explanation blue bibcodes open ADS page with paths to full text
Author name code: bryans
ADS astronomy entries on 2022-09-14
author:"Bryans, Paul"
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Title: Exploration of the Physical and Spectroscopic Characteristics
of Coronal Rain
Authors: Tyson, Kalista; Lacatus, Daniela; Paraschiv, Alin; Bryans,
Paul
2021AGUFMSH45B2381T Altcode:
The correlation between the phenomenon known as coronal rain and the
origin of the Suns heating and cooling mechanisms has become a popular
area for exploration in recent years. In this study, we explored the
specifics of how plasma flows are triggered and how material moves
along closed magnetic field entities. Using spectroscopic data from the
Interface Region Imaging Spectrograph (IRIS), we analyzed the Mg II,
Si IV and C II emission lines in relation to the different magnetic
structures, allowing us to study plasma under different emitting
regimes. We have extracted spectroscopic characteristics of these
emission lines for an off-limb prolonged coronal rain event taking place
above a quiescent active region system. Additionally, we augmented our
dataset with SDO/AIA coronal observations, highlighting corresponding
higher temperature structures. We report a case where recurring coronal
rain episodes occur over timescales of several hours. Our work reveals
a multitude of complex, differently oriented, and turbulent, structures
under what appeared to be a standard coronal rain event.
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Title: Measuring the Magnetic Origins of Solar Flares, Coronal Mass
Ejections, and Space Weather
Authors: Judge, Philip; Rempel, Matthias; Ezzeddine, Rana; Kleint,
Lucia; Egeland, Ricky; Berdyugina, Svetlana V.; Berger, Thomas; Bryans,
Paul; Burkepile, Joan; Centeno, Rebecca; de Toma, Giuliana; Dikpati,
Mausumi; Fan, Yuhong; Gilbert, Holly; Lacatus, Daniela A.
2021ApJ...917...27J Altcode: 2021arXiv210607786J
We take a broad look at the problem of identifying the magnetic
solar causes of space weather. With the lackluster performance
of extrapolations based upon magnetic field measurements in the
photosphere, we identify a region in the near-UV (NUV) part of the
spectrum as optimal for studying the development of magnetic free energy
over active regions. Using data from SORCE, the Hubble Space Telescope,
and SKYLAB, along with 1D computations of the NUV spectrum and numerical
experiments based on the MURaM radiation-magnetohydrodynamic and
HanleRT radiative transfer codes, we address multiple challenges. These
challenges are best met through a combination of NUV lines of bright Mg
II, and lines of Fe II and Fe I (mostly within the 4s-4p transition
array) which form in the chromosphere up to 2 × 10<SUP>4</SUP>
K. Both Hanle and Zeeman effects can in principle be used to derive
vector magnetic fields. However, for any given spectral line the τ
= 1 surfaces are generally geometrically corrugated owing to fine
structure such as fibrils and spicules. By using multiple spectral
lines spanning different optical depths, magnetic fields across nearly
horizontal surfaces can be inferred in regions of low plasma β, from
which free energies, magnetic topology, and other quantities can be
derived. Based upon the recently reported successful sub-orbital space
measurements of magnetic fields with the CLASP2 instrument, we argue
that a modest space-borne telescope will be able to make significant
advances in the attempts to predict solar eruptions. Difficulties
associated with blended lines are shown to be minor in an Appendix.
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Title: Hinode and IRIS Synoptic Observations of Solar Cycle Transition
at Mid-Latitudes
Authors: Egeland, R.; Centeno, R.; Lacatus, D.; de Toma, G.; Bryans,
P.; McIntosh, S.
2021AAS...23811324E Altcode:
Recent observations by McIntosh et al. using SDO/AIA coronal bright
point density and the magnetogram-derived large scale open magnetic
flux "g-nodes" have traced out extended solar cycle activity bands
that originate at ~55 degrees latitude and propagate toward the
equator. When the opposite hemisphere bands "terminate" at the equator,
this event corresponds with the rapid rise of new cycle flux and active
regions at mid-latitudes, ~35 degrees. We present weekly synoptic
high-resolution observations of mid-latitude (35-40 degrees) magnetic
flux and chromospheric emission from Hinode SOT/SP and IRIS starting
from March 2017 until today, covering the end of cycle 24 and the
beginnings of cycle 25. After carefully correcting for instrumental
shifts, noise, and solar B-angle effects, we analyze time series
of mean magnetic flux, chromospheric line intensity, and statistical
properties of magnetic regions for signals of a developing cycle 25 and
the passage of the activity bands in these typically quiet mid-latitude
regions. Initial results show that the statistical properties of our
activity metrics are roughly constant over the four year period, with
a step function increase in activity that corresponds to a change to a
lower observation latitude. Finally, we investigate the correspondence
of SDO/AIA coronal bright points in our observational field of view
to chromospheric emission and photospheric magnetic features.
