase of a flare using imaging and spectroscopic data
from Hinode/EIS, RHESSI and TRACE. We place these observations in
context by using a wide range of temperature observations from each
instrument. <BR /> Methods: We analyse sparse raster data from the
Hinode/EIS spectrometer to derive the density and line-of-sight velocity
in flare footpoints, in a GOES C6.6 flare observed on 05-June-2007. The
raster duration was 150s across the centre of a small active region,
allowing multiple exposures of the flare ribbons and footpoints. Using
RHESSI and Hinode/XRT we test both non-thermal and thermal models for
the HXR emission. <BR /> Results: During the flare impulsive phase, we
find evidence from XRT for flare footpoints at temperatures exceeding
7 MK. We measure the electron number density increasing up to a few
×10<SUP>10</SUP> cm<SUP>-3</SUP> in the footpoints, at temperatures
of ~1.5-2 MK, accompanied by small downflows at temperatures below
Fe XIII and upflows of up to ~140 km s<SUP>-1</SUP> at temperatures
above. This is reasonable in the context of HXR diagnostics of the
flare electron beam. The electrons inferred have sufficient energy to
affect the chromospheric ionisation structure. <BR /> Conclusions: EIS
sparse raster data coupled with RHESSI imaging and spectroscopy prove
useful here in studying the lower atmosphere of solar flares, and in
this event suggest heat deposition relatively high in the chromosphere
drives chromospheric evaporation while increasing the observed electron
densities at footpoints. However, from RHESSI spectral fitting it is
not possible to say whether the data are more consistent with a model
including a non-thermal beam, or purely thermal model.
---------------------------------------------------------
Title: Automated sunspot detection and the evolution of sunspot
magnetic fields during solar cycle 23
Authors: Watson, Fraser; Fletcher, Lyndsay
2011IAUS..273...51W Altcode: 2010arXiv1009.5884W
The automated detection of solar features is a technique which
is relatively underused but if we are to keep up with the flow of
data from spacecraft such as the recently launched Solar Dynamics
Observatory, then such techniques will be very valuable to the solar
community. Automated detection techniques allow us to examine a large
set of data in a consistent way and in relatively short periods of
time allowing for improved statistics to be carried out on any results
obtained. This is particularly useful in the field of sunspot study
as catalogues can be built with sunspots detected and tracked without
any human intervention and this provides us with a detailed account of
how various sunspot properties evolve over time. This article details
the use of the Sunspot Tracking And Recognition Algorithm (STARA)
to create a sunspot catalogue. This catalogue is then used to analyse
the magnetic fields in sunspot umbrae from 1996-2010, taking in the
whole of solar cycle 23.
---------------------------------------------------------
Title: Deep winds beneath Saturn's upper clouds from a seasonal
long-lived planetary-scale storm
Authors: Sánchez-Lavega, A.; del Río-Gaztelurrutia, T.; Hueso,
R.; Gómez-Forrellad, J. M.; Sanz-Requena, J. F.; Legarreta, J.;
García-Melendo, E.; Colas, F.; Lecacheux, J.; Fletcher, L. N.;
Barrado y Navascués, D.; Parker, D.; International Outer Planet
Watch Team; Akutsu, T.; Barry, T.; Beltran, J.; Buda, S.; Combs, B.;
Carvalho, F.; Casquinha, P.; Delcroix, M.; Ghomizadeh, S.; Go, C.;
Hotershall, J.; Ikemura, T.; Jolly, G.; Kazemoto, A.; Kumamori, T.;
Lecompte, M.; Maxson, P.; Melillo, F. J.; Milika, D. P.; Morales, E.;
Peach, D.; Phillips, J.; Poupeau, J. J.; Sussenbach, J.; Walker, G.;
Walker, S.; Tranter, T.; Wesley, A.; Wilson, T.; Yunoki, K.
2011Natur.475...71S Altcode:
Convective storms occur regularly in Saturn's atmosphere. Huge storms
known as Great White Spots, which are ten times larger than the regular
storms, are rarer and occur about once per Saturnian year (29.5 Earth
years). Current models propose that the outbreak of a Great White Spot
is due to moist convection induced by water. However, the generation of
the global disturbance and its effect on Saturn's permanent winds have
hitherto been unconstrained by data, because there was insufficient
spatial resolution and temporal sampling to infer the dynamics of
Saturn's weather layer (the layer in the troposphere where the cloud
forms). Theoretically, it has been suggested that this phenomenon
is seasonally controlled. Here we report observations of a storm
at northern latitudes in the peak of a weak westward jet during the
beginning of northern springtime, in accord with the seasonal cycle
but earlier than expected. The storm head moved faster than the jet,
was active during the two-month observation period, and triggered
a planetary-scale disturbance that circled Saturn but did not
significantly alter the ambient zonal winds. Numerical simulations
of the phenomenon show that, as on Jupiter, Saturn's winds extend
without decay deep down into the weather layer, at least to the
water-cloud base at pressures of 10-12bar, which is much deeper than
solar radiation penetrates.
---------------------------------------------------------
Title: Solar flares: observations vs simulations
Authors: Rubio da Costa, Fatima; Zuccarello, Francesca; Labrosse,
Nicolas; Fletcher, Lyndsay; Prosecký, Tomáš; Kašparová, Jana
2011IAUS..274..182R Altcode:
In order to study the properties of faint, moderate and bright flares,
we simulate the conditions of the solar atmosphere using a radiative
hydrodynamic model (Abbett & Hawley, 1999). A constant beam of
non-thermal electrons is injected at the apex of a 1D coronal loop and
heating from thermal soft X-ray emission is included. We compare the
results with some observational data in Ly-α (using TRACE 1216 and
1600 Å data and estimating the “pure” Ly-α emission) and in Hα
(data taken with a Multichannel Flare Spectrograph, at the Ondrejov
Observatory).
---------------------------------------------------------
Title: The Magnetic and Dynamic Properties of Flaring Active Regions
Authors: Watson, Fraser; Fletcher, L.
2011SPD....42.1201W Altcode: 2011BAAS..43S.1201W
As solar cycle 24 begins, the return of active regions and solar flares
provides new opportunities for the study of the sun, particularly with
the recently launched Solar Dynamics Orbiter. This allows these regions
to be studied in more detail than has previously been possible. We have
developed a magnetic segmentation algorithm that allows us to examine
magnetic structures within active region magnetograms and track their
evolution in space and time. With this, we can build up a picture of
the photospheric properties of the active region before and after
solar flares. We can then examine the structures for changes that
occur around the time of flaring and compare these with changes seen
in other active regions at times of emergence, flaring and decay. We
present the findings of a study of flaring active regions, most of
which come from SOHO/MDI data and two use data from SDO/HMI. These
two regions observed by HMI include two of the strongest flares seen
during the beginning of solar cycle 24 whilst the MDI regions are
very active regions from the peak of solar cycle 23. In this way we
can also compare any changes observed between the two cycles.
---------------------------------------------------------
Title: Doppler Signatures In EVE Spectra
Authors: Hudson, Hugh S.; Chamberlin, P.; Woods, T.; Fletcher, L.;
Graham, D.
2011SPD....42.2124H Altcode: 2011BAAS..43S.2124H
The Extreme-ultraviolet Variability Experiment (EVE) on SDO is providing
a comprehensive set of EUV spectra of the Sun as a star. The routine
sampling is with 10 s integrations at a resolution of 0.1 nm. Although
this resolution corresponds to only some 1000 km/s in velocity space,
we demonstrate that the instrument is stable enough to detect the SDO
orbital motion of a few km/s readily in the bright He II line at 30.4
nm. We find the random error in the centroid location of this line to be
less than one pm (less than 1 km/s) per 10 s integration. We also note
systematic effects from a variety of causes. For flare observations,
the line centroid position depends on the flare position. We discuss the
calibration of this effect and show that EVE can nonetheless provide
clear Doppler signatures that may be interpreted in terms of flare
dynamics. This information has some value in and of itself, because of
EVE's sensitivity, but we feel that it will be of greatest importance
when combined with imagery (e.g., via AIA) a modeling. We discuss flare
signatures in several events, e.g. the gamma-ray flare SOL2010-06-12
and SOL2011-02-16T:07:44, taking advantage of AIA image comparisons.
---------------------------------------------------------
Title: Uranus’ cloud structure and seasonal variability from
Gemini-North and UKIRT observations
Authors: Irwin, P. G. J.; Teanby, N. A.; Davis, G. R.; Fletcher,
L. N.; Orton, G. S.; Tice, D.; Kyffin, A.
2011Icar..212..339I Altcode:
Observations of Uranus were made in September 2009 with the
Gemini-North telescope in Hawaii, using both the NIFS and NIRI
instruments. Observations were acquired in Adaptive Optics mode and
have a spatial resolution of approximately 0.1″. <P />NIRI images
were recorded with three spectral filters to constrain the overall
appearance of the planet: J, H-continuum and CH<SUB>4</SUB>(long),
and long slit spectroscopy measurements were also made (1.49-1.79 μm)
with the entrance slit aligned on Uranus’ central meridian. To acquire
spectra from other points on the planet, the NIFS instrument was used
and its 3″ × 3″ field of view stepped across Uranus’ disc. These
observations were combined to yield complete images of Uranus at
2040 wavelengths between 1.476 and 1.803 μm. <P />The observed
spectra along Uranus central meridian were analysed with the NEMESIS
retrieval tool and used to infer the vertical/latitudinal variation
in cloud optical depth. We find that the 2009 Gemini data perfectly
complement our observations/conclusions from UKIRT/UIST observations
made in 2006-2008 and show that the north polar zone at 45°N has
continued to steadily brighten while that at 45°S has continued
to fade. The improved spatial resolution of the Gemini observations
compared with the non-AO UKIRT/UIST data removes some of the earlier
ambiguities with our previous analyses and shows that the opacity of
clouds deeper than the 2-bar level does indeed diminish towards the
poles and also reveals a darkening of the deeper cloud deck near the
equator, perhaps coinciding with a region of subduction. We find that
the clouds at 45°N,S lie at slightly lower pressures than the clouds
at more equatorial latitudes, which suggests that they might possibly
be composed of a different condensate, presumably CH<SUB>4</SUB> ice,
rather than H<SUB>2</SUB>S or NH<SUB>3</SUB> ice, which is assumed for
the deeper cloud. In addition, analysis of the centre-to-limb curves
of both the Gemini/NIFS and earlier UKIRT/UIST IFU observations shows
that the main cloud deck has a well-defined top, and also allows us
to better constrain the particle scattering properties. <P />Overall,
Uranus appeared to be less convectively active in 2009 than in the
previous 3 years, which suggests that now the northern spring equinox
(which occurred in 2007) is passed the atmosphere is settling back into
the quiescent state seen by Voyager 2 in 1986. However, a number of
discrete clouds were still observed, with one at 15°N found to lie
near the 500 mb level, while another at 30°N, was seen to be much
higher at near the 200 mb level. Such high clouds are assumed to be
composed of CH<SUB>4</SUB> ice.
---------------------------------------------------------
Title: Relationship Between Hard and Soft X-ray Emission Components
of a Solar Flare
Authors: Guo, Jingnan; Liu, Siming; Fletcher, Lyndsay; Kontar,
Eduard P.
2011ApJ...728....4G Altcode: 2010arXiv1012.4346G
X-ray observations of solar flares routinely reveal an impulsive
high-energy and a gradual low-energy emission component, whose
relationship is one of the key issues of solar flare study. The gradual
and impulsive emission components are believed to be associated with,
respectively, the thermal and nonthermal components identified in
spectral fitting. In this paper, a prominent ~50 s hard X-ray (HXR)
pulse of a simple GOES class C7.5 flare on 2002 February 20 is used to
study the association between high-energy, non-thermal, and impulsive
evolution, and low-energy, thermal, and gradual evolution. We use
regularized methods to obtain time derivatives of photon fluxes to
quantify the time evolution as a function of photon energy, obtaining
a break energy between impulsive and gradual behavior. These break
energies are consistent with a constant value of ~11 keV in agreement
with those found spectroscopically between thermal and non-thermal
components, but the relative errors of the former are greater than
15% and much greater than the few percent errors found from the
spectral fitting. These errors only weakly depend on assuming an
underlying spectral model for the photons, pointing to the current
data being inadequate to reduce the uncertainties rather than there
being a problem associated with an assumed model. The time derivative
method is used to test for the presence of a "pivot energy" in this
flare. Although these pivot energies are marginally consistent with
a constant value of ~9 keV, its values in the HXR rise phase appear
to be lower than those in the decay phase. Assuming that electrons
producing the high-energy component have a power-law distribution and
are accelerated from relatively hot regions of a background plasma
responsible for the observed thermal component, a low limit is obtained
for the low-energy cutoff. This limit is always lower than the break and
pivot energies and is located in the tail of the Maxwellian distribution
of the thermal component.
---------------------------------------------------------
Title: Jupiter In The Crosshairs: Recent Impacts And Their
Implications
Authors: Hammel, Heidi B.; de Pater, I.; Simon-Miller, A. A.; Fletcher,
L.; Boslough, M. B.; Orton, G. S.; Djorgovski, G.; Yanamandra-Fisher,
P.; Wong, M. H.; Hueso, R.; Sánchez-Lavega, A.; Go, C.; Wesley, A.;
Pérez-Hoyos, S.; Edwards, M.; Clarke, J. T.; Noll, K. S.
2011AAS...21715608H Altcode: 2011BAAS...4315608H
No abstract at ADS
---------------------------------------------------------
Title: The atmospheric influence, size and possible asteroidal nature
of the July 2009 Jupiter impactor
Authors: Orton, G. S.; Fletcher, L. N.; Lisse, C. M.; Chodas, P. W.;
Cheng, A.; Yanamandra-Fisher, P. A.; Baines, K. H.; Fisher, B. M.;
Wesley, A.; Perez-Hoyos, S.; de Pater, I.; Hammel, H. B.; Edwards,
M. L.; Ingersoll, A. P.; Mousis, O.; Marchis, F.; Golisch, W.;
Sanchez-Lavega, A.; Simon-Miller, A. A.; Hueso, R.; Momary, T. W.;
Greene, Z.; Reshetnikov, N.; Otto, E.; Villar, G.; Lai, S.; Wong, M. H.
2011Icar..211..587O Altcode:
Near-infrared and mid-infrared observations of the site of the 2009
July 19 impact of an unknown object with Jupiter were obtained within
days of the event. The observations were used to assess the properties
of a particulate debris field, elevated temperatures, and the extent
of ammonia gas redistributed from the troposphere into Jupiter's
stratosphere. The impact strongly influenced the atmosphere in a
central region, as well as having weaker effects in a separate field
to its west, similar to the Comet Shoemaker-Levy 9 (SL9) impact sites
in 1994. Temperatures were elevated by as much as 6 K at pressures
of about 50-70 mbar in Jupiter's lower stratosphere near the center
of the impact site, but no changes above the noise level (1 K) were
observed in the upper stratosphere at atmospheric pressures less than
∼1 mbar. The impact transported at least ∼2 × 10 <SUP>15</SUP>
g of gas from the troposphere to the stratosphere, an amount less
than derived for the SL9 C fragment impact. From thermal heating
and mass-transport considerations, the diameter of the impactor was
roughly in the range of 200-500 m, assuming a mean density of 2.5
g/cm <SUP>3</SUP>. Models with temperature perturbations and ammonia
redistribution alone are unable to fit the observed thermal emission;
non-gray emission from particulate emission is needed. Mid-infrared
spectroscopy of material delivered by the impacting body implies that,
in addition to a silicate component, it contains a strong signature
that is consistent with silica, distinguishing it from SL9, which
contained no evidence for silica. Because no comet has a significant
abundance of silica, this result is more consistent with a "rocky"
or "asteroidal" origin for the impactor than an "icy" or "cometary"
one. This is surprising because the only objects generally considered
likely to collide with Jupiter and its satellites are Jupiter-Family
Comets, whose populations appear to be orders of magnitude larger
than the Jupiter-encountering asteroids. Nonetheless, our conclusion
that there is good evidence for at least a major asteroidal component
of the impactor composition is also consistent both with constraints
on the geometry of the impactor and with results of contemporaneous
Hubble Space Telescope observations. If the impact was not simply a
statistical fluke, then our conclusion that the impactor contained
more rocky material than was the case for the desiccated Comet SL9
implies a larger population of Jupiter-crossing asteroidal bodies than
previously estimated, an asteroidal component within the Jupiter-Family
Comet population, or compositional differentiation within these bodies.
---------------------------------------------------------
Title: Jupiter's stratospheric hydrocarbons and temperatures after
the July 2009 impact from VLT infrared spectroscopy
Authors: Fletcher, L. N.; Orton, G. S.; de Pater, I.; Mousis, O.
2010A&A...524A..46F Altcode:
<BR /> Aims: Thermal infrared imaging and spectroscopy of the July 19,
2009 Jupiter impact site has been used to identify unique features
of the physical and chemical atmospheric response to this unexpected
collision. <BR /> Methods: Images and high-resolution spectra of
methane, ethane and acetylene emission (7-13 μm) from the 2009 impact
site were obtained by the Very Large Telescope (VLT) mid-infrared
camera/spectrometer instrument, VISIR. An optimal estimation retrieval
algorithm was used to determine the atmospheric temperatures and
hydrocarbon distribution in the month following the impact. <BR />
Results: Ethane spectra at 12.25 μm could not be explained by a
rise in temperature alone. Ethane was enhanced by 1.7-3.2 times the
background abundance on July 26, implying production as the result of
shock chemistry in a high C/O ratio environment, favouring an asteroidal
origin for the 2009 impactor. Small enhancements in acetylene emission
were also observed over the impact site. However, no excess methane
emission was found over the impact longitude, either with broadband
7.9-μm imaging 21 h after the impact, or with center-to-limb scans of
strong and weak methane lines between 7.9 and 8.1 μm in the ensuing
days, indicating either extremely rapid cooling in the initial stages,
or an absence of heating in the upper stratosphere (p < 10 mbar)
due to the near-horizontal orientation of the impact. Models of 12.3-μm
spectra are consistent with a ≈ 3 K rise in the lower stratosphere (p
> 10 mbar), though this solution is highly dependent on the spectral
properties of stratospheric debris. The enhanced ethane emission was
localised over the impact streak, and was diluted in the ensuing weeks
by redistribution of heated gases by zonal flow and mixing with the
unperturbed jovian air. <BR /> Conclusions: The different thermal
energy deposition profiles, in addition to the highly reducing (C/O
> 1) environment and shallow impactor angle, suggest that (a) the
2009 plume and shock-fronts did not reach the sub-microbar altitudes
of the Shoemaker-Levy 9 plumes; and (b) models of a cometary impact are
not directly applicable to the unique impact circumstances of July 2009.
---------------------------------------------------------
Title: Compositional Constraints on the Atmospheres of Uranus and
Neptune from Herschel and Spitzer Spectroscopic Observations
Authors: Orton, G. S.; Moreno, R.; Lellouch, E.; Fletcher, L. N.;
Hartogh, P.; Jarchow, C.; Feuchtgruber, H.; Line, M. R.; Herschel
Key Project On Water; Related Chemistry in Solar System Team
2010AGUFM.P14A..07O Altcode:
Key elements of planetary compositions provide one of the most
fundamental constraints on the origins and evolution of major
bodies in the solar system. For the icy giants, Uranus and Neptune,
acquiring compositional information has been a challenge because
of their faintness. Great strides have been made with the advent of
cryogenically cooled space-borne telescopes, however, and we report here
the most recent of these results from Spitzer and Herschel telescopes,
the latter including data taken within the framework of the Key Project
"Water and Related Chemistry in the Solar system". Our interpretation
of these results is set in the context of earlier results obtained by
the ISO LWS and SWS spectrometers, together with relevant Earth-based
observations. We will specifically discuss the chemical inventory and
abundances stratospheric hydrocarbons, the implications of thermal
structure for deep atmospheric composition, and improved constraints
on the D/H ratio in Neptune.
---------------------------------------------------------
Title: Solar Flares and the Chromosphere
Authors: Fletcher, L.; Turkmani, R.; Hudson, H. S.; Hawley, S. L.;
Kowalski, A.; Berlicki, A.; Heinzel, P.
2010arXiv1011.4650F Altcode:
A white paper prepared for the Space Studies Board, National Academy
of Sciences (USA), for its Decadal Survey of Solar and Space Physics
(Heliophysics), reviewing and encouraging studies of flare physics in
the chromosphere.
---------------------------------------------------------
Title: Unveiling Uranus' Clouds: New Observations From Gemini-North
NIFS And NIRI
Authors: Irwin, Patrick G. J.; Teanby, N. A.; Davis, G. R.; Fletcher,
L. N.; Orton, G.; Tice, D.
2010DPS....42.4404I Altcode: 2010BAAS...42.1045I
Observations of Uranus were made in September 2009 with the Gemini-North
telescope in Hawaii, using both the NIFS and NIRI instruments. Adaptive
optics were used to achieve a spatial resolution of approximately 0.1
arcsec. <P />NIRI images were recorded with three spectral filters
to constrain the overall appearance of the planet: J, H-continuum and
CH4(long), and long slit spectra (1.49 to 1.79 microns) were obtained
with the slit aligned on Uranus’ central meridian. In addition,
the NIFS instrument was used to acquire spectra from other points
on the planet, stepping the NIFS 3 x 3 arcsec field of view across
Uranus’ disc. These observations were combined to yield complete
images of Uranus at 2040 wavelengths between 1.476 and 1.803 microns
with a spectral resolution of 5000. <P />The observed spectra along
Uranus central meridian were analyzed with the NEMESIS retrieval
tool and used to infer the vertical/latitudinal variation in cloud
optical depth. We find that the 2009 Gemini data perfectly complement
our observations/conclusions from UKIRT/UIST observations made in
2006-2008 and show that the north polar zone at 45N has continued to
steadily brighten while that at 45S has continued to fade. The improved
spatial resolution of the Gemini observations compared with the non-AO
UKIRT/UIST data remove many of the earlier ambiguities inherent in the
previous analysis. <P />Overall, Uranus appeared to be less convectively
active in 2009 than in the previous 3 years, which suggests that now
the equinox (which occurred in 2007) is over the atmosphere is settling
back into the quiescent state seen by Voyager 2 in 1986. However, one
discrete cloud was captured in the NIFS observations and was estimated
to lie at a pressure level of 300-400 mbar.
---------------------------------------------------------
Title: The Optical Depth of White-light Flare Continuum
Authors: Potts, Hugh; Hudson, Hugh; Fletcher, Lyndsay; Diver, Declan
2010ApJ...722.1514P Altcode: 2010arXiv1004.1039P
The white-light continuum emission of a solar flare remains a puzzle as
regards its height of formation and its emission mechanism(s). This
continuum and its extension into the near-UV contain the bulk of
the energy radiated by a flare, and so its explanation is a high
priority. We describe a method to determine the optical depth of the
emitting layer and apply it to the well-studied flare of 2002 July
15, making use of MDI pseudo-continuum intensity images. We find the
optical depth of the visible continuum in all flare images, including
an impulsive ribbon to be small, consistent with the observation of
Balmer and Paschen edges in other events.
---------------------------------------------------------
Title: First Earth-based Detection of a Superbolide on Jupiter
Authors: Hueso, R.; Wesley, A.; Go, C.; Pérez-Hoyos, S.; Wong, M. H.;
Fletcher, L. N.; Sánchez-Lavega, A.; Boslough, M. B. E.; de Pater, I.;
Orton, G. S.; Simon-Miller, A. A.; Djorgovski, S. G.; Edwards, M. L.;
Hammel, H. B.; Clarke, J. T.; Noll, K. S.; Yanamandra-Fisher, P. A.
2010ApJ...721L.129H Altcode: 2010arXiv1009.1824H
Cosmic collisions on planets cause detectable optical flashes that
range from terrestrial shooting stars to bright fireballs. On 2010
June 3 a bolide in Jupiter's atmosphere was simultaneously observed
from the Earth by two amateur astronomers observing Jupiter in red and
blue wavelengths. The bolide appeared as a flash of 2 s duration in
video recording data of the planet. The analysis of the light curve
of the observations results in an estimated energy of the impact of
(0.9-4.0) × 10<SUP>15</SUP> J which corresponds to a colliding body of
8-13 m diameter assuming a mean density of 2 g cm<SUP>-3</SUP>. Images
acquired a few days later by the Hubble Space Telescope and other large
ground-based facilities did not show any signature of aerosol debris,
temperature, or chemical composition anomaly, confirming that the
body was small and destroyed in Jupiter's upper atmosphere. Several
collisions of this size may happen on Jupiter on a yearly basis. A
systematic study of the impact rate and size of these bolides can enable
an empirical determination of the flux of meteoroids in Jupiter with
implications for the populations of small bodies in the outer solar
system and may allow a better quantification of the threat of impacting
bodies to Earth. The serendipitous recording of this optical flash
opens a new window in the observation of Jupiter with small telescopes.
---------------------------------------------------------
Title: Vertical Cloud Structure Of The 2009 Jupiter Impact Based On
HST/WFC3 Observations
Authors: Perez-Hoyos, Santiago; Sanz-Requena, J. F.; Sanchez-Lavega,
A.; Wong, M.; Hueso, R.; Hammel, H. B.; Orton, G. S.; Fletcher,
L. N.; de Pater, I.; Simon-Miller, A. A.; Clarke, J. T.; Noll, K.;
Yanamandra-Fisher, P. A.
2010DPS....42.1107P Altcode: 2010BAAS...42R1018P
The impact of a body of unknown origin with Jupiter in July 2009
(Sánchez-Lavega et al., Astrophys. J. Lett, Vol. 715, L155. 2010)
produced an intense perturbation of the planet's atmosphere at the
visible levels. The perturbation was caused by dense aerosol material;
this strongly absorbing material expanded steadily as it was advected by
the local winds. This phenomenon was observed at high spatial resolution
by the Hubble Space Telescope in July, August, September and November
2009 with recently installed Wide Field Camera 3. In this work, we
present radiative transfer modeling of the observed reflectivity in the
near UV (200nm) to near IR (950nm) range. The geometrical and spectral
variations of reflectivity elucidate the main particle properties
(optical thickness, size, imaginary refractive index) and their temporal
evolution. The aerosol particles that formed during the impact have a
mean radius of about 1 micron and are located high in the atmosphere
(above 10 mbar), in good agreement ith ground-based observations in
deep methane absorption bands in the near infrared. The density of
this particle layer decreases with time until it approaches that of
the pre-impact atmosphere. These results are also discussed in terms of
what we know from other impacts in Jupiter (1994's SL9 event and 2010's
bolide). Acknowledgements: SPH, ASL and RH are supported by the Spanish
MICIIN AYA2009-10701 with FEDER and Grupos Gobierno Vasco IT-464-07.
---------------------------------------------------------
Title: Long-term Evolution of the Aerosol Debris Cloud Produced by
the 2009 Impact of an Object with Jupiter
Authors: Sanchez-Lavega, Agustin; Orton, G. S.; Hueso, R.;
Pérez-Hoyos, S.; Fletcher, L. N.; Garcia-Melendo, E.; Gomez,
J. M.; de Pater, I.; Wong, M.; Hammel, H. B.; Yanamandra-Fisher, P.;
Simon-Miller, M.; Barrado-Izagirre, N.; Marchis, F.; Mousis, O.; Ortiz,
J. L.; Garcia, J.; Cecconi, M.; Clarke, J. T.; Noll, K.; Pedraz, S.;
Wesley, A.; McConnel, N.; Kalas, P.; Graham, J.; McKenzie, L.; Reddy,
V.; Golisch, W.; Griep, D.; Sears, P.; International Outer PLanet Watch
(IOPW)
2010DPS....42.3101S Altcode: 2010BAAS...42Q1009S
We report the evolution of the cloud of aerosols produced in the
atmosphere of Jupiter by the impact of an object in 19 July 2009
(Sánchez-Lavega et al., Astrophys. J. Lett, Vol. 715, L155. 2010). This
study is based on images obtained with a battery of ground-based
telescopes and the Hubble Space Telescope in the visible and in
the deep near infrared absorption bands at 2.1-2.3 microns from the
impact date to 31 December 2009. The impact cloud expanded zonally
from 5000 km (July 19) to 225,000 km (about 180 deg in longitude by
29 October) and it was meridionally localized within a latitude band
from -53.5 deg to -61.5 deg. During the first two months it showed a
heterogeneous structure with embedded spots of a size of 500 - 1000
km. The cloud was mainly dispersed in longitude by the dominant zonal
winds and their meridional shear and, during the initial stages,
by the action of local motions perhaps originated by the thermal
perturbation produced at the impact site. The tracking of individual
spots within the impact cloud showed that the winds increase their
eastward velocity with altitude above the tropopause by 5-10 m/s. We
found evidence of discrete localized meridional motions in the
equatorward direction with speeds of 1 - 2 m/s. Measurements of the
cloud reflectivity evolution during the whole period showed that it
followed an exponential decrease with a characteristic time of 15 days,
shorter than the 45 - 200 days sedimentation time for the small aerosol
particles in the stratosphere. A radiative transfer model of the cloud
optical depth coupled to an advection model of the cloud dispersion
by the wind shears, reproduces this behavior. Acknowledgements: ASL,
RH, SPH, NBI are supported by the Spanish MICIIN AYA2009-10701 with
FEDER and Grupos Gobierno Vasco IT-464-07.
---------------------------------------------------------
Title: Seasonal and Temporal Changes on Jupiter and Saturn: A Review
of Ground-based Observations
Authors: Yanamandra-Fisher, Padma A.; Orton, G. S.; Fisher, B. M.;
Fletcher, L. N.; Miller, A. S.
2010DPS....42.1102Y Altcode: 2010BAAS...42.1017Y
We report on the seasonal and temporal changes observed on Jupiter and
Saturn, based on near- and mid-infrared data acquired from several
observatories (NASA/InfraRed Telescope Facility, NAOJ/Subaru,
ESO/Very Large Telescope) and provide compelling rationale for a
coordinated network of large telescopes for continued ground-based
observations. Jupiter has been experiencing an era of atmospheric
global upheaval since 2005, the observed atmospheric changes being
manifestations of changes in local meteorology and latent physical
parameters of the system, and occur on various timescales and
latitudes. The discrete storms in Jupiter's atmosphere have undergone
significant changes over the past decade. The merger of the three
white ovals into Oval BA and its subsequent color change in 2006
appear to be correlated to periodic interactions with the Great Red
Spot (GRS). Subsequent episodes of GRS-Oval BA interactions in 2006
and 2008 and the upcoming interaction in 2010 provide snapshots of
changes in the local meteorology. We identify relationships between
latent physical variables of the spatially and temporally changing
systems in terms of cloud opacities, aerosol distribution and thermal
fields. Ground-based near- and mid-infrared observations of Saturn from
1995 - 2009, covering half a Saturnian year, provide a rich data set
to model seasonal changes in Saturn's atmosphere from autumnal equinox
(1995) to vernal equinox (2009). Since 1995, as Saturn's south pole
received increasing solar insolation, its albedo exhibits an increase
in reflectivity at mid-latitudes in the southern hemisphere, decreasing
towards the equator, anti-correlated with the thermal field. Similar
to equatorial oscillations of temperatures on Earth and Jupiter, Saturn
displays stratospheric temperature oscillations, with a period of half
a Saturnian year, suggesting the influence of seasonal forcing. We
anticipate development of similar phenomena in the next few years,
as Saturn approaches northern solstice.
---------------------------------------------------------
Title: Mid-IR Atmospheric Tracers of Jupiter's Storm Oval BA
Authors: Shannon, Matthew J.; Orton, G.; Fletcher, L.
2010DPS....42.1103S Altcode: 2010BAAS...42R1017S
The 2005-2006 reddening of a major anticyclonic storm, known as
Oval BA, in Jupiter's turbulent atmosphere may well be a paradigm
for the formation of red-colored vortices on the giant planets,
including Jupiters Great Red Spot. Mid-infrared observations can be
effectively used to determine physical and chemical properties of the
atmosphere, and we present the results of mid-infrared thermal imaging
observations, collected from NASAs Infrared Telescope Facility (IRTF)
in Hawaii, ESOs Very Large Telescope (VLT) in Chile and the NAOJ Subaru
Telescope in Hawaii between spring of 2005 and summer of 2006. These
address the role of atmospheric tracers, including cloud opacity,
the ammonia gas content, and the variation of the fraction of para-
to ortho-hydrogen from local thermal equilibrium in assessing the rate
of upwelling. These properties were retrieved with the Oxford-developed
code, Nemesis, with the purpose of providing constraints on dynamical
models in an effort to identify the mechanism for the color change. The
most obvious change is that the temperature gradient from the inner to
the outer part of Oval BA increased over the time of the color change,
indicating a strengthening of the intensity of the vortex.
---------------------------------------------------------
Title: Saturn's "String of Pearls” After Five Years: Still There,
Moving Backwards Faster in the Voyager System
Authors: Baines, Kevin H.; Momary, T. W.; Fletcher, L. N.; Buratti,
B. J.; Brown, R. H.; Clark, R. N.; Nicholson, P. D.
2010DPS....42.4103B Altcode: 2010BAAS...42.1039B
Since July 2005, the Visual Infrared Mapping Spectrometer (VIMS) onboard
the Cassini Orbiter has been following an enigmatic feature centered
at 33.9 degrees (planetocentric ) north latitude. Observed in detail on
14 occasions between July 2005 and July 2010, the feature is seen only
in the 5-micron thermal window which probes large-particle clouds down
to the ∼ 4-bar level. This feature is comprised of a main cloud layer
near 1.5-3 bar which has 21-25 regularly spaced, near- uniformly-sized,
circularly-shaped clearings which together span, on average, 94 degrees
of longitude. In VIMS 5-micron imagery, which observes the warm glow of
Saturn generated at depth, these regularly spaced and shaped clearings
appear bright while the surrounding cloud, observed in silhouette,
appears dark- hence the colloquial name "String of Pearls". Each
clearing is about 1 degree of longitude (∼900 km) wide, and is,
on average over the five-years period, 4.3 degrees of longitude from
its neighbor. In latitude, adjacent pearls are typically 0.4 degrees -
or about 1 pearl radius - apart. At various times over the past five
years of observations, the longitudinal length has varied from 76 to 104
degrees and the mean separation between clearings has varied from 3.6 to
5.0 degrees, while the mean latitude of the structure has ranged from
32.9 to 34.8 degrees - or by 2 mean diameters of the pearls. The pearl
structure moves retrograde in the Voyager system (Desch and Kaiser,
Geophys. Res. Lett 8, 253-256, 1981) with an average speed over five
years of 21.84 ± 0.02 m/s. Since late 2007, the mean latitude increased
from 34.0 ± 0.2 to 34.5 ± 0.2 deg as the retrograde speed increased
from 21.73 ± 0.09 m/s to 22.02 ± 0.08 m/s, making it the fastest
moving retrograde feature observed by Cassini/VIMS in non-polar regions.
---------------------------------------------------------
Title: Saturn's Equatorial Plumes after Five Years: Still Lurking
under the Haze
Authors: Momary, Thomas W.; Baines, K. H.; Fletcher, L. N.; Buratti,
B. J.; Brown, R. H.; Clark, R. N.; Nicholson, P. D.
2010DPS....42.1119M Altcode: 2010BAAS...42.1021M
Numerous large, discrete cloud features have been observed for five
years underneath Saturn's equatorial haze. They were clearly observed on
three occasions - June 28, 2005, April 21, 2006 and May 1, 2010 - from a
vantage point directly over the knife-edge of the rings, which reduced
the ring obscuration of the disk to just ± 1 degrees of latitude
centered at the equator. These features are seen only in the 5-micron
thermal window which probes large-particle clouds down to the ∼ 4-bar
level. In VIMS 5-micron imagery, which observes the warm glow of Saturn
generated at depth, these deep clouds are observed in silhouette,
appearing as dark features against the background glow. Spectral
modeling indicates that they are primarily located in the 2-3 bar
region. However, smaller particles of ammonia may be present overhead
as a relatively small component of the 5-micron extinction. Indeed,
the correlation of these features with the exceedingly high and thick
equatorial haze layer indicates a plausible link: That these features
involve vertical transport of gaseous condensibles to the upper
troposphere forming the thick haze that is observed in images taken
in reflected sunlight. The features are concentrated in two narrow,
symmetrical cloudy zones between 4 and 8 degrees planetocentric latitude
in both hemispheres, where they cover significant fractions, although
varying, amounts of the total area of these latitudinal bands: ∼ 55%
in 2005-2006 vs ∼ 28% in 2010. The mean area of the average feature
was roughly constant over all three observations, with the longitudinal
extent of the average feature in 2005-2006 decreasing ∼10% from 8
degrees ( 8000 km) to 7.1 degrees in 2010 while the mean latitudinal
extent increased by ∼10% from 3.05 in 2005 vs 3.4 degrees in 2010.
---------------------------------------------------------
Title: Solar Flares and the Chromosphere: A white paper for the
Decadal Survey
Authors: Hudson, H. S.; Fletcher, L.; Turkmani, R.; Hawley, S. L.;
Kowalski, A. F.; Berlicki, A.; Heinzel, P.
2010helio2010....1H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Physical Structure and Chemical Composition of Neptune's
Atmosphere from Combined Herschel and Spitzer Spectral Observations
Authors: Orton, Glenn S.; Moreno, R.; Lellouch, E.; Fletcher, L. N.;
Hartogh, P.; Feuchtgruber, H.; Jarchow, C.; Cavalie, T.; Lara, L.;
Rengel, M.; Gonzalez, A.; Line, M.; Herschel HssO Key Project Team
2010DPS....42.4409O Altcode: 2010BAAS...42.1047O
We report the analysis of thermal-infrared observations of Neptune's
disk by experiments on the Spitzer and Herschel Space Telescopes. The
Spitzer data were obtained by the IRS instrument at wavelengths
between 5.2 and 21.5 microns at a spectral resolving power, R
70, and at wavelengths between 10 and 21.5 microns at R 600. The
Herschel observations were made by the PACS instrument's integral
field spectrometer between 51 and 220 microns at R 3000, within the
framework of the Key Project, “Water and Related Chemistry in the
Solar System”. Our analysis is set in the context of lower-resolution
spectra obtained by the ISO LWS and SWS spectrometers covering
wavelengths between 28 and 185 microns and the Akari IRC spectrometer
covering wavelengths between 5.8 and 13.3 microns at R 40, together
with spatially resolved ground-based studies of thermal emission. Our
results indicate that that global-mean tropospheric temperatures are
lower than those derived from the Voyager radio-occultation experiment,
and consistent with the ISO results. Preliminary results (Lellouch
et al. 2010 Astron. & Astrophys. In press) indicate that the D/H
ratio is 4.5±1.0 x 10<SUP>-5</SUP>, consistent with enrichment of
deuterium over the protosolar value, and the stratospheric column of
H<SUB>2</SUB>O is 2.1±0.5 x 10<SUP>14</SUP> cm<SUP>-2</SUP>. The
peak CH<SUB>4</SUB> abundance in the stratosphere is orders of
magnitude larger than if it were cold-trapped below the mean 54-Kelvin
tropopause minimum temperature - but consistent with injection from
Neptune's warmer south polar region. Good fits to a variety of other
stratospheric emission features are obtained: CO, CH<SUB>3</SUB>,
CO<SUB>2</SUB>, C<SUB>2</SUB>H<SUB>2</SUB>, C<SUB>2</SUB>H<SUB>4</SUB>,
C<SUB>2</SUB>H<SUB>6</SUB>, C<SUB>3</SUB>H<SUB>8</SUB>,
C<SUB>4</SUB>H<SUB>2</SUB>. It is also possible to obtain a better fit
to a spectral region dominated by C<SUB>2</SUB>H<SUB>6</SUB> emission
by adding 50-100 ppt of C<SUB>6</SUB>H<SUB>6</SUB>.
---------------------------------------------------------
Title: First Earth-based Detection of a Superbolide on Jupiter
Authors: Hueso, Ricardo; Wesley, A.; Go, C.; Perez-Hoyos, S.; Wong,
M. H.; Fletcher, L. N.; Sanchez-Lavega, A.; Boslough, M. B. E.;
de Pater, I.; Orton, G. S.; Simon-Miller, A. A.; Djorgovski,
S. G.; Edwards, M. L.; Hammel, H. B.; Clarke, J. T.; Noll, K. S.;
Yanamandra-Fisher, P. A.
2010DPS....42.3102H Altcode: 2010BAAS...42.1009H
On June 3, 2010 a bolide in Jupiter's atmosphere was observed from the
Earth for the first time. The flash was detected by amateur astronomers
A. Wesley and C. Go observing in two wavelength ranges. We present an
analysis of the light curve of those observations that allow estimating
the size of the object to be significantly smaller than the SL9 and
the July 2009 Jupiter impact. Observations obtained a few days later
by large telescopes including HST, VLT, Keck and Gemini showed no
signature of the impact in Jupiter atmosphere confirming the small
size of the impact body. A nearly continuous observation campaign
based on several small telescopes by amateurs astronomers might allow
an empirical determination of the flux of meteoroids in Jupiter with
implications for the populations of small bodies in the outer solar
system and may allow a better quantification of the threat of impacting
bodies to Earth. <P />Acknowledgements: RH, ASL and SPH are supported
by the Spanish MICIIN AYA2009-10701 with FEDER and Grupos Gobierno
Vasco IT-464-07. LNF is supported by a Glasstone Science Fellowship
at the University of Oxford.
---------------------------------------------------------
Title: Thermal Imaging of Jupiter's Giaht Vortices: the Great Red
Spot and Oval BA
Authors: Orton, G.; Fletcher, L.; Yanamandra-Fisher, P.; Mousis,
O.; Fisher, B.; Irwin, P.; Vanzi, L.; Fujiyoshi, T.; Fuse, T.;
Simon-Miller, A.
2010epsc.conf..674O Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Recovery of Neptune's Near-Polar Stratospheric Hot Spot
Authors: Orton, G.; Fletcher, L.; Yanamandra-Fisher, P.; Encrenaz,
T.; Leyrat, C.; Hammel, H.