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Title: Investigating the Chromospheric Footpoints of the Solar Wind
Authors: Bryans, Paul; McIntosh, Scott W.; Brooks, David H.; De
Pontieu, Bart
2020ApJ...905L..33B Altcode:
Coronal holes present the source of the fast solar wind. However,
the fast solar wind is not unimodal—there are discrete, but subtle,
compositional, velocity, and density structures that differentiate
different coronal holes as well as wind streams that originate within
one coronal hole. In this Letter we exploit full-disk observational
"mosaics" performed by the Interface Region Imaging Spectrograph
(IRIS) spacecraft to demonstrate that significant spectral variation
exists within the chromospheric plasma of coronal holes. The spectral
differences outline the boundaries of some—but not all—coronal
holes. In particular, we show that the "peak separation" of the Mg
II h line at 2803 Å illustrates changes in what appear to be open
magnetic features within a coronal hole. These observations point
to a chromospheric source for the inhomogeneities found in the fast
solar wind. These chromospheric signatures can provide additional
constraints on magnetic field extrapolations close to the source,
potentially on spatial scales smaller than from traditional coronal hole
detection methods based on intensity thresholding in the corona. This
is of increased importance with the advent of Parker Solar Probe and
Solar Orbiter and the ability to accurately establish the connectivity
between their in situ measurements and remote sensing observations of
the solar atmosphere.
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Title: A New Facility for Airborne Solar Astronomy: NASA's WB-57 at
the 2017 Total Solar Eclipse
Authors: Caspi, Amir; Seaton, Daniel B.; Tsang, Constantine C. C.;
DeForest, Craig E.; Bryans, Paul; DeLuca, Edward E.; Tomczyk,
Steven; Burkepile, Joan T.; Casey, Thomas "Tony"; Collier, John;
Darrow, Donald "DD"; Del Rosso, Dominic; Durda, Daniel D.; Gallagher,
Peter T.; Golub, Leon; Jacyna, Matthew; Johnson, David "DJ"; Judge,
Philip G.; Klemm, Cary "Diddle"; Laurent, Glenn T.; Lewis, Johanna;
Mallini, Charles J.; Parent, Thomas "Duster"; Propp, Timothy; Steffl,
Andrew J.; Warner, Jeff; West, Matthew J.; Wiseman, John; Yates,
Mallory; Zhukov, Andrei N.; NASA WB-57 2017 Eclipse Observing Team
2020ApJ...895..131C Altcode: 2020arXiv200409658C
NASA's WB-57 High Altitude Research Program provides a deployable,
mobile, and stratospheric platform for scientific research. Airborne
platforms are of particular value for making coronal observations
during total solar eclipses because of their ability both to follow the
Moon's shadow and to get above most of the atmospheric air mass that
can interfere with astronomical observations. We used the 2017 August
21 eclipse as a pathfinding mission for high-altitude airborne solar
astronomy, using the existing high-speed visible-light and near/midwave
infrared imaging suite mounted in the WB-57 nose cone. In this paper,
we describe the aircraft, the instrument, and the 2017 mission;
operations and data acquisition; and preliminary analysis of data
quality from the existing instrument suite. We describe benefits and
technical limitations of this platform for solar and other astronomical
observations. We present a preliminary analysis of the visible-light
data quality and discuss the limiting factors that must be overcome
with future instrumentation. We conclude with a discussion of lessons
learned from this pathfinding mission and prospects for future research
at upcoming eclipses, as well as an evaluation of the capabilities of
the WB-57 platform for future solar astronomy and general astronomical
observation.
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Title: Novel Measurements of Solar Corona during the July 2 2019
Total Eclipse over Chile
Authors: Monaghan, A.; Bryans, P.; Berkey, B.; Rivera, Y.
2019AGUFMSA33B3153M Altcode:
Physical features of the solar corona such as temperature, density,
and magnetic field, have been demonstrated to affect the polarization
of coronal light making polarimetry one of the most crucial diagnostic
tools for solar research. Although the history of polarimetry in solar
physics is long, the ever-advancing world of technology continually
provides opportunities for implementation with new instruments and
new methods. The pursuit of new measurements could shed light on
long-standing unsolved problems of the solar corona, and increase our
understanding of the corona, solar weather, and our sun. The PolarCam
snapshot micropolarizer camera from 4D Technologies could hold the
potential for novel exploration of the solar corona. Developed for
use in interferometric measurements, the PolarCam is sensitive
to linearly polarized light on a pixel scale and has the unique
potential for size- and weight-constrained measurements such as CubeSat
deployment. Similarly, the relatively unexplored Si X emission line
(1.43 microns) could provide novel measurements of the solar corona,
and shows great promise for magnetometry. <P />The 2019 Total Solar
Eclipse in Chile provided an opportunity for the exploration of the
Si X line as well as an investigation into the potential of PolarCam
and similar technology. A team from the High Altitude Observatory
(HAO) in Boulder observed the eclipse from Cerro Tololo Inter-American
Observatory, taking measurements of Si X (1.43 micron) and white-light
(734 nm) polarization. PolarCam observations, taken during total solar
eclipse, were quantitatively compared with ground-based white-light
coronagraph measurements, demonstrating the capabilities and limitations
of such a detector for coronal measurements. The instrument's potential
for future deployment in expeditions or cubesat missions is also
evaluated. Finally, preliminary data from the Si X experiment is
presented and possible avenues for further exploration are proposed.
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Title: Probing the solar corona with Sun-grazing comets: comparing
MHDsimulations with EUV observations
Authors: Jia, Y. D.; Pesnell, W. D.; Liu, W.; Downs, C.; Bryans, P.
2019AGUFMSH13A..03J Altcode:
Sun -grazing comets can dive within one solar radii of the Sun
's surface. The cometary materials expand along the comet's orbit,
and undergo various stages of fierce thermal-chemical reactions on
the scales of seconds to minutes. These reactions ionize cometary
ions through successive charge states , which is revealed by certain
emission lines in the AIA images. Such plasma reaction processes are
significantly affected by the transient structures in the corona, and
thus these structures are revealed by the structures and shapes of the
comet tail. We combine three numerical models: a global corona model,
particle transportation model, and cometary plasma interaction model
into one framework to simulate the interaction of Sun -grazing comets
in the low corona. In our framework, cometary ejecta are vaporized
and then ionized via multiple channels, and then confined by the
coronal magnetic field. Constrained by imaging observations of the
and cometary interaction images, we apply our framework to trace back
to the local condition of the ambient corona, and its spatiotemporal
variation. Previously, our model confirmed the importance of the
ambient magnetic field vector in shaping the tail. In this study,
we use the C/2011 W3 (Lovejoy) perihelion to determine the local
plasma and field conditions in the corona. Our framework is capable of
resolving structures from thousands of meters to tens of million meters,
so we can identify the fine spatial variations in plasma density and
magnetic field intensity, which may be visible in future/on-going
close-up coronal observations.
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Title: Coronal Hole Variation from Chromosphere to Solar Wind
Authors: Bryans, P.
2019AGUFMSH53B3369B Altcode:
Coronal holes (CHs) are most commonly defined as long-lived regions
of reduced intensity in EUV images, and known to be the source of the
fast solar wind. Recent analysis of the spectral characteristics of CHs,
using data from the Interface Region Imaging Spectrograph (IRIS) and the
Extreme Ultraviolet Imaging Spectrometer (EIS) on Hinode, belies their
apparent uniformity in imaging data. Despite the typical assertion
that CHs are the source of the fast solar wind, EIS measurements
show regions within a CH with indications of slow-wind composition
in the corona. The spectral signatures of these regions extend to the
chromosphere, as evidenced in the Mg II lines measured by IRIS, with
the possibility that differences in the coronal composition could also
have signatures in the lower solar atmosphere. In this presentation we
will explore what these spectroscopic measurements reveal about the
underlying magnetic field and discuss the implications of variations
in the chromosphere and corona on the solar wind.
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Title: Novel observations of the middle corona during the 2017 total
solar eclipse
Authors: Caspi, A.; Seaton, D. B.; Tsang, C.; DeForest, C.; Bryans,
P.; Samra, J.; DeLuca, E.; Tomczyk, S.; Burkepile, J.; Gallagher,
P.; Golub, L.; Judge, P. G.; Laurent, G. T.; West, M.; Zhukov, A.