2010epsc.conf..678O Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Jupiter 2010: A Busy Year
Authors: Go, C. Y.; Wesley, A.; Wong, M.; de Pater, I.; Sanchez-Lavega,
A.; Marcus, P.; Huesco, R.; Rogers, J.; Simon-Miller, A.; Orton,
G. S.; Yanamandra-Fisher, P.; Fletcher, L.
2010epsc.conf..915G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Potential for stratospheric Doppler windspeed measurements
of Jupiter by sub-millimetre spectroscopy
Authors: Hurley, J.; Irwin, P. G. J.; Ellison, B. N.; de Kok, R.;
Calcutt, S. B.; Teanby, N. A.; Fletcher, L. N.; Irshad, R.
2010P&SS...58.1489H Altcode:
The sub-millimetre/microwave range of the spectrum has been exploited
in the field of Earth observation by many instruments over the years
and has provided a plethora of information on atmospheric chemistry and
dynamics - however, this spectral range has not been fully explored
in planetary science, having been exclusively employed to carry out
ground-based measurements. To this end, a sub-millimetre instrument,
the Orbiter Terahertz Infrared Spectrometer (ORTIS), is studied by
the University of Oxford and the Rutherford Appleton Laboratory, to
meet the requirements of the European Space Agency's Cosmic Visions
2015-2025 programme - in particular, the Europa Jupiter System Mission
(EJSM), which has the European Space Agency and the National Aeronautics
and Space Administration as partners. ORTIS is designed to measure
atmospheric temperature, the abundance of stratospheric water vapour and
other jovian gases, and is intended to be capable of retrieving vertical
profiles of horizontal windspeed in the stratosphere for the first
time, from Doppler-shifted emission lines measured at high spectral
resolution. In this work, a preliminary study and implementation of the
estimation of windspeed profiles on simulated spectra representative
of Jupiter is presented, detailing the development of the retrieval
algorithm, showing that a sub-millimetre instrument such as ORTIS should
be able to retrieve windspeed profiles to an accuracy of about 15 m/s
between 70 and 200 km/0.1-10 mb using a single near-limb measurement,
for expected noise amplitudes.
---------------------------------------------------------
Title: From Large-scale Loops to the Sites of Dense Flaring Loops:
Preferential Conditions for Long-period Pulsations in Solar Flares
Authors: Foullon, C.; Fletcher, L.; Hannah, I. G.; Verwichte, E.;
Cecconi, B.; Nakariakov, V. M.; Phillips, K. J. H.; Tan, B. L.
2010ApJ...719..151F Altcode:
Long-period quasi-periodic pulsations (QPPs) of solar flares are
a class apart from shorter period events. By involving an external
resonator, the mechanism they call upon differs from traditional QPP
models, but has wider applications. We present a multi-wavelength
analysis of spatially resolved QPPs, with periods around 10 minutes,
observed in the X-ray spectrum primarily at energies between 3 and 25
keV. Complementary observations obtained in Hα and radio emission in
the kHz to GHz frequency range, together with an analysis of the X-ray
plasma properties provide a comprehensive picture that is consistent
with a dense flaring loop subject to periodic energization and
thermalization. The QPPs obtained in Hα and type III radio bursts,
with similar periods as the QPPs in soft X-rays, have the longest
periods ever reported for those types of data sets. We also report 1-2
GHz radio emission, concurrent with but unrestricted to the QPP time
intervals, which is multi-structured at regularly separated narrowband
frequencies and modulated with ~18 minute periods. This radio emission
can be attributed to the presence of multiple "quiet" large-scale loops
in the background corona. Large scale but shorter inner loops below
may act as preferential resonators for the QPPs. The observations
support interpretations consistent with both inner and outer loops
subject to fast kink magnetohydrodynamic waves. Finally, X-ray imaging
indicates the presence of double coronal sources in the flaring sites,
which could be the particular signatures of the magnetically linked
inner loops. We discuss the preferential conditions and the driving
mechanisms causing the repeated flaring.
---------------------------------------------------------
Title: Lepton models for TeV emission from SNR RX J1713.7-3946
Authors: Fan, Z. H.; Liu, S. M.; Yuan, Q.; Fletcher, L.
2010A&A...517L...4F Altcode: 2010arXiv1007.0796F
<BR /> Aims: SNR RX J1713.7-3946 is perhaps one of the best observed
shell-type supernova remnants with emissions dominated by energetic
particles accelerated near the shock front. The nature of the TeV
emission, however, is an issue still open to investigation. <BR />
Methods: We carried out a systematic study of four lepton models for the
TeV emission with the Markov chain Monte Carlo method. <BR /> Results:
It is shown that current data already give good constraints on the model
parameters. Two commonly used parametric models do not appear to fit the
observed radio, X-ray, and γ-ray spectra. Models motivated by diffusive
shock acceleration and by stochastic acceleration by compressive waves
in the shock downstream give comparably good fits. The former has a
sharper spectral cutoff in the hard X-ray band than the latter. Future
observations with the HXMT and NuSTAR may distinguish these two models.
---------------------------------------------------------
Title: OT1_lfletche_1: Nitrogen, Phosphorus and Sulphur Chemistry in
Saturn's Atmosphere: Internal and External Origins for HCN, HCP and CS
Authors: Fletcher, L. N.
2010hers.prop..978F Altcode:
Our understanding of some of the fundamental physiochemical processes
at work within Saturns gaseous atmosphere is presently limited by
the difficulties associated with detection of a number of atmospheric
species. Based on our new understanding of Saturns bulk composition
and chemistry from the Cassini mission, Herschel/HIFI offers an
unprecedented opportunity to detect these species for the first
time, and to place constraints on their origins. Radiative transfer
calculations have been used in tandem with chemical modelling to
select optimal transitions of HCN, HCP and CS for study by HIFI. These
species have never been detected before, but are expected to be
important secondary repositories for nitrogen, phosphorus and sulphur
in Saturns atmosphere. Furthermore, the superb spectral resolution
of heterodyne spectroscopy is ideal for distinguishing between broad
tropospheric absorptions and narrow stratospheric emissions, allowing
us to distinguish between internal and external origins for each
species. Tropospheric abundances will be compared to expectations from
state of the art thermochemical and photochemical models, in addition
to predictions of lightning-induced shock chemistry. Stratospheric
abundances will be interpreted in terms of external supply of N,
P and S-bearing materials, either from large asteroidal/cometary
impacts (where shock chemistry in impact plumes is also important) or
influx of material from Enceladus, the rings or interplanetary dust
particles. As a result, the HIFI search for the first signatures of
Saturns HCN, HCP and CS abundances will serve as vital constraints on
internal chemistry and the coupling between Saturns cold atmosphere
and external environment, revealing the fundamental processes at work
in the cold outer reaches of our Solar System.
---------------------------------------------------------
Title: Jupiter After the 2009 Impact: Hubble Space Telescope Imaging
of the Impact-generated Debris and its Temporal Evolution
Authors: Hammel, H. B.; Wong, M. H.; Clarke, J. T.; de Pater, I.;
Fletcher, L. N.; Hueso, R.; Noll, K.; Orton, G. S.; Pérez-Hoyos,
S.; Sánchez-Lavega, A.; Simon-Miller, A. A.; Yanamandra-Fisher, P. A.
2010ApJ...715L.150H Altcode:
We report Hubble Space Telescope images of Jupiter during the aftermath
of an impact by an unknown object in 2009 July. The 2009 impact-created
debris field evolved more slowly than those created in 1994 by the
collision of the tidally disrupted comet D/Shoemaker-Levy 9 (SL9). The
slower evolution, in conjunction with the isolated nature of this
single impact, permits a more detailed assessment of the altitudes and
meridional motion of the debris than was possible with SL9. The color
of the 2009 debris was markedly similar to that seen in 1994, thus this
dark debris is likely to be Jovian material that is highly thermally
processed. The 2009 impact site differed from the 1994 SL9 sites in UV
morphology and contrast lifetime; both are suggestive of the impacting
body being asteroidal rather than cometary. Transport of the 2009
Jovian debris as imaged by Hubble shared similarities with transport
of volcanic aerosols in Earth's atmosphere after major eruptions.
---------------------------------------------------------
Title: The Impact of a Large Object on Jupiter in 2009 July
Authors: Sánchez-Lavega, A.; Wesley, A.; Orton, G.; Hueso, R.;
Perez-Hoyos, S.; Fletcher, L. N.; Yanamandra-Fisher, P.; Legarreta,
J.; de Pater, I.; Hammel, H.; Simon-Miller, A.; Gomez-Forrellad,
J. M.; Ortiz, J. L.; García-Melendo, E.; Puetter, R. C.; Chodas, P.
2010ApJ...715L.155S Altcode: 2010arXiv1005.2312S
On 2009 July 19, we observed a single, large impact on Jupiter at
a planetocentric latitude of 55°S. This and the Shoemaker-Levy
9 (SL9) impacts on Jupiter in 1994 are the only planetary-scale
impacts ever observed. The 2009 impact had an entry trajectory in
the opposite direction and with a lower incidence angle than that
of SL9. Comparison of the initial aerosol cloud debris properties,
spanning 4800 km east-west and 2500 km north-south, with those produced
by the SL9 fragments and dynamical calculations of pre-impact orbit
indicates that the impactor was most probably an icy body with a size
of 0.5-1 km. The collision rate of events of this magnitude may be
five to ten times more frequent than previously thought. The search for
unpredicted impacts, such as the current one, could be best performed
in 890 nm and K (2.03-2.36 μm) filters in strong gaseous absorption,
where the high-altitude aerosols are more reflective than Jupiter's
primary clouds.
---------------------------------------------------------
Title: The Impact of a Large Object with Jupiter in July 2009
Authors: Sanchez-Lavega, Agustin; Wesley, A.; Orton, G.; Chodas,
P.; Hueso, R.; Perez-Hoyos, S.; Fletcher, L.; Yanamandra-Fisher, P.;
Legarreta, J.; Gomez-Forrellad, J. M.
2010EGUGA..1215311S Altcode:
The only major impact ever observed directly in the Solar System
was that of a large fragmented comet with Jupiter in July (1994)
(Comet Shoemaker-Levy 9; SL9). We report here the observation of a
second, single, large impact on Jupiter that occurred on 19 July
2009 at a latitude of -55° with an orthogonal entry trajectory
and a lower incidence angle compared to those of SL9. The size of
the initial aerosol cloud debris was 4,800 km East-West and 2,500 km
North-South. Comparison its properties with those produced by the SL9
fragments, coupled with dynamical calculations of possible pre-impact
orbits, indicates that the impactor was most probably an icy body
with a size of 0.5-1 km. We calculate that the rate of collisions of
this magnitude may be five to ten times more frequent than previously
thought. The search for unpredicted impacts, such as the current one,
could be best performed in the near-infrared methane absorption bands
at 890 nm and in the 2.12 to 2.3 μm K methane-hydrogen absorption
band, where the high-altitude aerosols detach by their brightness
relative to Jupiter's primary clouds. We present measurements of the
debris dispersion by Jovian winds from a long-term imaging campaign
with ground-based telescopes. Ackowledgements: Work was supported by
the Spanish MICIIN AYA2009-10701 with FEDER and Grupos Gobierno Vasco
IT-464-07, by NASA funds to JPL, Caltech, by the NASA Postdoctoral
Program at JPL, and by the Glasstone Fellowship program at Oxford.
---------------------------------------------------------
Title: Radio Observations And Modeling Of A Post-flare Arcade
Authors: Bain, Hazel; Fletcher, L.
2010AAS...21632105B Altcode: 2010BAAS...41..912B
We present observations of a flaring arcade which was observed by
RHESSI, TRACE and the Nobeyama Radioheliograph (NoRH). The event
occurred on the west limb of the Sun and whilst EUV observations reveal
an arcade structure, the radio emission appears as a single loop. NoRH
observations at 17 GHz and 34 GHz show that the spatial distribution
of brightness varies along the loop and the relative brightness of
looptop and footpoint sources varies over time. We concentrate our
investigation on the decay phase of the flare and using estimates of
relevant plasma parameters obtained from observations, we attempt to
reproduce the observed radio emission. We compare the gyrosynchrotron
emission from both a simple dipole and an arcade magnetic field
model to investigate line of sight enhancements from optically thin
plasma. Using a continuous thermal/nonthermal electron distribution
we investigate the contribution from hot thermal plasma. This work
was funded by an STFC studentship.
---------------------------------------------------------
Title: Neptune's atmospheric composition from AKARI infrared
spectroscopy
Authors: Fletcher, L. N.; Drossart, P.; Burgdorf, M.; Orton, G. S.;
Encrenaz, T.
2010A&A...514A..17F Altcode: 2010arXiv1003.5571F
<BR /> Aims: Disk-averaged infrared spectra of Neptune between 1.8 and
13 μm, obtained by the AKARI infrared camera (IRC) in May 2007, have
been analysed to (a) determine the globally-averaged stratospheric
temperature structure; (b) derive the abundances of stratospheric
hydrocarbons; and (c) detect fluorescent emission from CO at 4.7
μm. <BR /> Methods: Mid-infrared spectra (SG1 and SG2 channels of
AKARI/IRC), with spectral resolutions of 47 and 34 respectively, were
modelled using a line-by-line radiative transfer code to determine
the temperature structure between 1-1000 μbar and the abundances
of CH<SUB>4</SUB>, CH<SUB>3</SUB>D and higher-order hydrocarbons. A
full non-LTE radiative model was then used to determine the best
fitting CO profile to reproduce the fluorescent emission observed at
4.7 μm in the NG channel (with a spectral resolution of 135). <BR />
Results: The globally-averaged stratospheric temperature structure is
quasi-isothermal between 1-1000 μbar, which suggests little variation
in global stratospheric conditions since studies by the Infrared
Space Observatory a decade earlier. The derived CH<SUB>4</SUB> mole
fraction of (9.0 ± 3.0)× 10<SUP>-4</SUP> at 50 mbar, decreasing
to (0.9 ± 0.3)× 10<SUP>-4</SUP> at 1 μbar, is larger than that
expected if the tropopause at 56 K acts as an efficient cold trap,
but consistent with the hypothesis that CH<SUB>4</SUB> leaking through
the warm south polar tropopause (62-66 K) is globally redistributed by
stratospheric motion. The ratio of D/H in CH<SUB>4</SUB> of 3.0 ± 1.0
× 10<SUP>-4</SUP> supports the conclusion that Neptune is enriched
in deuterium relative to the other giant planets. We determine a mole
fraction of ethane of (8.5 ± 2.1)× 10<SUP>-7</SUP> at 0.3 mbar,
consistent with previous studies, and a mole fraction of ethylene of
5.0<SUB>-2.1</SUB><SUP>+1.8</SUP> × 10<SUP>-7</SUP> at 2.8 μbar. An
emission peak at 4.7 μm is interpreted as a fluorescent emission of CO,
and requires a vertical distribution with both external and internal
sources of CO. Finally, comparisons to previous L-band studies indicate
significant variability of Neptune's flux densities in the 3.5-4.1
μm range, related to changes in solar energy deposition.
---------------------------------------------------------
Title: Using Active Contours for Semi-Automated Tracking of UV and
EUV Solar Flare Ribbons
Authors: Gill, C. D.; Fletcher, L.; Marshall, S.
2010SoPh..262..355G Altcode: 2010SoPh..tmp...20G
Solar-flare UV and EUV images show elongated bright "ribbons" that
move over time. If these ribbons are assumed to locate the footpoints
of magnetic-field lines reconnecting in the corona, then it is clear
that studying their evolution can provide important insight into
the reconnection process. An image-processing method based on active
contours (commonly referred to as "snakes") is proposed as a method
for tracking UV and EUV flare ribbons and is tested on images from the
Transition Region and Coronal Explorer (TRACE). This paper introduces
the basic concepts of such an approach with a brief overview of the
history and theory behind active contours. It then details the specifics
of the snake algorithm developed for this work and shows the results of
running the algorithm on test images. The results from the application
of the developed algorithm are reported for six different TRACE flares
(five in UV and one in EUV). The discussion of these results uses the
output from an expert tracking the same ribbons by eye as a benchmark,
and against these the snake algorithm is shown to compare favourably
in certain conditions, but less so in others. The applicability of the
automated snake algorithm to the general problem of ribbon tracking
is discussed and suggestions for ways to improve the snake algorithm
are proposed.
---------------------------------------------------------
Title: Possible liquid water origin for Atacama Desert mudflow and
recent gully deposits on Mars
Authors: Heldmann, J. L.; Conley, C. A.; Brown, A. J.; Fletcher, L.;
Bishop, J. L.; McKay, C. P.
2010Icar..206..685H Altcode:
Evidence of recent gully activity on Mars has been reported based on the
formation of new light toned deposits within the past decade, the origin
of which remains controversial. Analogous recent light toned gully
features have formed by liquid water activity in the Atacama Desert
on Earth. These terrestrial deposits leave no mineralogical trace of
water activity but rather show an albedo difference due to particle size
sorting within a fine-grained mudflow. Therefore, spectral differences
indicating varying mineralogy between a recent gully deposit and the
surrounding terrain may not be the most relevant criteria for detecting
water flow in arid environments. Instead, variation in particle size
between the deposit and surrounding terrain is a possible discriminator
to identify a water-based flow. We show that the Atacama deposit is
similar to the observed Mars gully deposits, and both are consistent
with liquid water activity. The light-toned Mars gully deposits could
have formed from dry debris flows, but a liquid water origin cannot be
ruled out because not all liquid water flows leave hydrated minerals
behind on the surface. Therefore, the Mars deposits could be remnant
mudflows that formed on Mars within the last decade.
---------------------------------------------------------
Title: Silica Debris Star Systems — Spitzer Evidence for Lunar
Formation Events & Crustal Stripping or Magma Oceans &
Late Heavy Bombardments?
Authors: Lisse, C. M.; Chen, C. H.; Wyatt, M. C.; Morlok, A.; Thebault,
P.; Orton, G. S.; Fletcher, L. N.; Fujiwara, H.; Bridges, J. C.;
Elkins-Tanton, L. T.; Gaidos, E. J.; Trang, D.
2010LPI....41.2390L Altcode:
Recent work (Lisse et al., 2009) has detected amorphous silica and
SiO gas around 12-m.y.-old HD172555, at the right age to form rocky
planets. Here we discuss the location, lifetime, and source of the
material, using inferences gleaned from HD172555 and three new silica
systems.
---------------------------------------------------------
Title: The white-light continuum in the impulsive phase of a solar
flare.
Authors: Hudson, H. S.; Fletcher, L.; Krucker, S.
2010MmSAI..81..637H Altcode: 2010arXiv1001.1005H
We discuss the IR/visible/VUV continuum emission of the impulsive
phase of a solar flare, using TRACE UV and EUV images to characterize
the spectral energy distribution. This continuum has been poorly
observed but energetically dominates the radiant energy output
. Recent bolometric observations of solar flares furthermore point to
the impulsive phase as the source of a major fraction of the radiant
energy. This component appears to exhibit a Balmer jump and thus must
originate in an optically thin region above the quiet photosphere,
with an elevated temperature and strong ionization.
---------------------------------------------------------
Title: The chromosphere during solar flares .
Authors: Fletcher, L.
2010MmSAI..81..616F Altcode: 2010arXiv1001.0739F
The emphasis of observational and theoretical flare studies in the
last decade or two has been on the flare corona, and attention
has shifted substantially away from the flare's chromospheric
aspects. However, although the pre-flare energy is stored in the
corona, the radiative flare is primarily a chromospheric phenomenon,
and its chromospheric emission presents a wealth of diagnostics for
the thermal and non-thermal components of the flare. I will here review
the chromospheric signatures of flare energy release and the problems
thrown up by the application of these diagnostics in the context of
the standard flare model. I will present some ideas about the transport
of energy to the chromosphere by other means, and calculations of the
electron acceleration that one might expect in one such model.
---------------------------------------------------------
Title: Integrated Ly-alpha intensity emission in ribbon flares
Authors: Rubio da Costa, F.; Fletcher, L.; Labrosse, N.; Zuccarello, F.
2010MSAIS..14..193R Altcode:
We have analyzed two flares observed by TRACE in Ly alpha (on 8th
September 1999 and 28th February 1999) in order to deduce their
morphology, temporal evolution, radiative outputs and compare these
results with data obtained in the X-range (SXT and HXT on Yohkoh) and
with magnetograms (MDI/SOHO). These observational data and the results
obtained by a theoretical study of the intensity of the radiation
emitted by hydrogen lines, contribute to construct semi-empirical and
theoretical models of the chromospheric emission during flares. Future
observations by the planned Extreme Ultraviolet Imager selected for
the Solar Orbiter mission -which will have a Lyman alpha channel-
and this work, can help in designing observational flare studies.
---------------------------------------------------------
Title: Hubble Imaging of Jupiter after the 2009 Impact
Authors: Hammel, Heidi B.; Clarke, J. T.; de Pater, I.; Fletcher,
L. N.; Hueso, R.; Noll, K. S.; Orton, G. S.; Perez-Hoyos,
S.; Sanchez-Lavega, A.; Simon-Miller, A. A.; Wong, M. H.;
Yanamandra-Fisher, P. A.
2010AAS...21533407H Altcode: 2010BAAS...42..434H
On 19 July 2009, amateur astronomer Anthony Wesley discovered an
anomalous dark feature near Jupiter's south pole (planetographic
latitude -58° system III west longitude 305°). Additional observations
confirmed the new feature was an impact site created by an unknown
object (the only other observed collision with Jupiter occurred 15 years
earlier, when the shattered remains of Comet Shoemaker-Levy 9 created
huge atmospheric disturbances). A world-wide observing campaign was
initiated in response to this 2009 collision. We were awarded Directors
Discretionary Time to use the newly-installed Wide-Field Camera 3 (WFC3)
on Hubble Space Telescope. Observations were successfully obtained
with WFC3 on July 23, August 3, and August 8, and with the Advanced
Camera for Surveys' Solar Blind Channel in the UV on September 8. In
this talk, we will present a summary of the HST images. The evolution
of the impact debris field at UV, visible, near-IR wavelengths will
be discussed, along with a comparison to Hubble observations of the
Shoemaker-Levy 9 impact in 1994.
---------------------------------------------------------
Title: Elementary Energy Release Events in Flaring Loops: Effects
of Chromospheric Evaporation on X-Rays
Authors: Liu, Siming; Han, Feiran; Fletcher, Lyndsay
2010ApJ...709...58L Altcode: 2009arXiv0912.0402L
With the elementary energy release events introduced in a previous
paper, we model the chromospheric evaporation in flaring loops. The
thick-target hard X-ray (HXR) emission produced by electrons escaping
from the acceleration region dominates the impulsive phase, and
the thin-target emission from the acceleration region dominates the
low-energy thermal component in the gradual phase, as observed in
early impulsive flares. Quantitative details depend on properties of
the thermal background, which leads to variations in the correlation
between HXR flux and spectral index. For lower temperature and/or higher
density of the background electrons, the HXRs both rise and decay more
quickly with a plateau near the peak. The plateau is less prominent at
higher energies. Given the complexity of transport of mass, momentum,
and energy along loops in the impulsive phase, we propose a strategy
to apply this single-zone energy release and electron acceleration
model to observations of flares associated with single loops so that
the energy release, electron acceleration, and evaporation processes
may be studied quantitatively.
---------------------------------------------------------
Title: Non-LTE analysis of Uranus Observations from Spitzer
Authors: Zhang, X.; Martin-Torres, F.; Yung, Y. L.; Orton, G. S.;
Fletcher, L. N.
2009AGUFM.P32C..01Z Altcode:
Spitzer Infrared Spectrometer (IRS) observations of the disk of
Uranus between 5.2 and 32 microns (1920 cm-1-270 cm-1) contain a
wealth of information about the its cold atmosphere. In particular,
they enable the retrieval of temperature and the abundances of
several gaseous species as a function of pressure. They can also
be used to study the energetics of radiatively active species in
regions of Uranus’ atmosphere where Local Thermodynamic Equilibrium
(LTE) is expected to break down. Care must be taken in atmospheric
sounding not to assume that the atmospheric compounds emit according
to the Planck function at the local kinetic temperature. Many of the
ro-vibrational states of atmospheric constituents responsible for
infrared emissions have excitation temperatures that differ from the
local kinetic temperature. While non-LTE emission has been extensively
considered for remote sensing of the Earth, only one study by Appleby
(Icarus, 85, p355-379, 1990), who examined the radiative equilibrium
temperatures of methane (CH4) in the upper atmospheres of Jupiter,
Saturn, Uranus, and Neptune, has estimated the influence of non-LTE
effects in Uranus' upper atmosphere. Uranus is composed mainly of
hydrogen and helium. Helium is radiatively inactive, and hydrogen is
active only in its weak collision-induced absorption, and its quadrupole
lines. At low pressures, non-LTE processes involve the quantum levels
of the more abundant minor constituents become important. In the
case of Uranus the most important gas in the latter category is CH4,
which has a role rather analogous to that of carbon dioxide in the
Earth’s atmosphere. Since the work by Appleby, the spectroscopic
and kinetics information of methane and other hydrocarbons has
greatly improved and computer capabilities allow avoiding previous
simplifications. For example, the full coupling between CH4 v4 and the
higher-energy vibrational states emitting/absorbing in the near-IR is
now possible. In this presentation we analyze the non-LTE effects in
Spitzer data using a new non-local thermodynamic equilibrium radiative
transfer for the infrared emissions of CH4, C2H2, and C2H6 which are
observed in its spectrum.
---------------------------------------------------------
Title: HST Observations of the July 2009 Impact on Jupiter
Authors: de Pater, I.; Hammel, H. B.; Simon-Miller, A. A.; Clarke,
J. T.; Noll, K. S.; Orton, G. S.; Fletcher, L. N.; Yanamandra-Fisher,
P. A.; Sanchez-Lavega, A.; Hueso, R.; Perez-Hoyos, S.; Wong, M. H.
2009AGUFM.P14D..01D Altcode:
On UT 19 July 2009 amateur astronomer Anthony Wesley announced that
Jupiter might have been hit by an object, as evidenced from an anomalous
feature near Jupiter’s south pole (at a southern planetgraphic
latitude of 58 deg, and W. longitude III of 305 deg). A world-wide
observing campaign was initiated in response, including Hubble Space
Telescope Director Discretionary Time on the newly-installed WFC3
camera. Observations were made on July 23, August 3 and 8. In this talk
we will present a summary of the HST images at wavelengths between 400
and 900 nm. In particular, we will compare the initial HST observations
with contemporaneous data over a wide spectral range from the near-IR
(Keck) and mid-IR (Gemini-North, VLT, Gemini-South). The evolution of
the impact debris field at visible, near- and mid-IR wavelengths will
be discussed, along with a comparison to the Shoemaker-Levy 9 impact
in 1994.
---------------------------------------------------------
Title: A Mission Concept Study of a Dilute Aperture Visible Nulling
Coronagraph Imager (DAViNCI) for the Detection and Spectroscopy
of Exo-planets
Authors: Shao, Michael; Bairstow, S.; Deems, E.; Fletcher, L.; Levine,
B.; Orton, G.; Vasisht, G.; Wayne, L.; Zhao, F.; Clampin, M.; Lyon,
R.; Guyon, O.; Lane, B.; Havey, K.; Wynn, J.; Samuele, R.; Vasudevan,
G.; Woodruff, R.; Tolls, V.; Malbet, F.; Leger, A.
2009AAS...21460603S Altcode:
DAViNCI is a mission concept for the imaging and spectroscopy
of exo-planets from nearby stars. It is capable of surveying and
characterizing over 100 stars at an inner working angle of 35mas
at its maximum baseline. DAViNCI is a 4 aperture telescope imaging
system separated by a variable baseline whose light is combined
interfermometrically into a nulling coronagraph instrument coupled to an
imaging camera and spectrometer. We will describe the science potential
and configuration of DAViNCI, its architecture, its instruments, and the
results of mission and instrument studies in terms of capability and
cost. <P />This work was performed at the Jet Propulsion Laboratory,
California Institute of Technology, under contract to the National
Aeronautics and Space Administration.
---------------------------------------------------------
Title: Mapping potential vorticity dynamics on saturn: Zonal mean
circulation from Cassini and Voyager data
Authors: Read, P. L.; Conrath, B. J.; Fletcher, L. N.; Gierasch,
P. J.; Simon-Miller, A. A.; Zuchowski, L. C.
2009P&SS...57.1682R Altcode:
Maps of Ertel potential vorticity on isentropic surfaces (IPV) and
quasi-geostrophic potential vorticity (QGPV) are well established in
dynamical meteorology as powerful sources of insight into dynamical
processes involving 'balanced' flow (i.e. geostrophic or similar). Here
we derive maps of zonal mean IPV and QGPV in Saturn's upper troposphere
and lower stratosphere by making use of a combination of velocity
measurements, derived from the combined tracking of cloud features in
images from the Voyager and Cassini missions, and thermal measurements
from the Cassini Composite Infrared Spectrometer (CIRS) instrument. IPV
and QGPV are mapped and compared for the entire globe between latitudes
89<SUP>∘</SUP>S-82<SUP>∘</SUP>N. As on Jupiter, profiles of
zonally averaged PV show evidence for a step-like "stair-case" pattern
suggestive of local PV homogenisation, separated by strong PV gradients
in association with eastward jets. The northward gradient of PV (IPV
or QGPV) is found to change sign in several places in each hemisphere,
however, even when baroclinic contributions are taken into account. The
stability criterion with respect to Arnol'd's second stability theorem
may be violated near the peaks of westward jets. Visible, near-IR and
thermal-IR Cassini observations have shown that these regions exhibit
many prominent, large-scale eddies and waves, e.g. including 'storm
alley'. This suggests the possibility that at least some of these
features originate from instabilities of the background zonal flow.
---------------------------------------------------------
Title: Thermal Evolution and Composition of the July 2009 Jupiter
Impact Site from 7-25 Micron Imaging and Spectroscopy
Authors: Fletcher, L. N.; Orton, G. S.; Mousis, O.; de Pater,
I.; Hammel, H. B.; Golisch, W.; Edwards, M.; Yanamandra-Fisher,
P. A.; Fisher, B.; Greene, Z.; Lai, S.; Otto, E.; Reshetnikov, N.;
Sanchez-Lavega, A.; Simon-Miller, A. A.; Hueso, R.; Perez-Hoyos, S.
2009AGUFM.P14D..03F Altcode:
We present analysis of thermal-infrared imaging and spectroscopy of
the impact site near the south polar region of Jupiter (see Orton
et al., AGU 2009). Enhanced thermal emission was first detected
on July 20 2009 in 7-25 micron imaging from the MIRSI instrument
on NASA’s IRTF. These observations, just two rotations after the
impact, indicated the localised, high-temperature thermal signature
of the ejecta field, coincident with the location of high-altitude
particulate debris observed in the near-IR and visible. The impact
feature was most visible in the 9-11 micron range, suggestive of
enhanced emission from hydrocarbons and ammonia gas in the lower
stratosphere. Subsequent thermal imaging of the impact region
reveals the radiative cooling of the impact site and the changing
morphology due to the redistribution of material by Jupiter’s zonal
and meridional wind field. We acquired Gemini-N/Michelle imaging on
July 22, Gemini-S/TReCS imaging on July 24 and August 5 and 9, and an
extensive campaign of VLT/VISIR imaging on July 24, 26 and August 5, 10,
15, 16, at which point (4 weeks after the impact) the thermal signature
could no longer be reliably distinguished, even with sub-arcsecond
diffraction-limited angular resolution. Tropospheric and stratospheric
temperatures and aerosol opacity are derived via optimal estimation
retrievals (Fletcher et al. 2009, Icarus, 200, p154). Enhancement
of hydrocarbons and gaseous ammonia are determined via iterative
forward modelling, aided by spectral observations obtained with the
slit aligned east-west through the impact feature from Gemini-S/TReCS
(July 24) and VLT/VISIR (July 26, August 12-13). Low-resolution N-band
(8-13 microns) Gemini-S/TReCS spectra confirm the enhanced emission
over a broad range of wavelengths; Q-band (17-25 micron) spectra are
used to study upper tropospheric temperatures in the aftermath of
the collision and the rate of radiative cooling. VLT/VISIR spectra
provide higher spectral resolutions in narrow wavelength ranges near
8.02, 10.49, 11.31, 11.60, 12.24 and 13.36 microns, sensitive to NH3,
CH4 and hydrocarbon emission features. Iterative forward modelling of
these spectra will be used to deduce the unique chemical composition and
the three-dimensional thermal structure of the impact site, compared
with the ‘unperturbed’ atmosphere at the same latitude. * Fletcher
is supported by an appointment to the NASA Postdoctoral Program at
the Jet Propulsion Laboratory/California Institute of Technology,
administered by Oak Ridge Associated Universities through a contract
with NASA. We wish to acknowledge the invaluable contributions of the
support staff at IRTF, VLT and Gemini.
---------------------------------------------------------
Title: Hard X-ray emission from a flare-related jet
Authors: Bain, H. M.; Fletcher, L.
2009A&A...508.1443B Altcode:
Aims. We aim to understand the physical conditions in a jet event
which occurred on the 22nd of August 2002, paying particular attention
to evidence for non-thermal electrons in the jet material.<BR />
Methods: We investigate the flare impulsive phase using multiwavelength
observations from the Transition Region and Coronal Explorer (TRACE)
and the Reuven Ramaty High Energy Spectroscopic Imager (RHESSI)
satellite missions, and the ground-based Nobeyama Radioheliograph
(NoRH) and Radio Polarimeters (NoRP).<BR /> Results: We report what we
believe to be the first observation of hard X-ray emission formed in a
coronal jet. We present radio observations which confirm the presence of
non-thermal electrons present in the jet at this time. The evolution of
the event is best compared with the magnetic reconnection jet model in
which emerging magnetic field interacts with the pre-existing coronal
field. We calculate an apparent jet velocity of ~500 km s<SUP>-1</SUP>
which is consistent with model predictions for jet material accelerated
by the J×B force resulting in a jet velocity of the order of the
Alfvén speed (~100-1000 km s<SUP>-1</SUP>).<BR />
---------------------------------------------------------
Title: Emitted Power of Saturn Based on Cassini/CIRS Observations
Authors: Li, L.; Conrath, B. J.; Gierasch, P. J.; Achterberg, R. K.;
Nixon, C. A.; Flasar, F. M.; Simon-Miller, A. A.; Fletcher, L. N.;
Read, P. L.; Baines, K. H.; West, R. A.; Ingersoll, A. P.; Vasavada,
A. R.; Orton, G. S.
2009AGUFM.P32C..03L Altcode:
We are evaluating the energy balance of Saturn through Cassini
observations, utilizing in particular CIRS observations from 7 to
500 micron and ISS/VIMS observations from 0.25 to 5.1 micron. The
CIRS observations are utilized to compute the emitted power of Saturn
between 2004 and 2009. Compared with the Voyagers' results, Cassini’s
observations display significant variations in the global emitted
power between the Voyager epoch (1979-1982) and the current Cassini
time period (2004-2009). In addition, the meridional distribution of
emitted power measured by Cassini shows that the emitted power is ~20%
higher in the southern hemisphere than in the northern hemisphere. This
is different from the Voyager results, which showed the two hemispheres
to be roughly equal in emitted power. It is unclear whether the
differences between the Voyager and Cassini epochs are due to the
seasonal or inter-annual variations or both, but the time variations
from 2004 to 2009 suggest that seasonal variations are at least part
of the reason. The Cassini Equinox and Solstice Extended missions
will continue to provide more knowledge of the seasonal/inter-annual
variations of the emitted power. The computation of the reflected solar
power by fitting Minnaert coefficient/Barkstrom model for each latitude
bin or by directly utilizing the observed reflected radiance at each
pixel of the globe is still in process. Combining the emitted power and
the reflected solar power, we will estimate the energy balance of Saturn
and its meridional distribution and seasonal/inter- annual variability.
---------------------------------------------------------
Title: Near-Infrared Spectroscopy and Imaging of the 2009 Jupiter
impact debris field: Constraints on particle composition, size and
vertical distribution
Authors: Yanamandra-Fisher, P. A.; Orton, G. S.; Fletcher, L. N.;
Fisher, B.; Greene, Z.; Otto, E.; Reshetnikov, N.; Golisch, W.;
Lystrup, M. B.; Shara, M.; Moskovitz, N. A.; Trilling, D.; Reddy,
V.; Rivkin, A.; Grundy, W. M.; Emery, J. P.; Kim, J.; Baines, K. H.;
Griep, D.; Sears, P.
2009AGUFM.P31A1228Y Altcode:
We present results of near-infrared imaging and spectroscopy of the
2009 Jupiter impact site and its associated debris field during the
time period from 20 July 2009 (approximately 20 hours after impact) to
31 August 2009 (nearly six weeks post-impact). Our data were acquired
with NASA/InfraRed Telescope Facility (IRTF) facility instruments,
SpeX, 1- to 5-micron spectrometer and its guide camera, and NSFCam2,
1- to 5-micron multi-spectral camera. On 20 July, the impact site
appeared as a localized region, close to and brighter than Jupiter's
south polar haze. The impact site then expanded longitudinally in both
directions. Nearly five weeks later, the debris field continues to
spread, characterized by a few localized structures or cores near the
original impact longitude, surrounded by material which is extended
by about 7 degrees in latitude and 80 degrees in longitude. Early
multi-spectral images and spectra of the debris identify ammonia as a
constituent. Spectra and images of the debris material in subsequent
weeks, redistributed by the zonal and meridional wind field of Jupiter,
indicates the debris continues to be very prominent at 2 microns;
comparable in reflectivity to the south polar haze and high in the
atmosphere, implying small particles. The cores of the debris field were
the only components of the neutral atmosphere detectable in the strong
methane-absorbing 3.2- to 3.4-micron region as late as 6 August, but
they were no longer detectable as of 18 August. In the 2-micron region,
the debris reflectivity also diminished with time, mostly likely as a
result of downward sedimentation. Our results will be compared to the
those from SL9 fragment impacts and the "undisturbed" Jovian atmosphere,
constraining the vertical distribution of the perturbation, composition
and particle sizes of the debris.
---------------------------------------------------------
Title: Debris Field of the July 19, 2009, Impact in Jupiter and Its
Long-term Evolution
Authors: Orton, G. S.; Wesley, A.; Mousis, O.; Fletcher, L. N.;
Yanamandra-Fisher, P. A.; Fisher, B.; Simon-Miller, A. A.; Greene,
Z. S.; de Pater, I.; Hammel, H. B.; Reshetnikov, N.; Otto, E.; Lai,
S.; Rogers, J.; Sanchez-Lavega, A.; Perez-Hoyos, S.; Hueso, R.;
Golisch, W.; Griep, D.; Sears, P.; Lystrup, M. B.; Shara, M.; Young,
L.; Grundy, W. M.; Moskovitz, N. A.; Rivkin, A. S.; Reddy, V.; Emery,
J. P.; Trilling, D.; Ziffer, J.
2009AGUFM.P14D..04O Altcode:
A multi-platform suite of imaging and spectroscopic observations of
Jupiter's atmosphere tracked the evolution of the debris field of an
unknown impactor on 2009 July 19. The initial debris field is similar
to those of intermediate Shoemaker-Levy 9 fragments, suggesting a
body hundreds of meters in size, if icy, entering from the west and
slightly north. The field is detectable in the visible as dark material
and in the near-IR by high-altitude particulate reflectivity; it was
quickly redistributed by different zonal flows across its latitudinal
range. At first, the particulate field was highly correlated with areas
of enhanced temperatures and enhanced ammonia and ethane emission,
but this was no longer true by mid-August. As of Sept. 2, the debris
field was undetectable in the thermal, detectable in the visible with
good seeing, and still prominent near 2 microns wavelength. Visibly,
the impact "scar" consists of two dark regions along the same latitude,
ostensibly different from the central bright region associated with
the near-IR debris pattern. Both morphologies show eastern and western
extensions propagating away from the original impact site, which appear
to be influenced by flows around vortices previously undetected in
Jupiter atmosphere. These observations define the flow field just
north of Jupiter's southern polar vortex at higher altitudes than
tracked in Jupiter's main cloud deck.
---------------------------------------------------------
Title: Thermal and Near-Infrared Structural Evolution of the 2009
Wesley Jupiter Impact from 1.5-24.5 Micron Imaging
Authors: Greene, Z. S.; Orton, G. S.; Fletcher, L. N.;
Yanamandra-Fisher, P. A.; Mousis, O.; Fisher, B.; Reshetnikov, N.;
Lai, S.; Otto, E.; Hammel, H. B.; de Pater, I.; Edwards, M.
2009AGUFM.P33B1282G Altcode:
We show the morphological evolution of the remnant scar from the Jupiter
impact (July 19, 2009) at mid- and near-infrared wavelengths. Data
taken less than 24 hours after the impact using NASA’s IRTF capture
the initial structure at a wide range of wavelengths from 1.5-24.5
microns. Furthermore, images obtained from NASA’s Infrared Telescope
Facility, Gemini North and South, and the Very Large Telescope in
the subsequent weeks allow us to monitor the evolving morphology of
the feature as zonal and meridional winds redistributed the impact
debris through Jupiter’s atmosphere. Our observations indicate
that the feature expanded primarily in the longitudinal direction
in both the mid- and near-infrared, but underwent separation in
the latitudinal direction much earlier in the thermal. The impact
feature also became indistinguishable from its Jovian background in
the thermal as of mid-August, whereas the scar remains distinct in the
near-infrared. Timelines and images at various thermal and near-infrared
wavelengths will be used to show the rapid evolution of the debris from
July 20 to late August. *This work was performed at the Jet Propulsion
Laboratory, California Institute of Technology, sponsored by the Summer
Undergraduate Research Fellowship (SURF) program.
---------------------------------------------------------
Title: Modelling the Longitudinal Asymmetry in Sunspot Emergence:
The Role of the Wilson Depression
Authors: Watson, F.; Fletcher, L.; Dalla, S.; Marshall, S.
2009SoPh..260....5W Altcode: 2009arXiv0909.0914W
The distributions of sunspot longitude at first appearance and at
disappearance display an east-west asymmetry that results from a
reduction in visibility as one moves from disk centre to the limb. To
first order, this is explicable in terms of simple geometrical
foreshortening. However, the centre-to-limb visibility variation is
much larger than that predicted by foreshortening. Sunspot visibility
is also known to be affected by the Wilson effect: the apparent `dish'
shape of the sunspot photosphere caused by the temperature-dependent
variation of the geometrical position of the τ=1 layer. In this article
we investigate the role of the Wilson effect on the sunspot appearance
distributions, deducing a mean depth for the umbral τ=1 layer of 500
- 1500 km. This is based on the comparison of observations of sunspot
longitude distribution and Monte Carlo simulations of sunspot appearance
using different models for spot growth rate, growth time and depth of
Wilson depression.
---------------------------------------------------------
Title: Observations of a solar flare and filament eruption in Lyman
α and X-rays
Authors: Rubio da Costa, F.; Fletcher, L.; Labrosse, N.; Zuccarello, F.
2009A&A...507.1005R Altcode: 2009arXiv0909.4705R
Context: Lα is a strong chromospheric emission line, which has been
relatively rarely observed in flares. The Transition Region and Coronal
Explorer (TRACE) has a broad “Lyman α” channel centered at 1216
Å used primarily at the beginning of the mission. A small number of
flares were observed in this channel. <BR />Aims: We aim to characterise
the appearance and behaviour of a flare and filament ejection which
occurred on 8th September 1999 and was observed by TRACE in Lα, as well
as by the Yohkoh Soft and Hard X-ray telescopes. We explore the flare
energetics and its spatial and temporal evolution. We have in mind the
fact that the Lα line is a target for the Extreme Ultraviolet Imaging
telescope (EUI) which has been selected for the Solar Orbiter mission,
as well as the LYOT telescope on the proposed SMESE mission. <BR
/>Methods: We use imaging data from the TRACE 1216 Å, 1600 Å and
171 Å channels, and the Yohkoh hard and soft X-ray telescopes. A
correction is applied to the TRACE data to obtain a better estimate of
the pure Lα signature. The Lα power is obtained from a knowledge of
the TRACE response function, and the flare electron energy budget is
estimated by interpreting Yohkoh/HXT emission in the context of the
collisional thick target model. <BR />Results: We find that the Lα
flare is characterised by strong, compact footpoints (smaller than the
UV ribbons) which correlate well with HXR footpoints. The Lα power
radiated by the flare footpoints can be estimated, and is found to be
on the order of 10<SUP>26</SUP> erg s<SUP>-1</SUP> at the peak. This is
less than 10% of the power inferred for the electrons which generate
the co-spatial HXR emission, and can thus readily be provided by
them. The early stages of the filament eruption that accompany the
flare are also visible, and show a diffuse, roughly circular spreading
sheet-like morphology, with embedded denser blobs. <BR />Conclusions:
On the basis of this observation, we conclude that flare and filament
observations in the Lα line with the planned EUI and LYOT telescopes
will provide valuable insight into solar flare evolution and energetics,
especially when accompanied by HXR imaging and spectroscopy.
---------------------------------------------------------
Title: Infrared and Microwave Observations of Uranus: Implications
for Temperature, Composition, Circulation and a Standard Calibration
Model for Herschel
Authors: Hofstadter, Mark D.; Orton, G.; Fletcher, L.; Mainzer, A.;
Merlet, C.; Hines, D.; Hammel, H.; Burgdorf, M.; Moses, J.; Butler,
B.; Gurwell, M.
2009DPS....41.2803H Altcode:
The Spitzer Infrared Spectrometer observed Uranus in December 2007
between 5 and 21.5 microns. Disk-averaged temperatures are retrieved
between 2 bars and the microbar level, yielding a profile warmer than
found by Voyager 2. A substantial rise in temperature near 8 microbars
is also found - consistent with Voyager results. The methane mixing
ratio, constrained by 7-micron emission, is between 5% and 60% of
saturation at the Tropopause. The presence of both absorption and
emission by CH4 and CH3D will allow us to constrain the D/H ratio
and the mixing ratio of methane in the 2-bar region. The abundance
of stratospheric hydrocarbons varies strongly with longitude, while
temperature does not. Minimal longitudinal and latitudinal variability
of tropospheric temperatures indicates that Uranus may be adequate as
a calibration source in the far-infrared through the submillimeter,
which is useful to the Herschel Space Telescope. Strong latitudinal
gradients in composition, however, as revealed by imaging at 1 mm to 20
cm, do need to be accounted for. The Submillimeter Array imaged Uranus
in 2006 at 1.4 mm, and the Very Large Array imaged Uranus between 2005
and 2009 at wavelengths from 7 mm to 20 cm. These data indicate there
is a latitudinally varying abundance of a microwave absorber near the
1-bar level, with H2S being a likely candidate. The disk-averaged IR
data confirms the presence of an opacity source besides that of H2 in
this altitude region. The VLA data also imply an unexpected vertical
distribution of opacity at pressures of tens-of-bars in the equatorial
region, believed to be related to the liquid-water cloud. Much of
this work was carried out at JPL/Caltech, under contract with NASA. We
acknowledge the support of NASA's Planetary Astronomy and Atmospheres
programs, and the Spitzer, SMA, VLA, and VLT observatories.
---------------------------------------------------------
Title: First Observations of the 2009 Collision in Jupiter's
Atmosphere
Authors: Orton, Glenn S.; Fletcher, L.; Wesley, A.; Yanamandra-Fisher,
P.; Fisher, B.; Mousis, O.; Golisch, W.; de Pater, I.; Marchis, F.;
Kalas, P.; Fitzgerald, M.; Graham, J.; Wong, M.; Rogers, J.; Momary,
T.; Sanchez-Lavega, A.; Hammel, H.; Simon-Miller, A.
2009DPS....41.1001O Altcode:
We report initial observations of the debris from the first
documented impact of a body with Jupiter since the collisions of
Comet Shoemaker-Levy 9 fragments 15 years ago. Visible observations
by AW at 14:01 UT on 2009 July 19 recorded an unusual blackened
region with fainter ejecta near the edge of Jupiter's South Polar
Region. 0.89-micron CH<SUB>4</SUB> band imaging (A. Cidadao, D. Peach)
on the subsequent rotation showed this site to be bright. Two rotations
later at NASA's IRTF, a series of near-IR (1.58-4.78 micron) images with
SpeX and NSFCam2 were recorded which verified the unmistakable signature
of high-altitude particulate debris in even stronger CH<SUB>4</SUB>
and H<SUB>2</SUB> absorption. Spectra were also recorded in the 0.8-2.5
micron region. Images of thermal emission between 7 and 25 microns with
MIRSI instrument recorded enhanced emission associated with ammonia gas
and an increase of temperatures in the upper troposphere at the site of
the impact and debris field. No enhancement of temperatures was detected
near the 10-mbar level of the stratosphere. During the same rotation,
Keck-II NIRC2 images at 2.124 microns detected an impact site, centered
at 305±1.5°W longitude and 57±1.5°S planetographic latitude,
with two prominent features and an ejecta field annulus which extends
toward the west by 10° in longitude. The distinct detail of the initial
images and references to existing images suggest that the impact may
have occurred within a 10-hour period before its initial detection in
the visible. Comparisons with published analyses of the Shoemaker-Levy
9 impacts suggest an impactor on the order of hundreds of meters in
size, something unlikely to have been detected in advance. There is no
evidence at any wavelength for additional impacts. As of this writing,
a vigorous campaign to characterize the impact site is being mounted
at several observatories, and more details will inevitably follow.
---------------------------------------------------------
Title: The Case for Uranus and Neptune
Authors: Hofstadter, Mark D.; Sotin, C.; Brooks, S.; Fletcher,
L.; Friedson, A.; Moeller, R.; Murphy, N.; Orton, G.; Spilker, T.;
Wenkert, D.
2009DPS....41.1606H Altcode:
Uranus and Neptune are composed mostly of ices, such as H2O, making
them fundamentally different from Jupiter or Saturn. These ice giants,
and their unique satellites and rings, have an important story to
tell us about the formation, evolution, and structure of planets in
our Solar System and beyond. To understand that story, we must learn
the basic properties of their interiors. We do not know if they have
extensive solid- or liquid-water layers (making them almost overgrown
icy satellites) or if the H2O-H2 phase diagram allows structures unlike
any other planet in our solar system. How internal heat is transported
through the interior and atmosphere is also important to learn. We
wish to know the nature of atmospheric convection and circulation and
how they relate to internal and solar forcing. We also wish to know the
composition and temperature of the atmosphere as a function of latitude,
altitude, and time. One of the great surprises of the Voyager encounters
was the discovery of strongly tilted dipole magnetic fields, offset
from the planet's centers. How and where is the field generated? How
does its unique geometry affect the transfer of energy from the solar
wind to the magnetosphere? A mission to Uranus or Neptune, supported
by healthy ground-based observing and laboratory campaigns, should be a
priority for the next decade. Either planet can serve as the archetypal
ice giant, but cross-disciplinary priorities can be used to choose one
over the other. A recent JPL study identified trajectories that could
deliver significant science payloads into orbit around either planet,
and found that it may be possible to do so at Uranus for under the New
Frontiers cost cap and using solar-power. This research was carried
out at JPL/Caltech under contract with NASA.
---------------------------------------------------------
Title: Saturn Atmospheric Science in the Next Decade
Authors: Orton, Glenn S.; Fletcher, L.; Stallard, T.; Baines, K.;
Sayanagi, K.; Huestis, D.; Yung, Y.; Edgington, S.; Gulkis, S.; Moses,
J.; Martin-Torres, F.
2009DPS....41.1603O Altcode:
Although observed from the Earth, Pioneer 11, Voyagers 1 and 2, and now
Cassini in its primary and 2-year extended mission, the characterization
of fundamental atmospheric properties and processes in Saturn remains
incomplete. Many open questions about the atmosphere could be addressed
in the next decade: <P />- SEASONS: How do seasons affect (a) the global
distribution of gaseous constituents and aerosols; and (b) temperatures
and the stability against convection and large scale-atmospheric
transport? Will a warm polar vortex appear at the northern pole with
greater radiative input? <P />- HEXAGON: What is the vertical structure
of the hexagon, what is driving and maintaining it; and why is there
no feature of similar longevity at the south pole? <P />- COMPOSITION
AND CHEMISRY: What are the noble gas and oxygen abundances? What is
the relation of stratospheric hydrocarbon distributions to radiative
climate influences and photochemistry? What is the rate of influx of
ring and other exogenic materials into the atmosphere? <P />- CLOUDS
AND HAZES: What is the tropospheric cloud inventory, and what are the
different cloud compositions and optical properties? What is producing
the haze material? What is the relation between observable clouds
and lightning discharges? What is the relation between the fine-scale
cloud structure identified at 5 microns and the <P />distribution of
condensates, such as ammonia? Do 5-micron clouds have counterparts
at other altitude levels? <P />- DYNAMICS: What is the source of the
strong equatorial upwelling and strong prograde jet? What changes when
we see the emergence of Great White Storms? How is energy transported
by waves between atmospheric levels, via the SAO and by vertical waves
observed in stellar occultations and RSS profiles? What effect does
the ephemeral nature of Saturn's slowly-moving thermal waves have on
the atmosphere? Will the tropospheric hotspots at each pole persist?
---------------------------------------------------------
Title: Meridional Distributions of Methylacetylene and Diacetylene
in Saturn's Stratosphere from CIRS/Cassini Observations.
Authors: Guerlet, Sandrine; Fouchet, T.; Moses, J. I.; Fletcher,
L. N.; Bézard, B.; Simon-Miller, A. A.; Flasar, F. M.
2009DPS....41.2804G Altcode:
The Composite InfraRed Spectrometer (CIRS) aboard the Cassini spacecraft
provides a unique opportunity to perform limb observations of Saturn's
stratosphere. This viewing geometry favors the detection of minor
species and allows the retrieval of their abundance profile with
a larger vertical extent and higher vertical resolution than nadir
observations. <P />Following our work on acetylene, ethane and propane
(Guerlet et al. 2009), we will present the first maps of the volume
mixing ratio of methylacetylene (CH3C2H) and diacetylene (C4H2), from
45°N to 80°S and 3 mbar to 0.05 mbar. These results were obtained from
an analysis of CIRS limb observations using a line-by-line radiative
transfer model coupled to an inversion algorithm. We have also analyzed
sets of nadir CIRS spectra, which are sensitive to C4H2 around 0.5
mbar, extending the meridional coverage up to 88°S and 65°N at this
pressure level. <P />These molecules are minor by-products of the
methane photochemistry, but their abundances give important insights
on the main chemical pathways, as we will show their distributions
compare with our previously derived C2H2 variations. C4H2 and CH3C2H
have also rather short lifetimes (25-80 years at 1 mbar) compared to
the main hydrocarbons' lifetimes (ethane and acetylene, resp. 700 and
100 years at 1 mbar) making them good tracers of seasonal stratospheric
dynamics. They display some small-scale variations in their meridional
distribution which could be symptomatic of vertical and/or meridional
dynamics. We will compare the distribution of C3H4 and C4H2 we derived
with the predictions of the photochemical seasonal model of Julie Moses
(Moses and Greathouse, 2005).
---------------------------------------------------------
Title: Changing Seasons on Saturn: If Winter's Here, Can Spring be
Far Behind?
Authors: Yanamandra-Fisher, Padma A.; Orton, G. S.; Fisher, B. M.;
Baines, K.; Fletcher, L.; Fujiyoshi, T.; Fuse, T.
2009DPS....41.2805Y Altcode:
Ground-based near- and mid-infrared observations of Saturn from 1995
- 2009, covering half a Saturnian year, provide a rich data set to
model seasonal changes in both Saturn's atmosphere and its rings as
a function of solar elevation. We acquired near-infrared data from
NASA/Infrared Telescope Facility (IRTF); and mid-infrared data from
NASA/IRTF and NAOJ/Subaru Facility. Our data set covers the period
from autumnal equinox (1995) to the upcoming vernal equinox (2009); and
provides a bridge between Voyager encounters and Cassini prime mission,
with temporal and spatial context for spacecraft observations. We
shall present results illustrating: (1) changes in thermal fields on
the planet; (2) evolution/distribution of various chemical species;
(3) development of clouds and other discrete features; (4) thermal
properties of the main rings and (5) models for these trends.
---------------------------------------------------------
Title: Unsteady signatures from solar flares: reconnection,
acceleration or transport?
Authors: Fletcher, Lyndsay; Liu, Siming
2009shin.confE.195F Altcode:
The energy for solar flares is liberated from coronal stored energy
via the process of reconnection. Observationally, solar flares are
inherently bursty, in time and in space. The primary signatures
of flare energy release are produced by accelerated electrons and
ions, i.e. hard X-rays and gamma-rays, and radio. White light and
ultraviolet chromospheric emission are also closely related to
the primary energy release. All of these signatures demonstrate
intermittency, on timescales from tens of milliseconds up to some
tens of seconds. However, it is not clear from the outset how much
of this intermittency is due to the energy release process, how much
to the acceleration process, and how much to the energy transport
process. I will review the flare main observations and discuss what
each observable timescale might tell us about the basic processes
associated with flare energisation.
---------------------------------------------------------
Title: Elementary Energy Release Events in Solar Flares
Authors: Liu, Siming; Fletcher, Lyndsay
2009ApJ...701L..34L Altcode: 2009arXiv0907.1874L
Most theoretical investigations of particle acceleration during solar
flares cannot be applied to observations for detailed study of the time
evolution. We propose a phenomenological model for turbulence evolution
and stochastic particle acceleration that links observations to the
energy release and particle acceleration through two coefficients
characterizing particle interactions with turbulent electromagnetic
fields. In the linear regime the particle distribution does not affect
the turbulence energy cascade. It is shown that electron acceleration
critically depends on the intensity of small-scale turbulence and
an impulsive nonthermal component only appears near the peak of the
gradually evolving turbulence intensity. The model naturally reproduces
the soft-hard-soft pattern of hard X-ray pulses, and we attribute
the observed change in flux and spectral index correlation from
the rise to decay phase of some pulses to changes in the background
plasma. Detailed modeling of well observed individual events will
probe the energy release processes.
---------------------------------------------------------
Title: Phosphine on Jupiter and Saturn from Cassini/CIRS
Authors: Fletcher, L. N.; Orton, G. S.; Teanby, N. A.; Irwin, P. G. J.
2009Icar..202..543F Altcode:
The global distribution of phosphine (PH <SUB>3</SUB>) on Jupiter
and Saturn is derived using 2.5 cm <SUP>-1</SUP> spectral resolution
Cassini/CIRS observations. We extend the preliminary PH <SUB>3</SUB>
analyses on the gas giants [Irwin, P.G.J., and 6 colleagues,
2004. Icarus 172, 37-49; Fletcher, L.N., and 9 colleagues, 2007a. Icarus
188, 72-88] by (a) incorporating a wider range of Cassini/CIRS datasets
and by considering a broader spectral range; (b) direct incorporation
of thermal infrared opacities due to tropospheric aerosols and (c)
using a common retrieval algorithm and spectroscopic line database
to allow direct comparison between these two gas giants. The results
suggest striking similarities between the tropospheric dynamics in
the 100-1000 mbar regions of the giant planets: both demonstrate
enhanced PH <SUB>3</SUB> at the equator, depletion over neighbouring
equatorial belts and mid-latitude belt/zone structures. Saturn's
polar PH <SUB>3</SUB> shows depletion within the hot cyclonic polar
vortices. Jovian aerosol distributions are consistent with previous
independent studies, and on Saturn we demonstrate that CIRS spectra
are most consistent with a haze in the 100-400 mbar range with a mean
optical depth of 0.1 at 10 μm. Unlike Jupiter, Saturn's tropospheric
haze shows a hemispherical asymmetry, being more opaque in the
southern summer hemisphere than in the north. Thermal-IR haze opacity
is not enhanced at Saturn's equator as it is on Jupiter. Small-scale
perturbations to the mean PH <SUB>3</SUB> abundance are discussed both
in terms of a model of meridional overturning and parameterisation
as eddy mixing. The large-scale structure of the PH <SUB>3</SUB>
distributions is likely to be related to changes in the photochemical
lifetimes and the shielding due to aerosol opacities. On Saturn, the
enhanced summer opacity results in shielding and extended photochemical
lifetimes for PH <SUB>3</SUB>, permitting elevated PH <SUB>3</SUB>
levels over Saturn's summer hemisphere.
---------------------------------------------------------
Title: Signatures of spatially extended reconnection in solar flares
Authors: Fletcher, Lyndsay
2009shin.confE.162F Altcode:
Solar flare ribbons, visible in H alpha and ultraviolet, suggest
strongly that flare reconnection happens not just in one or two spots in
the corona but over an extended region. X-ray and white light footpoints
on the other hand usually only occur in a couple of locations. What can
we say about the spatial extent and distribution of coronal reconnection
sites from such observations? In this talk I will discuss some recent
observations and simulations of 3D reconnection, and whether they
together provide evidence for large-scale (i.e. active-region scale)
current sheets.
---------------------------------------------------------
Title: Jupiter
Authors: Marchis, F.; Hueso Alonso, R.; Mousis, O.; Orton, G.;
Fletcher, L.; Perez-Hoyos, S.; Keck, W. M., II
2009IAUC.9060....3M Altcode: 2009IAUC.9060C...1M
F. Marchis, University of California at Berkeley and SETI Institute; and
R. Hueso Alonso, University of the Basque Country, further report on a
preliminary analysis of observations of Jupiter's atmosphere collected
by O. Mousis, Observatoire de Besancon; G. Orton and L. Fletcher,
Jet Propulsion Laboratory; and S. Perez-Hoyos, University of the
Basque Country, recorded with the Very Large Telescope (Yepun) and its
adaptive-optics system NACO during July 26.311-26.370. Images taken
with the IB248 filter (centered at 2.48 microns; width 0.06 microns)
revealed that the feature located between 295 deg and 315 deg west
longitude (in System III) and centered at 55 deg south latitude has
a significantly evolved shape by comparison with the Keck telescope
K_p (2.12 microns) data taken on July 20.468 (noted above). Six days
after this observation, the two maxima are now barely distinguishable,
separated by 8 deg in latitude. The brightest peak is centered at
312 deg west. The continued longitudinal shearing is consistent with
several amateur observations of the site and with the behavior of the
impact sites associated with the impacts of D/1993 F2 in 1994.
---------------------------------------------------------
Title: Observations of conduction driven evaporation in the early
rise phase of solar flares
Authors: Battaglia, M.; Fletcher, L.; Benz, A. O.
2009A&A...498..891B Altcode: 2009arXiv0903.2754B
Context: The classical flare picture features a beam of electrons, which
were accelerated in a site in the corona, hitting the chromosphere. The
electrons are stopped in the dense chromospheric plasma, emitting
bremsstrahlung in hard X-rays. The ambient material is heated by the
deposited energy and expands into the magnetic flare loops, a process
termed chromospheric evaporation. In this view hard X-ray emission from
the chromosphere is succeeded by soft-X-ray emission from the hot plasma
in the flare loop, the soft X-ray emission being a direct consequence
of the impact of the non-thermal particle beam. However, observations
of events exist in which a pronounced increase in soft X-ray emission
is observed minutes before the onset of the hard X-ray emission. Such
pre-flare emission clearly contradicts the classical flare picture. <BR
/>Aims: For the first time, the pre-flare phase of such solar flares
is studied in detail. The aim is to understand the early rise phase of
these events. We want to explain the time evolution of the observed
emission by means of alternative energy transport mechanisms such as
heat conduction. <BR />Methods: RHESSI events displaying pronounced
pre-flare emission were analyzed in imaging and spectroscopy. The time
evolution of images and full sun spectra was investigated and compared
to the theoretical expectations from conduction driven chromospheric
evaporation. <BR />Results: The pre-flare phase is characterized by
purely thermal emission from a coronal source with increasing emission
measure and density. After this earliest phase, a small non-thermal
tail to higher energies appears in the spectra, becoming more and
more pronounced. However, images still only display one X-ray source,
implying that this non-thermal emission is coronal. The increase of
emission measure and density indicates that material is added to the
coronal region. The most plausible origin is evaporated material from
the chromosphere. Energy provided by a heat flux is capable of driving
chromospheric evaporation. We show that the often used classical Spitzer
treatment of the conductive flux is not applicable. The conductive
flux is saturated. During the preflare-phase, the temperature of the
coronal source remains constant or increases. Continuous heating in the
corona is necessary to explain this observation. <BR />Conclusions:
The observations of the pre-flare phase of four solar flares are
consistent with chromospheric evaporation driven by a saturated heat
flux. Additionally, continuous heating in the corona is necessary to
sustain the observed temperature.
---------------------------------------------------------
Title: Hard X-ray Emission From A Flare-related Jet
Authors: Bain, Hazel; Fletcher, L.
2009SPD....40.3606B Altcode:
Solar X-ray jets were first observed by Yohkoh (Shibata 1992,
Strong 1992). During these events, collimated flows of plasma
are accelerated in the corona. Previous observations have detected
jet-related electrons directly in space as well as via radio signatures
(type III bursts). However the major diagnostic of fast electrons
is bremsstrahlung X-ray emission, but until now we have never seen
any evidence of hard X-ray emission directly from the jet in the
corona. This could be because it is rare to find a coronal jet dense
enough to provide a bremsstrahlung target for the electrons, or hot
enough to generate high energy thermal emission. We report what we
believe to be the first observation of hard X-ray emission formed in
a coronal jet. The event occurred on the 22nd of August 2002 and its
evolution was observed by a number of instruments. In particular we
study the pre-impulsive and impulsive phase of the flare using data
from RHESSI, TRACE and the Nobeyama Radioheliograph. During this period
RHESSI observed significant hard X-ray emission to energies as high as
50 keV in the jet. Radio observations from the Nobeyama Radioheliograph
show a positive spectral index for the ejected material, which may be
explained by optically-thick gyrosynchrotron emission from non-thermal
electrons in the jet. <P />HMB gratefully acknowledges the support of
an SPD and STFC studentship. LF gratefully acknowledges the support of
an STFC Rolling Grant, and financial support by the European Commission
through the SOLAIRE Network (MTRN-CT_2006-035484)
---------------------------------------------------------
Title: Flares and the chromosphere
Authors: Hudson, Hugh S.; Fletcher, Lyndsay
2009EP&S...61..577H Altcode: 2009EP&S...61L.577H
The chromosphere (the link between the photosphere and the corona)
plays a crucial role in flare and CME development. In analogies between
flares and magnetic substorms, it is normally identified with the
ionosphere, but we argue that the correspondence is not exact. Much
of the important physics of this interesting region remains to be
explored. We discuss chromospheric flares in the context of recent
observations of white-light flares and hard X-rays as observed by
TRACE and RHESSI, respectively. We interpret key features of these
observations as results of the stepwise changes a flare produces in
the photospheric magnetic field.
---------------------------------------------------------
Title: A “perfect” Late Phase Flare Loop: X-ray And Radio Studies
Authors: Bain, Hazel; Fletcher, L.
2009SPD....40.1917B Altcode:
We present observations of a GOES X3.1 class flare which occurred on the
24th August 2002. The event was observed by a number of instruments
including RHESSI, TRACE and NoRH. This flare is particularly
interesting due to its position and orientation on the west limb
of the Sun. The flare appears to be perpendicular to the line of
sight making it possible to ascertain the geometrical parameters of
the post flare arcade loops. We investigate the decay phase of the
flare by comparing X-ray and radio observations of the post flare
arcade loops with models of soft x-ray and thermal gyrosynchrotron
emission to characterise the electron distribution present within the
loop. <P />HMB gratefully acknowledges the support of an SPD and STFC
studentship. LF gratefully acknowledges the support of an STFC Rolling
Grant, and financial support by the European Commission through the
SOLAIRE Network (MTRN-CT_2006-035484)
---------------------------------------------------------
Title: Change of Seasons on Jovian Planets: Ground-based High Spatial
Thermal Observations
Authors: Yanamandra-Fisher, Padma A.; Orton, G.; Fletcher, L. N.;
Fisher, B. M.; Fujiyoshi, T.; Fuse, T.; Hayward, T.; de Buizer, J.
2009AAS...21430504Y Altcode:
We report on the seasonal changes observed on all four of the solar
system jovian planets, based on mid-infrared data acquired from
several observatories (NASA/IRTF, NAOJ/Subaru, ESO/VLT) from 2005 to
present. Jupiter's atmosphere underwent a global upheaval, from color
transformation of discrete and axisymmetric features to interaction
of giant vortices; Saturn is approaching its vernal equinox in August
2009 and its cold northern hemisphere is emerging into sunlight after
years of obscuration; Saturn rings are closing towards their edge-on
apparition; Uranus underwent its equinox in 2007, where seasons last
20 years and its north pole is warming up; and Neptune demonstrated
a warm south pole, with a possible mechanism for escape of methane
into the stratosphere. Although each planet is at a different stage
of its seasonal cycle, taken together, our observations illustrate
several overarching science investigations of the local meteorology
on Jovian planets: What are the circulation patterns? What explains
the warm south poles? What are the variations in the distribution of
key chemical species such as ammonia, phosphine, and other hydrocarbons?
---------------------------------------------------------
Title: Evolution of an eruptive flare loop system
Authors: Romano, P.; Zuccarello, F.; Fletcher, L.; Rubio da Costa,
F.; Bain, H. M.; Contarino, L.
2009A&A...498..901R Altcode:
Context: Flares, eruptive prominences and coronal mass ejections are
phenomena where magnetic reconnection plays an important role. However,
the location and the rate of the reconnection, as well as the mechanisms
of particle interaction with ambient and chromospheric plasma are still
unclear. <BR />Aims: In order to contribute to the comprehension of the
above mentioned processes we studied the evolution of the eruptive flare
loop system in an active region where a flare, a prominence eruption
and a CME occurred on August 24, 2002. <BR />Methods: We measured the
rate of expansion of the flare loop arcade using TRACE 195 Å images
and determined the rising velocity and the evolution of the low and high
energy hard X-ray sources using RHESSI data. We also fitted HXR spectra
and considered the radio emission at 17 and 34 GHZ. <BR />Results:
We observed that the top of the eruptive flare loop system initially
rises with a linear behavior and then, after 120 mn from the start of
the event registered by GOES at 1-8 Å, it slows down. We also observed
that the heating source (low energy X-ray) rises faster than the top
of the loops at 195 Å and that the high energy X-ray emission (30-40
keV) changes in time, changing from footpoint emission at the very
onset of the flare to being coincident during the flare peak with the
whole flare loop arcade. <BR />Conclusions: The evolution of the loop
system and of the X-ray sources allowed us to interpret this event in
the framework of the Lin & Forbes model (2000), where the absolute
rate of reconnection decreases when the current sheet is located at an
altitude where the Alfvén speed decreases with height. We estimated
that the lower limit for the altitude of the current sheet is 6 ×
10<SUP>4</SUP> km. Moreover, we interpreted the unusual variation of
the high energy HXR emission as a manifestation of the non thermal
coronal thick-target process which appears during the flare in a manner
consistent with the inferred increase in coronal column density.
---------------------------------------------------------
Title: Saturn's north polar region at depth: The North Polar Hexagon
and North Polar Cyclone observed over two years by Cassini/VIMS
Authors: Baines, K. H.; Momary, T. W.; Fletcher, L. N.; Kim, J. H.;
Showman, A. P.; Atreya, S. K.; Brown, R. H.; Buratti, B. J.; Clark,
R. N.; Nicholson, P. D.
2009EGUGA..11.3375B Altcode:
For over two years beginning in October, 2006, Saturn's north polar
region has been observed periodically from clear vantage points over
high northern latitudes by the Visual Infrared Mapping Spectrometer
onboard the Cassini/Huygens orbiter, The latest observations,
acquired on June 15 and December 16, 2008, are especially clear,
as they were obtained from sub-spacecraft latitudes poleward of 70
degrees N and at close range (< 450,000 altitude for June; <
510,000 for December). With much of the polar region under nighttime
conditions, we used Saturn's thermal glow as a source of light to
map clouds in silhouette, monitoring their movement with time to
determine the polar wind structure. We find a cyclone at the north
pole, with winds exceeding 135 m/s near 88.3 degrees N. latitude
(planetocentric, pc). The center of the cyclone, at the exact pole,
is covered by a small (< 500 km in diameter) cloud. Equatorward,
winds fall off to ~10 m/s near the poleward edge of the hexagon near 78
degrees pc. Within the hexagon itself, clouds move at ~ 125 m/s. The
hexagon itself stays nearly fixed in the rotational system of Saturn
established by Voyager. However, while the hexagonal feature stayed
fixed to high accuracy from late 2006 through early 2008 (<0.5
deg of movement over 16 months), we find that since February, 2008,
the hexagon has rotated 8.9 degrees in longitude in the retrograde
direction. Between the detailed June and December 2008 observations,
the feature rotated 1.2 degrees, retrograde, corresponding to
0.0065 degree/day or 2 cm/s, retrograde. Beginning in June, 2008,
sunlight is seen reaching cloud features within the hexagon as polar
winter wanes. New results of cloudtop altitude are presented based
on the reflected sunlight observed in various methane and hydrogen
atmospheric absorption bands. These are compared to the cloud bottom
pressures which we have determined to be near the 2-bar level based on
analysis of 5-micron thermal spectra. Clouds observed in sunlight and
at 5-micron are coherent, indicating little vertical shear in zonal
winds in the north polar region.
---------------------------------------------------------
Title: Problems and Solutions in the Analysis of Spitzer IRS
Observations of Uranus and Neptune: Results for Temperature Structure
and Composition
Authors: Orton, G.; Fletcher, L.; Mainzer, A.; Line, M.; Merlet, C.;
Hines, D.; Hammel, H.; Burgdorf, M.; Moses, J.
2009EGUGA..11.3525O Altcode:
Mid-infrared spectra of the disks of Uranus and Neptune were obtained
with Spitzer's very sensitive Infrared Spectrometer (IRS). The
IRS covered the wavelength range of 5 to 21.5 μm with a resolving
power of ~90 and of 10 to 36.5 μm with a resolving power of ~600,
although there were problems with the high-resolution modes at
the longest wavelengths. The spectra do not resolve the disks of
either planet, but they are nonetheless replete with information
about the global-mean temperature structure and composition of both
planets. This presentation will concentrate on the approaches used
to derive temperatures and compositions. Derivation of an average
temperature profile will be demonstrated principally using spectra
of Uranus, using the collision-induced absorption "continuum" and
quadrupole lines of molecular hydrogen. Derivation of composition
will be demonstrated princially using spectra of Neptune, covering
features arising from methyl, methane, acetylene, ethyene, ethane,
diacetylene, methylacetylene, and carbon dioxide. The benefits of
recent improvements in spectroscopic parameters will be demonstrated,
and the need for improvements in others outlined.
---------------------------------------------------------
Title: Partially-erupting prominences: a comparison between
observations and model-predicted observables
Authors: Tripathi, D.; Gibson, S. E.; Qiu, J.; Fletcher, L.; Liu,
R.; Gilbert, H.; Mason, H. E.
2009A&A...498..295T Altcode: 2009arXiv0902.1228T
Aims: We investigate several partially-erupting prominences to
study their relationship with other CME-associated phenomena and
compare these observations with observables predicted by a model
of partially-expelled-flux-ropes (Gibson & Fan 2006a, ApJ,
637, L65; 2006b, J. Geophys. Res., 111, 12103). <BR />Methods: We
studied 6 selected events with partially-erupting prominences using
multi-wavelength observations recorded by the Extreme-ultraviolet
Imaging Telescope (EIT), Transition Region and Coronal Explorer
(TRACE), Mauna Loa Solar Observatory (MLSO), Big Bear Solar Observatory
(BBSO), and Soft X-ray Telescope (SXT). The observational features
associated with partially-erupting prominences were then compared
with the predicted observables from the model. <BR />Results: The
partially-expelled-flux-rope (PEFR) model can explain the partial
eruption of these prominences, and in addition predicts a variety
of other CME-related observables that provide evidence of internal
reconnection during eruption. We find that all of the partially-erupting
prominences studied in this paper exhibit indirect evidence of internal
reconnection. Moreover, all cases showed evidence of at least one
observable unique to the PEFR model, e.g., dimmings external to the
source region and/or a soft X-ray cusp overlying a reformed sigmoid. <BR
/>Conclusions: The PEFR model provides a plausible mechanism to explain
the observed evolution of partially-erupting-prominence-associated
CMEs in our study.
---------------------------------------------------------
Title: Energy Release and Transfer in Solar Flares: Simulations of
Three-Dimensional Reconnection
Authors: Birn, J.; Fletcher, L.; Hesse, M.; Neukirch, T.
2009ApJ...695.1151B Altcode:
Using three-dimensional magnetohydrodynamic simulations we investigate
energy release and transfer in a three-dimensional extension of the
standard two-ribbon flare picture. In this scenario, reconnection is
initiated in a thin current sheet (suggested to form below a departing
coronal mass ejection) above a bipolar magnetic field. Two cases are
contrasted: an initially force-free current sheet (low beta) and a
finite-pressure current sheet (high beta), where beta represents the
ratio between gas (plasma) and magnetic pressure. The energy conversion
process from reconnection consists of incoming Poynting flux turned
into up- and downgoing Poynting flux, enthalpy flux, and bulk kinetic
energy flux. In the low-beta case, the outgoing Poynting flux is the
dominant contribution, whereas the outgoing enthalpy flux dominates
in the high-beta case. The bulk kinetic energy flux is only a minor
contribution in the downward direction. The dominance of the downgoing
Poynting flux in the low-beta case is consistent with an alternative to
the thick target electron beam model for solar flare energy transport,
suggested recently by Fletcher & Hudson, whereas the enthalpy
flux may act as an alternative transport mechanism. For plausible
characteristic parameters of the reconnecting field configuration, we
obtain energy release timescales and energy output rates that compare
favorably with those inferred from observations for the impulsive phase
of flares. Significant enthalpy flux and heating are found even in the
initially force-free case with very small background beta, resulting
mostly from adiabatic compression rather than Ohmic dissipation. The
energy conversion mechanism is most easily understood as a two-step
process (although the two steps may occur essentially simultaneously):
the first step is the acceleration of the plasma by Lorentz forces
in layers akin to the slow shocks in the Petschek reconnection
model, involving the conversion of magnetic energy to bulk kinetic
energy. However, due to pressure gradient forces that oppose the Lorentz
forces in approximate, or partial force balance, the accelerated plasma
becomes slowed down and compressed, whereby the bulk kinetic energy
is converted to heat, either locally deposited or transported away by
enthalpy flux and deposited later. This mechanism is most relevant in
the downflow region, which is more strongly governed by force balance;
it is less important in the outflow above the reconnection site,
where more energy remains in the form of fast bulk flow.
---------------------------------------------------------
Title: Inertial Alfvén Wave Acceleration of Solar Flare Electrons
Authors: McClements, K. G.; Fletcher, L.
2009ApJ...693.1494M Altcode:
The possibility that electrons could be accelerated by inertial Alfvén
waves to hard X-ray-emitting energies in the low solar corona during
flares is investigated theoretically. This investigation is prompted
in part by recent microwave observations indicating that the coronal
magnetic field is strong enough that the Alfvén velocity c<SUB>A</SUB>
above active regions could be of the order of a tenth of the speed of
light or more; electrons can be accelerated to velocities in excess of
c<SUB>A</SUB> on collisionless timescales via reflection by a single
inertial Alfvén wave pulse. It is shown that the fraction of particles
accelerated is a sensitive function of the initial electron temperature
and the transverse length scale δx of the shear Alfvén wave pulse;
under typical pre-flare coronal conditions, a significant fraction of
the electron population can be accelerated if δx is of the order of
a few meters or less.
---------------------------------------------------------
Title: Retrievals of atmospheric variables on the gas giants from
ground-based mid-infrared imaging
Authors: Fletcher, L. N.; Orton, G. S.; Yanamandra-Fisher, P.; Fisher,
B. M.; Parrish, P. D.; Irwin, P. G. J.
2009Icar..200..154F Altcode:
Thermal-infrared imaging of Jupiter and Saturn using the NASA/IRTF
and Subaru observatories are quantitatively analyzed to assess
the capabilities for reproducing and extending the zonal mean
atmospheric results of the Cassini/CIRS experiment. We describe the
development of a robust, systematic and reproducible approach to the
acquisition and reduction of planetary images in the mid-infrared
(7-25 μm), and perform an adaptation and validation of the optimal
estimation, correlated- k retrieval algorithm described by Irwin
et al. [Irwin, P., Teanby, N., de Kok, R., Fletcher, L., Howett,
C., Tsang, C., Wilson, C., Calcutt, S., Nixon, C., Parrish, P.,
2008. J. Quant. Spectrosc. Radiat. Trans. 109 (6), 1136-1150] for
channel-integrated radiances. Synthetic spectral analyses and a
comparison to Cassini results are used to verify our abilities to
retrieve temperatures, haze opacities and gaseous abundances from
filtered imaging. We find that ground-based imaging with a sufficiently
high spatial resolution is able to reproduce the three-dimensional
temperature and para-H <SUB>2</SUB> fields measured by spacecraft
visiting Jupiter and Saturn, allowing us to investigate vertical wind
shear, pressure and, with measured cloud-top winds, Ertel potential
vorticity on potential temperature surfaces. Furthermore, by scaling
vertical profiles of NH <SUB>3</SUB>, PH <SUB>3</SUB>, haze opacity
and hydrocarbons as free parameters during thermal retrievals, we
can produce meridional results comparable with CIRS spectroscopic
investigations. This paper demonstrates that mid-IR imaging instruments
operating at ground-based observatories have access to several
dynamical and chemical diagnostics of the atmospheric state of the
gas giants, offering the prospect for quantitative studies over much
longer baselines and often covering much wider areas than is possible
from spaceborne platforms.
---------------------------------------------------------
Title: Methane and its isotopologues on Saturn from Cassini/CIRS
observations
Authors: Fletcher, L. N.; Orton, G. S.; Teanby, N. A.; Irwin, P. G. J.;
Bjoraker, G. L.
2009Icar..199..351F Altcode:
High spectral resolution observations from the Cassini Composite
Infrared Spectrometer [Flasar, F.M., and 44 colleagues, 2004. Space
Sci. Rev. 115, 169-297] are analysed to derive new estimates
for the mole fractions of CH <SUB>4</SUB>, CH <SUB>3</SUB>D and
<SUP>13</SUP>CH <SUB>4</SUB> of (4.7±0.2)×10, (3.0±0.2)×10 and
(5.1±0.2)×10 respectively. The mole fractions show no hemispherical
asymmetries or latitudinal variability. The analysis combines data
from the far-IR methane rotational lines and the mid-IR features
of methane and its isotopologues, using both the correlated- k
retrieval algorithm of Irwin et al. [Irwin, P., and 9 colleagues,
2008. J. Quant. Spectrosc. Radiat. Trans. 109, 1136-1150] and a
line-by-line approach to evaluate the reliability of the retrieved
quantities. C/H was found to be enhanced by 10.9±0.5 times the
solar composition of Grevesse et al. [Grevesse, N., Asplund, M.,
Sauval, A., 2007. Space Sci. Rev. 130 (1), 105-114], 2.25±0.55
times larger than the enrichment on Jupiter, and supporting the
increasing fractional core mass with distance from the Sun predicted
by the core accretion model of planetary formation. A comparison of
the jovian and saturnian C/N, C/S and C/P ratios suggests different
reservoirs of the trapped volatiles in a primordial solar nebula whose
composition varies with distance from the Sun. This is supported by
our derived D/H ratio in methane of (1.6±0.2)×10, which appears to
be smaller than the jovian value of Lellouch et al. [Lellouch, E.,
Bézard, B., Fouchet, T., Feuchtgruber, H., Encrenaz, T., de Graauw,
T., 2001. Astron. Astrophys. 370, 610-622]. Mid-IR emission features
provided an estimate of C12/C13=91.8-7.8+8.4, which is consistent with
both the terrestrial ratio and jovian ratio, suggesting that carbon
was accreted from a shared reservoir for all of the planets.
---------------------------------------------------------
Title: Ultra-violet footpoints as tracers of coronal magnetic
connectivity and restructuring during a solar flare
Authors: Fletcher, L.