2019AGUFMSH13A..10C Altcode:
Total solar eclipses offer rare opportunities to study the middle
corona. This intriguing region contains complex interfaces and
transitions between physical regimes, but has historically been
under-observed due to the challenges of observing its dim emission so
close to the bright inner corona and blinding solar disk. The unique
circumstances of a total solar eclipse coupled with a high-altitude
observing platform provide nearly space-quality observing conditions,
including for wavelengths inaccessible by ground-based observatories,
but with availability of ground-quality resources, including high-speed,
high-resolution, wide-field coronography typically inaccessible
from space. We used the 2017 August 21 "Great American" total solar
eclipse to observe the solar corona from ~1.02 to ~3 R<SUB>Sun</SUB>
in both visible (533.9 ± 4.75 nm) and medium-wave infrared (3-5
μm) light using stabilized telescopes on two of NASA's WB-57F
high-altitude research aircraft. This pathfinding mission utilized
existing instrumentation to evaluate the platform performance, guide
instrumentation development, and explore new discovery space for
future studies of the middle corona. <P />We present the high-speed
(30 Hz), high-resolution (3 arcsec/pixel) visible and IR observations
obtained during the eclipse, and analysis of these observations
in the context of coronal structure and dynamics. We discuss the
limitations of the prototype data and pathways forward for future
instrumentation and missions optimized for the range of observable
parameters in the middle corona. We also discuss the benefits of
such eclipse studies to an understanding of the corona as a single,
unified system, from its origins at the solar surface to its extension
into the heliosphere, particularly within the context of a developing
multi- and inter-disciplinary research collaboration, COHERENT (the
"Corona as a Holistic Environment" Research Network).
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Title: Solar Eclipse Observations from the Ground and Air from 0.31
to 5.5 Microns
Authors: Judge, Philip; Berkey, Ben; Boll, Alyssa; Bryans, Paul;
Burkepile, Joan; Cheimets, Peter; DeLuca, Edward; de Toma, Giuliana;
Gibson, Keon; Golub, Leon; Hannigan, James; Madsen, Chad; Marquez,
Vanessa; Richards, Austin; Samra, Jenna; Sewell, Scott; Tomczyk,
Steven; Vera, Alysha
2019SoPh..294..166J Altcode:
We present spectra and broad-band polarized light data from a novel
suite of instruments deployed during the 21st August 2017 total solar
eclipse. Our goals were to survey solar spectra at thermal infrared
wavelengths during eclipse, and to test new technology for measuring
polarized coronal light. An infrared coronal imaging spectrometer,
flown at 14.3 km altitude above Kentucky, was supported on the ground
by observations from Madras, Oregon (elevation 683 m) and Camp Wyoba
on Casper Mountain, Wyoming (2402 m). In Wyoming we deployed a new
infrared Fourier Transform Spectrometer (FTS), three low-dispersion
spectrometers loaned to us by Avantes, a novel visible-light camera
PolarCam, sensitive to linear polarization, and one of two infrared
cameras from FLIR Systems, the other operated at Madras. Circumstances
of eclipse demanded that the observations spanned 17:19 to 18:26
UT. We analyze spectra of the limb photosphere, the chromosphere,
prominences, and coronal lines from 310 nm to 5.5 μm. We calibrated
data photometrically using the solar disk as a source. Between different
spectrometers, the calibrations were consistent to better than 13%. But
the sensitivities achieved were insufficient to detect coronal lines
from the ground. The PolarCam data are in remarkable agreement with
polarization data from the K-Cor synoptic instrument on Mauna Loa, and
with FLIR intensity data acquired in Madras. We discuss new results,
including a detection of the He I 1083 nm multiplet in emission during
the whole of totality. The combination of the FTS and AIR-Spec spectra
reveals for the first time the effects of the telluric extinction
on the infrared coronal emission lines, to be observed with upcoming
Daniel K. Inouye Solar Telescope.
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Title: Instrument Calibration of the Interface Region Imaging
Spectrograph (IRIS) Mission
Authors: Wülser, J. -P.; Jaeggli, S.; De Pontieu, B.; Tarbell,
T.; Boerner, P.; Freeland, S.; Liu, W.; Timmons, R.; Brannon, S.;
Kankelborg, C.; Madsen, C.; McKillop, S.; Prchlik, J.; Saar, S.;
Schanche, N.; Testa, P.; Bryans, P.; Wiesmann, M.
2018SoPh..293..149W Altcode:
The Interface Region Imaging Spectrograph (IRIS) is a NASA small
explorer mission that provides high-resolution spectra and images of
the Sun in the 133 - 141 nm and 278 - 283 nm wavelength bands. The
IRIS data are archived in calibrated form and made available to the
public within seven days of observing. The calibrations applied to
the data include dark correction, scattered light and background
correction, flat fielding, geometric distortion correction, and
wavelength calibration. In addition, the IRIS team has calibrated the
IRIS absolute throughput as a function of wavelength and has been
tracking throughput changes over the course of the mission. As a
resource for the IRIS data user, this article describes the details
of these calibrations as they have evolved over the first few years
of the mission. References to online documentation provide access to
additional information and future updates.