2009A&A...493..241F Altcode:
Context: The bright, compact ultraviolet sources that appear in flare
ribbons are interpreted as sites of energisation of the chromosphere,
most likely by electron beams from the corona. Previously we have
developed an algorithm to track these compact sources in observations by
the Transition Region and Coronal Explorer (TRACE), recording position
and intensity. We now exploit this further. <BR />Aims: We aim at
identifying conjugate footpoint pairs by cross-correlating the TRACE
1600 Å lightcurves in one particular event - the 2002-July-17 M 8.5
flare. We also seek the spatial relationship between the magnetic flux
transfer (reconnection) rate, well-connected locations, and energy input
by electrons. <BR />Methods: We performed wavelet à trous filtering
on the UV light curves, followed by a linear cross-correlation,
to identify well-correlated pairs. We used RHESSI data to determine
the locations of strong electron beam input. <BR />Results: Maps of
footpoint pairs were produced in which we can identify well-separated
locations that have well-correlated 1600 Å light curves. The time
lag between credible conjugate footpoint brightenings can be a few
seconds. The flare magnetic connectivity is found to evolve with
time. RHESSI hard X-ray sources are found where the flux transfer
rate is highest. <BR />Conclusions: We propose that the correlated
footpoints are in fact conjugate pairs that are magnetically linked. In
some instances, this linkage may be via a coronal null. The time lag
in many cases is consistent with excitation by relativistic particles,
but correlations with a longer time lag may suggest excitation by waves.
---------------------------------------------------------
Title: Commission 10: Solar Activity
Authors: Klimchuk, James A.; van Driel-Gesztelyi, Lidia; Schrijver,
Carolus J.; Melrose, Donald B.; Fletcher, Lyndsay; Gopalswamy,
Natchimuthuk; Harrison, Richard A.; Mandrini, Cristina H.; Peter,
Hardi; Tsuneta, Saku; Vršnak, Bojan; Wang, Jing-Xiu
2009IAUTA..27...79K Altcode: 2008arXiv0809.1444K
Commission 10 deals with solar activity in all of its forms,
ranging from the smallest nanoflares to the largest coronal mass
ejections. This report reviews scientific progress over the roughly
two-year period ending in the middle of 2008. This has been an exciting
time in solar physics, highlighted by the launches of the Hinode and
STEREO missions late in 2006. The report is reasonably comprehensive,
though it is far from exhaustive. Limited space prevents the inclusion
of many significant results. The report is divided into the following
sections: Photosphere and chromosphere; Transition region; Corona and
coronal heating; Coronal jets; flares; Coronal mass ejection initiation;
Global coronal waves and shocks; Coronal dimming; The link between low
coronal CME signatures and magnetic clouds; Coronal mass ejections in
the heliosphere; and Coronal mass ejections and space weather. Primary
authorship is indicated at the beginning of each section.
---------------------------------------------------------
Title: Polar Phenomena in Outer Planet Atmospheres
Authors: Orton, G.; Fletcher, L.; Yanamandra-Fisher, P.; Leyrat, C.;
Greathouse, T.; Parrish, P.; Encrenaz, T.; Simon-Miller, A.
2008AGUFM.P11B1272O Altcode:
Infrared observations of the polar regions of the outer planets
have revealed similarities to the Earth's atmosphere and some new
phenomena. The most dominant force which is apparent in time-dependent
studies of the poles is seasonal radiative forcing, which was detected
in Saturn's stratosphere as early as 1973. For Saturn, Uranus and
Neptune, planets with substantial obliquities, the seasonally dependent
changes are predictable and can be used to constrain abundances of
optically active gases and the rate of restoration by stratospheric
circulation. In the case of Neptune, recent evidence shows that the
heating is sufficient to allow a "leak" from the reservoir of methane
in the deep atmosphere into the polar stratosphere. New thermal images
of Uranus show that the winter pole of Uranus which has only recently
emerged fully from darkness is colder than when it was in the middle of
winter when Voyager 2 visited, confirming the substantial seasonal phase
delay associated with radiative heating and cooling models. Even Jupiter
with its 3-degree obliquity shows clear evidence for seasonal forcing of
temperatures in the upper troposphere and stratosphere. The second most
prominent characteristic of the resolvable polar temperature fields in
Jupiter and Saturn is the formation of polar vortices. Jupiter's polar
vortices are cold, similar to those detected in the terrestrial planets;
they have sharp equatorward boundaries which are characterized by Rossby
waves which rotate at the speed of the local zonal wind flow and are
coincident with the similarly irregular boundaries of a polar haze, also
known as "polar hoods". The cold vortex at Saturn's northern winter pole
is muted, but Saturn also has a unique "warm polar vortex" in the south
(late summer) pole which shows no apparent wave structure. Saturn's
warm polar vortex has no counterpart in the Earth's atmosphere,
where summer radiative warming simply dissipates the cold winter
vortex. Saturn also possesses dynamically driven hot regions within
2 degrees of its poles where dynamics is driving relatively dry air
downwards, causing adiabatic warming and clearing the atmosphere; this
phenomenon also has no terrestrial counterpart. Jupiter's upper polar
stratosphere is warmed in discrete local regions by Joule heating from
energetic particles cascading into the neutral atmosphere. The northern
auroral-related polar "hot spot" has a very predictable geometry,
but an amplitude that is variable over time scales of months. On
the other hand, the stratosphere 25-30 degrees from Neptune's pole
shows signs of ephemeral hot spots which are more likely to related
to dynamics. These phenomena provide a rich basis of constraints for
global climate models which must, at least for Jupiter, be coupled
with models of auroral energy transport.
---------------------------------------------------------
Title: A General Radiative Seasonal Climate Model Applied to Saturn,
Uranus, and Neptune.
Authors: Greathouse, T. K.; Strong, S.; Moses, J.; Orton, G.; Fletcher,
L.; Dowling, T.
2008AGUFM.P21B..06G Altcode:
With similar compositions, a range of planet-sun distances, different
orbital periods, and a variety of axial tilts, the Giant Planets are
a unique test set for seasonal climate variation studies. We have
created a general radiative seasonal climate model in an attempt to
reproduce observed and predict future stratospheric temperatures of the
Giant Planets. We present here a description of the radiative heating
and cooling algorithms used in calculating the change in temperature
with time. We will discuss the methods used to decrease run time,
the opacity tables used, and indicate where more detailed opacity
information would prove useful. We will use Saturn seasonal models to
show the impact variations of the key coolants, acetylene and ethane,
and the dominant heaters, methane and aerosols, have on predicted
stratospheric temperatures. We will also present the initial results
from the application of our model to the atmospheres of Uranus and
Neptune. The same planet independent heating/cooling code implemented
in our radiative seasonal climate model is being incorporated into
the global circulation model EPIC. This work was funded by NASA PATM
grants NNX08AE64G and NNX08AL95G.
---------------------------------------------------------
Title: Spatial and Temporal Relationships Between WL/UV Continuum
and hard X-ray Footpoints in Solar Flares
Authors: Hudson, H. S.; Fletcher, L.; McTiernan, J.
2008AGUFMSH41A1605H Altcode:
Hard X-rays show the presence of energetic electrons in the
impulsive phase of a solar flare. According to standard models, these
electrons contain a large fraction of the total flare energy. We
show that comparable amounts of energy are present in the compact,
rapidly variable WL and UV bright points that constitute white-light
flares. This suggests that these structures can be identified with
each other, and indeed the image centroids and time variations match
well. There are image differences that we believe mainly to be due to
the different resolving powers of Hinode and TRACE WL/UV imaging on the
one hand, and RHESSI hard X-rays on the other. We therefore also use
RHESSI modeling software to simulate hard X-ray images using TRACE and
Hinode data as templates to understand this relationship more precisely.
---------------------------------------------------------
Title: Saturn's South Polar Vortex Compared to Other Large Vortices
in the Solar System
Authors: Dyudina, U. A.; Ingersoll, A. P.; Ewald, S. P.; Vasavada,
A. R.; West, R. A.; Baines, K. H.; Momary, T. W.; Barbara, J. M.;
Del Genio, A. D.; Porco, C. C.; Achterberg, R. K.; Flasar, F.;
Simon-Miller, A. A.; Fletcher, L. N.
2008AGUFM.P11C1283D Altcode:
Observations made by the Imaging Science Subsystem (ISS), Visible
and In- frared Mapping Spectrometer (VIMS) and the long-wavelength
Composite Infrared Spectrometer (CIRS) aboard the Cassini spacecraft
reveal that the large, long-lived cyclonic vortex at Saturn's south
pole has a 4200-km-diameter cloud-free nearly circular region. This
region has a 4 K warm core extending from the troposphere into the
stratosphere, concentric cloud walls extending 20-70 km above the
internal clouds, and numerous external clouds whose an- ticyclonic
vorticity suggests a convective origin. The rotation speeds of the
vortex reach 150-190 m/s, and may strengthen with depth. The Saturn
polar vortex has features in common with terrestrial hurricanes and
with the Venus polar vortex. Neptune and other giant planets may also
have strong polar vortices.
---------------------------------------------------------
Title: Deuterium in the Outer Planets: New Constraints and New
Questions from Infrared Spectroscopy
Authors: Fletcher, L. N.; Orton, G. S.; Mainzer, A.; Line, M. R.;
Merlet, C.; Burgdorf, M.; Irwin, P. G.
2008AGUFM.P21B..04F Altcode:
We discuss how new observations of far-infrared rotational lines of
HD and mid-infrared vibrational features of CH3D are challenging the
accepted measurements for the deuterium abundance in the outer solar
system. New derivations of D/H will be presented from the Cassini
Composite Infrared Spectrometer (CIRS) for Saturn, the Spitzer Infrared
Spectrometer (IRS) for Uranus and Neptune and the grism mode of the
AKARI Infrared camera (IRC) for Neptune. Many thousands of spatially
resolved Cassini/CIRS spectra at an unapodized spectral resolution of
0.25 cm-1 covering a variety of latitudes on Saturn have been acquired
during Cassini's prime mission, and are coadded to give ten independent
estimates of the HD mole fraction and hundreds of estimates of the
CH3D mole fraction. Spitzer/IRS acquired disc-averaged spectra of
Uranus during Cycle 1 and more recently with Director Discretionary
time in December 2007. Neptune disc-averaged spectra were acquired
during Cycle 2 (November 2005). ISAS/JAXA's AKARI satellite recorded
disc-integrated spectra of Neptune in May 2007 with a resolving
power of 50 in the 5.5-13 micron range. These spectra have been
analysed using two separated radiative transfer and retrieval models
to check for consistency of results. On Saturn, we retrieve lower
estimates of D/H from HD and CH3D than were obtained from ISO/SWS
by Lellouch et al. (2001). Preliminary analysis of Uranus spectra
suggest that the CH3D/CH4 ratio is significantly smaller than that
predicted by the HD abundance determined from ISO/SWS by Feuchtgruber
et al. (1999), suggesting a Uranian ratio more like that of Saturn,
or a substantially different fractionation factor from that in the
current literature. Furthermore, although constraints on CH3D from
mid-IR Neptune spectroscopy are weaker, preliminary findings are that
the CH3D/CH4 ratio is lower than that obtained by Orton et al. (1992)
and inferred from HD measurements from ISO/SWS (Feuchtgruber et al.,
1999). Fletcher is supported by an appointment to the NASA Postdoctoral
Program at the Caltech/Jet Propulsion Laboratory, administered by Oak
Ride Associated Universities through a contract with NASA.
---------------------------------------------------------
Title: Saturn and Jupiter: Surprising Similarities and Stark
Differences in Dynamics and Chemistry in the Gas Giants as Revealed
by Galileo, Cassini, and New Horizons
Authors: Baines, K. H.; Fletcher, L. N.; Momary, T. W.; West, R. A.;
Atreya, S. K.; Brown, R. H.; Showman, A. P.; Simon-Miller, A. A.
2008AGUFM.P21B..05B Altcode:
Imagery and spectra obtained by a variety of spacecraft over the
past decade have revealed much about the atmospheres of the two gas
giants. A partial listing of salient phenomena documented by these
spacecraft on both planets include aurorae, lightning, the 3-D nature
of zonal winds, thunderstorm-related clouds, spectrally-identifiable
ammonia clouds, wave features, and long-lived discrete features at
mid-latitudes and near the poles. Temporal variability in regional
cloud structures are observed - seasonally on Saturn, more episodically
on Jupiter. Molecular abundances of disequilibrium gases also vary
spatially on both planets. These and other relevant phenomena will
be discussed in this talk comparing the dynamics and chemistry of the
two gas giants of our solar system.
---------------------------------------------------------
Title: Correlative Analysis of the Interaction of a Large Red
Oval with the Great Red Spot and Oval BA in May - August 2008:
Local Meteorology
Authors: Yanamandra-Fisher, P. A.; Orton, G. S.; Fletcher, L. N.;
Simon-Miller, A.
2008AGUFM.P11A1257Y Altcode:
We acquired visible, near- and mid-infrared observations via a
coordinated global campaign to observe the close encounter between
the Great Red Spot and Oval BA, involving Hubble Space Telescope
(HST), NASA/InfraRed Telescope Facility (IRTF)(NSFCAM2/MIRSI),
Telescopio Nazionale Galileo (TNG)/NICS (with adaptive optics),
Very Large Telescope (VLT)/VISIR, NOAJ/Subaru/COMICS and UKIRT/UIST
(with tip-tilt). Although initial results indicate that changes in the
albedo of the visible cloud deck and thermal field in the troposphere
recovered shortly after the passage of the large red anticyclonic oval
between the GRS and Oval BA, at near-infrared wavelengths, changes
in the atmosphere are still occurring (as of this writing). The
interaction started late June 2008. The small red oval, drifting
eastward toward the GRS, was entrained in the peripheral flow south
of the GRS. After being squeezed between the GRS and Oval BA, the
elongated large red oval emerged, with part of it following a spiral
path as it was entrained in the northern flow around the GRS, while
another portion reformed itself slightly north of its pre-interaction
latitude, indicating that the nature of the passage may have occurred
at higher altitudes. By 10 July 2008, remnants of the red oval were
still recognizable as a distinct feature as high-altitude particles in
the near infrared. The red oval and Oval BA continued to drift eastward
of the GRS. By 27 July 2008, the GRS and Oval BA were still observable
at as relatively bright, discrete features in the reflected sunlight,
with only the GRS showing a bright 4.78-micron annulus. However, the
pre-encounter 4.78-micron bright annulus of the large red oval was
not detectable. We shall present correlative analysis of the local
meteorology of the interaction in terms of variations of the wind
field, spectral composition, and tropospheric properties and compare
with similar properties prior to the current interaction.
---------------------------------------------------------
Title: Hard X-ray emission from the solar corona
Authors: Krucker, S.; Battaglia, M.; Cargill, P. J.; Fletcher, L.;
Hudson, H. S.; MacKinnon, A. L.; Masuda, S.; Sui, L.; Tomczak, M.;
Veronig, A. L.; Vlahos, L.; White, S. M.
2008A&ARv..16..155K Altcode: 2008A&ARv.tmp....8K
This review surveys hard X-ray emissions of non-thermal electrons in the
solar corona. These electrons originate in flares and flare-related
processes. Hard X-ray emission is the most direct diagnostic of
electron presence in the corona, and such observations provide
quantitative determinations of the total energy in the non-thermal
electrons. The most intense flare emissions are generally observed
from the chromosphere at footpoints of magnetic loops. Over the years,
however, many observations of hard X-ray and even γ-ray emission
directly from the corona have also been reported. These coronal sources
are of particular interest as they occur closest to where the electron
acceleration is thought to occur. Prior to the actual direct imaging
observations, disk occultation was usually required to study coronal
sources, resulting in limited physical information. Now RHESSI has
given us a systematic view of coronal sources that combines high
spatial and spectral resolution with broad energy coverage and high
sensitivity. Despite the low density and hence low bremsstrahlung
efficiency of the corona, we now detect coronal hard X-ray emissions
from sources in all phases of solar flares. Because the physical
conditions in such sources may differ substantially from those of
the usual “footpoint” emission regions, we take the opportunity
to revisit the physics of hard X-radiation and relevant theories of
particle acceleration.
---------------------------------------------------------
Title: Impulsive Flare Energy Transport by Large-Scale Alfven Waves,
and Flare Electron Acceleration
Authors: Fletcher, L.; Hudson, H. S.
2008ESPM...12.3.62F Altcode:
The impulsive phase of a solar flare marks the epoch of rapid conversion
of energy stored in the pre-flare coronal magnetic field. Hard X-ray
observations imply that a substantial fraction of flare energy released
during the impulsive phase is converted to the kinetic energy of mildly
relativistic electrons (10-100 keV). The liberation of the magnetic free
energy can occur as the coronal magnetic field reconfigures and relaxes
following reconnection. Motivated by observations pointing to a high
local Alfven speed in parts of the corona, and by considerations from
magnetospheric physics, we investigate a scenario in which products of
the reconfiguration - large-scale Alfven wave pulses - transport the
energy and magnetic-field changes rapidly through the corona to the
lower atmosphere. We investigate the opportunities that such a scenario
offers for heating of the chromospheric plasma in flare footpoints, and
for electron acceleration, and confront our findings with observational
constraints, including energetics, HXR timing, and radio signatures.
---------------------------------------------------------
Title: Observations of the Interaction of a Large Red Oval with
the Great Red Spot and Oval BA in May-Aug 2008: Thermal Emission
Properties
Authors: Orton, Glenn S.; Fletcher, L. N.; Yanamandra-Fisher, P. A.;
Mousis, O.; Van den Anck, M.; Edkins, E.; Line, M.; Fujiyoshi,
T.; Fuse, T.; Rogers, J.; Sanchez-Lavega, A.; Simon-Miller, A.;
Chanover, N.
2008DPS....40.5002O Altcode: 2008BAAS...40..487O
Thermal-infrared observations of the close passage of Jupiter's Great
Red Spot and Oval BA serendipitously observed their interaction
with a smaller and younger red anticyclone in late June through
August of 2008. Filtered radiometric images were obtained at the
NASA IRTF's MIRSI instrument at 7.85 - 24.5 microns, together with
imaging between 8.8 and 24.5 microns and 7-14 micron spectroscopy at
higher spatial resolution with the Subaru Telescope COMICS and the
Very Large Telescope (Melipal) VISIR instruments over several nights
in this time frame. The data were acquired during regularly scheduled
observations at the IRTF and Subaru, service time at the VLT, and VLT
target-of-opportunity observations triggered by this event. We derive
maps of temperature structure in the 100-400 mbar range, variations of
the para-hydrogen fraction and ammonia gas abundance near 300 mbar, and
relative cloud opacities at the 600-mbar level and deeper. Before the
interaction, the small red spot is clearly identified as a well-defined
anticyclone with strongly-defined boundaries of peripheral subsidence
and a cold and cloudy central upwelling. Drifting eastward toward the
Great Red Spot, it was captured in the periphery of southbound flow
around the GRS around July 1 and was recognizable over the next few
days as a narrow, cold cloud feature, stretched around the GRS south
periphery. The data suggest that a portion of it became entrained in
the GRS itself and formed a very elongated and nearly spiral feature,
while another portion remained outside the GRS and temporarily reformed
to its east, accompanied by smaller fragments. As of this writing, the
event is still taking place, and conclusions are tentative. Variations
of tropospheric properties will be scrutinized and compared with prior
conditions, as well as visible color changes and near-infrared tracking
of upper-tropospheric particulates.
---------------------------------------------------------
Title: Investigation of Lyman <alpha> Emission in a Solar Flare
Authors: Rubio da Costa, F.; Fletcher, L.; Labrosse, N.; Zuccarello, F.
2008ESPM...12.2.64R Altcode:
The TRACE satellite observed a small number of solar flares in the
Lyman alpha channel, which have until now not been analysed. We look at
a well-observed flare on 8th September 1999 to investigate different
topics. We carry out a study of the spatial and temporal evolution of
the flare and associated filament eruption in Lyman alpha, hard X-rays
and soft X-rays, and examine the flare energetics using the hard X-rays
(in the collisional thick target approximation) to estimate the energy
flux carried by electrons, and TRACE Lyman alpha/1600 Å channels to
estimate the temperature and radiative power in UV. We will use these
observations to anticipate what can be observed in the future by the
proposed SMESE satellite mission, and to compare with predictions of
semi-empirical and theoretical models of the flare chromosphere.
---------------------------------------------------------
Title: The Strongest Jet Ever Detected and a New Thermal Wave in
Saturn's Equatorial Stratosphere
Authors: Li, Liming; Gierasch, P.; Achterberg, R.; Conrath, B.;
Flasar, M.; Vasavada, A.; Ingersoll, A.; Banfield, D.; Simon-Miller,
A.; Fletcher, L.
2008DPS....40.5306L Altcode: 2008BAAS...40..495L
The strongest stratospheric jet yet detected, with a speed between 500
and 600 m/s, has been discovered in the equatorial region of Saturn
by combining the nadir and limb observations of Composite Infrared
Spectrometer (CIRS) aboard the Cassini spacecraft. A similar jet
was discovered on Jupiter. These discoveries raise the possibility
that intense jets are common in the equatorial stratospheres of giant
planets. The jet's velocity is steady during the observational period
(March, 2005 to January, 2008), but variations over a longer time-scale
are possible and may be associated with the semi-annual oscillations
of Saturn&#226&#8364&#8482s low-latitude stratospheric
temperatures. An equatorial wave with wavenumber 9 is revealed in the
stratosphere of Saturn by the CIRS high spatial-resolution thermal
maps. The equatorial wave has a westward phase velocity of 10-110
m/s relative to the background current, indicating that it is an
equatorial Rossby wave. The discovery of an equatorial wave in the
stratosphere suggests that Saturn's equatorial oscillations may be
driven by vertically propagating waves, the same mechanism that drives
the quasi-biennial oscillation (QBO) on Earth.
---------------------------------------------------------
Title: Hard X-ray Emission from a Flare-related Jet
Authors: Bain, H. M.; Fletcher, L.
2008ESPM...122.102B Altcode:
We report the observation of hard X-ray emission which we attribute to
a flare-related jet. The event occurred on the 22nd of August 2002 and
its evolution was observed by a number of instruments. In particular we
study the pre-impulsive and impulsive phase of the flare using data from
RHESSI and the TRACE 195 passband. During this period RHESSI observes
significant hard X-ray emission to energies as high as 50 keV in the
jet. Estimates from RHESSI spectroscopy suggest a temperature of the
order of approximately 20MK for this time. Radio observations from the
Nobeyama Radioheliograph (NoRH) show a positive spectral index for the
ejected material backing the presence of non-thermal emission. This
also shows the jet to be optically thick at radio frequencies, possibly
due to free-free absorption.
---------------------------------------------------------
Title: First Results of Infrared Spectroscopy of Neptune From
AKARI IRC
Authors: Burgdorf, Martin J.; Drossart, P.; Encrenaz, T.; Fletcher,
L. N.; Orton, G.
2008DPS....40.5009B Altcode: 2008BAAS...40..489B
Disk-integrated spectra of Neptune were recorded on 2007-05-13, between
1.8 and 13 microns, using both the prism and the grism of the Infrared
Camera on board ISAS/JAXA's AKARI satellite. The spectral resolving
power was about 140 in the interval 2.5 - 5 microns and between 20 and
50 at other wavelengths. As Triton was included in the field of view at
a distance of only 6 arcsec in the cross-dispersion direction, we had
to subtract its contribution to the near-infrared spectra. <P />From
the mid-infrared spectra we determine the stratospheric temperature
and the CH<SUB>4</SUB> mixing ratio. We find good agreement with
the observations obtained with the infrared spectrometer aboard
Spitzer on 2005-11-20, with possible differences in the measured
emission of ethane and methane between the two observatories being
less than 10%. In contrast to this we find in the near-infrared flux
densities up to a factor five weaker than previous measurements,
confirming the presence of meteorological variations. <P />At short
wavelength, an emission peak at 4.7 microns can be interpreted as due
to fluorescent emission of CO. A similar emission feature has been
detected previously on Uranus (Encrenaz et al, A&A, 2004). As on
Uranus, the fluorescent dominant emission comes from CO (2-1) band,
and fits the observed peak. The contribution from the (1-0) band is
strongly self-absorbed, and weaker. Synthetic spectra are calculated
from a non-LTE radiative model, including solar radiation absorption,
self-absorption in the resonant fluorescent (1-0) band, and frequency
redistribution from vibrational CO bands. The spectra are compared
to constrain the vertical variation of CO abundance as measured from
submm range (Hesman et al, Icarus, 2007), the information from the
fluorescence emission coming from as deep as the 1 bar level.
---------------------------------------------------------
Title: Jupiter's South Equatorial Belt Outbreak Spots and the SEB
Fade and Revival Cycle
Authors: Go, Christopher; de Pater, I.; Marcus, P.; Rogers, J.;
Simon-MIller, A.; Wong, M.; Orton, G.; Baines, K.; Asay-Davis, X.;
Yanamandra-Fisher, P.; Fletcher, L.
2008DPS....40.4306G Altcode: 2008BAAS...40..475G
Amateur planetary imagers chronicled the 2007 upheaval of Jupiter,
providing an opportunity to observe the Fade/Revival Cycle of the
South Equatorial Belt (SEB). When the outbreaks of convective white
spots in the SEB stopped, the SEB faded and the wake of the GRS
disappeared. When an outbreak appeared, the SEB revival occurred--and
the GRS wake became turbulent once more. The distinctive dark red
color of the SEB is also associated with material brought up by SEB
outbreaks. <P />This poster will show the SEB Fade and Revival cycle
and how the SEB Outbreak plays a role in this cycle from images from
various amateur astronomers, along with images from the Hubble Space
Telescope, ground based observatories and various spacecraft.
---------------------------------------------------------
Title: Saturn's North Polar Vortex Revealed by Cassini/VIMS: Zonal
Wind Structure and Constraints on Cloud Distributions
Authors: Baines, Kevin H.; Momary, T. W.; Fletcher, L. N.; Buratti,
B. J.; Roos-Serote, M.; Showman, A. P.; Brown, R. H.; Clark, R. N.;
Nicholson, P. D.
2008DPS....40.5309B Altcode: 2008BAAS...40..495B
We present the first high-spatial resolution, near-nadir imagery and
movies of Saturn's north polar region that reveal the wind structure
of a north polar vortex. Obtained by Cassini/VIMS on June 15, 2008
from high over Saturn's polar region (sub-spacecraft latitude of
65 degrees N. lat) at an altitude of 0.42 million km during the long
polar night, these 210-per-pixel images of the polar region north of 73
degrees N. latitude show several concentric cloud rings and hundreds
of individual cloud features in silhouette against the 5-micron
background thermal glow of Saturn's deep atmosphere. In contrast to
the clear eye of the south polar vortex, the north polar vortex sports
a central cloud feature about 650-km in diameter. Zonal winds reach
a maximum of 150 m/s near 88 degrees N. latitude (planetocentric)
- comparable to the south polar vortex maximum of 190 m/s near 88
degrees S. latitude - and fall off nearly monotonically to 10 m/s near
80 degrees N. latitude. At slightly greater distance from the pole,
inside the north polar hexagon in the 75-77 degree N. latitude region,
zonal winds increase dramatically to 130 m/s, as silhouetted clouds are
seen speeding aroud the "race track” of the hexagonal feature. VIMS
5-micron thermal observations over a 1.6-year period from October 29,
2006 to June 15, 2008 are consistent with the polar hexagon structure
itself remaining fixed in the Voyager-era radio rotation rate (Desch
and Kaiser, Geophys. Res. Lett, 8, 253-256, 1981) to within an accuracy
of 3 seconds per rotational period. This agrees with the stationary
nature of the wave in this rotation system found by Godfrey (Icarus 76,
335-356, 1988), but is inconsistent with rotation rates found during
the current Cassini era.
---------------------------------------------------------
Title: The Pre-flare Phase: Key to Understanding Energy and Mass
Transport in Flare Loops
Authors: Battaglia, M.; Fletcher, L.; Benz, A. O.
2008ESPM...12.2.85B Altcode:
In the classical solar flare scenario, the chromosphere is heated by an
incident beam of supra-thermal electrons that were accelerated in the
corona, then precipitated downward along the field lines of a magnetic
loop. The hot chromospheric plasma expands and fills the magnetic
loops. This process has been termed chromospheric evaporation. The
classical scenario causes characteristic emission in soft- and hard
X-rays, both from the corona and the chromosphere. The time evolution of
this emission follows a specific pattern known as the Neupert effect. <P
/>Recent observations indicate that this scenario is only applicable for
about half of the observed flares (Veronig et al. 2002). The early rise
phase of many events is dominated by increasing soft X-ray emission up
to minutes before the onset of the hard X-ray emission. This pre-heating
clearly contradicts the classical Neupert scenario and indicates that
other mechanisms of energy transport such as thermal conduction have
to be at work. It also implies that the pre-flare energy release is
dominated by heating, not acceleration. While energy transport by
thermal conduction and subsequent chromospheric evaporation has been
studied in some detail for the decay phase of solar flares, we present
the first comprehensive study of the early phases of 4 pre-heating
events. We analyze the time evolution of those events in imaging and
spectroscopy using data from the RHESSI satellite and demonstrate how
this can improve our understanding of heating and evaporation processes
in coronal loops and the initiation of particle acceleration.
---------------------------------------------------------
Title: Saturn's Dynamic Atmosphere at Depth: Physical Characteristics
and Zonal Winds Derived from Clouds Near the 2-bar Level and Their
Dynamical Implications from Cassini-Huygens/VIMS
Authors: Momary, Thomas W.; Baines, K. H.; Fletcher, L. N.; Kim, J. H.;
Buratti, B. J.; Roos-Serote, M.; Showman, A. P.; Brown, R. H.; Clark,
R. N.; Nicholson, P. D.; Cassini/VIMS Science Team
2008DPS....40.4113M Altcode: 2008BAAS...40..472M
A wide variety of cloud structures - comprised, putatively, of ammonia
and ammonia hydrosulfide , but perhaps with an admixture of water - has
been characterized by Cassini/VIMS, including dozens of axisymmetric
zonal features, planetary waves, classic vortex structures at both
the north and south poles, and a hexagonal slow-speed wave feature
centered on the north pole. At depth, the axisymmetric zonal features
average just 1.7 degrees in latitudinal width, less than half of
that at the 0.05- and 0.5-bar levels observed in reflected sunlight,
suggesting that either (1) the patterns of ascending/descending motion
have smaller latitudinal length scales at > 1.3 bar than at shallower
levels, and/or (2) horizontal mixing is better able to "smooth out" the
cloud structure at shallow levels than at depth. Numerous long-lived
(> 1.5-years) discrete cloud structures have been observed in the
northern hemisphere, including annular ("donut") clouds near 49 and
57 degrees north latitude (planetocentric) and a "string of pearls”
of some two-dozen similarly sized ( 1500 km diameter) cloud-clearings
nearly uniformly spaced across 100 degrees of longitude near 33.5
degrees latitude. The "string of pearls” and the mid-latitude annular
cloud exhibit the fastest retrograde speeds on Saturn (in the Voyager
rotational frame). In the south, the fastest retrograde jet correlates
with the only thunderstorm-associated clouds observed on Saturn. VIMS
daytime spectra indicate that two kinds of clouds predominate there:
spectrally bright and spectrally dark. The bright clouds are the
first spectrally-identified ammonia clouds on Saturn, presumably
formed by ammonia-laden air propelled upward by thunderstorm-related
convection originating > 75 km below. Thus both vertically-extensive
(thunderstorms) and long-lived, coherent cloud features ("pearls” and
"donuts") correlate well with retrograde motions, perhaps indicating
unusually low vertical shears there which preserve coherency and allow
convective flows to rise relatively unimpeded over large vertical
distances.
---------------------------------------------------------
Title: Energy Release and Transport in Solar Flares: Three-Dimensional
MHD Simulations
Authors: Birn, J.; Birn, J.; Fletcher, L.; Hesse, M.; Neukirch, T.
2008ESPM...12.3.33B Altcode:
Using three-dimensional magnetohydrodynamic (MHD) simulations,
we investigate energy release and transfer in a three-dimensional
extension of the standard two-ribbon flare picture. In this scenario
reconnection is initiated in a thin current sheet (suggested to form
below a departing coronal mass ejection) above a bipolar magnetic
field. Two cases are contrasted: an initially force-free current sheet
(low beta) and a finite-pressure current sheet (high beta). The energy
conversion process from reconnection consists of incoming Poynting flux
(from the release of magnetic energy) turned into up- and downgoing
Poynting flux, enthalpy flux and bulk kinetic energy flux. In the
low-beta case, the outgoing Poynting flux is the dominant contribution,
whereas the outgoing enthalpy flux dominates in the high-beta case. The
bulk kinetic energy flux is only a minor contribution, particularly
in the downward direction. The dominance of the downgoing Poynting
flux in the low-beta case, which may be seen as an Alfvenic pulse, is
consistent with an alternative to the thick target electron beam model
for solar flare energy transport, suggested recently by Fletcher and
Hudson. For plausible characteristic parameters of the reconnecting
field configuration, we obtain energy release time scales and and
energy output rates that compare favorably with those inferred from
observations for the impulsive phase of flares.
---------------------------------------------------------
Title: The Continuing Evolution of the Interaction of a Large Red
Oval with the Great Red Spot and Oval BA in May - August 2008:
Near-Infrared Properties
Authors: Yanamandra-Fisher, Padma A.; Orton, G. S.; Fletcher, L. N.;
Tanga, P.; Cecconi, M.; Adamoli, G.; Irwin, P.; Holt, D.; Grimes,
H.; Edkins, E.; Brookhart, M.; Adamson, A.
2008DPS....40.4103Y Altcode: 2008BAAS...40..469Y
We acquired near- and mid-infrared observations via a coordinated
global campaign to observe the close encounter between the Great
Red Spot and Oval BA, involving NASA/InfraRed Telescope Facility
(IRTF)(NSFCAM2/MIRSI), Telescopio Nazionale Galileo (TNG)/NICS (with
adaptive optics), Very Large Telescope (VLT)/VISIR, NOAJ/Subaru/COMICS
and UKIRT/UIST (with tip-tilt). We focus on near-infrared observations
where the longest-lasting changes to the atmosphere occurred and report
on the evolution of a large red anticyclonic vortex that passed between
them because of the unexpected nature of the event. The interaction
started late June 2008. After being squeezed between the much larger
GRS and Oval BA 1-3 July 2008, the large red oval emerged slightly
north of its pre-interaction latitude, indicating that the nature of
the passage may have occurred at higher altitudes. By 10 July 2008,
remnants of the red oval were still recognizable as a distinct feature
as high-altitude particles in the near infrared. The red oval and Oval
BA continued to drift eastward of the GRS. Some peripheral material from
the red oval appeared to have become entrained around the GRS northern
boundary. By 27 July 2008, the GRS and Oval BA were still observable
at as relatively bright, discrete features in the reflected sunlight,
with only the GRS showing a bright 4.78-micron annulus. However, the
pre-encounter 4.78-micron bright annulus of the large red oval was not
detectable. In reflected sunlight from upper-atmospheric particulates,
the large red oval had evolved into a main core, accompanied by a number
of small discrete features, quasi-evenly located between the main core
and the northeast quadrant of the GRS. The GRS-Oval BA-large red oval
complex continues to evolve in the near-infrared. As of this writing,
we continue to acquire further observations of the three-oval complex.
---------------------------------------------------------
Title: Spitzer IRS Analysis of Neptune
Authors: Line, Michael R.; Orton, G. S.; Fletcher, L. N.; Mahmud,
A.; Moses, J. I.; Mainzer, A. K.; Yung, Y. L.
2008DPS....40.4203L Altcode: 2008BAAS...40..473L
Recent (2005) Spitzer Infrared Spectrometer (IRS) data of Neptune
between 5 and 20 um contain a wealth of information about the chemical
composition and temperature structure of its cold atmospheres. Emission
features in its spectrum arise from many hydrocarbons, including
ethane, acetylene and methane, and they appear to be superimposed
on top of a collision-induced H2 continuum. As the derivation of all
other parameters depends on the assumed temperature profile, special
efforts were taken to ensure that the stratospheric profile between 1
bar and 0.3 mbar matched the H2 continuum and the H2 S(1) quadrupole
feature at 17 um. Additionally we matched the methane v4 feature at
7.7 um in order to constrain the stratospheric temperature profile
above the 0.3-mbar level as well as the methane stratospheric volume
mixing ratios (VMRs). After the determination of the temperature
profile and methane VMRs, the VMRs for several species were then
determined through fitting their corresponding features in the spectrum,
initially by scaling existing photochemical models (see Mahmud et al.,
this conference). These species include methylacetylene, diacetylene,
benzene, acetylene, ethane, methyl radical, ethylene and carbon dioxide
which are all derived from methane photochemistry. <P />I would like
to acknowledge the NASA USRP program for supporting this work.
---------------------------------------------------------
Title: Solar Flare Impulsive-phase Footpoints in Extreme UV, Soft
X-Rays and Hard X-Rays
Authors: Bain, H. M.; Fletcher, L.
2008ASPC..397..157B Altcode:
We examine the flare of 14 March 2002, which has early impulsive phase
TRACE 171 Å channel EUV footpoints co-spatial with RHESSI foopoints
at energies between 6 and 50 keV. Surprisingly, the HXR spectrum from
these footpoint sources at this time is clearly thermal, consistent
with plasma temperatures up to 30 MK. The evidence points to impulsive
thermal footpoint emission, such as was observed previously with the
Yohkoh Soft X-ray Telescope, implying that the upper chromosphere or
transition region plasma is heated rapidly to temperatures of millions
of degrees.
---------------------------------------------------------
Title: A Testbed for Advanced Cold Curation of Astromaterials
Authors: Fletcher, L. A.; Bastien, R.; Allen, C. C.
2008M&PSA..43.5066F Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Changing Characteristics of Jupiter's Little Red SPOT
Authors: Cheng, A. F.; Simon-Miller, A. A.; Weaver, H. A.; Baines,
K. H.; Orton, G. S.; Yanamandra-Fisher, P. A.; Mousis, O.; Pantin,
E.; Vanzi, L.; Fletcher, L. N.; Spencer, J. R.; Stern, S. A.; Clarke,
J. T.; Mutchler, M. J.; Noll, K. S.
2008AJ....135.2446C Altcode:
The Little Red Spot (LRS) in Jupiter's atmosphere was investigated in
unprecedented detail by the New Horizons spacecraft together with the
Hubble Space Telescope (HST) and the Very Large Telescope (VLT). The LRS
and the larger Great Red Spot (GRS) of Jupiter are the largest known
atmospheric storms in the solar system. Originally a white oval, the
LRS formed from the mergers of three smaller storms in 1998 and 2000,
and became as red as the GRS between 2005 and 2006. Here we show that
circulation and wind speeds in the LRS have increased substantially
since the Voyager and Galileo eras when the oval was white. The maximum
tangential velocity of the LRS is now 172 ± 18 m s<SUP>-1</SUP>, close
to the highest values ever seen in the GRS, which has also evolved both
in size and maximum wind speed. The cloud-top altitudes of the GRS and
LRS are similar, both storms extending much higher in the atmosphere
than other Jovian anti-cyclonic systems. The similarities in wind
speeds, cloud morphology, and coloring suggest a common dynamical
mechanism explaining the reddening of the two largest anticyclonic
systems on Jupiter. These storms will not be observed again from close
range until at least 2016.
---------------------------------------------------------
Title: The role of large-scale Alfvén waves in solar flare energy
release and particle acceleration
Authors: Fletcher, L.; Hudson, H. S.
2008AGUSMSH51C..06F Altcode:
The impulsive phase of a solar flare marks the epoch of rapid conversion
of energy stored in the pre-flare coronal magnetic field. Hard X-ray
observations imply that a substantial fraction of flare energy
released during the impulsive phase is converted to the kinetic
energy of mildly relativistic electrons (10-100 keV). The liberation
of the magnetic free energy can occur as the coronal magnetic field
reconfigures and relaxes following reconnection. We investigate
a scenario, inspired in part by magnetospheric physics, in which
products of the reconfiguration - large-scale Alfvén wave pulses
- transport the energy and magnetic-field changes rapidly through
the corona to the lower atmosphere. This offers two possibilities
for electron acceleration. Firstly, in a coronal plasma with E <
me/mp, the waves propagate as inertial Alfvén waves. In the presence
of strong spatial gradients, these generate field-aligned electric
fields that can accelerate electrons to energies on the order of 10
keV and above, including by repeated interactions between electrons
and wavefronts. Secondly, when they reflect in the chromosphere,
a cascade to high wave numbers may develop. This will also accelerate
electrons by turbulence, in a medium with a locally high electron number
density. This concept, which bridges MHD-based and particle- based
views of a flare, provides an interpretation of the recently-observed
rapid variations of the line-of-sight component of the photospheric
magnetic field across the flare impulsive phase, and offers solutions
to some perplexing flare problems, such as the flare "number problem" of
finding and resupplying sufficient electrons to explain impulsive-phase
hard X-ray emission.
---------------------------------------------------------
Title: The NEMESIS planetary atmosphere radiative transfer and
retrieval tool
Authors: Irwin, P. G. J.; Teanby, N. A.; de Kok, R.; Fletcher, L. N.;
Howett, C. J. A.; Tsang, C. C. C.; Wilson, C. F.; Calcutt, S. B.;
Nixon, C. A.; Parrish, P. D.
2008JQSRT.109.1136I Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Impulsive Phase Flare Energy Transport by Large-Scale Alfvén
Waves and the Electron Acceleration Problem
Authors: Fletcher, L.; Hudson, H. S.
2008ApJ...675.1645F Altcode: 2007arXiv0712.3452F
The impulsive phase of a solar flare marks the epoch of rapid conversion
of energy stored in the preflare coronal magnetic field. Hard X-ray
observations imply that a substantial fraction of flare energy released
during the impulsive phase is converted to the kinetic energy of mildly
relativistic electrons (10-100 keV). The liberation of the magnetic free
energy can occur as the coronal magnetic field reconfigures and relaxes
following reconnection. We investigate a scenario in which products
of the reconfiguration—large-scale Alfvén wave pulses—transport
the energy and the magnetic field changes rapidly through the
corona to the lower atmosphere. This offers two possibilities
for electron acceleration. First, in a coronal plasma with β <
m<SUB>e</SUB>/m<SUB>p</SUB>, the waves propagate as inertial Alfvén
waves. In the presence of strong spatial gradients, these generate
field-aligned electric fields that can accelerate electrons to energies
on the order of 10 keV and above, including by repeated interactions
between electrons and wave fronts. Second, when they reflect and
mode-convert in the chromosphere, a cascade to high wavenumbers
may develop. This will also accelerate electrons by turbulence, in
a medium with a locally high electron number density. This concept,
which bridges MHD-based and particle-based views of a flare, provides
an interpretation of the recently observed rapid variations of the
line-of-sight component of the photospheric magnetic field across the
flare impulsive phase, and offers solutions to some perplexing flare
problems, such as the flare "number problem" of finding and resupplying
sufficient electrons to explain the impulsive-phase hard X-ray emission.
---------------------------------------------------------
Title: Atacama Desert Mudflow as an Analog for Recent Gully Activity
on Mars
Authors: Heldmann, J. L.; Conley, C.; Brown, A. J.; Fletcher, L.;
Bishop, J. L.; McKay, C. P.
2008LPI....39.2214H Altcode:
We discuss light-toned gully deposits in the Atacama Desert that share
similar morphologic and spectral signatures with the new Mars gully
deposits. We suggest that, similar to the Atacama deposits, the Mars
gully features may be remnant mudflows.
---------------------------------------------------------
Title: Curation of Frozen Samples
Authors: Fletcher, L. A.; Allen, C. C.; Bastien, R.
2008LPI....39.2202F Altcode:
We discuss the design, installation, and testing of a cold glovebox
system to be used for the curation of future frozen samples.
---------------------------------------------------------
Title: Global and temporal variations in hydrocarbons and nitriles
in Titan's stratosphere for northern winter observed by Cassini/CIRS
Authors: Teanby, N. A.; Irwin, P. G. J.; de Kok, R.; Nixon, C. A.;
Coustenis, A.; Royer, E.; Calcutt, S. B.; Bowles, N. E.; Fletcher,
L.; Howett, C.; Taylor, F. W.
2008Icar..193..595T Altcode:
Mid-infrared spectra measured by Cassini's Composite InfraRed
Spectrometer (CIRS) between July 2004 and January 2007 ( L=293°-328°)
have been used to determine stratospheric temperature and abundances
of C <SUB>2</SUB>H <SUB>2</SUB>, C <SUB>3</SUB>H <SUB>4</SUB>, C
<SUB>4</SUB>H <SUB>2</SUB>, HCN, and HC <SUB>3</SUB>N. Over 65,000 nadir
spectra with spectral resolutions of 0.5 and 2.5 cm <SUP>-1</SUP> were
used to probe spatial and temporal composition variations in Titan's
stratosphere. Cassini's 180° orbital transfer in mid-2006 allowed
low emission angle observations of the north polar region for the
first time in the mission and allowed us to probe the full latitude
range. We present the first measurements of composition variations
within the polar vortex, which display increasing abundances right
up to 90° N. The lack of a homogeneous abundance-latitude variation
within the vortex indicates limited horizontal mixing and suggests
that subsidence is greatest at the vortex core. Contrary to numerical
model predictions and tropospheric cloud observations, we do not see
any evidence for a secondary circulation cell near the south pole,
which suggests a single Hadley-type circulation in the stratosphere at
this epoch. This difference can be reconciled if the secondary cell is
restricted to altitudes below 100 km, where there is no sensitivity
in our data. Temporal variations in composition were observed in the
south, with volatile species becoming less abundant as the season
progressed. The observed variations are compared to numerical model
predictions and observations from Voyager.
---------------------------------------------------------
Title: Depth of a strong jovian jet from a planetary-scale disturbance
driven by storms
Authors: Sánchez-Lavega, A.; Orton, G. S.; Hueso, R.; García-Melendo,
E.; Pérez-Hoyos, S.; Simon-Miller, A.; Rojas, J. F.; Gómez,
J. M.; Yanamandra-Fisher, P.; Fletcher, L.; Joels, J.; Kemerer, J.;
Hora, J.; Karkoschka, E.; de Pater, I.; Wong, M. H.; Marcus, P. S.;
Pinilla-Alonso, N.; Carvalho, F.; Go, C.; Parker, D.; Salway, M.;
Valimberti, M.; Wesley, A.; Pujic, Z.
2008Natur.451.1022S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Invisible sunspots and rate of solar magnetic flux emergence
Authors: Dalla, S.; Fletcher, L.; Walton, N. A.
2008A&A...479L...1D Altcode: 2008arXiv0801.0703D
Aims:We study the visibility of sunspots and its influence on observed
values of sunspot region parameters. <BR />Methods: We use Virtual
Observatory tools provided by AstroGrid to analyse a sample of 6862
sunspot regions. By studying the distributions of locations where
sunspots were first and last observed on the solar disk, we derive the
visibility function of sunspots, the rate of magnetic flux emergence
and the ratio between the durations of growth and decay phases of solar
active regions. <BR />Results: We demonstrate that the visibility
of small sunspots has a strong centre-to-limb variation, far larger
than would be expected from geometrical (projection) effects. This
results in a large number of young spots being invisible: 44% of new
regions emerging in the west of the Sun go undetected. For sunspot
regions that are detected, large differences exist between actual
locations and times of flux emergence, and the apparent ones derived
from sunspot data. The duration of the growth phase of solar regions
has been, up to now, underestimated. <P />Appendix A is only available
in electronic form at http://www.aanda.org
---------------------------------------------------------
Title: Atacama Desert Mudflow as an Analog for Recent Gully Activity
on Mars
Authors: Heldmann, J. L.; Conley, C.; Brown, A. J.; Fletcher, L.
2008LPICo1303...44H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Temperature and Composition of Saturn’s Polar Hot Spots
and Hexagon
Authors: Fletcher, L. N.; Irwin, P. G. J.; Orton, G. S.; Teanby,
N. A.; Achterberg, R. K.; Bjoraker, G. L.; Read, P. L.; Simon-Miller,
A. A.; Howett, C.; de Kok, R.; Bowles, N.; Calcutt, S. B.; Hesman,
B.; Flasar, F. M.
2008Sci...319...79F Altcode:
Saturn’s poles exhibit an unexpected symmetry in hot, cyclonic polar
vortices, despite huge seasonal differences in solar flux. The cores of
both vortices are depleted in phosphine gas, probably resulting from
subsidence of air into the troposphere. The warm cores are present
throughout the upper troposphere and stratosphere at both poles. The
thermal structure associated with the marked hexagonal polar jet at
77°N has been observed for the first time. Both the warm cyclonic
belt at 79°N and the cold anticyclonic zone at 75°N exhibit the
hexagonal structure.
---------------------------------------------------------
Title: Depth of a strong jovian jet from a planetary-scale disturbance
driven by storms
Authors: Sánchez-Lavega, A.; Orton, G. S.; Hueso, R.; García-Melendo,
E.; Pérez-Hoyos, S.; Simon-Miller, A.; Rojas, J. F.; Gómez,
J. M.; Yanamandra-Fisher, P.; Fletcher, L.; Joels, J.; Kemerer, J.;
Hora, J.; Karkoschka, E.; de Pater, I.; Wong, M. H.; Marcus, P. S.;
Pinilla-Alonso, N.; Carvalho, F.; Go, C.; Parker, D.; Salway, M.;
Valimberti, M.; Wesley, A.; Pujic, Z.
2008Natur.451..437S Altcode:
The atmospheres of the gas giant planets (Jupiter and Saturn)
contain jets that dominate the circulation at visible levels. The
power source for these jets (solar radiation, internal heat, or both)
and their vertical structure below the upper cloud are major open
questions in the atmospheric circulation and meteorology of giant
planets. Several observations and in situ measurements found intense
winds at a depth of 24bar, and have been interpreted as supporting an
internal heat source. This issue remains controversial, in part because
of effects from the local meteorology. Here we report observations
and modelling of two plumes in Jupiter's atmosphere that erupted at
the same latitude as the strongest jet (23°N). The plumes reached
a height of 30km above the surrounding clouds, moved faster than any
other feature (169ms<SUP>-1</SUP>), and left in their wake a turbulent
planetary-scale disturbance containing red aerosols. On the basis of
dynamical modelling, we conclude that the data are consistent only
with a wind that extends well below the level where solar radiation
is deposited.
---------------------------------------------------------
Title: Impulsive Flare Energy Transport by Large-Scale Alfven Waves
and the Electron Acceleration Problem
Authors: Fletcher, L.; Hudson, H. S.
2007AGUFMSM53B1278F Altcode:
In this poster, we investigate an alternative scenario for solar
flare energy transport. Usually, the energy stored in the solar
corona and released during a flare is thought to be transported to
the lower atmosphere by electron beams. However, based on microwave
observations, magnetic fields of the order of a few 100 Gauss to
a kilogauss are measured in the corona above the core of an active
region. This implies an Alfvén speed on the order of 0.1c, meaning
that Alfvén wave pulses become plausible agents for transporting
the stored energy of the flare. We investigate this scenario, and the
opportunities it presents for both heating the lower chromosphere and
accelerating electrons to HXR-emitting energies.
---------------------------------------------------------
Title: Observations of Jupiter Supporting the New Horizons Encounter
and During a Period of "Global Upheaval"
Authors: Orton, G.; Baines, K.; Yanamandra-Fisher, P.; Mousis, O.;
Vanzi, L.; Hayward, T.; De Buizer, J.; Simon-Miller, A.; Bjoraker,
G.; Fletcher, L.; Gladstone, R.; Edkins, E.; Kemerer, J.; Sitko, M.;
Lynch, D.
2007AGUFM.P53C..03O Altcode:
Observations of Jupiter were made between February and June of 2007
to provide an expanded spectral coverage and timeline for the New
Horizons remote-sensing of Jupiter's atmosphere. From March to May,
two prominent vertical jets in the southern portion of Jupiter's North
Temperate Belt (NTBs) initiated a major darkening of this region,
and their wakes restored the darker color of the belt but not its
bright 5-micron appearance. A brightening of the southern component
of the dark South Equatorial Belt (SEBs) was interrupted by a series
of vertical outbursts from which a darker material emanated in both
directions was appeared bright at 5 microns.It also generated a series
of anticyclonic vortices with upwelling interiors and substantial
downwelling annuli which continue to this writing.
---------------------------------------------------------
Title: Characteristics of Titan's stratospheric aerosols and
condensate clouds from Cassini CIRS far-infrared spectra
Authors: de Kok, R.; Irwin, P. G. J.; Teanby, N. A.; Nixon, C. A.;
Jennings, D. E.; Fletcher, L.; Howett, C.; Calcutt, S. B.; Bowles,
N. E.; Flasar, F. M.; Taylor, F. W.
2007Icar..191..223D Altcode:
Four broad spectral features were identified in far-infrared limb
spectra from the Cassini Composite Infrared Spectrometer (CIRS), two
of which have not been identified before. The features are broader
than the spectral resolution, which suggests that they are caused
by particulates in Titan's stratosphere. We derive here the spectral
properties and variations with altitude for these four features for
six latitudes between 65° S and 85° N. Titan's main aerosol is called
Haze 0 here. It is present at all wavenumbers in the far-infrared and is
found to have a fractional scale height (i.e., the aerosol density scale
height divided by the atmospheric density scale height) between 1.5
and 1.7 with a small increase in opacity in the north. A second feature
around 140 cm <SUP>-1</SUP> (Haze A) has similar spatial properties to
Haze 0, but has a smaller fractional scale height of 1.2-1.3. Both Haze
0 and Haze A show an increase in retrieved abundance below 100 km. Two
other features (Haze B around 220 cm <SUP>-1</SUP> and Haze C around
190 cm <SUP>-1</SUP>) have a large maximum in their density profiles
at 140 and 90 km, respectively. Haze B is much more abundant in the
northern hemisphere compared to the southern hemisphere. Haze C also
shows a large increase towards the north, but then disappears at 85° N.
---------------------------------------------------------
Title: The relative timing of supra-arcade downflows in solar flares
Authors: Khan, J. I.; Bain, H. M.; Fletcher, L.
2007A&A...475..333K Altcode:
Context: Supra-arcade downflows (generally dark, sunward-propagating
features located above the bright arcade of loops in some solar flares)
have been reported mostly during the decay phase, although some
have also been reported during the rise phase of solar flares. <BR
/>Aims: We investigate, from a statistical point of view, the timing
of supra-arcade downflows during the solar flare process, and thus
determine the possible relation of supra-arcade downflows to the primary
or secondary energy release in a flare. <BR />Methods: Yohkoh Soft
X-ray Telescope (SXT) imaging data are examined to produce a list of
supra-arcade downflow candidates. In many of our events supra-arcade
downflows are not directly observed. However, the events do show
laterally moving (or “waving”) bright rays in the supra-arcade
fan of coronal rays which we interpret as due to dark supra-arcade
downflows. The events are analysed in detail to determine whether the
supra-arcade downflows (or the proxy waving coronal rays) occur during
a) the rise and/or decay phases of the soft X-ray flare and b) the flare
hard X-ray bursts. It is also investigated whether the supra-arcade
downflows events show prior eruptive signatures as seen in SXT, other
space-based coronal data, or reported in ground-based Hα images. <BR
/>Results: A substantial majority of supra-arcade downflow events show
downflows which start during the soft X-ray flare rise phase (73%),
occur during hard X-ray bursts (90%), and have prior eruptive signatures
associated with them (73%). However, we find a single event (2% of the
total) which clearly and unambiguously showed supra-arcade downflows
starting during the soft X-ray flare decay phase. <BR />Conclusions:
Since the majority of supra-arcade downflows occur during the rise
phase of the soft X-ray flare and the time of hard X-ray bursts, and
have prior eruptive signatures this suggests that they are related
to the main flare energy release process. Furthermore, the suggested
association of supra-arcade downflows with recently reconnected
magnetic field lines means they may indeed be considered as evidence
for a magnetic reconnection process. The single supra-arcade downflow
event which unambiguously started during the decay phase of the flare
occurred during hard X-ray bursts and thus appears to be related to
late energy release.
---------------------------------------------------------
Title: Observations of Simultaneous Coronal Loop Shrinkage and
Expansion during the Decay Phase of a Solar Flare
Authors: Khan, J. I.; Fletcher, L.; Nitta, N. V.
2007ASPC..369..485K Altcode:
We report what we believe are the first direct and unambiguous
observations of simultaneous coronal magnetic flux loop shrinkage
and expansion during the decay phase of a solar flare. The retracting
and expanding loops were observed nearly face-on (i.e., with the loop
major axis approximately orthogonal to the line of sight) in emission in
imaging data from the Yohkoh Soft X-ray Telescope (SXT). The retracting
loop is observed to shrink with a speed of 165±26 km s^{-1}. The
faint outward moving loop-like feature occurred ∼200 arcsec above
the shrinking loop during the time of the shrinking loop. We estimate
the speed of the outward moving loop was ∼280±130 km s^{-1}. We
interpret the shrinking loop and simultaneous outward moving loop as
direct evidence for reconnected magnetic field lines during a flare.
---------------------------------------------------------
Title: Structure and Dynamics of the Little Red Spot on Jupiter
Authors: Cheng, Andrew F.; Simon-Miller, A.; Weaver, H. A.; Baines,
K. H.; Orton, G. S.; Yanamandra-Fisher, P. A.; Mousis, O.; Pantin, E.;
Vanzi, L.; Fletcher, L. N.; Spencer, J.; Stern, A.; New Horizons Team
2007DPS....39.1903C Altcode: 2007BAAS...39..444C
The New Horizons spacecraft obtained high resolution images of the
Little Red Spot in Jupiter's atmosphere, during the New Horizons
Jupiter encounter in January - March, 2007. The Little Red Spot
is an Earth-sized storm that formed from the coalescence of three,
60-year old, white ovals starting in 1998 and that became clearly red
in 2006. The New Horizons observations have been combined for the
first time with Jupiter observations from the Very Large Telescope
array in Chile and from the Hubble Space Telescope to determine the
three-dimensional structure and dynamics of the Little Red Spot. Within
this cold anticyclonic oval, the peak wind speeds reach 170 m/s, and
the vertical gradient length, from the thermal wind equation, exceeds
90 km. Horizontal flow divergences are identified. The dynamical
structure of the Little Red Spot is similar to that of the Great Red
Spot. It is suggested that both spots may now persist for centuries,
although the Little Red Spot attained its current state only recently.
---------------------------------------------------------
Title: Zonal Mean Dynamics On Saturn From Cassini And Voyager Data
Authors: Read, Peter L.; Fletcher, L. N.; Irwin, P. G.; Achterberg,
R. K.; Conrath, B. J.; Cassini CIRS Team
2007DPS....39.3705R Altcode: 2007BAAS...39..487R
A high resolution global map of zonal mean zonal winds and
potential vorticity in Saturn's upper troposphere and stratosphere
has been constructed, assuming geostrophic thermal wind balance,
from a combination of cloud-level winds (derived from Voyager and
Cassini images) and profiles of temperature and molecular hydrogen
para-fraction retrieved from measurements by the Cassini Composite
InfraRed Spectrometer (CIRS) between October 2004 and March 2006. Away
from the equator, the results show a clear pattern of alternating jet
streams extending to polar latitudes, all of which are found to decay
significantly with height between 200 and <5 hPa pressure. The
equatorial jet also exhibits strong decay with height into the lower
stratosphere, but with evidence of some more complex structure in
the middle and upper stratosphere. Potential vorticity profiles show
evidence for a hyper-staircase structure, much as found on Jupiter,
though with some intriguing differences. Like Jupiter, Saturn's zonal
flow appears to be close to neutral stability relative to Arnol'd's
second stability theorem. This allows an estimation of the upper
tropospheric Rossby deformation radius as a function of latitude,
that ranges from 2000 km at high latitudes to more than 8000 km in
the sub-tropics. These results will be presented and discussed in the
context of their implications for global atmospheric dynamics on Saturn
and the other outer planets.
---------------------------------------------------------
Title: Meridional variations in stratospheric acetylene and ethane
in the southern hemisphere of the saturnian atmosphere as determined
from Cassini/CIRS measurements
Authors: Howett, C. J. A.; Irwin, P. G. J.; Teanby, N. A.;
Simon-Miller, A.; Calcutt, S. B.; Fletcher, L. N.; de Kok, R.
2007Icar..190..556H Altcode:
These are the first results from nadir studies of meridional variations
in the abundance of stratospheric acetylene and ethane from Cassini/CIRS
data in the southern hemisphere of Saturn. High resolution, 0.5
cm <SUP>-1</SUP>, CIRS data was used from three data sets taken in
June-November 2004 and binned into 2° wide latitudinal strips to
increase the signal-to-noise ratio. Tropospheric and stratospheric
temperatures were initially retrieved to determine the temperature
profile for each latitude bin. The stratospheric temperature at 2
mbar increased by 14 K from 9° to 68° S, including a steep 4 K
rise between 60° and 68° S. The tropospheric temperatures showed
significantly more meridional variation than the stratospheric ones,
the locations of which are strongly correlated to that of the zonal
jets. Stratospheric acetylene abundance decreases steadily from 30 to
68° S, by a factor of 1.8 at 2.0 mbar. Between 18° and 30° S the
acetylene abundance increases at 2.0 mbar. Global values for acetylene
have been calculated as (1.9±0.19)×10 at 2.0 mbar, (2.6±0.27)×10
at 1.6 mbar and (3.1±0.32)×10 at 1.4 mbar. Global values for ethane
are also determined and found to be (1.6±0.25)×10 at 0.5 mbar and
(1.4±0.19)×10 at 1.0 mbar. Ethane abundance in the stratosphere
increases towards the south pole by a factor of 2.5 at 2.0 mbar. The
increase in stratospheric ethane is especially pronounced polewards
of 60° S at 2.0 mbar. The increase of stratospheric ethane towards
the south pole supports the presence of a meridional wind system in
the stratosphere of Saturn.
---------------------------------------------------------
Title: The 2007 Jupiter's North Temperate Belt Disturbance:
I. Overview and jet stream changes.
Authors: Sanchez-Lavega, Agustin; Orton, G. S.; Hueso, R.;
Garcia-Melendo, E.; Perez-Hoyos, S.; Simon-Miller, A.; Rojas, J. F.;
Gomez, J. M.; Yanamandra-Fisher, P. A.; Fletcher, L.; Joels, J.;
Kemerer, J.; Hora, J.; Karkoschka, E.; de Pater, I.; Wong, M. H.;
Marcus, P. S.; Pinilla, N.; International Outer Planet Watch (IOPW)
2007DPS....39.0104S Altcode: 2007BAAS...39S.407S
Changes in belts and zones of Jupiter are sometimes virulent, starting
from a localized eruption followed by the development of a planetary
scale disturbance. The archetype of this phenomenology occurs rarely,
about once every fifteen years, at 23° North latitude where the
highest speed Jovian jet stream resides. In late March 2007 two
nearly simultaneous eruptions of bright plumes separated by 63,000
km (55° longitude) occurred in the peak of the jet, causing a new
disturbance. Here we present detailed observations of the disturbance
onset and evolution, and of the related changes and deep extent of the
jet based on Hubble Space Telescope images and ground-based observations
in the visible and near infrared. The plumes reached a height elevation
of 30 km relative to background clouds and, moving faster eastward
than any other feature in the planet at about 165 m/s, generated a
turbulent and complex periodic pattern in their wake, injecting a
large amount of red aerosols. Only small changes were detected in
the jet wind velocity profile as measured before the disturbance and
after its dissipation. Radiative transfer of cloud vertical structure,
mesoscale models of the plumes and a general circulation model of the
turbulent pattern require the jet stream to be robust extending down
to at least 5-7 bar pressure, the base of the water clouds, well below
the sunlight penetration level. <P />Acknowledgments: this work was
supported by the Spanish MEC-PNAYA. We acknowledge the HST director's
discretionary time (GO/DD11310) for June 5 observations. And GO/DD10782
for March 08 and May 11 data.
---------------------------------------------------------
Title: Spaceward Bound: Field Training for the Next Generation of
Space Explorers
Authors: McKay, C. P.; Coe, L. K.; Battler, M.; Bazar, D.; Conrad,
L.; Day, B.; Fletcher, L.; Green, R.; Heldmann, J.; Muscatello, T.;
Rask, J. C.; Smith, H.; Sun, H.; Zubrin, R.
2007LPICo1371.3028M Altcode: 2007eelo.work.3028M
No abstract at ADS
---------------------------------------------------------
Title: Observations of Jupiter Supporting the New Horizons Encounter
and During a Period of "Global Upheaval"
Authors: Orton, Glenn S.; Yanamandra-Fisher, P. A.; Baines, K. H.;
Momary, T.; Mousis, O.; Vanzi, L.; Hayward, T.; DeBuizer, J.;
Simon-Miller, A.; Bjoraker, G.; Fletcher, L.; Edkins, E.; Joels, J.;
Kemerer, J.; Parrish, P.
2007DPS....39.0103O Altcode: 2007BAAS...39..407O
Multi-spectral observations of Jupiter obtained between February
and September of 2007 provided both increased spectral support
and an extended timeline for the New Horizons remote-sensing of
its atmosphere. The observations also tracked a series of rapid
changes in Jupiter's atmosphere. Data were acquired at NASA's
Infrared Telescope Facility (MIRSI, NSFCam2 and SpeX), Gemini/South
(T-ReCS), ESO's Very Large Telescope (VISIR) and Lick observatory
(the Aerospace VNIRIS spectrometer). Mid-infrared observations from
the large telescopes optimized spatial resolution in the mid-infrared
by minimizing the effects of diffraction. In mid-February, the north
and south auroral-generated stratospheric hot spots were resolved
spatially, possibly for the first time; the southern one being bright
in methane, ethylene and ethane emission. In contrast, the northern
one was recognizable in all of these emissions, but barely above the
background level. Subsequent observation in March and later did not
detect any enhanced emission from the north. Observations of polar
regions provided evidence of distinct boundaries to polar airmasses
which coincided with the locations of high-altitude haze layers. These
high-resolution images revealed that temperatures in the interior of
the Great Red Spot were not elliptically symmetric but were warmer to
the south and center of the vortex. Observations from March to June
coincided with the initiation of several vertical jets in the southern
portion of Jupiter's North Temperate Belt (NTBs), which precede a
major color change in the entire belt and often signal the beginning
of an epoch of "global upheaval" in Jupiter's cloud system with major
disruptions to its typical appearance. Observations from May through
this writing tracked the initiation of similar weaker jets in the
southern portion of the South Equatorial Belt (SEBs). Our observations
determine the altitude of these outbursts, and their influence on the
temperature field and the distribution of para-hydrogen and ammonia.
---------------------------------------------------------
Title: Saturn's South Polar Vortex: A Possible Gas-Giant Analog to
a Terrestrial Hurricane
Authors: Dyudina, Ulyana A.; Ingersoll, A. P.; Ewald, S. P.; Vasavada,
A. R.; West, R. A.; Del Genio, A.; Barbara, J.; Porco, C. C.; Porco,
C. C.; Achterberg, R. K.; Flasar, F. M.; Simon-Miller, A. A.; Fletcher,
L. N.
2007DPS....39.3709D Altcode: 2007BAAS...39..488D
Observations made by the Cassini spacecraft reveal a large, long-lived
vortex anchored to the south pole of Saturn that shares many properties
with terrestrial hurricanes. Among these are: a central eye with
cyclonic vorticity, an outer region where vorticity is near zero,
a warm temperature anomaly within the eye, concentric eyewall clouds
that extend two pressure scale heights above the clouds within the eye,
numerous small clouds whose anticyclonic vorticity suggests a convective
origin, and evidence, at high altitudes, of excess cyclonic rotation not
balanced by the inward pressure force, implying outward flow. Besides
differences of scale, the main distinctions between hurricanes on
Earth and the one seen on Saturn are the static, polar location of
the latter and the lack of a liquid ocean to support it. This is the
first hurricane-like vortex detected on a planet other than Earth.
---------------------------------------------------------
Title: Condensation during Titan's Polar Winter
Authors: de Kok, Remco; Irwin, P. G.; Teanby, N. A.; Fletcher, L. N.;
Howett, C. J.; Calcutt, S. B.; Bowles, N. E.; Taylor, F. W.
2007DPS....39.5611D Altcode: 2007BAAS...39..530D
Titan is currently experiencing winter in its northern hemisphere
and the lower atmosphere of its north polar region has been in
prolonged darkness since the solstice in October 2002. As a result,
the north polar region is currently characterised by cold stratospheric
temperatures and there is enrichment of trace gases due to downward
atmospheric motion (e.g. Teanby et al., Icarus 181 pp. 243-255,
2006). These conditions make the polar winter very suitable for
cloud formation in the stratosphere. <P />A simple transport and
condensation model has been made to explore condensation processes in
Titan's northern stratosphere. In the model, the atmosphere is advected
downwards and clouds are formed as the saturation pressure of various
gases is reached. Upper limits of the gases C<SUB>4</SUB>N<SUB>2</SUB>
and propionitrile (C<SUB>2</SUB>H<SUB>5</SUB>CN) were determined
from Cassini Composite Infrared Spectrometer data to assess scenarios
of chemical disequilibrium where the gas phase is far less abundant
than the solid phase. The upper limit for C<SUB>4</SUB>N<SUB>2</SUB>
is 9e-9, which discounts the massive C<SUB>4</SUB>N<SUB>2</SUB>
build-up in the polar winter proposed by Samuelson et al. (PSS 45,
pp. 941-948, 1997) to explain the observed C<SUB>4</SUB>N<SUB>2</SUB>
cloud at the Voyager epoch. The propionitrile upper limit is 8e-9,
which is several orders of magnitude less than needed to create the
condensate feature at 220 cm<SUP>-1</SUP> of Khanna (Icarus 177,
pp. 116-121) and de Kok et al. (Icarus, in press), assuming it is
propionitrile ice, under the steady-state conditions explored by the
aformentioned model. HCN ice seems to play an important role in the
formation of a massive polar cloud (Haze B in de Kok et al., Icarus,
in press), because of the unavailability of sufficient condensable gas
other than HCN (and possibly HC<SUB>3</SUB>N) to produce the condensate
features seen in far-infrared spectra at 220 cm<SUP>-1</SUP>.
---------------------------------------------------------
Title: Jovian Wind Periodicity Revisited
Authors: Tsavaris, Irene; Simon-Miller, A. A.; Orton, G. S.; Fisher,
B.; Yanamandra-Fisher, P. A.; Parrish, P.; Fletcher, L.; Joels, J.
2007DPS....39.1906T Altcode: 2007BAAS...39..445T
Prior analysis of Jupiter's zonal wind field offered slight evidence
of periodicity on short time scales, though time coverage was marginal
(Simon-Miller et al. 2007 Icarus 186, 192-203). Though the winds are
measured through tracking of tropospheric clouds, it was hoped that some
relation could be found between stratospheric temperature oscillations
(the Quasi-Quadrennial Oscillation) and tropospheric winds. However,
complicating the analysis was the fact that the pressure levels of the
tracked cloud features are unknown, and are spatially and temporally
variable. Thermal wind analysis for a few of the dates showed cloud
level variations could easily account for most of the wind speed
variability, except at 7 deg. S latitude. New images, acquired in
2006 and 2007, have allowed the extension of the zonal wind time base,
improving the periodogram analysis. We will present results based on
our newest zonal wind and temperature profiles.
---------------------------------------------------------
Title: Characterising Saturn's vertical temperature structure from
Cassini/CIRS
Authors: Fletcher, L. N.; Irwin, P. G. J.; Teanby, N. A.; Orton, G. S.;
Parrish, P. D.; de Kok, R.; Howett, C.; Calcutt, S. B.; Bowles, N.;
Taylor, F. W.
2007Icar..189..457F Altcode:
Thermal infrared spectra of Saturn from 10-1400 cm <SUP>-1</SUP>
at 15 cm <SUP>-1</SUP> spectral resolution and a spatial resolution
of 1°-2° latitude have been obtained by the Cassini Composite
Infrared Spectrometer [Flasar, F.M., and 44 colleagues, 2004. Space
Sci. Rev. 115, 169-297]. Many thousands of spectra, acquired over
eighteen-months of observations, are analysed using an optimal
estimation retrieval code [Irwin, P.G.J., Parrish, P., Fouchet,
T., Calcutt, S.B., Taylor, F.W., Simon-Miller, A.A., Nixon, C.A.,
2004. Icarus 172, 37-49] to retrieve the temperature structure and
para-hydrogen distribution over Saturn's northern (winter) and southern
(summer) hemispheres. The vertical temperature structure is analysed
in detail to study seasonal asymmetries in the tropopause height
(65-90 mbar), the location of the radiative-convective boundary
(350-500 mbar), and the variation with latitude of a temperature knee
(between 150 and 300 mbar) which was first observed in inversions of
Voyager/IRIS spectra [Hanel, R., and 15 colleagues, 1981. Science 212,
192-200; Hanel, R., Conrath, B., Flasar, F.M., Kunde, V., Maguire,
W., Pearl, J.C., Pirraglia, J., Samuelson, R., Cruikshank, D.P.,
Gautier, D., Gierasch, P.J., Horn, L., Ponnamperuma, C., 1982. Science
215, 544-548]. Uncertainties due to both the modelling of spectral
absorptions (collision-induced absorption coefficients, tropospheric
hazes, helium abundance) and the nature of our retrieval algorithm are
quantified. Temperatures in the stratosphere near 1 mbar show a 25-30
K temperature difference between the north pole and south pole. This
asymmetry becomes less pronounced with depth as the radiative time
constant for the atmospheric response increases at deeper pressure
levels. Hemispherically-symmetric small-scale temperature structures
associated with zonal winds are superimposed onto the temperature
asymmetry for pressures greater than 100 mbar. The para-hydrogen
fraction in the 100-400 mbar range is greater than equilibrium
predictions for the southern hemisphere and parts of the northern
hemisphere, and less than equilibrium predictions polewards of 40°
N. The temperature knee between 150-300 mbar is larger in the summer
hemisphere than in the winter, smaller and higher at the equator,
deeper and larger in the equatorial belts and small at the poles. Solar
heating on tropospheric haze is proposed as a possible mechanism
for this effect; the increased efficiency of ortho- to para-hydrogen
conversion in the southern hemisphere is consistent with the presence
of larger aerosols in the summer hemisphere, which we demonstrate to be
qualitatively consistent with previous studies of Saturn's tropospheric
aerosol distribution.
---------------------------------------------------------
Title: Observations of Jupiter supporting the New Horizons encounter
and at the onset of a period of "global upheaval"
Authors: Orton, G.; Yanamandra-Fisher, P.; Baines, K.; Mousis, O.;
Vanzi, L.; Hayward, T.; De Buizer, J.; Simon-Miller, A.; Bjoraker,
G.; Fletcher, L.; Edkins, E.; Kemerer, J.
2007epsc.conf..611O Altcode:
Observations of Jupiter were made between February and June of 2007 to
provide both increased spectral support and an extended timeline for the
New Horizons remotesensing of Jupiter's atmosphere. Several ground-based
facilities were used, using the NASA Infrared Telescope Facility
(MIRSI and NSFCam2 mid- and near-infrared instruments, respectively),
Gemini/South (T-Recs mid-infrared camera/spectrometer), and ESO's Very
Large Telescope (VISIR mid-infrared camera/spectrometer). Midinfrared
observations from the large telescopes provide the maximum possible
spatial resolution in the mid-infrared, as the point-response
function is primarily defined by the limitations of diffraction
rather than atmospheric turbulence. In mid-February, the north
and south auroral-generated stratospheric hot spots were resolved
spatially, possibly for the first time; the southern one being bright
in methane, ethylene and ethane emission. In contrast, the northern
one was recognizable in all of these emissions, but barely above the
background level. Subsequent observations in March and thereafter
did not detect any enhanced emission from the north. Observations
of polar regions provided evidence of distinct boundaries to polar
airmasses which coincided with the locations of high-altitude haze
layers. These high-resolution images revealed that temperatures in
the interior of the Great Red Spot were not elliptically symmetric but
were warmer to the south and center of the vortex. Observations from
March to June coincided with the initiation of several vertical jets in
the southern portion of Jupiter's North Temperate Belt (NTBs), which
precede a major color change in the entire belt and often signal the
beginning of an epoch of "global upheaval" in Jupiter's cloud system
with major disruptions to its typical appearance. Our observations
determine the altitude of these outbursts and their influence on the
temperature field.
---------------------------------------------------------
Title: Solar active region emergence and flare productivity
Authors: Dalla, Silvia C.; Fletcher, Lyndsay; Walton, Nicholas A.
2007HiA....14..614D Altcode: 2006IAUSS...3E..45D
We use the workflow capabilities of the AstroGrid Virtual Observatory
system (<http://www.astrogrid.org>) to analyse the relation
between flare productivity and location of Active Region (AR)
emergence on the Sun. Specifically, we investigate whether emergence
of a new region near existing ones results in increased productivity
of the new and/or pre-existing AR. To address this question, we build
a series of workflows that perform queries to catalogues of regions and
flares, and operations on the results of the queries. There is a strong
East-West asymmetry in the location of emergence of new regions. We do
not find a significant difference between the flaring rate of paired
and isolated regions, when we choose a value of 12° as the cutoff
between the two populations.
---------------------------------------------------------
Title: Flare productivity of newly-emerged paired and isolated solar
active regions
Authors: Dalla, S.; Fletcher, L.; Walton, N. A.
2007A&A...468.1103D Altcode:
Aims:We investigate whether sunspot regions that emerge near existing
ones are more flare productive than those that emerge isolated. <BR
/>Methods: We analyse a sample of 2115 new regions obtained from the
USAF/Mount Wilson catalogue of sunspot regions. For our analysis
we use AstroGrid, a Virtual Observatory developed in the UK, to
build a series of workflows that perform queries to catalogues
of solar regions and flares, and operations on the results of the
queries. If a new region emerged through the solar surface within
12° of a pre-existing one, we classify it as paired, otherwise as
isolated. <BR />Results: We find that paired regions are more flare
productive than isolated ones, although this is a small effect. Here
only soft X-ray flares of magnitude greater than C1.0 are considered,
and flare productivity is characterised by the percentage of regions
that produced at least one flare over 4 days since emergence, and by
the average number of flares over the same period. For paired regions,
we also consider the flare productivity of the nearby companion region
and find that if a flare does happen within the pair, it will more
likely take place in the companion region than in the newly-emerged
one. Our results show that although emergence in proximity to another
region can slightly increase the probability of a flare taking place,
presumably by increasing the likelihood of magnetic reconnection and
significant change in magnetic topology, this is not a large effect. It
appears that intrinsic properties of the region are the key factor
in determining whether or not it will produce flares, as opposed to
interaction with pre-existing regions.
---------------------------------------------------------
Title: Energy Deposition in White Light Flares with TRACE and RHESSI
Authors: Fletcher, L.; Hannah, I. G.; Hudson, H. S.; Metcalf, T. R.
2007ASPC..368..423F Altcode:
In Fletcher et al. (2007) we investigated the white light (WL) continuum
during solar flares and its relationship to energy deposition by
electron beams. In 9 flare events, spanning GOES classifications from
C4.8 to M9.1, we have high cadence TRACE WL and RHESSI hard X-ray
observations, and compare the WL radiative power output with that
provided by flare electrons. Under the thick--target model assumptions,
we find that the electron beam must extend down to 15--20 keV, and the
energy input to the chromosphere should occur within the collisional
stopping depth of these electrons - approximately 2× 10<SUP>-4</SUP>
g cm<SUP>-2</SUP>. In this short paper, we discuss some ideas on flare
WL emission, summarise the results of the Fletcher et al. (2007)
study and discuss their implications for chromospheric heating and
white light flare emission.
---------------------------------------------------------
Title: Electron Acceleration By Inertial Alfven Waves In The Impulsive
Phase Of A Solar Flare
Authors: Hudson, Hugh S.; Fletcher, L.
2007AAS...210.9303H Altcode: 2007BAAS...39R.211H
The impulsive phase of a solar flare marks the epoch of rapid conversion
of energy stored in the pre-flare coronal magnetic field. Hard X-ray
observations imply that a substantial fraction of flare energy released
during the impulsive phase is converted to the kinetic energy of mildly
relativistic electrons (10-100 keV). The liberation of the magnetic
free energy occurs as the coronal magnetic field reconfigures and
relaxes following reconnection. Therefore, we investigate a scenario
in which the electron acceleration is caused by the agents of this
reconfiguration -- the large-scale Alfven waves which propagate the
field changes throughout the atmosphere. In a plasma with β <
m<SUB>e</SUB>/m<SUB>p</SUB>, these waves propagate as inertial
Alfven waves which, in the presence of strong spatial gradients,
generate field-aligned electric fields that can accelerate electrons
to energies on the order of 10 keV and above. This novel view also
provides an interpretation of the recently-observed rapid variations of
the line-of-sight component of the photospheric magnetic field during
the flare impulsive phase, and offers solutions to some perplexing flare
problems, such as the flare “number problem” of finding sufficient
and resupplying sufficient electrons to explain the impulsive-phase
hard X-ray emission.
---------------------------------------------------------
Title: The meridional phosphine distribution in Saturn's upper
troposphere from Cassini/CIRS observations
Authors: Fletcher, L. N.; Irwin, P. G. J.; Teanby, N. A.; Orton, G. S.;
Parrish, P. D.; Calcutt, S. B.; Bowles, N.; de Kok, R.; Howett, C.;
Taylor, F. W.
2007Icar..188...72F Altcode:
The Cassini Composite Infrared Spectrometer (CIRS) has been used
to derive the vertical and meridional variation of temperature and
phosphine (PH <SUB>3</SUB>) abundance in Saturn's upper troposphere. PH
<SUB>3</SUB> has a significant effect on the measured radiances in the
thermal infrared and between May 2004 and September 2005 CIRS recorded
thousands of spectra in both the far (10-600 cm <SUP>-1</SUP>) and mid
(600-1400 cm <SUP>-1</SUP>) infrared, at a variety of latitudes covering
the southern hemisphere. Low spectral resolution (15 cm <SUP>-1</SUP>)
data has been used to constrain the temperature structure of the
troposphere between 100 and 500 mbar. The vertical distributions of
phosphine and ammonia were retrieved from far-infrared spectra at
the highest spectral resolution (0.5 cm <SUP>-1</SUP>), and lower
resolution (2.5 cm <SUP>-1</SUP>) mid-infrared data were used to map
the meridional variation in the abundance of phosphine in the 250-500
mbar range. Temperature variations at the 250 mbar level are shown
to occur on the same scale as the prograde and retrograde jets in
Saturn's atmosphere [Porco, C.C., and 34 colleagues, 2005. Science
307, 1243-1247]. The PH <SUB>3</SUB> abundance at 250 mbar is found
to be enhanced at the equator when compared with mid-latitudes. At
mid latitudes we see anti-correlation between temperature and PH
<SUB>3</SUB> abundance at 250 mbar, phosphine being enhanced at 45° S
and depleted at 25 and 55° S. The vertical distribution is markedly
different polewards of 60-65° S, with depleted PH <SUB>3</SUB> at
500 mbar but a slower decline in abundance with altitude when compared
with the mid-latitudes. This variation is similar to the variations of
cloud and aerosol parameters observed in the visible and near infrared,
and may indicate the subsidence of tropospheric air at polar latitudes,
coupled with a diminished sunlight penetration depth reducing the rate
of PH <SUB>3</SUB> photolysis in the polar region.
---------------------------------------------------------
Title: Birth and evolution of a dense coronal loop in a complex
flare region
Authors: Bone, L.; Brown, J. C.; Fletcher, L.; Veronig, A.; White, S.
2007A&A...466..339B Altcode:
Context: During the 14th/15th of April 2002, several flares occurred
in NOAA active region complex 9893/9910. Two of these were previously
interpreted as having anomalously high coronal column densities. <BR
/>Aims: We develop a scenario using multiwavelength observations
to explain the high coronal column density (≈10<SUP>20</SUP>
cm<SUP>-2</SUP>) present at the onset of the 14th April 2002 M3.7
hard X-ray event. <BR />Methods: Prior to this event a series of
flares occurred in close temporal and spatial proximity. We observe
the sequence of flares in a multiwavelength regime from radio to hard
X-rays. This allows us to study the particle acceleration and plasma
evaporation in these events. <BR />Results: The observations of these
flares lead us to propose a sequence of reconnections between multiple
systems of loops in a 3 dimensional field geometry. We suggest that
the dense loops in the M3.7 event can be explained as being already
filled with plasma from the earlier events; these loops then themselves
become unstable or reconnect leading to particle acceleration into
an overdense coronal environment. We explore the possibility that a
high-beta disruption is behind the instability of these dense loops,
leading to the 14th April 2002 M3.7 event and the observation of hard
X-rays in the corona at energies up to ≈50 keV.
---------------------------------------------------------
Title: Fast Alfvén Wave Heating and Acceleration of Ions in a
Nonuniform Magnetoplasma
Authors: McKay, R. J.; McClements, K. G.; Fletcher, L.
2007ApJ...658..631M Altcode:
A test-particle approach is used to study the collisionless
response of protons to cold plasma fast Alfvén waves propagating
in a nonuniform magnetic field: specifically, a two-dimensional
X-point field. The field perturbations associated with the waves,
which are assumed to be azimuthally symmetric and invariant in the
direction orthogonal to the X-point plane, are exact solutions of the
linearized ideal magnetohydrodynamic (MHD) equations. The protons are
initially Maxwellian, at temperatures that are consistent with the
cold plasma approximation. Two kinds of wave solution are invoked:
global perturbations, with inward- and outward-propagating components;
and localized purely inward-propagating waves, the wave electric
field E having a preferred direction. In both cases the protons are
effectively heated in the direction parallel to the magnetic field,
although the parallel velocity distribution is generally non-Maxwellian
and some protons are accelerated to highly suprathermal energies. This
heating and acceleration can be attributed to the fact that protons
undergoing EXB drifts due to the presence of the wave are subject to
a force in the direction parallel to B. The localized wave solution
produces more effective proton heating than the global solution,
and successive wave pulses have a synergistic effect. This process,
which could play a role in both solar coronal heating and late-phase
heating in solar flares, is effective for all ion species, but it has
a negligible direct effect on electrons. However, both electrons and
heavy ions would be expected to acquire a temperature comparable to
that of the protons on collisional timescales.
---------------------------------------------------------
Title: Spaceward Bound: Field Training for the Next Generation of
Space Explorers
Authors: McKay, C. P.; Coe, L. H.; Battler, M.; Bazar, D.; Boston, P.;
Conrad, L.; Day, B.; Fletcher, L.; Graham, P.; Green, R.; Heldmann,
J.; Muscatello, T.; Rask, J.; Smith, H.; Sun, H.; Zubrin, R.
2007LPI....38.1467M Altcode:
Spaceward Bound is an educational program developed at NASA Ames
in partnership with The Mars Society, and funded by the Exploration
Systems Mission Directorate (ESMD) at NASA Headquarters.
---------------------------------------------------------
Title: Oxygen compounds in Titan's stratosphere as observed by
Cassini CIRS
Authors: de Kok, R.; Irwin, P. G. J.; Teanby, N. A.; Lellouch, E.;
Bézard, B.; Vinatier, S.; Nixon, C. A.; Fletcher, L.; Howett, C.;
Calcutt, S. B.; Bowles, N. E.; Flasar, F. M.; Taylor, F. W.
2007Icar..186..354D Altcode:
We have investigated the abundances of Titan's stratospheric oxygen
compounds using 0.5 cm<SUP>-1</SUP> resolution spectra from the
Composite Infrared Spectrometer on the Cassini orbiter. The CO abundance
was derived for several observations of far-infrared nadir spectra,
taken at a range of latitudes (75° S-35° N) and emission angles
(0°-60°), using rotational lines that have not been analysed before
the arrival of Cassini at Saturn. The derived volume mixing ratios
for the different observations are mutually consistent regardless of
latitude. The weighted mean CO volume mixing ratio is 47±8 ppm if CO
is assumed to be uniform with latitude. H<SUB>2</SUB>O could not be
detected and an upper limit of 0.9 ppb was determined. CO<SUB>2</SUB>
abundances derived from mid-infrared nadir spectra show no significant
latitudinal variations, with typical values of 16±2 ppb. Mid-infrared
limb spectra at 55° S were used to constrain the vertical profile of
CO<SUB>2</SUB> for the first time. A vertical CO<SUB>2</SUB> profile
that is constant above the condensation level at a volume mixing ratio
of 15 ppb reproduces the limb spectra very well below 200 km. This
is consistent with the long chemical lifetime of CO<SUB>2</SUB> in
Titan's stratosphere. Above 200 km the CO<SUB>2</SUB> volume mixing
ratio is not well constrained and an increase with altitude cannot be
ruled out there.
---------------------------------------------------------
Title: A TRACE White Light and RHESSI Hard X-Ray Study of Flare
Energetics
Authors: Fletcher, L.; Hannah, I. G.; Hudson, H. S.; Metcalf, T. R.
2007ApJ...656.1187F Altcode:
In this paper we investigate the formation of the white-light (WL)
continuum during solar flares and its relationship to energy deposition
by electron beams inferred from hard X-ray emission. We analyze nine
flares spanning GOES classifications from C4.8 to M9.1, seven of which
show clear cospatial RHESSI hard X-ray and TRACE WL footpoints. We
characterize the TRACE WL/UV continuum energy under two simplifying
assumptions: (1) a blackbody function, or (2) a Paschen-Balmer
continuum model. These set limits on the energy in the continuum,
which we compare with that provided by flare electrons under the
usual collisional thick-target assumptions. We find that the power
required by the white-light luminosity enhancement is comparable to
the electron beam power required to produce the HXR emission only if
the low-energy cutoff to the spectrum is less than 25 keV. The bulk
of the energy required to power the white-light flare (WLF) therefore
resides at these low energies. Since such low-energy electrons cannot
penetrate deep into a collisional thick target, this implies that the
continuum enhancement is due to processes occurring at moderate depths
in the chromosphere.
---------------------------------------------------------
Title: Vertical profiles of HCN, HC <SUB>3</SUB>N, and C <SUB>2</SUB>H
<SUB>2</SUB> in Titan's atmosphere derived from Cassini/CIRS data
Authors: Teanby, N. A.; Irwin, P. G. J.; de Kok, R.; Vinatier, S.;
Bézard, B.; Nixon, C. A.; Flasar, F. M.; Calcutt, S. B.; Bowles,
N. E.; Fletcher, L.; Howett, C.; Taylor, F. W.
2007Icar..186..364T Altcode:
Mid-infrared limb spectra in the range 600-1400 cm<SUP>-1</SUP>
taken with the Composite InfraRed Spectrometer (CIRS) on-board
the Cassini spacecraft were used to determine vertical profiles of
HCN, HC<SUB>3</SUB>N, C<SUB>2</SUB>H<SUB>2</SUB>, and temperature
in Titan's atmosphere. Both high (0.5 cm<SUP>-1</SUP>) and low
(13.5 cm<SUP>-1</SUP>) spectral resolution data were used. The 0.5
cm<SUP>-1</SUP> data gave profiles at four latitudes and the 13.5
cm<SUP>-1</SUP> data gave almost complete latitudinal coverage of
the atmosphere. Both datasets were found to be consistent with each
other. High temperatures in the upper stratosphere and mesosphere
were observed at Titan's northern winter pole and were attributed to
adiabatic heating in the subsiding branch of a meridional circulation
cell. On the other hand, the lower stratosphere was much colder in
the north than at the equator, which can be explained by the lack
of solar radiation and increased IR emission from volatile enriched
air. HC<SUB>3</SUB>N had a vertical profile consistent with previous
ground based observations at southern and equatorial latitudes,
but was massively enriched near the north pole. This can also be
explained in terms of subsidence at the winter pole. A boundary
observed at 60° N between enriched and un-enriched air is consistent
with a confining polar vortex at 60° N and HC<SUB>3</SUB>N's short
lifetime. In the far north, layers were observed in the HC<SUB>3</SUB>N
profile that were reminiscent of haze layers observed by Cassini's
imaging cameras. HCN was also enriched over the north pole, which
gives further evidence for subsidence. However, the atmospheric
cross section obtained from 13.5 cm<SUP>-1</SUP> data indicated
a HCN enriched layer at 200-250 km, extending into the southern
hemisphere. This could be interpreted as advection of polar enriched
air towards the south by a meridional circulation cell. This is
observed for HCN but not for HC<SUB>3</SUB>N due to HCN's longer
photochemical lifetime. C<SUB>2</SUB>H<SUB>2</SUB> appears to have a
uniform abundance with altitude and is not significantly enriched in
the north. This is consistent with observations from previous CIRS
analysis that show increased abundances of nitriles and hydrocarbons
but not C<SUB>2</SUB>H<SUB>2</SUB> towards the north pole.
---------------------------------------------------------
Title: A Magnetometer For The Solar Orbiter Mission
Authors: Carr, C. M.; Horbury, T. S.; Balogh, A.; Baumjohann, W.;
Bavassano, B.; Breen, A.; Burgess, D.; Cargill, P. J.; Brooker, N.;
Erdõs, G.; Fletcher, L.; Forsyth, R. J.; Giacalone, J.; Glassmeier,
K. -H.; Hoeksema, J. T.; Goldstein, M. L.; Lockwood, M.; Magnes, W.;
Masimovic, M.; Marsch, G.; Matthaeus, W. H.; Murphy, N.; Nakariakov,
V. M.; Pacheco, J. R.; Pincon, J. -L.; Riley, P.; Russell, C. T.;
Schwartz, S. J.; Szabo, A.; Thompson, M.; Vainio, R.; Velli, M.;
Vennerstrom, S.; Walsh, R.; Wimmer-Schweingruber, R.; Zank, G.
2007ESASP.641E..41C Altcode:
The magnetometer is a key instrument to the Solar Orbiter mission. The
magnetic field is a fundamental parameter in any plasma: a precise
and accurate measurement of the field is essential for understanding
almost all aspects of plasma dynamics such as shocks and stream-stream
interactions. Many of Solar Orbiter's mission goals are focussed
around the links between the Sun and space. A combination of in situ
measurements by the magnetometer, remote measurements of solar magnetic
fields and global modelling is required to determine this link and
hence how the Sun affects interplanetary space. The magnetic field
is typically one of the most precisely measured plasma parameters and
is therefore the most commonly used measurement for studies of waves,
turbulence and other small scale phenomena. It is also related to the
coronal magnetic field which cannot be measured directly. Accurate
knowledge of the magnetic field is essential for the calculation of
fundamental plasma parameters such as the plasma beta, Alfvén speed
and gyroperiod. We describe here the objectives and context of magnetic
field measurements on Solar Orbiter and an instrument that fulfils those
objectives as defined by the scientific requirements for the mission.
---------------------------------------------------------
Title: New upper limits for hydrogen halides on Saturn derived from
Cassini-CIRS data
Authors: Teanby, N. A.; Fletcher, L. N.; Irwin, P. G. J.; Fouchet,
T.; Orton, G. S.
2006Icar..185..466T Altcode:
Far infrared spectra (10-600 cm <SUP>-1</SUP>) from Cassini's
Composite InfraRed Spectrometer (CIRS) were used to determine
improved upper limits of hydrogen halides HF, HCl, HBr, and HI in
Saturn's atmosphere. Three observations, comprising a total of 3088
spectra, gave 3 σ upper limits on HF, HCl, HBr, and HI volume mole
fractions of 8.0×10, 6.7×10, 1.3×10, and 1.4×10, respectively,
at the 500 mbar pressure level. These upper limits confirm sub-solar
abundances of halide species for HF, HCl, and HBr in Saturn's upper
atmosphere—consistent with predictions from thermochemical models and
influx of material from meteoroids. Our upper limit for HCl is 16 times
lower than the tentative detection at 1.1×10 reported by Weisstein and
Serabyn [Weisstein, E.W., Serabyn, E., 1996. Icarus 123, 23-36]. These
observations are not sensitive to the deep halide abundance, which is
expected to be enriched relative to the solar composition.
---------------------------------------------------------
Title: Comparison of Earth-Based Longitudinal Studies and Cassini
CIRS Observations of Saturn's Temperature Field: Modifications of
Seasonal Forcing Models and the Discovery of Nonseasonal Low-Latitude
Thermal Oscillations
Authors: Orton, G.; Parrish, P.; Yanamandra-Fisher, P.; Fisher,
B.; Fletcher, L.; Irwin, P.; Nelson, J.; Gezari, D.; Fuse, T.;
Fujiyoshi, T.
2006AGUFM.P41C1306O Altcode:
During the sequence of observations made by Cassini CIRS from 2004 to
the present, supporting observations of Saturn have been made in the
same spectral region. Most of these were taken at NASA's 3-m Infrared
Telescope Facility (IRTF), but they were supplemented by observations
from the 8.2-m Subaru Telescope. An examination of temperature field
retrieved from form spacecraft and earth-based observations has required
us to assess carefully the limitation of vertical sensitivity for the
ground-based images and the calibration of both geometry and absolute
radiance. Keeping those limitations in mind, the combination of the
two data sets has provided evidence that is consistent with the absence
of effective cloud opacity in the mid- and far-infrared. Furthermore,
the full sequence of ground-based imaging stretches back as early as
1990. These observations clearly indicate the expected hemispherically
antisymmetric seasonal forcing, but with relaxation times considerably
shorter than the 9-year scales in both the stratosphere and upper
troposphere expected from gaseous constituents alone. An important non-
seasonal effect was also noted in the long-term behavior of the equator
and low-latitude regions which undergo a periodic oscillation with an
alternating phases of thermal waves at the equator and at latitudes
5-25 degrees poleward in both hemispheres over a period of 20 years
or longer. The observed behavior is consistent with the different
stratospheric temperature profiles of these regions. This phenomenon
is best explained by the presence of upwelling thermal waves which are
similar to the Earth's quasi-biennial oscillation (QBO) and Jupiter's
quasi-quadrennial oscillation (QQO).
---------------------------------------------------------
Title: Solar And Cosmic Ray Physics And The Space Environment:
Studies For And With LISA
Authors: Shaul, D. N. A.; Aplin, K. L.; Araújo, H.; Bingham, R.;
Blake, J. B.; Branduardi-Raymont, G.; Buchman, S.; Fazakerley, A.;
Finn, L. S.; Fletcher, L.; Glover, A.; Grimani, C.; Hapgood, M.;
Kellet, B.; Matthews, S.; Mulligan, T.; Ni, W. -T.; Nieminen, P.;
Posner, A.; Quenby, J. J.; Roming, P.; Spence, H.; Sumner, T.; Vocca,
H.; Wass, P.; Young, P.
2006AIPC..873..172S Altcode:
With data analysis preparations for LISA underway, there has been
renewed interest in studying solar, cosmic ray and environmental
physics for, and using LISA. The motivation for these studies is two
fold. The primary incentive is to predict and consequently minimize
the impact of disturbances associated with these factors, to maximize
LISA's gravitational wave scientific yield. The second stimulus is
the unique opportunity that is afforded by LISA's long-baseline
3-spacecraft configuration for studies of solar, cosmic ray and
environmental physics. Here we present an overview of recent progress
in these studies.
---------------------------------------------------------
Title: Optimal filtering of solar images using soft morphological
processing techniques
Authors: Marshall, S.; Fletcher, L.; Hough, K.
2006A&A...457..729M Altcode:
Context: .CCD images obtained by space-based astronomy and solar
physics are frequently spoiled by galactic and solar cosmic rays, and
particles in the Earth's radiation belt, which produces an overlaid,
often saturated, speckle.<BR /> Aims: .We describe the development
and application of a new image-processing technique for the removal of
this noise source, and apply it to SOHO/LASCO coronagraph images.<BR />
Methods: .We employ soft morphological filters, a branch of non-linear
image processing originating from the field of mathematical morphology,
which are particularly effective for noise removal.<BR /> Results:
.The soft morphological filters result in a significant improvement in
image quality, and perform significantly better than other currently
existing methods based on frame comparison, thresholding, or simple
morphologies.<BR /> Conclusions: .This is a promising and adaptable
technique that should be extendable to other space-based solar and
astronomy datasets.
---------------------------------------------------------
Title: Titan's Stratospheric Aerosols and Condensate Clouds as
Observed with Cassini CIRS
Authors: de Kok, Remco; Irwin, P. G.; Teanby, N. A.; Samuelson, R. E.;
Nixon, C. A.; Jennings, D. E.; Fletcher, L.; Howett, C.; Calcutt,
S. B.; Bowles, N. E.; Flasar, F. M.; Taylor, F. W.; Cassini/CIRS Team
2006DPS....38.2203D Altcode: 2006BAAS...38R.519D
Four broad spectral features were identified in far-infrared limb
spectra from the Cassini Composite Infrared Spectrometer (CIRS). The
features are broader than the spectral resolution, which suggests that
they are caused by particulates in Titan's stratosphere. We derive here
the spectral properties and variations with altitude and latitude for
these four features. Titan's main aerosol is called Haze 0 here. It
is present at all wavenumbers in the far-infrared and is found to
have a fractional scale height between 1.6-1.7 with a small increase
in opacity in the north. A second feature around 140 cm<SUP>-1</SUP>
(Haze A) has similar spatial properties to Haze 0, but has a smaller
fractional scale height of 1.2-1.3. Both Haze 0 and Haze A show an
increase in abundance below 100 km, perhaps indicative of a scattering
cloud. Two other features (Haze B around 220 cm<SUP>-1</SUP> and Haze
C around 190 cm<SUP>-1</SUP>) have a large maximum in their density
profiles at 140 km and 90 km respectively. Haze B is much more abundant
in the northern hemisphere compared to the southern hemisphere. Haze
C also shows a large increase towards the north, but then disappears
at 85<SUP>o</SUP>N. This work is supported by the Prins Bernhard
Cultuurfond and Pieter Beijer Fonds.
---------------------------------------------------------
Title: Variations In The Abundance Of Acetylene And Ethane In The
Atmosphere Of Saturn, As Deduced From Cassini/CIRS And IRTF/MIRI
Measurements.
Authors: Howett, Carly; Irwin, P.; Yanamandra-Fisher, P.; Parrish,
P.; Orton, G.; Fletcher, L.; Teanby, N.; CIRS Team
2006DPS....38.3907H Altcode: 2006BAAS...38..555H
High resolution data taken by Cassini/CIRS from June to November
2004 are analysed to deduce variations in the abundance of acetylene
and ethane. The data has good spatial coverage of Saturn's southern
latitudes covering 5 to 80 S, binned by latitude into strips of 2
degrees. Tropospheric and stratospheric temperatures are initially
deduced using the hydrogen S(1) continuum and the methane v<SUB>4</SUB>
band. Using the retrieved temperature profiles latitudinal variations
in the abundance of acetylene and ethane are determined using the
v<SUB>5</SUB> band of acetylene and the v<SUB>9</SUB> band of ethane. <P
/>These results are compared with ground-based observations of Saturn
taken with MIRSI on the IRTF in January and February 2006. Temperature
profiles are derived from fitting the hydrogen S(1) continuum and
the methane v<SUB>4</SUB> band. Variations in the abundance of the two
hydrocarbons are then determined using the R branch of the v<SUB>5</SUB>
band of acetylene and the v<SUB>9</SUB> band of ethane. <P />This
research was funded by the UK Particle Physics and Astronomy Research
Council and the NASA Cassini Project.
---------------------------------------------------------
Title: The Vortex Formerly Known as White Oval BA: Temperature
Structure, CloudProperties and Dynamical Simulation
Authors: Orton, Glenn S.; Yanamandra-Fisher, P. A.; Parrish, P. D.;
Mousis, O.; Pantin, E.; Fuse, T.; Fujiyoshi, T.; Simon-Miller, A.;
Morales-Juberias, R.; Tollestrup, E.; Connelley, M.; Trujillo, C.;
Hora, J.; Irwin, P.; Fletcher, L.; Hill, D.; Kollmansberger, S.
2006DPS....38.3902O Altcode: 2006BAAS...38..554O
White Oval BA, constituted from 3 predecessor vortices (known as
Jupiter's "classical" White Ovals) after successive mergers in 1998
and 2000, became second-largest vortex in the atmosphere of Jupiter
(and possibly the solar system) at the time of its formation. While
it continues in this distinction,it required a name change after
a 2005 December through 2006 February transformation which made it
appear visually the same color as the Great Red Spot. Our campaign
to understand the changes involved examination of the detailed
color and wind field using Hubble Space Telescope instrumentation
on several orbits in April. The field of temperatures, ammonia
distribution and clouds were also examined using the mid-infrared
VISIR camera/spectrometer on ESO's 8.2-m Very Large Telescope, the
NASA Infrared telescope with the mid-infrared MIRSI instrument and
the refurbished near-infrared facility camera NSFCam2. High-resolution
images of the Oval were made before the color change with the COMICS
mid-infrared facility on the 8.2-m Subaru telescope.We are using
these images, togther with images acquired at the IRTF and with
the Gemini/North NIRI near-infrared camera between January, 2005,
and August, 2006, to characterize the extent to which changes in
storm strength (vorticity, postive vertical motion) influenced (i)
the depth from which colored cloud particles may have been "dredged
up" from depth or (ii) the altitude to which particles may have been
lofted and subject to high-energy UV radiation which caused a color
change, as alternative explanations for the phenomenon. Clues to this
will provide clues to the chemistry of Jupiter's cloud system and its
well-known colors in general. The behavior of Oval BA, its interaction
with the Great Red Spot in particular,are also being compared with
dynamical models run with the EPIC code.
---------------------------------------------------------
Title: Vertical Profiles Of Nitrile Compounds In Titan's Atmosphere
Measured By Cassini CIRS As A Tracer Of Atmospheric Circulation
Authors: Teanby, Nicholas A.; Irwin, P. G.; de Kok, R.; Vinatier, S.;
Bezard, B.; Nixon, C. A.; Flasar, M.; Calcutt, S. B.; Bowles, N. E.;
Fletcher, L.; Howett, C.; Taylor, F. W.
2006DPS....38.3204T Altcode: 2006BAAS...38..543T
The vertical profiles of nitrile compounds including HCN and HC3N
were derived from mid-infrared observations taken with the Composite
InfraRed Spectrometer (CIRS) on board the Cassini orbiter. <P />Nitrile
compounds are created by photochemical reactions and have lifetimes
ranging from under a year to tens of years - of the same order as
a Titan year. Therefore, abundance variations can be used to probe
atmospheric motion. <P />We used the limb sounding capabilities of CIRS
to retrieve vertical profiles of HCN and HC3N from 85S to 85N. First,
the segment of the mid-IR spectrum from 1240-1360cm-1 was used to
retrieve temperature. Second, sub-spectra were extracted from the
600-750cm-1 region and used to obtain vertical profiles of nitriles. The
limiting vertical resolution of these profiles is determined by the
field-of-view size at the tangent height, which varied between 10 and
50km. <P />Both high (0.5cm-1) and low (13.5cm-1) spectral resolution
data were used to derive the abundance profiles. The high resolution
data was more precise, but only covered a few discrete latitudes,
whereas the low resolution data covered almost the entire limb from
north- to south-pole, but required verification by comparison with
the high resolution data. <P />HC3N was massively enriched near the
north pole, which can be explained in terms of subsidence. A boundary
observed at 60N between enriched and un-enriched air is consistent with
a confining polar vortex at 60N and HC3N's short lifetime. <P />HCN
was also enriched over the north pole, which gives further evidence
for subsidence. However, the atmospheric cross section obtained from
13.5cm-1 data indicated a HCN enriched layer at 200-250km, extending
into the southern hemisphere. This could be interpreted as advection
of polar enriched air towards the south by a meridional circulation
cell. This is observed for HCN but not for HC3N due to HCN's longer
photochemical lifetime.
---------------------------------------------------------
Title: Modelling Temperature Distribution Along A Magnetic Field Line
Authors: Pollock, J. A.; Fletcher, L.
2006IAUJD...3E...4P Altcode:
Fast electrons moving along a magnetic field line in the solar
atmosphere undergo collisions with the particles of the background
plasma. In doing so, they deposit some of their energy into the
background plasma, increasing its temperature. In addition to this
temperature increase, the plasma also undergoes radiative and conductive
cooling, which alters the temperature distribution along the field
line. Using stochastic simulations, we can model the movement of fast
electrons along a field line and calculate changes in their energy
as they undergo collisions. We use this data to map the temperature
distribution along the field line, including radiative and conductive
cooling, for injected electron beams of various initial distributions
and injection parameters. Temperature maps, and the radiation maps
that arise from them, can be compared with observations from RHESSI
and other satellites.
---------------------------------------------------------
Title: Observations of simultaneous coronal loop shrinkage and
expansion during the decay phase of a solar flare
Authors: Khan, J. I.; Fletcher, L.; Nitta, N. V.
2006A&A...453..335K Altcode:
We report what we believe are the first direct and unambiguous
observations of simultaneous coronal magnetic flux loop shrinkage
and expansion during the decay phase of a solar flare. The retracting
and expanding loops were observed nearly face-on (i.e., with the loop
major axis approximately orthogonal to the line of sight) in emission
in imaging data from the Yohkoh Soft X-ray Telescope (SXT). The
retracting loop is observed to shrink with a speed of 118 ± 66 km
s<SUP>-1</SUP>. The faint outward moving loop-like feature occurred
~200´´ above the shrinking loop during the time of the shrinking
loop. We estimate the speed of the outward moving loop was ~129 ± 74
km s<SUP>-1</SUP>. We interpret the shrinking loop and simultaneous
outward moving loop as direct evidence for reconnected magnetic field
lines during a flare.
---------------------------------------------------------
Title: Comparison of the Energy Spectra and Number Fluxes From a
simple Flare Model to Observations
Authors: Hannah, Iain G.; Fletcher, Lyndsay
2006SoPh..236...59H Altcode:
In this paper, we investigate the energy spectra produced by a
simple test particle X-point model of a solar flare for different
configurations of the initial electromagnetic field. We find that
once the reconnection electric field is larger than 1 Vm<SUP>-1</SUP>
the particle distribution transits from a heated one to a partially
accelerated one. As we close the separatrices of the X-point and
the angle in the inflow direction widens we find that more particles
are accelerated out of the thermal distribution and this power-law
component extends to lower energies. When we introduce a guiding
magnetic field component we find that more particles are energised,
but only up to a maximum energy dictated primarily by the reconnection
electric field. Despite being able to accelerate particles to
observable energies and demonstrate behaviour in the energy spectra
that is consistent with observations, this single X-line model can
only deliver the number fluxes required for microflares.
---------------------------------------------------------
Title: Modelling Temperature Distribution Along A Field Line
Authors: Pollock, Jennifer A.; Fletcher, L.
2006SPD....37.0108P Altcode: 2006BAAS...38R.216P
Fast electrons moving along a magnetic field line in the solaratmosphere
undergo collisions with the particles of the backgroundplasma. In
doing so, they deposit some of their energy into thebackground plasma,
increasing its temperature. In addition to thistemperature increase,
the plasma also undergoes radiative and conductivecooling, which alters
the temperature distribution along the field line.Using stochastic
simulations, we can model the movement of fastelectrons along a field
line and calculate changes in their energy asthey undergo collisions. We
use this data to map the temperaturedistribution along the field line,
including radiative and condutivecooling, for injected electron beams
of various initial distributionsand injection parameters. Temperature
maps, and the radiation maps that arise from them, can be compared
with observations from RHESSI and other satellites.
---------------------------------------------------------
Title: Latitudinal variations of HCN, HC <SUB>3</SUB>N, and C
<SUB>2</SUB>N <SUB>2</SUB> in Titan's stratosphere derived from
Cassini CIRS data
Authors: Teanby, N. A.; Irwin, P. G. J.; de Kok, R.; Nixon, C. A.;
Coustenis, A.; Bézard, B.; Calcutt, S. B.; Bowles, N. E.; Flasar,
F. M.; Fletcher, L.; Howett, C.; Taylor, F. W.
2006Icar..181..243T Altcode:
Mid- and far-infrared spectra from the Composite InfraRed Spectrometer
(CIRS) have been used to determine volume mixing ratios of nitriles
in Titan's atmosphere. HCN, HC <SUB>3</SUB>N, C <SUB>2</SUB>H
<SUB>2</SUB>, and temperature were derived from 2.5 cm <SUP>-1</SUP>
spectral resolution mid-IR mapping sequences taken during three flybys,
which provide almost complete global coverage of Titan for latitudes
south of 60° N. Three 0.5 cm <SUP>-1</SUP> spectral resolution far-IR
observations were used to retrieve C <SUB>2</SUB>N <SUB>2</SUB> and act
as a check on the mid-IR results for HCN. Contribution functions peak
at around 0.5-5 mbar for temperature and 0.1-10 mbar for the chemical
species, well into the stratosphere. The retrieved mixing ratios of
HCN, HC <SUB>3</SUB>N, and C <SUB>2</SUB>N <SUB>2</SUB> show a marked
increase in abundance towards the north, whereas C <SUB>2</SUB>H
<SUB>2</SUB> remains relatively constant. Variations with longitude
were much smaller and are consistent with high zonal wind speeds. For
90°-20° S the retrieved HCN abundance is fairly constant with a
volume mixing ratio of around 1 × 10 <SUP>-7</SUP> at 3 mbar. More
northerly latitudes indicate a steady increase, reaching around 4 × 10
<SUP>-7</SUP> at 60° N, where the data coverage stops. This variation
is consistent with previous measurements and suggests subsidence over
the northern (winter) pole at approximately 2 × 10 <SUP>-4</SUP>
m s <SUP>-1</SUP>. HC <SUB>3</SUB>N displays a very sharp increase
towards the north pole, where it has a mixing ratio of around 4 ×
10 <SUP>-8</SUP> at 60° N at the 0.1-mbar level. The difference in
gradient for the HCN and HC <SUB>3</SUB>N latitude variations can be
explained by HC <SUB>3</SUB>N's much shorter photochemical lifetime,
which prevents it from mixing with air at lower latitude. It is also
consistent with a polar vortex which inhibits mixing of volatile rich
air inside the vortex with that at lower latitudes. Only one observation
was far enough north to detect significant amounts of C <SUB>2</SUB>N
<SUB>2</SUB>, giving a value of around 9 × 10 <SUP>-10</SUP> at 50°
N at the 3-mbar level.
---------------------------------------------------------
Title: Organization and variation of Saturn's temperature field from
Cassini CIRS and supporting ground-based observations
Authors: Orton, G.; Parrish, P.; Yanamandra-Fisher, P.; Fisher, B.;
Fletcher, L.; Irwin, P.; Flasar, M.; Achterberg, R.; Conrath, B.;
Simon-Miller, A.
2006cosp...36.2583O Altcode: 2006cosp.meet.2583O
An extended set of observations of Saturn s thermal field has been
made by Cassini s Composite Infrared Spectrometer CIRS complemented
by ground-based stations NASA s Infrared Telescope Facility Gemini
North Telescope W M Keck Observatory and the Subaru Japanese National
Telescope Observations by the large telescopes have provided high
diffraction-limited spatial resolution of Saturn s disk on the order
of 5000 km although so far these all have been at single points in
time Thermal images from the NASA IRTF are characterized by spatial
resolutions of approximately 13 000 km but have been made at more
frequent intervals in time usually once every month except during
solar conjunction Cassini CIRS observations of Saturn s temperature
field have been made primarily in a mode in which a single hemisphere
is mapped by scanning the central meridian while Saturn rotates
CIRS spatial resolutions are typically 10 000 km in these maps but
observations with spatial resolutions as high as 3 000 km have been
made These observations including support imaging stretching several
years before the Cassini arrival at Saturn show a warming of the south
polar region as a result of increased seasonal sunlight a very hot
south polar spot and a possible warm polar vortex in the south polar
region Zonal thermal waves also exist at 16 28 38 and 52 degrees S
planetocentric but they are not always present CIRS measurements of
the shadowed north polar region do not show a cold counterpart to the
warm south pole but a more detailed structure Saturn s
---------------------------------------------------------
Title: Latitudinal variations in the temperature and composition of
Saturn's upper troposphere from Cassini/CIRS
Authors: Fletcher, L. N.; Irwin, P. G. J.; Teanby, N. A.; Orton, G. S.;
Parrish, P. D.; Calcutt, S. B.; Bowles, N.; de Kok, R.; Howett, C.;
Cassini/Cirs Team
2006cosp...36..853F Altcode: 2006cosp.meet..853F
The Cassini Composite Infrared Spectrometer CIRS Flasar et al 2004 has
been used to derive the meridional variation of temperature phosphine
PH 3 and ammonia NH 3 abundance in Saturn s upper troposphere 0 8
to 0 1 atm Since orbital insertion in July 2004 CIRS has recorded
thousands of spectra in both the far 10 - 600 cm -1 and mid 600 -
1400 cm -1 infrared at a variety of apodized spectral resolutions 0 5 -
15 0 cm -1 and viewing geometries covering both hemispheres of the gas
giant We use a non-linear optimal estimation retrieval code Irwin et al
2004 to derive vertical profiles of temperature composition and aerosol
abundance The abundances of NH 3 and PH 3 are retrieved from rotational
lines in the 10 - 200 cm -1 region and the nu 4 fundamental of PH 3 at
1070 - 1200 cm -1 Latitudinal temperature variations at the 0 25 atm are
shown to occur on the same scale as the prograde and retrograde jets
in Saturn s atmosphere Porco et al 2005 The distribution of phosphine
a disequilibrium species in Saturn s cold upper troposphere Orton et al
2000 2001 may be used as a tracer for the upwelling of constituent-rich
air from deeper within the atmosphere Elevated abundances of PH 3 at
polar and equatorial latitudes correlations of PH 3 and NH 3 with the
belt-zone temperature structure deviations of parahydrogen fraction
from local thermochemical equilibrium at the equator and evidence for
atmospheric heating by aerosols at 0 25 atm will also be
---------------------------------------------------------
Title: Organic Matter Analysis of the Hyper-Arid Peruvian Desert in
comparison to other Hyper-Arid Environments
Authors: Valdivia-Silva, J. E.; Fletcher, L. E.; Navarro-González,
R.; McKay, C. P.; Pérez Montano, S.; Condori Apaza, R.; Conley, C. A.
2005AGUFM.P51D0949V Altcode:
The Peruvian Desert is located along the Pacific coast of southern
Peru and is a continuation of the Atacama Desert in Chile. The Peruvian
Desert at the Pampas of La Joya has extreme environmental conditions,
such as hyperaridity, and a complete absence of macroscopic life. La
Joya contains volcanic soils with the presence of magnetite and
quartz. Furthermore, the El Niño phenomena, centralized directly off
the coast-line near La Joya, provides stronger climactic effects on
this desert, resulting in higher levels of precipitation which should
allow for the development of microscopic life. Taking into account
that life is based on carbon, here we search for relationships between
soil organic matter detected by oxidation versus pyrolisis (pyr-GC-MS)
techniques. Our preliminary results showed similar levels of organic
compounds to Yungay, the hyper-arid core of the Atacama Desert,
similar levels of organic compounds to the Antarctic Dry Valleys,
and direct correlation between oxidation and pyrolitic techniques.
---------------------------------------------------------
Title: a Solar Science Case with Astrogrid: Flare Productivity of
Recently-Emerged Paired and Isolated Active Regions
Authors: Dalla, S.; Fletcher, L.; Walton, N. A.
2005ESASP.600E.117D Altcode: 2005dysu.confE.117D; 2005ESPM...11..117D
No abstract at ADS
---------------------------------------------------------
Title: Multiwavelength Observations of a Partially Occulted Solar
Flare
Authors: Bone, L.; Brown, J. C.; Fletcher, L.
2005ESASP.600E..38B Altcode: 2005ESPM...11...38B; 2005dysu.confE..38B
No abstract at ADS
---------------------------------------------------------
Title: Coronal Heating and X-Ray Emission from a Beam of Fast
Electrons
Authors: Pollock, J. A.; Fletcher, L.
2005ESASP.600E.138P Altcode: 2005dysu.confE.138P; 2005ESPM...11..138P
No abstract at ADS
---------------------------------------------------------
Title: X-Ray Quasi-Periodic Pulsations in Solar Flares as
Magnetohydrodynamic Oscillations
Authors: Foullon, C.; Verwichte, E.; Nakariakov, V. M.; Fletcher, L.
2005ESASP.600E..33F Altcode: 2005ESPM...11...33F; 2005dysu.confE..33F
No abstract at ADS
---------------------------------------------------------
Title: Temperature Structure of Saturn from Spectral Mapping by
Cassini CIRS and Joint High-Resolution Subaru COMICS and IRTF MIRSI
Mid-Infrared Imaging
Authors: Orton, G.; Parrish, P.; Yanamandra-Fisher, P.; Fletcher, L.;
Irwin, P.; Fuse, T.; Fujiyoshi, T.; Hagopian, H.; Laakso, T.; Vogt,
M.; Lotoszinski, J.; Hora, J.
2005AGUFM.P11C0129O Altcode:
We report on a joint project of Cassini and ground-based support
observations of Saturn's temperature field. Several sequences
of CIRS spectra were made during 2004-2005 which scanned Saturn's
central meridian using its FP1 (long wavelength-) and its FP3 and FP4
(intermediate- and short-wavelength) focal planes for the purpose of
determining temperatures between 1 microbar and 400 mbar total pressure
at spatial resolutions ranging from 170 to 3800 km (from 0.5 to 11
great-circle degrees). These infrequent observations (2004 Oct 30;
2005 March 10, April 8-9, May 22) were supplemented by a program at
the NASA Infrared Telescope Facility of thermal imaging using the MIRSI
mid-infrared camera spectrometer with diffraction-limited resolutions of
~3000 km, which provided a time sequence which is particularly valuable
for characterizing wave structure and other time-dependent phenomena and
for verifying CIRS temperature maps at 10 mbar or between 100 and 400
mbar pressure. We also obtained diffraction-limited resolutions of 1000
km thermal images of Saturn from the Subaru Japanese National Telescope
using their COMICS facility mid-infrared camera/spectrometer on 2005
April 30 and May 24, providing spatial resolution commensurate with
the Cassini/CIRS, global imaging, the opportunity for center-to-limb
studies, and the means to track variability in PH3 and cloud optical
thickness in very faint spectral regions. The meridional variability of
temperatures is consistent with the seasonal dependence of temperatures
documented by two decades of thermal monitoring of Saturn at the IRTF.
---------------------------------------------------------
Title: TRACE white light and RHESSI hard X-rays
Authors: Fletcher, L.; Allred, J.; Hannah, I.; Hudson, H.; Metcalf, T.
2005AGUFMSH13A0286F Altcode:
We study the energetics of RHESSI and TRACE observations for a
sample of 11 solar flares well observed in the TRACE “white light"
channel. In general, the data show excellent correlations between hard
X-rays and white light. We discuss the energetics of this relationship
based upon simple models for the visible/UV continuum, namely (i)
a non-thermal approximation (Balmer and Paschen continuum), (ii)
a thermal approximation (blackbody), and (iii) model spectra derived
from radiation-hydrodynamic modeling. We relate the white-light energy
and the low-energy cutoff energy of the primary electron spectrum
required for energetic equivalence. This comparison will be made in
the context of the flare WL morphology and in comparison with RHESSI
hard X-ray images.
---------------------------------------------------------
Title: X-Ray Quasi-Periodic Pulsations in Solar Flares as
Magnetohydrodynamic Oscillations
Authors: Foullon, C.; Verwichte, E.; Nakariakov, V. M.; Fletcher, L.
2005ESASP.596E..46F Altcode: 2005ccmf.confE..46F
No abstract at ADS
---------------------------------------------------------
Title: The Observational Motivation for Computational Advances in
Solar Flare Physics
Authors: Fletcher, Lyndsay
2005SSRv..121..141F Altcode:
A solar flare is a violent and transient release of energy in the
corona of the Sun, associated with the reconfiguration of the coronal
magnetic field. The major mystery of solar flare physics is the precise
nature of the conversion of stored magnetic energy into the copious
accelerated particles that are observed indirectly by the radiation
that they produce, and also directly with in situ detectors. This
presents a major challenge for theory and modeling. Recent years have
brought significant observational advances in the study of solar
flares, addressing the storage and release of magnetic energy, and
the acceleration and propagation of fast electrons and ions. This
paper concentrates on two topics relevant to the early phase of a
flare, magnetic reconnection and charged particle acceleration and
transport. Some recent pertinent observations are reviewed and pointers
given for the directions that, this reviewer suggests, computational
models should now seek to take.
---------------------------------------------------------
Title: X-ray quasi-periodic pulsations in solar flares as
magnetohydrodynamic oscillations
Authors: Foullon, C.; Verwichte, E.; Nakariakov, V. M.; Fletcher, L.
2005A&A...440L..59F Altcode:
We report the first observation at high spatial resolution of
long-period quasi-periodic pulsations (QPP) of X-ray radiation during
solar flares, made possible with the Reuven Ramaty High Energy Solar
Spectroscopic Imager (RHESSI), supported by complementary data at other
wavelengths from space-based and ground-based telescopes. Evidence
for the presence of a transequatorial loop possibly responsible for
the detected periodicity connected with its kink mode is found. Our
findings suggest that QPP can be interpreted as a periodic pumping
of electrons in a compact flaring loop, modulated by oscillations
in a magnetically linked and larger loop acting as a long-period
magnetohydrodynamic resonator.
---------------------------------------------------------
Title: Flows in the solar atmosphere due to the eruptions on the
15th July, 2002
Authors: Harra, L. K.; Démoulin, P.; Mandrini, C. H.; Matthews,
S. A.; van Driel-Gesztelyi, L.; Culhane, J. L.; Fletcher, L.
2005A&A...438.1099H Altcode:
Which kind of flows are present during flares? Are they compatible
with the present understanding of energy release and which model
best describes the observations? We analyze successive flare events
in order to answer these questions. The flares were observed in the
magnetically complex NOAA active region (AR) 10030 on 15 July 2002. One
of them is of GOES X-class. The description of these flares and how
they relate to the break-out model is presented in Gary & Moore
(2004). The Coronal Diagnostic Spectrometer on board SOHO observed
this active region for around 14 h. The observed emission lines
provided data from the transition region to the corona with a field
of view covering more than half of the active region. In this paper
we analyse the spatially resolved flows seen in the atmosphere from
the preflare to the flare stages. We find evidence for evaporation
occurring before the impulsive phase. During the main phase, the
ongoing magnetic reconnection is demonstrated by upflows located at
the edges of the flare loops (while downflows are found in the flare
loops themselves). We also report the impact of a filament eruption
on the atmosphere, with flows up to 300 km s<SUP>-1</SUP> observed at
transition-region temperatures in regions well away from the location
of the pre-eruptive filament. Our results are consistent with the
predictions of the break out model before the impulsive phase of the
flare; while, as the flare progresses, the directions of the flows are
consistent with flare models invoking evaporation followed by cooling
and downward plasma motions in the flare loops.
---------------------------------------------------------
Title: Saturn's atmospheric structure: the intercomparison of
Cassini/CIRS-derived temperatures with ground-based determinations
Authors: Parrish, P. D.; Orton, G. S.; Yanamandra-Fisher, P. A.;
Fletcher, L.; Irwin, P. G. J.; Teanby, N.; Flasar, F. M.; Nixon,
C. A.; Simon-Miller, A. A.; Cassini CIRS Team
2005DPS....37.3019P Altcode: 2005BAAS...37R.680P
Although Saturn is similar to that of Jupiter in several respects,
it has yet to be qualitatively-determined whether Saturn experiences
similar seasonal variation of its equatorial stratosphere as have
been observed on Jupiter [Orton et al., 1991; Flasar et al., 2003]
and Earth [Linzen, 1968; reviewed by Baldwin et al., 2003]. While the
nature of the radiatively-based, seasonal forcing on Jupiter is not
fully understood, the modulated-temperatures are thought to play an
important role in the transport of momentum between the troposphere and
the stratosphere of any planet [Friedson, 1999]. The recent arrival of
the Cassini-Huygens spacecraft to the Saturnian system provides an ideal
opportunity to study this phenomena on Saturn. Specifically, what is
the spatial orientation and temporal organisation of the atmospheric
structure at upper-tropospheric/lower-stratospheric altitudes with
regard to the dynamical models of other, better-characterised
planets? The preliminary analysis, comparing Cassini Composite
Infrared Spectrometer-derived temperatures with those obtained
via images taken with NASA's Infrared Telescope Facility will
be presented. <P />Baldwin, M.P. et al. (2001). Rev. Geophys.,
29: 179-229. <P />Flasar, F.M. et al. (2003). Nature, 429(6969):
132-135. <P />Friedson, A.J (1999). Icarus, 137(1):34-55. <P />Lindzen,
R.S. et al. (1968). J. Atmos. Sci., 25: 1095-1107. <P />Orton,
G.S. et al. (1991). Science, 252: 537-542. <P />Acknowledgements:
The acquisition of data described here was accomplished through the
coordinated effort of Cassini-Huygens project staff, Deep Space Network
personel and the CIRS instrument and science-planning teams with funding
provided by NASA/JPL, the UK Particle Physics and Astronomy Council,
NASA/GSFC and the National Research Council Research Associate Program.
---------------------------------------------------------
Title: Vertical profiles and latitudinal variations of nitrile
abundances in Titan's atmosphere derived from Cassini/CIRS limb and
nadir data
Authors: Teanby, N. A.; Irwin, P. G. J.; de Kok, R.; Nixon, C. A.;
Coustenis, A.; Bézard, B.; Calcutt, S. B.; Bowles, N. E.; Flasar,
F. M.; Fletcher, L.; Howett, C.; Taylor, F. W.; CIRS Team
2005DPS....37.4102T Altcode: 2005BAAS...37..707T
The Cassini/Huygens spacecraft entered orbit around Saturn on
1<SUP>st</SUP> July 2004. Since then, the Composite InfraRed
Spectrometer (CIRS) has successfully returned thousands of infrared
spectra of Titan at resolutions from 0.5--15 cm<SUP>-1</SUP> in the mid-
and far-IR (10--1400 cm<SUP>-1</SUP> or 1000--7 μ m). This spectral
region is rich in features from many nitrile compounds, which allows
their abundance to be retrieved. <P />Nitrile species provide the
possibility of tracing atmospheric circulation on Titan. One Titan year
lasts 30 earth years. Therefore, with photochemical lifetimes ranging
from under a year to tens of years, nitrile abundances can be used
to probe time scales relevant to atmospheric motion. The observed
variations can then be compared to predictions from dynamical and
photochemical models. <P />We have used the limb sounding capabilities
of CIRS to retrieve vertical profiles of nitrile species, including
HCN and HC<SUB>3</SUB>N. First, the segment of the mid-IR spectrum
from 1240-1360 cm<SUP>-1</SUP> was used to retrieve stratospheric
temperature. Second, sub-spectra were extracted from the 10--800
cm<SUP>-1</SUP> region and used to obtain vertical profiles of
nitriles. The limiting vertical resolution of these profiles is
determined by the field of view size at the tangent height, which
varies between 10 and 50 km. Profiles from the equator and north polar
region will be presented. <P />We also discuss the latitude variation
of nitrile compounds derived from over 18000 nadir spectra selected
from 2.5 cm<SUP>-1</SUP> resolution mapping sequences taken from July
2004 to April 2005 and covering 90S to 60N. Contribution functions for
these observations peak around 3 mbar, well into the stratosphere. HCN,
HC<SUB>3</SUB>N, and C<SUB>2</SUB>N<SUB>2</SUB> all display a marked
increase toward the north. HCN displays a 4 fold increase from 0--60N. A
simple 1D numerical model coupled with the HCN variation implies a
downwelling velocity of 0.3 mms<SUP>-1</SUP>. The nadir determinations
will be compared with vertical profiles derived from the limb data.
---------------------------------------------------------
Title: Latitudinal Variation in Temperature and Composition of
Saturn's Upper Troposphere from Cassini/CIRS as a Tracer For
Atmospheric Dynamics
Authors: Fletcher, L. N.; Irwin, P. G. J.; Teanby, N.; Orton, G.;
Parrish, P.; de Kok, R.; Calcutt, S.; Howett, C.; Read, P. L.; Taylor,
F. W.; Cassini CIRS Team
2005DPS....37.3006F Altcode: 2005BAAS...37Q.678F
The presence of the Cassini Huygens spacecraft in the Saturnian
system provides an unprecedented opportunity to study the dynamics
of the gas giant in more detail than ever before. Infrared spectra
from Saturn's southern hemisphere have been obtained by the Composite
Infrared Spectrometer (CIRS), at both a high (0.5cm<SUP>-1</SUP>) and
medium (2.5cm<SUP>-1</SUP>) apodized spectral resolution. Latitudinal
variations of temperature and composition in Saturn's upper troposphere
are measured using an optimal estimation retrieval code developed
in Oxford. The far infrared (10-600cm<SUP>-1</SUP>) continuum is
modelled by varying temperature, para-hydrogen fraction and aerosol
opacity, with temperature contribution functions sensing pressures
from 0.1 to 0.5atm. Abundances and fractional scale heights of
ammonia and phosphine are then retrieved from rotational lines in the
10-200cm<SUP>-1</SUP> region. The mid infrared (600-1400cm<SUP>-1</SUP>)
provides temperature profiles from 600-700cm<SUP>-1</SUP>, whilst
the ν <SUB>4</SUB> fundamental of phosphine at 1118cm<SUP>-1</SUP>
is used to retrieve a further measure of its abundance. Results
are compared to global data from the Mid Infrared Spectrometer
and Imager (MIRSI) instrument on NASA's Infrared Telescope
Facility. Measurement from filters covering the collision induced
absorption of hydrogen in the 400-600cm<SUP>-1</SUP> region and the
ν <SUB>2</SUB> phosphine fundamental near to 1000cm<SUP>-1</SUP>
were obtained using the same retrieval scheme. <P />The distribution
of phosphine and ammonia is a balance between vertical transport and
photochemical destruction. Elevated abundances of these gases are
used as tracers for regions of upwelling constituent-rich air from
deeper within the troposphere. Variations in retrieved optical depth
due to aerosols, and deviations of parahydrogen fraction from local
thermal equilibrium are also presented. Using an assumed stratospheric
abundance of methane, the mid infrared spectra were used to obtain
preliminary measures of the [D]/[H] ratio in methane of (1.96± 0.80)
× 10<SUP>-5</SUP> and a [<SUP>12</SUP>C]/[<SUP>13</SUP>C] ratio of
78.5<SUB>-14.0</SUB><SUP>+21.9</SUP>. <P />Acknowledgement: This work
is funded by the UK Particle Physics and Astronomy Research Council.
---------------------------------------------------------
Title: Titan's Oxygen compound distributions and condensate
characteristics from Cassini/CIRS observations
Authors: de Kok, R.; Irwin, P. G. J.; Teanby, N. A.; Fletcher, L.;
Calcutt, S. B.; Howett, C.; Taylor, F. W.; Bowles, N. E.; Cassini
CIRS Team
2005DPS....37.4508D Altcode: 2005BAAS...37Q.718D
The Cassini/CIRS instrument has measured Titan's infrared spectrum
many times since its arrival at Saturn in July 2004. Observations
were made both in nadir and in limb geometry, at a wide range of
latitudes and altitudes. <P />Using nadir and limb data with the
highest spectral resolution obtainable by CIRS (0.5 cm<SUP>-1</SUP>),
the stratospheric emission of carbon dioxide at 667 cm<SUP>-1</SUP>
was analysed. Results of this analysis include the variations of the
CO<SUB>2</SUB> concentration with latitude, and the variation with
altitude. The latter is critical for understanding the oxygen chemistry
in Titan's atmosphere and can constrain the nature of Titan's oxygen
source. The abundance of CO was also determined and an upper limit was
set for the H<SUB>2</SUB>O abundance. <P />CIRS has the capability
to measure, for the first time, the spectral region between 10-200
cm<SUP>-1</SUP>. This region is mainly dominated by collision induced
absorption and includes the rotational lines of e.g. CH<SUB>4</SUB>,
HCN and CO. In this region, at least two broad spectral features were
also identified, possibly caused by condensates. CIRS data with low
spectral resolution (15 cm<SUP>-1</SUP>) was used to obtain dependences
with latitude and altitude of these features, therefore constraining
their possible sources.
---------------------------------------------------------
Title: Electron Acceleration at Reconnecting X-Points in Solar Flares
Authors: Hamilton, B.; Fletcher, L.; McClements, K. G.; Thyagaraja, A.
2005ApJ...625..496H Altcode:
The acceleration of electrons in solar flares is simulated using an
extended version of a full orbit test-particle code previously used to
compute losses of fusion alpha particles from tokamaks and to study
flare proton acceleration. The magnetic and electric fields in the
model are obtained from solutions of the linearized MHD equations
for reconnecting modes at a magnetic X-point with zero equilibrium
current. The magnetic field is assumed to have a small finite
component perpendicular to the plane of the X-point. The version of
the code used in the simulations is fully relativistic and includes
Coulomb collisions. It is demonstrated that electrons cross the system
boundary at distinct footpoints with the relative numbers and energy
distribution at each footpoint sensitive to the longitudinal magnetic
field component and collision time. These results are discussed in
the context of recent flare observations showing asymmetric hard X-ray
emission from the chromospheric footpoints of magnetic loops.
---------------------------------------------------------
Title: TRACE and RHESSI observations of white-light flares
Authors: Hudson, H. H.; Metcalf, T.; Wolfson, J.; Fletcher, L.;
Khan, J.
2005AGUSMSP51C..03H Altcode:
TRACE gives a photometrically stable, high-resolution view of the
visible and UV emissions of solar flares, with enough diagnostic power
to distinguish photospheric from chromospheric contributions. These
emissions dominate the radiant energy of a flare and correspond
well with hard X-ray emission in the impulsive phase. We survey
these data with reference to well-observed events of 4~October~2002
and 4~November~2003, on the disk (M4; S19W09) and on the limb (X17;
S19W83) respectively. We analyze the spatial and temporal properties
of the footpoint sources in these two events, characterizing their
physical parameters (contrast, image gradients, apparent motions). The
brightest kernels of the 4~October~2002 event have intensities twice
that of the quiet photosphere, and have sizes close to the Nyquist
limit of the TRACE pixels (0.5~arc~sec). The white-light footpoint
sources can be considered as a proxy for the target region of fast
electrons studied via hard X-ray bremsstrahlung. We compare RHESSI
hard X-ray footpoint sources with their white-light counterparts and
estimate filling factors for the hard X-ray emission itself.
---------------------------------------------------------
Title: Fip Enhancement by Alfvén Ionization
Authors: Diver, D. A.; Fletcher, L.; Potts, H. E.
2005SoPh..227..207D Altcode:
Alfvén ionization is offered as a possible mechanism underlying the
enhanced population of low first ionization potential (FIP) species
in the solar corona. In this process, the photospheric flow impinging
on the magnetic structure of a coronal flux tube collides with, and
displaces, ions in the magnetised plasma within the flux tube. This
leads to pockets of charge imbalance that persist due to the impeded
electron transport perpendicular to the magnetic field. The localised
electric field then energises electrons to the impact ionization energy
threshold of low-FIP components in the surface flow. Such species remain
trapped in the plasma, and drift up the magnetic structure, causing a
localised population enhancement compared to photospheric levels. We
find that this mechanism successfully accounts for observed biases for
flow speeds known to exist in the photosphere, and moreover explains
certain anomalous abundances which do not fit into existing theories.
---------------------------------------------------------
Title: Multialtitude Observations of a Coronal Jet during the Third
Whole Sun Month Campaign
Authors: Ko, Y. -K.; Raymond, J. C.; Gibson, S. E.; Alexander, D.;
Strachan, L.; Holzer, T.; Gilbert, H.; Cyr, O. C. St.; Thompson, B. J.;
Pike, C. D.; Mason, H. E.; Burkepile, J.; Thompson, W.; Fletcher, L.
2005ApJ...623..519K Altcode:
On 1999 August 26, a coronal jet occurred at the northwest limb near
a sigmoid active region (AR 8668) that was the target for a joint
observation plan (SOHO joint observing program 106) during the third
Whole Sun Month Campaign. This jet was observed by several instruments
at the limb (SOHO/CDS, SOHO/EIT, TRACE, and Mauna Loa Solar Observatory
CHIP and PICS) and at 1.64 R<SUB>solar</SUB> (SOHO/UVCS). At the limb,
this jet event displayed both low- and high-temperature components. Both
high- and low-temperature components were evident during the early phase
(first 20 minutes) of the event. However, the low-temperature component
is maintained for ~1 hr after the higher temperature component is
gone. There is a second brightening (a possible second jet) seen by
EIT and TRACE about 50 minutes after the onset of the first jet. The
line-of-sight motion at the limb began with a 300 km s<SUP>-1</SUP>
redshift and evolved to a 200 km s<SUP>-1</SUP> blueshift. At
1.64 R<SUB>solar</SUB>, the intensities of Lyα and Lyβ in the jet
increased by a factor of several hundred compared with the background
corona. The C III λ977 line also brightened significantly. This
indicates low-temperature [~(1-2)×10<SUP>5</SUP> K] emission in the
jet, while the intensities of O VI λ1032 and O VI λ1037 increased
by as much as a factor of 8. The UVCS data show evidence of heating at
the early phase of the event. The Doppler shift in the lines indicates
that the line-of-sight (LOS) velocity in the jet started from ~150
km s<SUP>-1</SUP> in blueshift and ended at ~100 km s<SUP>-1</SUP>
in redshift. This LOS motion seen at 1.64 R<SUB>solar</SUB> was
apparently opposite to what was observed when the jet emerged from the
limb. The Doppler dimming analysis indicates that the radial outflow
speed correlates with the magnitude of the LOS speed. Interestingly,
UVCS observations at 2.33 and 2.66 R<SUB>solar</SUB> show no trace of
the jet and SOHO/LASCO observations also yield no firm detection. We
find that a simple ballistic model can explain most of the dynamical
properties of this jet, while the morphology and the thermal properties
agree well with reconnection-driven X-ray jet models.
---------------------------------------------------------
Title: Rhessi Microflare Statistics
Authors: Hannah, I. G.; Christe, S.; Krucker, S.; Hudson, H. S.;
Fletcher, L.; Hendry, M. A.
2004ESASP.575..259H Altcode: 2004soho...15..259H
No abstract at ADS
---------------------------------------------------------
Title: On the Role of Fast Shocks in Creating Relativistic Electrons
in the Solar Corona
Authors: Hesse, M.; Fletcher, L.; Neukirch, T.
2004AGUFMSH24A..05H Altcode:
The existence of fast shocks, at the interface between reconnection
outflow jets and underlying magnetic loops, has been suggested by a
number of researchers. Should they exist, fast shocks would provide
an effective mechanism to convert a large fraction of the combined
kinetic energy in the reconnection outflow into thermal energy of the
shocked plasma. Since this process affects directly a large number of
particles, it may provide a solution to the problem of explaining the
number of electrons that are apparently involved in the generation
of the high-energy X-ray signatures observed by RHESSI. In order
to investigate this possibility further, we present the results of
fully-electromagnetic, relativistic, particle-in-cell simulations
of fast shock structure and evolution. In particular, we discuss the
effect on downstream nonthermal electrons of parameters such as Mach
number, plasma beta, and the angle between shock normal and the upstream
magnetic field. We will compare our results to earlier kinetic studies
of fast shocks, and provide an evaluation of the shock mechanism as a
means to explain nonthermal, relativistic electron distributions such
as expected in conjunction with RHESSI X-ray events.
---------------------------------------------------------
Title: The hard X-ray spectral structure of flare ribbons
Authors: Hudson, H.; Fletcher, L.; Krucker, S.; Pollock, J.
2004AGUFMSH24A..02H Altcode:
We examine the spatial distribution of hard X-ray spectral parameters
in flares exhibiting the classic two-ribbon structure using RHESSI
observations. The flares studied include July~15 and July~17, 2002,
and October~29, 2003. We confirm the existence of a tendency for
the localization of the hard X-ray sources into dominant bright
“footpoint” regions which do not show ribbon structure as extensive
as that seen in Hα or UV~images. As a part of the study we characterize
the ribbons photometrically in the EUV as observed by TRACE, confirming
earlier results that find complicated relationships between EUV and
hard X-rays. We seek an empirical explanation for the restricted
hard X-ray footpoints in terms of a spatial analog of the well-known
“soft-hard-soft” morphology: the regions of weaker hard X-ray emission
correspond to steeper X-ray energy spectra and hence to softer electron
precipitation spectra. This relationship may be as predicted by the
1D radiation hydrodynamics models of flaring loops.
---------------------------------------------------------
Title: Overview of Solar Flares
Authors: Hudson, Hugh; Fletcher, Lyndsay; Khan, Josef I.; Kosugi, Takeo
2004ASSL..314..153H Altcode:
This chapter reviews the physics of solar flares, with special emphasis
on the past decade. During this decade first Yohkoh and then TRACE
have drastically improved our observational capabilities for flares,
with contributions also from the essentially non-flare instrumentation
on SOHO and of course the ground-based observatories. In this review
we assess how these new observations have changed our understanding
of the basic physics of flares and consider the implications of these
results for future observations with FASR. The discussion emphasizes
flaring loops, flare ejecta, particle acceleration, and microflares.
---------------------------------------------------------
Title: Tracking of TRACE Ultraviolet Flare Footpoints
Authors: Fletcher, Lyndsay; Pollock, Jennifer A.; Potts, Hugh E.
2004SoPh..222..279F Altcode:
Solar flares produce bright, compact sources of UV emission in the
lower atmosphere, identified as flare footpoints. Observed at high time
cadence with the Transition Region and Coronal Explorer, groups of UV
footpoints define flare `ribbons' which move as the flare progresses. We
have developed a procedure to track individual bright kernels within
flare ribbons, enabling us to study the motion of these sites of
excitation through the solar chromosphere. We have applied this to a
flare observed by TRACE in the 1600 Å passband at 2-s cadence. In this
event, the footpoints have an average speed of 15 km s<SUP>−1</SUP>,
with a superposed random `meandering' component, consistent with the
footpoint magnetic field being anchored around the edges of granular
cells. Examining the brightness as a function of time, we find that
the timing of peaks in brightness is significantly correlated with
the timing of peaks in the product of the footpoint speed with the
line-of-sight magnetic field strength at the footpoint location;
in other words with a measure of the coronal reconnection rate.
---------------------------------------------------------
Title: Electron Inertial Effects on Rapid Energy Redistribution at
Magnetic X-Points
Authors: McClements, K. G.; Thyagaraja, A.; Ben Ayed, N.; Fletcher, L.
2004ApJ...609..423M Altcode: 2004astro.ph..1573M
The evolution of nonpotential perturbations to a current-free
magnetic X-point configuration is studied, taking into account
electron inertial effects as well as resistivity. Electron inertia
is shown to have a negligible effect on the evolution of the system
whenever the collisionless skin depth is less than the resistive scale
length. Nonpotential magnetic field energy in this resistive MHD limit
initially reaches equipartition with flow energy, in accordance with
ideal MHD, and is then dissipated extremely rapidly on an Alfvénic
timescale that is essentially independent of Lundquist number. In
agreement with resistive MHD results obtained by previous authors, the
magnetic field energy and kinetic energy are then observed to decay on
a longer timescale and exhibit oscillatory behavior, reflecting the
existence of discrete normal modes with finite real frequency. When
the collisionless skin depth exceeds the resistive scale length, the
system again evolves initially according to ideal MHD. At the end of
this ideal phase, the field energy decays typically on an Alfvénic
timescale, while the kinetic energy (which is equally partitioned
between ions and electrons in this case) is dissipated on the electron
collision timescale. The oscillatory decay in the energy observed in
the resistive case is absent, but short-wavelength structures appear
in the field and velocity profiles, suggesting the possibility of
particle acceleration in oppositely directed current channels. The
model provides a possible framework for interpreting observations of
energy release and particle acceleration on timescales down to less
than a second in the impulsive phase of solar flares.
---------------------------------------------------------
Title: Meeting report: Core to corona: UKSP 2004
Authors: Fletcher, Lyndsay; Erdelyi, Robert
2004A&G....45c..33F Altcode:
The UK solar physics community gathered with the MIST community in
Edinburgh from 29 March - 1 April 2004, with a programme that reflected
the strength and diversity of UK research in the field. Lyndsay Fletcher
and Robert Erdelyi report.
---------------------------------------------------------
Title: The hard X-ray spectral structure of flare ribbons
Authors: Fletcher, L.; Hudson, H. S.; Krucker, S.; Pollock, J. A.
2004AAS...204.5403F Altcode: 2004BAAS...36..758F
We examine the spatial distribution of hard X-ray spectral parameters
in flares exhibiting the classic two-ribbon structure using RHESSI
observations. The flares studied include July 15 and July 17, 2002,
and October 29, 2003. We confirm the existence of a tendency for
the localization of the hard X-ray sources into dominant bright
“footpoint” regions which do not show ribbon structure as extensive
as that seen in Hα or UV images. As a part of the study we characterize
the ribbons photometrically in the EUV as observed by TRACE, confirming
earlier results that find complicated relationships between EUV and
hard X-rays. We seek an empirical explanation for the restricted
hard X-ray footpoints in terms of a spatial analog of the well-known
“soft-hard-soft” morphology: the regions of weaker hard X-ray emission
correspond to steeper X-ray energy spectra and hence to softer electron
precipitation spectra. This relationship may be as predicted by the
1D radiation hydrodynamics models of flaring loops.
---------------------------------------------------------
Title: Multi-Altitude Observations of a Coronal Jet
Authors: Ko, Y. -K.; Raymond, J. C.; Gibson, S. E.; Alexander, D.;
Strachan, L.; Holzer, T.; Gilbert, H.; St. Cyr, O. C.; Thompson,
B. J.; Pike, C. D.; Burkepile, J.; Thompson, W.; Fletcher, L.
2004AAS...204.5413K Altcode: 2004BAAS...36..759K
A coronal jet occurred on August 26, 1999 at the NW limb near a sigmoid
active region (AR8668). This jet was observed by several instruments
at the limb (SOHO/CDS, SOHO/EIT, TRACE, MLSO/CHIP, MLSO/PICS) and
at 1.64 Ro (SOHO/UVCS). At the limb, this jet event has both low and
high temperature components. The high temperature component appeared
at the early phase (first 20 minutes) of the event along with the low
temperature component while the latter seems to last long ( ∼ 1 hour)
after the higher temperature component was gone. The line-of-sight
motion at the limb started with red-shifted (by as much as 300 km/s)
and turned blue-shifted (by as much as 200 km/s). At 1.64 Ro, the
intensities of Lyα , Lyβ in the jet increased by a factor of several
hundreds compared with the background corona. C III λ 977 line also
brightened significantly. This indicates low temperature ( ∼ 1-2×
10<SUP>5</SUP> K) emission in the jet, while the intensities of O VI
λ 1032 and O VI λ 1037 increased by a factor of as large as 8. Both
UVCS and CDS data show evidence of heating at the early phase of the
event. The line-of-sight velocity seen at 1.64 Ro started with ∼ 150
km/sec in blue shift and ended at ∼ 100 km/sec in red shift. This is
apparently opposite to what were observed when the jet emerged from
the limb. The Doppler dimming analysis indicates that the radial
outflow speed correlates with the magnitude of the line-of-sight
speed. Interestingly, UVCS observations at 2.33 and 2.66 Ro show no
trace of the jet and LASCO observations also yield no firm sight of the
jet. In this paper, we present the observations by these instruments
and discuss the dynamical structure and physical properties of this
jet. Y.-K. Ko acknowledges the support by NASA grant NAG5-12865.
---------------------------------------------------------
Title: Electron inertia modifications to X-point reconnection in
solar flares
Authors: McClements, K. G.; Thyagaraja, A.; Ben Ayed, N.; Fletcher, L.
2004cosp...35.1242M Altcode: 2004cosp.meet.1242M
The evolution of perturbations to a current-free magnetic X-point
is studied as a paradigm for short timescale energy release in
solar flares, taking into account electron inertia as well as
resistivity. Electron inertia is found to have a negligible effect
whenever the collisionless skin depth is less than the resistive scale
length. Non-potential magnetic field energy in this resistive MHD limit
initially reaches equipartition with flow energy, in accordance with
ideal MHD, and is then dissipated extremely rapidly, on an Alfvénic
timescale that is essentially independent of Lundquist number. In
agreement with resistive MHD results obtained by previous authors [1],
the magnetic field energy and kinetic energy are then observed to decay
on a longer timescale and exhibit oscillatory behavior, reflecting the
existence of discrete normal modes with finite real frequency. When the
collisionless skin depth exceeds the resistive scale length, the field
energy again decays on an Alfvénic timescale, while the kinetic energy
(which is equally partitioned between ions and electrons in this case)
decays on the electron collision timescale. In this regime filaments
appear in the field and velocity profiles, suggesting the possibility
of particle acceleration in oppositely-directed current channels and
symmetrical precipitation out of the acceleration region. Both the rapid
decay in field energy and the filamentation process arise from phase
mixing associated with a continuous eigenmode spectrum that replaces
the discrete resistive MHD spectrum [2]. Because of the Alfvénic
timescale of the field decay, very modest perturbation amplitudes are
sufficient for the corresponding inductive electric fields to produce
hard X-ray emitting electrons on sub-second timescales. The model thus
provides a framework for interpreting observations of short timescale
energy release and particle acceleration in the impulsive phase of
flares. This work was supported by the United Kingdom Engineering
and Physical Sciences Research Council [1] Craig I. J. D. &
Watson P. G. Astrophys. J 393, 385 (1992) [2] McClements K. G. &
Thyagaraja A. Plasma Phys. Control. Fusion 46, 39 (2004)
---------------------------------------------------------
Title: Hubble Goes IMAX: 3D Visualization of the GOODS Southern
Field for a Large Format Short Film
Authors: Summers, F. J.; Stoke, J. M.; Albert, L. J.; Bacon, G. T.;
Barranger, C. L.; Feild, A. R.; Frattare, L. M.; Godfrey, J. P.;
Levay, Z. G.; Preston, B. S.; Fletcher, L. M.; GOODS Team
2003AAS...203.8603S Altcode: 2003BAAS...35.1345S
The Office of Public Outreach at the Space Telescope Science Institute
is producing a several minute IMAX film that will have its world
premiere at the January 2004 AAS meeting. The film explores the rich
tapestry of galaxies in the GOODS Survey Southern Field in both two
and three dimensions. This poster describes the visualization efforts
from FITS files through the galaxy processing pipeline to 3D modelling
and the rendering of approximately 100 billion pixels. The IMAX film
will be shown at a special session at Fernbank Science Center, and
the video will be shown at the STScI booth.
---------------------------------------------------------
Title: UKSP: Solar physics in Dublin
Authors: Erdélyi, R.; Fletcher, L.; Doyle, G. J.
2003A&G....44c..13E Altcode:
This year's annual UK Solar Physics meeting took place in Dublin from
7-11 April 2003, overlapping with the National Astronomy Meeting. R
Erdélyi, L Fletcher and G J Doyle summarize.
---------------------------------------------------------
Title: Field-Guided Proton Acceleration at Reconnecting x-Points
in Flares
Authors: Hamilton, B.; McClements, K. G.; Fletcher, L.; Thyagaraja, A.
2003SoPh..214..339H Altcode: 2003astro.ph..1359H
An explicitly energy-conserving full orbit code CUEBIT, developed
originally to describe energetic particle effects in laboratory fusion
experiments, has been applied to the problem of proton acceleration
in solar flares. The model fields are obtained from solutions of the
linearised MHD equations for reconnecting modes at an X-type neutral
point, with the additional ingredient of a longitudinal magnetic field
component. To accelerate protons to the highest observed energies
on flare timescales, it is necessary to invoke anomalous resistivity
in the MHD solution. It is shown that the addition of a longitudinal
field component greatly increases the efficiency of ion acceleration,
essentially because it greatly reduces the magnitude of drift motions
away from the vicinity of the X-point, where the accelerating component
of the electric field is largest. Using plasma parameters consistent
with flare observations, we obtain proton distributions extending up
to γ-ray-emitting energies (> 1 MeV). In some cases the energy
distributions exhibit a bump-on-tail in the MeV range. In general,
the shape of the distribution is sensitive to the model parameters.
---------------------------------------------------------
Title: RHESSI Workshop Reports: Multiwavelength Correlative Studies
of RHESSI events
Authors: Fletcher, L.; RHESSI Workshop Series Working Group 4 Team
2003SPD....34.1402F Altcode: 2003BAAS...35..829F
In this talk we will report on the projects and progress of RHESSI
Working Group 4, 'Multi-Wavelength Correlative Studies'. The remit of
this working group is to use diagnostics from space and ground-based
instrumentation in tandem with RHESSI to further our understanding
of the fast particles and plasmas produced during large and small
flaring events, and to illuminate the magnetic environment in which
these take place. Topics being studied include the Neupert effect,
hot coronal sources and coronal mass motions, and flare footpoint
evolution. The April 21st 2002 X1.5 flare is a focus for much of the
group's activities. This event has excellent multiwavelength coverage
and shows many interesting features such as coronal downflows, moving
RHESSI coronal sources, and very compact hard X-ray footpoints.
---------------------------------------------------------
Title: The Energy Release Process in Solar Flares; Constraints from
TRACE Observations
Authors: Fletcher, L.; Warren, H. P.
2003LNP...612...58F Altcode: 2003ecpa.conf...58F
The Transition Region And Coronal Explorer Satellite, TRACE, launched
in 1998, has proved a valuable tool in the study of solar flares. UV
and EUV observations of the impulsive and gradual phases of many tens
of flares have been made. TRACE's excellent spatial resolution and
image cadence on the order of one second allow the rearrangement of the
magnetic field to be tracked in some detail. The combination of these
observations with data from other instruments, and with magnetic field
reconstructions, have provided strong evidence for (a) UV emission as a
beam proxy in the impulsive phase (b) long duration coronal heating in
the gradual phase (c) very complex and varied magnetic geometries. We
review the observational evidence for the above, discussing implications
for energy release.
---------------------------------------------------------
Title: Charged particle dynamics in X-type neutral points
Authors: Hamilton, B.; Fletcher, L.; McClements, K. G.; Thyagaraja, A.
2002ESASP.506..291H Altcode: 2002svco.conf..291H; 2002ESPM...10..291H
We have developed a novel algorithm for the calculation of test
particle orbits in electromagnetic fields. We have applied this
to the problem of determining ion and electron orbits in an X-type
magnetic configuration, of a type that may occur during reconnection
in the corona above a flaring region. Particles in our simulation gain
energy through interaction with the normal modes of oscillation of the
X-type structure. We find that the addition of a longitudinal magnetic
field component to a model proposed by Craig and McClymont [ApJ 371,
L41 (1991)] produces a much greater efficiency in accelerating
protons. Results of different simulations are presented and the
sensitivity of the results to the parameters of the magnetic environment
is discussed.
---------------------------------------------------------
Title: Chaotic dynamics and collisionless reconnection at an X-type
neutral point
Authors: Hannah, Iain G.; Fletcher, Lyndsay; Hendry, Martin A.
2002ESASP.506..295H Altcode: 2002svco.conf..295H; 2002ESPM...10..295H
The chaotic dynamics of test particle orbits in a magnetic X-type
neutral point have been investigated through the use of Lyapunov
Characteristic Exponents (LCE), with the aim of solving the Pesin
Identity (sum of the positive LCE) as a Monte Carlo integration
problem. Treating the identity in this manner allows the phase space
of a system to be intelligently sampled for the most chaotic orbits,
as these orbits contribute most to the integral. This analysis so
far has concentrated on how the chaotic behaviour relates to particle
acceleration and energy gain, with future work to examine whether the
chaos can produce an "anomalous resistivity" affecting the reconnection
rate.
---------------------------------------------------------
Title: Energetic particles in the solar atmosphere
Authors: Fletcher, Lyndsay
2002ESASP.506..223F Altcode: 2002svco.conf..223F; 2002ESPM...10..223F
This article reviews the evidence for, and the nature of, accelerated
particles in the lower solar atmosphere. Particle distributions with
significantly non-thermal components are ubiquitous throughout the
solar atmosphere, and we concentrate primarily on those arising in
solar flares. We mention the main diagnostics for accelerated flare
electrons and ions, and discuss the more popular theoretical ideas
regarding their acceleration.
---------------------------------------------------------
Title: Mapping RHESSI footpoints with potential-field models
Authors: Fletcher, L.; Hudson, H. S.; Metcalf, T. R.
2002AGUFMSH52A0452F Altcode:
RHESSI hard X-ray observations help us to identify the locations of
magnetically conjugate footpoints, and to study their apparent motions
during the evolution of the impulsive phase of a flare. We put this
information into the context of an M-class flare that occurred 2002
March 14 01:50 UT (GOES peak time) at S12, E23 (NOAA region 9866) by
making potential-field mappings of the coronal magnetic structure. In
principle the hard X-ray sources (plus the mapping) constrain the
site of magnetic energy release, and the maps reveal the location
of the stored energy. The RHESSI source centroids can be determined
to better than 1” (rms) for an M-class flare. This analysis is an
exploration of the feasibility of such an approach, since full success
would require understanding the magnetic restructuring in detail. If
suitable X-class RHESSI flares occur we will be able to present data
with better precision.
---------------------------------------------------------
Title: Spectral and Spatial Variations of Flare Hard X-ray Footpoints
Authors: Fletcher, L.; Hudson, H. S.
2002SoPh..210..307F Altcode:
In a sample of strong RHESSI M-class flares we have made a study of
the relationship between the `hardness' of the HXR spectrum and the
intensity in the 30-50 keV energy range. In all events we find clear
evidence for a `soft-hard-soft' pattern of correlation between hardness
and flux, on time scales as short as 10 s. We investigate whether or
not this pattern is intrinsic to the acceleration mechanism. The RHESSI
images in this energy range are dominated by footpoint brightenings,
and we have searched for a correlation between footpoint separation
velocity and spectral hardness, to be compared qualitatively with
theoretical flare models. We find quite systematic footpoint motions,
and also note that episodes in which footpoint separation varies
rapidly often correspond with episodes of significant change in the
flare spectral index, though not as the simplest flare models would
predict. We report also on one of our events, on 14 March 2002, which
exhibits highly sheared HXR footpoint ribbons extending over a scale
of 100 arc sec. For this flare we find a correlation between footpoint
motion and hard X-ray flux.
---------------------------------------------------------
Title: Magnetic flux ropes: Would we know one if we saw one?
Authors: Gibson, S. E.; Low, B. C.; Leka, K. D.; Fan, Y.; Fletcher, L.
2002ESASP.505..265G Altcode: 2002IAUCo.188..265G; 2002solm.conf..265G
There has been much debate lately about whether twisted magnetic flux
ropes exist in the corona. When asked for observational evidence
of them, the temptation is to show images of apparently twisted
structures. However, we must be very careful of projection effects in
interpreting these observations. Two critical aspects of understanding
how we might observe flux ropes are 1) the 3D nature of the flux rope,
and 2) physically, which bits are visible and for what reasons? In
this paper we will use a simple but physically reasonable 3D analytic
model to address these two issues, and develop techniques that can in
future be used on more general models, both analytic and numerical.
---------------------------------------------------------
Title: High-energy solar radiation with RHESSI
Authors: Fletcher, L.
2002Obs...122..249F Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Structure and Evolution of a Sigmoidal Active Region
Authors: Gibson, S. E.; Fletcher, L.; Del Zanna, G.; Pike, C. D.;
Mason, H. E.; Mandrini, C. H.; Démoulin, P.; Gilbert, H.; Burkepile,
J.; Holzer, T.; Alexander, D.; Liu, Y.; Nitta, N.; Qiu, J.; Schmieder,
B.; Thompson, B. J.
2002ApJ...574.1021G Altcode:
Solar coronal sigmoidal active regions have been shown to be precursors
to some coronal mass ejections. Sigmoids, or S-shaped structures,
may be indicators of twisted or helical magnetic structures, having
an increased likelihood of eruption. We present here an analysis of a
sigmoidal region's three-dimensional structure and how it evolves in
relation to its eruptive dynamics. We use data taken during a recent
study of a sigmoidal active region passing across the solar disk
(an element of the third Whole Sun Month campaign). While S-shaped
structures are generally observed in soft X-ray (SXR) emission, the
observations that we present demonstrate their visibility at a range of
wavelengths including those showing an associated sigmoidal filament. We
examine the relationship between the S-shaped structures seen in SXR
and those seen in cooler lines in order to probe the sigmoidal region's
three-dimensional density and temperature structure. We also consider
magnetic field observations and extrapolations in relation to these
coronal structures. We present an interpretation of the disk passage
of the sigmoidal region, in terms of a twisted magnetic flux rope
that emerges into and equilibrates with overlying coronal magnetic
field structures, which explains many of the key observed aspects of
the region's structure and evolution. In particular, the evolving flux
rope interpretation provides insight into why and how the region moves
between active and quiescent phases, how the region's sigmoidicity is
maintained during its evolution, and under what circumstances sigmoidal
structures are apparent at a range of wavelengths.
---------------------------------------------------------
Title: Emergence of twisted magnetic flux into the corona
Authors: Gibson, S.; Low, B. C.; Fan, Y.; Fletcher, L.
2002AAS...200.3603G Altcode: 2002BAAS...34..693G
The interaction between emerging magnetic structures and preexisting
overlying coronal structures will be addressed using a combination of
observations and physical models that incorporate a range of twisted
magnetic topologies. Solar explosive events such as coronal mass
ejections (CMEs) and flares are commonly considered to be driven by
the free magnetic energy stored in twisted (current carrying) coronal
magnetic fields. Understanding the origin and the three-dimensional
nature of these twisted coronal magnetic structures is a crucial step
towards explaining and predicting CMEs and flares. One possible and
appealing picture is that the twisted coronal magnetic structures
form as a result of the emergence of twisted magnetic flux tubes
from the solar interior. We might imagine a scenario where a flux
rope forms sub-photospherically, emerges through the photosphere,
exists in the corona until it loses its stability and erupts in a
CME which moves out through interplanetary space until ultimately
impacting on the Earth's magnetosphere. Attractively simple as this
picture is, reality is likely to be more complicated since the various
regimes are physically very different and pre-existing structures
would get in the way of our traveling flux rope. We will concentrate
on joining up two of these regimes, by considering how a flux rope
could rise from beneath the photosphere and emerge into the corona,
interacting with pre-existing coronal structures. We will approach this
problem by using a combination of numerical models of the flux rope
emergence from beneath the photosphere, analytic models of coronal
dynamic and equilibrium magnetic structures, and photospheric and
coronal observations of the 3-d structure and evolution of a so-called
"sigmoidal", or S-shaped active region. In so doing we hope to gain
essential insight into how twisted magnetic fields are formed and how
they could be ultimately removed from the solar corona.
---------------------------------------------------------
Title: 2-ribbon flares: observations vs. models
Authors: Fletcher, Lyndsay
2002ocnd.confE..10F Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Magnetic Structure and Generation of EUV Flare Ribbons
Authors: Fletcher, L.; Hudson, H.
2001SoPh..204...69F Altcode:
The `ribbons' of two-ribbon flares show complicated patterns reflecting
the linkages of coronal magnetic field lines through the lower solar
atmosphere. We describe the morphology of the EUV ribbons of the July
14, 2000 flare, as seen in SOHO, TRACE, and Yohkoh data, from this
point of view. A successful co-alignment of the TRACE, SOHO/MDI and
Yohkoh/HXT data has allowed us to locate the EUV ribbon positions on
the underlying field to within ∼ 2”, and thus to investigate the
relationship between the ribbons and the field, and also the sites
of electron precipitation. We have also made a determination of the
longitudinal magnetic flux involved in the flare reconnection event,
an important parameter in flare energetic considerations. There are
several respects in which the observations differ from what would be
expected in the commonly-adopted models for flares. Firstly, the flare
ribbons differ in fine structure from the (line-of-sight) magnetic
field patterns underlying them, apparently propagating through regions
of very weak and probably mixed polarity. Secondly, the ribbons split
or bifurcate. Thirdly, the amount of line-of-sight flux passed over by
the ribbons in the negative and positive fields is not equal. Fourthly,
the strongest hard X-ray sources are observed to originate in stronger
field regions. Based on a comparison between HXT and EUV time-profiles
we suggest that emission in the EUV ribbons is caused by electron
bombardment of the lower atmosphere, supporting the hypothesis that
flare ribbons map out the chromospheric footpoints of magnetic field
lines newly linked by reconnection. We describe the interpretation of
our observations within the standard model, and the implications for
the distribution of magnetic fields in this active region.
---------------------------------------------------------
Title: Numerical Modelling of Trapped Electrons in an Expanding
Solar Loop
Authors: Fletcher, L.; Hudson, H.
2001AGUFMSH42A0777F Altcode:
Recent observations with the Yohkoh Hard X-ray telescope and the
Nobeyama Radioheliograph [Hudson et al., 2001] have shown a moving
hard X-ray coronal source, associated in space and time with moving
microwave and decimeter sources. Because of the electron energies
involved in producing these emissions, we hypothesize that the
radiation indicates the presence of a coronal population of high
energy electrons, trapped in a magnetic loop which is expanding
outward. The expansion will lead to a `betatron' deceleration effect,
which, combined with the normal Coulomb scattering and energy losses,
will lead to an evolution of the particle energy density, spectrum and
pitch angle distribution. We model this process using a stochastic
test particle simulation. >http://isass1.solar.isas.ac.jp/
~hudson/drafts/apr18.pdf</a>
---------------------------------------------------------
Title: A Relationship Between Transition Region Brightenings,
Abundances, and Magnetic Topology
Authors: Fletcher, Lyndsay; López Fuentes, Marcelo C.; Mandrini,
Cristina H.; Schmieder, Brigitte; Démoulin, Pascal; Mason, Helen E.;
Young, Peter R.; Nitta, Nariaki
2001SoPh..203..255F Altcode:
We present multi-instrument observations of active region (AR) 8048,
made between 3 June and 5 June 1997, as part of the SOHO Joint Observing
Program 33. This AR has a sigmoid-like global shape and undergoes
transient brightenings in both soft X-rays and transition region
(TR) lines. We compute a magneto-hydrostatic model of the AR magnetic
field, using as boundary condition the photospheric observations of
SOHO/MDI. The computed large-scale magnetic field lines show that the
large-scale sigmoid is formed by two sets of coronal loops. Shorter
loops, associated with the core of the SXT emission, coincide with
the loops observed in the hotter CDS lines. These loops reveal a
gradient of temperature, from 2 MK at the top to 1 MK at the ends. The
field lines most closely matching these hot loops extend along the
quasi-separatrix layers (QSLs) of the computed coronal field. The TR
brightenings observed with SOHO/CDS can also be associated with the
magnetic field topology, both QSL intersections with the photosphere,
and places where separatrices issuing from bald patches (sites where
field lines coming from the corona are tangent to the photosphere)
intersect the photosphere. There are, furthermore, suggestions that
the element abundances measured in the TR may depend on the type
of topological structure present. Typically, the TR brightenings
associated with QSLs have coronal abundances, while those associated
with BP separatrices have abundances closer to photospheric values. We
suggest that this difference is due to the location and manner in which
magnetic reconnection occurs in two different topological structures.
---------------------------------------------------------
Title: Evidence for the Flare Trigger Site and Three-Dimensional
Reconnection in Multiwavelength Observations of a Solar Flare
Authors: Fletcher, L.; Metcalf, T. R.; Alexander, D.; Brown, D. S.;
Ryder, L. A.
2001ApJ...554..451F Altcode:
Based on a multiwavelength data set and a topological model for
the magnetic field, we argue that a M1.9 flare which occurred on
1993 May shows evidence of three-dimensional coronal reconnection
in a spine-fan configuration. Images from the Transition Region and
Coronal Explorer allow the detailed examination of the structures
involved in the flare and preflare in the 171 Å (1 MK) EUV passband
and the Lyα (10,000-20,000 K) passband. Yohkoh Hard X-ray Telescope
maps the position of nonthermal electron precipitation and the
Soft X-ray Telescope reveals preflare and flare heating on large
and small scales. While the flare appears to be driven by changes in
small-scale field close to the photosphere, near the interface between
strong opposite magnetic polarities, the result is the disruption of
large-scale field. We demonstrate how this observed activity on large
and small scales, along with many other aspects of the flare, suggests
a qualitative explanation in the three-dimensional reconfiguration of
coronal magnetic field, following a small-scale flux cancellation at
the photosphere.
---------------------------------------------------------
Title: Ribbons and field at high resolution
Authors: Fletcher, L.; Hudson, H. S.
2001AGUSM..SH31D10F Altcode:
The TRACE data let us define the geometry of flare ribbons with great
precision, as for example in the Bastille Day 2000 flare. We study the
UV and EUV ribbon motions for this event in comparison with the loops
seen by SXT and in the TRACE high-temperature response, and compare
these also with the photospheric magnetic field as observed by MDI. In
this work we assume the standard model for large-scale coronal magnetic
reconnection as a source of flare energy, and search for a correlation
between footpoint locations, magnetic field strength and flare energy
release as measured by hard X-ray emission.
---------------------------------------------------------
Title: CDS UV Brightenings Explained by Quasi-separatrices and Bald
Patches in an S-shape active region
Authors: Schmieder, B.; Démoulin, P.; Fletcher, L.; López Fuentes,
M. C.; Mandrini, C. H.; Mason, H. E.; Young, P. R.; Nitta, N.
2001IAUS..203..314S Altcode:
We present multi-instrument observations of AR 8048, made between
June 3 and June5 1997 as part of SoHO JOP033. This active region
has a sigmoid-like global shape and undergoes transient erupting
phenomena which releases the stored energy. Using a force free
field approach, we defined coronal magnetic field lines which fit
with the observations. The large-scale magnetic field lines confirms
the sigmoid characteristics of the active region. The study in 3D of
the configuration explained where and how the energy is released at
different places. The Ne VI brightenings correspond to the location
of tangent to the photosphere field lines, named "bald patch", they
are localized in the low transition region and represent feet of field
lines. The Si XII brightenings at coronal temperature are at the top
of coronal loops joining quasi-separatrices.
---------------------------------------------------------
Title: SOHO/UVCS Observations of a Coronal Jet During the Third
Whole Sun Month Campaign
Authors: Ko, Y. -K.; Raymond, J.; Gibson, S.; Strachan, L.; Alexander,
D.; Fletcher, L.; Holzer, T.; Gilbert, H.; Burkepile, J.; St. Cyr,
C.; Thompson, B.
2000SPD....31.0271K Altcode: 2000BAAS...32R.823K
On August 26 1999, a coronal jet occurred at the north west limb
near a sigmoid active region which has been the target for a joint
observation plan during the third Whole Sun Month Campaign. This jet
was observed by several instruments at the limb (SOHO/CDS, SOHO/EIT,
TRACE, MLSO/CHIP, MLSO/PICS), at 1.7 Ro (SOHO/UVCS), and at the outer
corona (SOHO/LASCO). At 1.7 Ro, the intensities of Lyman alpha, Lyman
beta in the jet increased by as large a factor of 100 compared with the
background corona, while those for O VI 1032 and O VI 1037 increased
by a factor of 2. C III 977 line also brightened significantly. The
line shift in the lines indicates that the line-of-sight velocity in
the jet started from 150 km/sec blue shift and ended at 120 km/sec
red shift. This line-of-sight motion seen at 1.7 Ro apparently was
opposite that observed when the jet emerged from the limb. In this
paper, we present the observation by SOHO/UVCS and discuss the dynamic
structure and physical properties of this jet as it passed through
1.7 Ro. Comparisons will be shown with the observations from other
instruments. This work is supported by NASA Grant number NAG5-7822.
---------------------------------------------------------
Title: Evidence for the Flare Trigger Site and 3-D Reconnection in
Multi-Wavelength Observations of a Solar Flare
Authors: Metcalf, T. R.; Fletcher, L.; Alexander, D.; Brown, D. S.;
Ryder, L. A.
2000SPD....31.0261M Altcode: 2000BAAS...32..822M
Based on a multi-wavelength data set and a topological model for the
magnetic field, we argue that a M1.9 flare which occurred on 3-May-99
shows evidence of 3-d reconnection through a coronal null. Images
from the Transition Region and Coronal Explorer allow the detailed
examination of the structures involved in the flare and pre-flare in
the 171 Angstroms (1MK) EUV passband, and the Lyman α (10,000-20,000K)
passband. Yohkoh Hard X-ray Telescope maps the position of non-thermal
electron precipitation and the Soft X-ray Telescope reveals pre-flare
and flare heating on large and small-scales. While the flare appears
to trigger in small scale field close to the photosphere, near the
interface between strong opposite magnetic polarities, the large-scale
field is directly involved in or affected by all phases of the flare. We
demonstrate how this observed activity on large and small scales, along
with many other aspects of the flare find a qualitative explanation
in the three-dimensional reconfiguration of coronal magnetic field,
following a small-scale flux cancelation at the photosphere. This
work is supported by the TRACE and SXT projects at LMSAL (contract
NAS5-38099 and NAS8-40801).
---------------------------------------------------------
Title: Observations of H-alpha Polarization in Flares
Authors: Mickey, D. L.; Metcalf, T. R.; Fletcher, L.
2000SPD....31.0255M Altcode: 2000BAAS...32R.820M
Max Millennium Coordinated Observing Plan #006 has as its goal the
measurement of H-alpha linear polarization, a possible signature of
low-energy proton beams in solar flares. Such observations have been
attempted in the past, but the results were inconclusive. A campaign
involving Mees Solar Observatory and Big Bear Solar Observatory,
together with Yohkoh, SOHO and TRACE spacecraft, was carried
out during the latter half of March 2000. We present preliminary
results from the observations with the Imaging Vector Magnetograph
at Mees Solar Observatory. The IVM was operated in a standard mode,
except that the spectral scan was limited to one point in the core
of H-alpha and one in the blue wing. This limited spectral sampling,
together with a recently upgraded data acquisition system, permitted
a complete measurement of Stokes vectors every 3.5 seconds. The field
of view was 280 arc sec square, with one arc sec pixels. A second
camera, exposed simultaneously but with a broad-band filter, provides
images which allow compensation for relative image motion and stretch
between exposures. Approximately two dozen flares were observed by
the IVM during the campaign, including one X-class and one M-class
flare. We present samples of the observations, including relevant
spacecraft observations, and discuss the sensitivity of the IVM to
linear polarization under these conditions. This work was supported
in part by the SXT project at LMSAL (contract NAS5-38099) and by NASA
grant NAG5-4941.
---------------------------------------------------------
Title: Electron Trapping and Precipitation in Asymmetric Solar
Flare Loops
Authors: Aschwanden, M. J.; Fletcher, L.; Sakao, T.; Kosugi, T.;
Hudson, H.
2000IAUS..195..375A Altcode:
Acceleration, propagation, and energy loss of particles energized in
solar flares cannot be studied separately because their radiative
signatures observed in the form of hard X-ray bremsstrahlung or
radio gyrosynchrotron emission represent a convolution of all these
processes. We analyze hard X-ray emission from solar flares using
a kinematic model that includes free-streaming electrons (having an
energy-dependent time-of-flight delay) as well as temporarily trapped
electrons (which are pitch-angle scattered by Coulomb collisional
scattering) to determine various physical parameters (trapping times,
flux asymmetry, loss-cone angles, magnetic mirror ratios) in flare
loops with asymmetric magnetic fields.
---------------------------------------------------------
Title: Electron Kinematics near the Loss-Cone
Authors: Fletcher, L.; Aschwanden, M. J.
2000SPD....31.0247F Altcode: 2000BAAS...32..819F
With the upcoming launch of the HESSI satellite, we expect that
problems of non-thermal electron transport and radiation signatures
will once more be the subject of some attention, since this is an
integral part of the calculation of the spectral and spatial behavior
of the radiative signatures which will be observed by HESSI. Problems
of particle transport in coronal magnetic traps are often treated by
making simple geometrical and timescale arguments for the fractions of
accelerated particles which are trapped and precipitate from coronal
loops. Such arguments are used to calculate the populations of,
for example, directly precipitating and trap-precipitating particles
(which can in principle be identified from hard X-ray time-series),
or coronal versus footpoint emission ratios (which can be studied from
spatially resolved HXR data). Using numerical simulation and analytic
arguments we have studied the dynamics of particles within coronal
traps, paying particular attention to the behavior in the vicinity
of the loss-cone. We find that over a broad range of normally-assumed
coronal parameters, such as mirror-ratio, loop length and loop density,
(a) electrons cannot pass easily from the trap region to the loss-cone,
so that (b) there is no collisionless trap-precipitating component and
(c) a large fraction of accelerated particles will lose their entire
energy budget within the coronal loop. We discuss what this means
for our current understanding of the solar flare environment and our
interpretation of radiative signatures. This work was supported by
the Yohkoh/SXT project at LMSAL (NASA grant NAS8-40801) and by the
U.K. Particle Physics and Astronomy Research Council.
---------------------------------------------------------
Title: Dynamics in Restructuring Active Regions Observed During
Soho/Yohkoh/Gbo Campaigns
Authors: Schmieder, B.; Deng, Y.; Mandrini, C. H.; Rudawy, P.; Nitta,
N.; Mason, H.; Fletcher, L.; Martens, P.; Brynildsen, N.
2000AdSpR..25.1879S Altcode:
JOP17 and JOP 33 are SOHO Joint Observing Programs in collaboration
with Yohkoh/SXT and ground based observatories (GBO's), dedicated to
observe dynamical events through the atmosphere. During runs of these
programs we observed in restructuring active regions (ARs), surges,
subflares, bright knots, but not large flares and jets. From these
observations we have been able to derive some of the responses of the
coronal and chromospheric plasma to the evolution of the photospheric
magnetic field. Emerging flux in an AR led to the formation of Arch
Filament Systems in the chromosphere, hot loops and knots in the
transition region, and X-ray loops. Frequent surges have been observed
in relation to parasitic or mixed polarities, but coronal jets have not
yet been found. We discuss the possible mechanisms acting during the
restructuring of the active regions (reconnection or “sea-serpent”
geometries)
---------------------------------------------------------
Title: High-resolution Observations of Plasma Jets in the Solar Corona
Authors: Alexander, David; Fletcher, Lyndsay
1999SoPh..190..167A Altcode:
We present recent observations of coronal jets, made by TRACE and
Yohkoh/SXT on 28 May and 19 August 1998. The high spatial resolution
of TRACE enables us to see in detail the process of material ejection;
in the line of Fe ix (one million degrees) we see both bright emitting
material and dark absorbing/scattering material being ejected, i.e.,
both hot and cold material, highly collimated and apparently ejected
along the direction of the overlying field lines. Bright ejecta are
seen simultaneously in Lyman α for one event and Yohkoh/SXT in the
other. The jets on the two days are different in that the 19 August
jet displays the morphology typical of a one-sided anemone jet while
the 28 May jet exhibits a two-sided jet morphology. The 19 August jet
shows evidence for rotation and an interesting bifurcation at large
distances from the energy release site. We study the physical properties
and energetics of these jetting events, and conclude that existing
theoretical models capture the essential physics of the jet phenomena.
---------------------------------------------------------
Title: Looptop Hard X-ray Sources
Authors: Fletcher, L.
1999ESASP.448..693F Altcode: 1999mfsp.conf..693F; 1999ESPM....9..693F
No abstract at ADS
---------------------------------------------------------
Title: What is Moss?
Authors: Berger, T. E.; De Pontieu, B.; Fletcher, L.; Schrijver,
C. J.; Tarbell, T. D.; Title, A. M.
1999SoPh..190..409B Altcode:
TRACE observations of active regions show a peculiar extreme ultraviolet
(EUV) emission over certain plage areas. Termed `moss' for its spongy,
low-lying, appearance, observations and modeling imply that the
phenomenon is caused by thermal conduction from 3-5 MKcoronal loops
overlying the plage: moss is the upper transition region emission of
hot coronal loops. The spongy appearance is due to the presence of
chromospheric jets or `spicules' interspersed with the EUV emission
elements. High cadence TRACE observations show that the moss EUV
elements interact with the chromospheric jets on 10 s time scales. The
location of EUV emission in the moss does not correlate well to the
locations of underlying magnetic elements in the chromosphere and
photosphere, implying a complex magnetic topology for coronal loop
footpoint regions. We summarize here the key observations leading to
these conclusions and discuss new implications for understanding the
structuring of the outer solar atmosphere.
---------------------------------------------------------
Title: Plasma Diagnostics of Transition Region “Moss” using SOHO/CDS
and TRACE
Authors: Fletcher, Lyndsay; De Pontieu, Bart
1999ApJ...520L.135F Altcode:
Recent observations of solar active regions with the Transition Region
and Coronal Explorer (TRACE) have revealed finely textured, low-lying
EUV emission, called the “moss,” appearing as a bright dynamic
pattern with dark inclusions. The moss has been interpreted as the
upper transition region by Berger and coworkers. In this study we use
SOHO Coronal Diagnostic Spectrometer and TRACE observations of Active
Region 8227 on 1998 May 30 to determine the physical parameters of the
moss material. We establish that the plasma responsible for the moss
emission has a temperature range of (0.6-1.5)×10<SUP>6</SUP> K and
is associated with hot loops (T>2×10<SUP>6</SUP> K). Moss plasma
has an electron density of (2-5)×10<SUP>9</SUP> cm<SUP>-3</SUP> at a
temperature of 1.3×10<SUP>6</SUP> K, giving a pressure of 0.7-1.7 dynes
cm<SUP>-2</SUP> (a few times higher than in coronal loops observed in
the TRACE Fe IX/X λ171 passband). The volume filling factor of the
moss plasma is of order 0.1, and the path along which the emission
originates is of order 1000 km long.
---------------------------------------------------------
Title: Coronal Loop Oscillations Observed with the Transition Region
and Coronal Explorer
Authors: Aschwanden, Markus J.; Fletcher, Lyndsay; Schrijver, Carolus
J.; Alexander, David
1999ApJ...520..880A Altcode:
We report here, for the first time, on spatial oscillations of coronal
loops, which were detected in extreme-ultraviolet wavelengths (171 Å)
with the Transition Region and Coronal Explorer, in the temperature
range of T<SUB>e</SUB>~1.0-1.5 MK. The observed loop oscillations
occurred during a flare that began at 1998 July 14, 12:55 UT and are
most prominent during the first 20 minutes. The oscillating loops
connect the penumbra of the leading sunspot to the flare site in
the trailing portion. We identified five oscillating loops with an
average length of L=130,000+/-30,000 km. The transverse amplitude
of the oscillations is A=4100+/-1300 km, and the mean period
is T=280+/-30 s. The oscillation mode appears to be a standing
wave mode (with fixed nodes at the footpoints). We investigate
different MHD wave modes and find that the fast kink mode with a
period τ=205(L/10<SUP>10</SUP> cm)(n<SUB>e</SUB>/10<SUP>9</SUP>
cm<SUP>-3</SUP>)<SUP>1/2</SUP>(B/10 G)<SUP>-1</SUP> s provides the
best agreement with the observed period. We propose that the onset
of loop oscillations in distant locations is triggered by a signal or
disturbance that propagates from the central flare site with a radial
speed of ~700 km s<SUP>-1</SUP>. Because the observed loop oscillation
periods are comparable to photospheric 5 minute oscillations, a resonant
coupling between the two systems is possible. We further find evidence
for global extreme-UV dimming in the entire active region possibly
associated with a coronal mass ejection.
---------------------------------------------------------
Title: A new view of the solar outer atmosphere by the Transition
Region and Coronal Explorer
Authors: Schrijver, C. J.; Title, A. M.; Berger, T. E.; Fletcher, L.;
Hurlburt, N. E.; Nightingale, R. W.; Shine, R. A.; Tarbell, T. D.;
Wolfson, J.; Golub, L.; Bookbinder, J. A.; DeLuca, E. E.; McMullen,
R. A.; Warren, H. P.; Kankelborg, C. C.; Handy, B. N.; De Pontieu, B.
1999SoPh..187..261S Altcode:
The Transition Region and Coronal Explorer (TRACE) - described in the
companion paper by Handy et al. (1999) - provides an unprecedented
view of the solar outer atmosphere. In this overview, we discuss the
initial impressions gained from, and interpretations of, the first
million images taken with TRACE. We address, among other topics,
the fine structure of the corona, the larger-scale thermal trends,
the evolution of the corona over quiet and active regions, the high
incidence of chromospheric material dynamically embedded in the coronal
environment, the dynamics and structure of the conductively dominated
transition region between chromosphere and corona, loop oscillations
and flows, and sunspot coronal loops. With TRACE we observe a corona
that is extremely dynamic and full of flows and wave phenomena, in
which loops evolve rapidly in temperature, with associated changes in
density. This dynamic nature points to a high degree of spatio-temporal
variability even under conditions that traditionally have been referred
to as quiescent. This variability requires that coronal heating can
turn on and off on a time scale of minutes or less along field-line
bundles with cross sections at or below the instrumental resolution
of 700 km. Loops seen at 171 Å (∼1 MK) appear to meander through
the coronal volume, but it is unclear whether this is caused by the
evolution of the field or by the weaving of the heating through the
coronal volume, shifting around for periods of up to a few tens of
minutes and lighting up subsequent field lines. We discuss evidence
that the heating occurs predominantly within the first 10 to 20 Mm
from the loop footpoints. This causes the inner parts of active-region
coronae to have a higher average temperature than the outer domains.
---------------------------------------------------------
Title: Deconvolution of Directly Precipitating and Trap-precipitating
Electrons in Solar Flare Hard X-Rays. III.Yohkoh Hard X-Ray Telescope
Data Analysis
Authors: Aschwanden, Markus J.; Fletcher, Lyndsay; Sakao, Taro;
Kosugi, Takeo; Hudson, Hugh
1999ApJ...517..977A Altcode:
We analyze the footpoint separation d and flux asymmetry A of
magnetically conjugate double footpoint sources in hard X-ray images
from the Yohkoh Hard X-Ray Telescope (HXT). The data set of 54 solar
flares includes all events simultaneously observed with the Compton
Gamma Ray Observatory (CGRO) in high time resolution mode. From the CGRO
data we deconvolved the direct-precipitation and trap-precipitation
components previously (in Paper II). Using the combined measurements
from CGRO and HXT, we develop an asymmetric trap model that allows
us to quantify the relative fractions of four different electron
components, i.e., the ratios of direct-precipitating (q<SUB>P1</SUB>,
q<SUB>P2</SUB>) and trap-precipitating electrons (q<SUB>T1</SUB>,
q<SUB>T2</SUB>) at both magnetically conjugate footpoints. We find mean
ratios of q<SUB>P1</SUB>=0.14+/-0.06, q<SUB>P2</SUB>=0.26+/-0.10,
and q<SUB>T</SUB>=q<SUB>T1</SUB>+q<SUB>T2</SUB>=0.60+/-0.13. We
assume an isotropic pitch-angle distribution at the
acceleration site and double-sided trap precipitation
(q<SUB>T2</SUB>/q<SUB>T1</SUB>=q<SUB>P2</SUB>/q<SUB>P1</SUB>)
to determine the conjugate loss-cone angles
(α<SUB>1</SUB>=42<SUP>deg</SUP>+/-11<SUP>deg</SUP> and
α<SUB>2</SUB>=52<SUP>deg</SUP>+/-10<SUP>deg</SUP>) and magnetic
mirror ratiosat both footpoints (R<SUB>1</SUB>=1.6,...,4.0 and
R<SUB>2</SUB>=1.3,...,2.5). From the relative displacement of
footpoint sources we also measure altitude differences of hard
X-ray emission at different energies, which are found to decrease
systematically with higher energies, with a statistical height
difference of h<SUB>Lo</SUB>-h<SUB>M1</SUB>=980+/-250 km and
h<SUB>M1</SUB>-h<SUB>M2</SUB>=310+/-300 km between the three lower
HXT energy channels (Lo, M1, M2).
---------------------------------------------------------
Title: Plasma Diagnostics of Transition Region “Moss” using SOHO/CDS
and TRACE
Authors: Fletcher, L.; de Pontieu, B.
1999AAS...194.7902F Altcode: 1999BAAS...31..963F
Recent observations of solar active regions with the Transition
Region And Coronal Explorer (TRACE) have revealed finely textured,
low-lying extreme ultraviolet (EUV) emission, called the “moss”,
appearing as a bright dynamic pattern with dark inclusions. The moss
has been interpreted as the upper transition region by Berger et al.,
(1999). In this study we use simultaneous SOHO Coronal Diagnostic
Spectrometer (CDS) and TRACE observations of Active Region (AR)
8227 on 30-May-1998 to determine the physical parameters of the moss
material. A differential emission measure (DEM) analysis and other
diagnostic tools establish that the plasma responsible for the moss
emission has a temperature range of 0.6-1.5 * 10(6) K and is associated
with hot loops (T > 2 * 10(6) K) observed with CDS. This plasma
has an electron density of 2-5* 10(9) cm(-3) at a temperature of 1.3 *
10(6) K, giving a pressure of 0.7-1.7 dyne cm(-2) . Both the density
and pressure in the moss plasma are a few times higher than in coronal
loops observed in the TRACE Fe IX/X 171 Angstroms passband. The volume
filling factor of the moss plasma is of the order 0.1 and the path
along which the emission originates is of the order 1,000 km long.
---------------------------------------------------------
Title: Dynamics and Plasma Diagnostics of Transition Region “Moss”
using SOHO/CDS, TRACE and SVST (La Palma)
Authors: de Pontieu, B.; Berger, T. E.; Fletcher, L.; Schrijver,
C. J.; Title, A. M.
1999AAS...194.7804D Altcode: 1999BAAS...31..961D
Recent observations of solar active regions with the Transition
Region And Coronal Explorer (TRACE) have revealed finely textured,
low-lying extreme ultraviolet (EUV) emission, called the “moss”,
appearing as a bright dynamic pattern with dark inclusions. The moss
has been interpreted as the upper transition region by Berger et al.,
(1999). In this poster we study the physical conditions in the moss
plasma, as well as its dynamics and connections to photosphere and
chromosphere. Using simultaneous SOHO Coronal Diagnostic Spectrometer
(CDS) and TRACE observations of Active Region (AR) 8227 on 30-May-1998
we determine the physical parameters of the moss material. We find T_e =
0.6-1.5 10(6) K and n_e = 2-5 10(9) cm(-3) at a temperature of 1.3 10(6)
K. The pressure in the moss plasma is higher than that in coronal loops
observed in the TRACE Fe IX/X 171 Angstroms passband, and moss emission
is associated with high temperature loops, observed by SXT and by CDS
in lines of T_max > 2.5 10(6) K. The volume filling factor of the
moss plasma is of the order 0.1 and the path along which the emission
originates is of the order 1,000 km long. We examine the dynamics of
the moss plasma, by making comparisons of TRACE 171 Angstroms movies
with SVST (La Palma) Ca II K-line, Hα , and G-band movies. Local
Correlation Tracking (LCT) flowmapping techniques are used to establish
the photospheric flowfield in plage regions with and without associated
moss. The relation of moss emission to chromospheric spicules or fibrils
is examined in detail using Hα movies and dopplergrams. In addition,
several miniflare events occuring in plage regions are analyzed using
TRACE and SVST movies. This research was supported by NASA contract
NAS5-38099 (TRACE) and NASA SR&T grant NASW-98008.
---------------------------------------------------------
Title: Rendering Three-Dimensional Solar Coronal Structures of Active
Region 8227
Authors: Gary, G. A.; Alexander, D.; Fletcher, L.
1999AAS...194.7807G Altcode: 1999BAAS...31..962G
Coronal X-ray and EUV synthesized images of Active Region 8227
(May-June 1996) are constructed and compared with TRACE, Yohkoh/SXT, and
SOHO/EIT observations. Using the rendering technique of Gary (1997) and
Alexander, Gary, and Thompson (1998), specific geometric and physical
models are used to integrate the plasma emission along the line of sight
to obtain a rendered image. The instrumental profiles are convolved
in the integration process as well as unique heating functions. We
analyze coronal X-ray and EUV structures via the constructing of
synthesized images and investigate how different heating rates within
the active region loop system affect the emission characteristics. The
intercomparison of the emission seen in different telescopes with
that predicted by the assumed model provides a diagnostic tool for
determining the properties of the heating and a physical explanation for
the observed distributions. Of particular note is the presence of bright
EUV emission at the base of hot X-ray loops, reminiscent of the "moss"
observed by Berger & et al. (1999), and Fletcher & De Pontieu
(1999). Gary, G. A.: 1997, Solar Physics, 174, 241. Alexander, D.,
Gary, G. A., and Thompson, B.J.: 1998, Proc. 2nd ASPE, PASP Conference
Series. Berger, T. E., De Pontieu, B., Schrijver, C. J., Title, A. M.,
1999. ApJ Letts. (submitted) Fletcher, L., De Pontieu, B. 1999, ApJ
Letts. (submitted)
---------------------------------------------------------
Title: Calentamiento de arcos coronales en una región activa por
reconfiguración topológica del campo magnético.
Authors: López Fuentes, M.; Mandrini, C. H.; Démoulin, P.; Schmieder,
B.; Fletcher, L.; Mason, H.
1999BAAA...43...24L Altcode:
We study the active region (AR) 8048 observed on June 1997 in several
wavelenghts. The combined observations obtained using CDS (SOHO)
and SXT (Yohkoh) show the heating of the coronal magnetic loops at
different atmospheric altitudes. Extrapolating the magnetic field in the
corona from longitudinal magnetograms from MDI (SOHO), we determine the
location of Bald Patches in the surroundings of the leading spot. This
magnetic feature, the emergence of parasitic magnetic polarities and
the observed photospheric motions provide the conditions to explain
the observed heating.
---------------------------------------------------------
Title: Generation of solar Hα impact polarization by fragmented
evaporative upflows
Authors: Fletcher, L.; Brown, J. C.
1998A&A...338..737F Altcode:
In this paper a novel mechanism is proposed for the generation of Hα
impact polarization observed during some solar flares. Rather than
being generated by the primary particle beams transporting energy from
the chromosphere to the corona, we suggest that following heating,
the solar chromosphere evaporates in a fragmented manner, and that
impact excitations in the regions of interaction of hot evaporating
and cool non-evaporating material locally generates impact-polarized
Hα emission. This thermal upflow model is more consistent with
the large areas and times over which polarization is observed than
are beam models. A simple model for the process is given, and the
resulting polarization is calculated and compared with observations,
under two assumptions about the number density of neutral particles
in the interaction regions.
---------------------------------------------------------
Title: A Model for Hard X-Ray Emission from the Top of Flaring Loops
Authors: Fletcher, L.; Martens, P. C. H.
1998ApJ...505..418F Altcode:
The frequent occurrence of hard X-ray emission from the top of
flaring loops was one of the discoveries by the Hard X-Ray Telescope
on board the Japanese Yohkoh satellite. In this paper we take a flare
current-sheet geometry and show how the combined effect of magnetic
field convergence and pitch-angle scattering of nonthermal electrons
injected at the top of the loop results in the generation of a looptop
source with properties akin to those observed by Yohkoh. We demonstrate
that a looptop source can be produced in both impulsive and gradual
phase loops. We further present a possible mechanism for the generation
of high-temperature “ridges” in the loop legs.
---------------------------------------------------------
Title: A Possible Third Festoon Flow in Atalanta Planitia, Venus
Authors: Fletcher, L.; Wright, H.; Grosfils, E.; Reinen, L.; Gilmore,
M.; Kozak, S.
1998LPI....29.1188F Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Hard X-Ray Emission from a Mirror Trap at the Top of
Reconnecting Loops
Authors: Martens, P. C. H.; Fletcher, L.
1998ASSL..229..269M Altcode: 1998opaf.conf..269M
No abstract at ADS
---------------------------------------------------------
Title: Surges and filaments in active regions during SOHO campaigns
Authors: Schmieder, B.; Deng, Y.; Rudawy, P.; Nitta, N.; Mandrini,
C. H.; Fletcher, L.; Martens, P.; Innes, D.; Young, P.; Mason, H.
1998ESASP.421..323S Altcode: 1998sjcp.conf..323S
No abstract at ADS
---------------------------------------------------------
Title: SOHO: een zonne-observatorium in de ruimte.
Authors: Fletcher, L.
1998Zenit..25....4F Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Numerical simulations of coronal particle trapping.
Authors: Fletcher, L.
1997A&A...326.1259F Altcode:
In this paper the trapping of high energy particles in solar coronal
loops is addressed. Using simulations, the time evolution of electrons
and protons trapped in a magnetic bottle is calculated under various
scattering conditions and the results compared with loss-cone
analysis. Thereafter the case of time-dependent injection into a
magnetic loop is addressed, and the results compared with previous
analytic work on X and γ-ray delay times.
---------------------------------------------------------
Title: Magnetic pumping in the cataclysmic variable AE Aquarii.
Authors: Kuijpers, J.; Fletcher, L.; Abada-Simon, M.; Horne, K. D.;
Raadu, M. A.; Ramsay, G.; Steeghs, D.
1997A&A...322..242K Altcode:
We propose that the radio outbursts of the cataclysmic variable
AE Aqr are caused by eruptions of bubbles of fast particles from
a magnetosphere surrounding the white dwarf. We investigate the
acceleration process of magnetic pumping in the magnetosphere which
is periodically driven both by the relative motion with the companion
and with the infalling spray of gas at the spin frequency of the white
dwarf. As the accretion rate is relatively low, the conversion of spin
energy into acceleration (rather than heating) of electrons and protons
can be efficient. The accelerated particles are trapped in the white
dwarf magnetosphere until their total energy content becomes comparable
to that of the trapping magnetic field structure and a MHD instability
sets in. Synchrotron radiation is emitted in the expelled expanding
plasmoid at radio and down to millimetric wavelengths. We find that
there is sufficient energy transferred from the rotation energy of the
rapidly-spinning white dwarf to fast particles by magnetic pumping to
explain quiescent and flaring radio emissions.
---------------------------------------------------------
Title: Particle Acceleration and Transport in Reconnecting Plasmas
Authors: Fletcher, Lyndsay; Petkaki, Panagiota
1997SoPh..172..267F Altcode: 1997ESPM....8..267F
We model the behaviour of particles in and around X-type magnetic
configurations, a possible solar flare reconnection geometry. Particles
are accelerated by a time-varying electric field close to the neutral
point, and followed by integrating the equations of motion. When
their motion becomes adiabatic a stochastic simulation is used to
model their further transport in a collisional magnetised medium.
---------------------------------------------------------
Title: O^{5+} Acceleration by Turbulence in Polar Coronal Holes
Authors: Fletcher, L.; Huber, M. C. E.
1997ESASP.404..379F Altcode: 1997cswn.conf..379F
No abstract at ADS
---------------------------------------------------------
Title: Are Coronal Mass Ejections Caused by Magnetic Pumping?
Authors: Kuijpers, Jan; Fletcher, Lyndsay
1996SoPh..169..415K Altcode:
Magnetic pumping in the solar corona is revisited. We derive conditions
under which magnetic pumping can be the cause of heating of loops
rather than of particle acceleration. Candidate sources for such a
process are coronal mass ejections (CMEs). Large loops are susceptible
to heating primarily of protons by magnetic compressions with periods
between 50 and 5000 s, the observed spectrum of the photospheric
driver. Efficient heating by pumping occurs since in these large loops
the density is low enough that the proton-proton collision time is
comparable to the periods of the external compressions. We suggest
that CMEs may be pressure-driven explosions of large-beta loops
caused by magnetic pumping, in contrast to current-driven `flares'
in low-beta environments.
---------------------------------------------------------
Title: The height distribution of non-thermal X-ray sources in
impulsive solar flares.
Authors: Fletcher, L.
1996A&A...310..661F Altcode:
In this paper we use numerical simulations to accurately model the
evolution of non-thermal electron distributions in coronal loops,
from which we calculate electron bremsstrahlung height versus energy
distributions. The results are compared with results of the Yohkoh
satellite and it is found that a model taking into account the full
complexity of electron transport can explain what is observed,
for quite reasonable loop parameters. We test three loop models,
the first with no field convergence, the second with field convergence
occurring rapidly and only in the chromosphere and the third where field
convergence occurs slowly in the corona. We demonstrate the effects
of varying parameters of the loop (such as density, length and field
strength), and of the beam (spectral index, pitch angle distribution)
and outline parameter regimes in which best agreement with the data can
be found. Broadly, densities between 2x10^10^ and 3x10^11^cm^-3^ and
coronal half-lengths L=~1.3-2.7x10^9^cm give qualitatively acceptable
results. Finally we discuss possible tests to distinguish between the
various models which can explain the height distribution.
---------------------------------------------------------
Title: Triggering the radio emission from AE Aqr:
Authors: Steeghs, D.; Kuijpers, J.; Fletcher, L.; et al.
1996ASSL..208..167S Altcode: 1996IAUCo.158..167S; 1996cvro.coll..167S
No abstract at ADS
---------------------------------------------------------
Title: On Determining Flare Beam Parameters from Loop-top Hard
X-ray Sources
Authors: Fletcher, L.
1996ApL&C..34..151F Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Radio Emission from AE Aquarii
Authors: Abada-Simon, M.; Bastian, T. S.; Fletcher, L.; Horne, K.;
Kuijpers, J.; Steeghs, D.; Bookbinder, J. A.
1996ASPC...93..182A Altcode: 1996ress.conf..182A
No abstract at ADS
---------------------------------------------------------
Title: The Height Distribution of Hard X-rays in Impulsive Solar
Flares
Authors: Fletcher, L.
1996mpsa.conf..549F Altcode: 1996IAUCo.153..549F
No abstract at ADS
---------------------------------------------------------
Title: On the generation of loop-top impulsive hard X-ray sources.
Authors: Fletcher, L.
1995A&A...303L...9F Altcode:
Recently observed with the Hard X-ray Telescope onboard Yohkoh,
loop-top hard X-ray sources have focussed interest on energy release
in solar flares. Possibly a direct indication of the site of particle
acceleration, they have thus far only been interpreted as thermal
sources. In this letter we propose instead that the sources arise as
a result of transport effects, and show using a stochastic simulation
of non-thermal electron transport in a simple loop model, that many
characteristics of the loop-top source can be reproduced.
---------------------------------------------------------
Title: Solar flare Hα impact polarization from high energy electrons?
Authors: Fletcher, L.; Brown, J. C.
1995A&A...294..260F Altcode:
In this paper we investigate the possibility of obtaining Hα line
linear polarization in solar flares following the excitation of
neutral hydrogen by energetic electron beams with a large initial
pitch angle. We compare the factors affecting the sign, magnitude and
intensity of polarized radiation collisionally excited by electron
and proton beams and present a calculation of the polarization which
could be observed from an electron beam, using a stochastic simulation
to solve the Fokker-Planck evolution equation for the electron beam in
the collisionally thick chromosphere, in the presence of a converging
magnetic field. We find that polarization from electron beams is
possible but requires extreme energy fluxes which are unlikely to be
present for any length of time during solar flares.
---------------------------------------------------------
Title: Modelling particle transport with stochastic simulations
Authors: Fletcher, Lyndsay
1994SSRv...68..239F Altcode:
We use stochastic simulations to calculate the evolution of particle
distributions in complex situations. Comparison of numerical and
analytical solutions is made, for the case of electrons moving from
the corona to the chromosphere and undergoing pure scattering. A
temporally fragmented beam injection is treated, under various
atmospheric conditions.
---------------------------------------------------------
Title: Foreword
Authors: van den Oord, Bert; Kuijpers, Jan; Kuperus, Max; Benz, A. O.;
Brown, J. C.; Einaudi, G.; Kuperus, M.; Raadu, M. A.; Trottet, G.;
van den Oord, G. H. J.; Vlahos, L.; Zheleznyakov, V. V.; Wijburg,
Marion; Fletcher, Lyndsay; Volwerk, Martin
1994SSRv...68D..17V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Hα impact polarization as a solar and astrophysical particle
diagnostic
Authors: Fletcher, Lyndsay
1993PhDT.......113F Altcode:
No abstract at ADS
---------------------------------------------------------
Title: H-alpha polarization of wind-heated optical bullets in SS 433.
Authors: Brown, J. C.; Fletcher, L.
1992A&A...259L..43B Altcode:
Mechanisms for energy supply to the optical bullets are discussed. It is
pointed out that in the case of heating by bullet collisions with the
system wind, recently shown to be a likely heating candidate, impact
polarization of the H-alpha line should be generated. An estimate
shows that this line polarization should be at least 0.2 percent and
orthogonal to the jet, precessing with it on the sky. This should be
observable and is proposed as a diagnostic of the wind heating model,
in contrast to turbulent internal heating.
---------------------------------------------------------
Title: Asymmetric Flux Loops in Active Regions - Part Two
Authors: Petrovay, K.; Brown, J. C.; van Driel-Gesztelyi, L.; Fletcher,
L.; Marik, M.; Stewart, G.
1990SoPh..127...51P Altcode:
We propose that magnetic flux loops in the subphotospheric layers
of the Sun are seriously asymmetrical as a consequence of the drag
force exerted on them because of the different rotational rate of the
surrounding plasma. In numerical models of stationary slender flux
loops in the plane parallel approximation we show that a serious
tilt is both possible and probable. Observational facts (see van
Driel-Gesztelyi and Petrovay, 1989; Paper I) strongly support the case
for high asymmetry. The different stability of p and f spots may also
be related to such an asymmetry.
---------------------------------------------------------
Title: Aerodynamic heating and thermal protection systems
Authors: Fletcher, L. S.
1978PrAA...59.....F Altcode:
The aerothermal environment is considered, taking into account
the aerothermal environment for the Pioneer Venus multiprobe
mission, shuttle elevon cove aerodynamic heating by ingested flow,
aerothermodynamic base heating, vortices induced in a stagnation region
by wakes, three-dimensional shock-wave interference heating prediction,
methods for predicting radiation-coupled flowfields about planetary
entry probes, shock-tube studies of silicon-compound vapors, and Mach
number and wall temperature effects on turbulent heat blockage. A
comparison of calculated and measured rocket plume infrared radiation
is discussed along with a band model for calculating radiance and
transmission of water vapor and carbon dioxide, and a comparison
of theoretical and experimental infrared radiation from a rocket
exhaust. Thermal protection systems are examined and attention
is given to the effect of melt removal by aerodynamic shear on
melt-through of metal plates, the ablation performance of tungsten
and copper-infiltrated tungsten systems in arc jets, the asymmetric
nose-tip shape change during atmospheric entry, the high-pressure arc
test performance of carbon-carbon nose tips, and segmented tungsten
nose tips for high-performance flight vehicles. Individual items were
announced in issues 07, 08, 17, and 18, 1977.
---------------------------------------------------------
Title: A Search for a Buried Meteorite
Authors: Fletcher, L.
1906Natur..74..490F Altcode:
No abstract at ADS
---------------------------------------------------------
Title: L'Uranolithe de Crumlin
Authors: Fletcher, L.
1903BSAFR..17..142F Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Fall of a Meteoric Stone near Crumlin (Co. Antrim) September 13
Authors: Fletcher, L.
1902Natur..66..577F Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Supposed Occurrence of Widespread Meteoritic Showers
Authors: Fletcher, L.
1891Natur..43R.295F Altcode:
No abstract at ADS