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Title: Interaction between cool material from Sun-grazing comets
and the low corona
Authors: Jia, Yingdong; Pesnell, William; Liu, Wei; Downs, Cooper;
Bryans, Paul
2018cosp...42E1613J Altcode:
Sun-grazing comets dive into altitudes lower than 1 solar radius from
the chromosphere. Cool materials of temperature lower than 10 ^{3}K
explode from the comet into the 10 ^{6} K corona. These materials
undergone various stages of rapid chemical reactions in scales of
seconds to minutes. Such reactions Structures in such images of
various wavelengths indicate strong variation in ambient conditions
of the corona. We combine three numerical models: low corona model,
particle transportation model, and cometary plasma interaction model
into one framework to model the interaction of Sun-grazing comets in the
low corona. In our framework, cometary vapor are ionized via multiple
channels, and then detained by the coronal magnetic field. In seconds,
these ions are further ionized into their highest charge state, which
is revealed by certain emission lines. Constrained by coronal graphs
and cometary interaction images, we apply our framework to trace back
to the local condition of the ambient corona, and its spatial/time
variation. Our frame work is able to resolve structures of sub-million
meters to tens of million meters. Once trained by multiple stages of
the comet's journey in the low corona, this framework can identify the
fine spatial variations in plasma density and magnetic field intensity,
which may be visible to future close-up observations.
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Title: New Coronal Science from NASA WB-57F High-Altitude Aircraft
Observations of the 2017 Total Solar Eclipse
Authors: Caspi, Amir; DeLuca, . Edward; Tomczyk, Steven; DeForest,
Craig; Bryans, Paul; Seaton, Daniel; Tsang, Constantine
2018cosp...42E.526C Altcode:
Total solar eclipses present rare opportunities to study the
complex solar corona, down to altitudes of just a few percent of
a solar radius above the surface, using ground-based and airborne
observatories that would otherwise be dominated by the intense solar
disk and high sky brightness. Studying the corona is critical to
gaining a better understanding of physical processes that occur on
other stars and astrophysical objects, as well as understanding the
dominant driver of space weather that affects human assets at Earth and
elsewhere. For example, it is still poorly understood how the corona
is heated to temperatures of 1-2 MK globally and up to 5-10 MK above
active regions, while the underlying chromosphere is 100 times cooler;
numerous theories abound, but are difficult to constrain due to the
limited sensitivities and cadences of prior measurements. The stability
of large-scale coronal structures and the extent of their reach to the
middle and outer corona are also not well known, limited in large part
by sensitivities and fields of view of existing observations.Airborne
observations during a total eclipse provide unique advantages. By
flying in the stratosphere at altitudes of 50 kft or higher, they
avoid all weather, the seeing quality is enormously improved, and
additional wavelengths such as near-IR also become available due to
significantly reduced water absorption. An airborne observatory can
also follow the Moon's shadow, increasing the total observing time by
50% or more.We present current results of solar coronal measurements
from airborne observations of the 2017 Great American Total Solar
Eclipse using two of NASA's WB-57 high-altitude research aircraft,
each equipped with two 8.7" telescopes feeding high-sensitivity visible
(green line and nearby continuum) and medium-wave IR (3-5 {μ}m) cameras
operating at high cadence (30 Hz) with ∼3 arcsec/pixel platescale and
±3 R_{sun} fields of view. The aircraft flew along the eclipse path,
separated by ∼110 km, to observe a summed ∼7.5 minutes of totality
in both visible and MWIR. These observations enable groundbreaking
studies of high-speed coherent motion - including possible Alfvén
waves and nanojets - in the lower and middle corona that could shed
light on coronal heating processes and the formation and stability of
coronal structures. Our MWIR observations of a cool prominence and
hot coronal active region plasma will be combined with spectra from
the AIR-Spec instrument, flown concurrently on NCAR's HIAPER GV. We
review the WB-57 eclipse mission and the current results of analysis
on the visible and IR coronal measurements, along with an outlook for
future analysis and missions.
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Title: Eclipse Science from 50,000 Feet: New Coronal Results from
NASA WB-57F High-Altitude Aircraft Observations of the 2017 Total
Solar Eclipse
Authors: Caspi, Amir; Tsang, Constantine; Seaton, Daniel B.; DeForest,
Craig; Bryans, Paul; DeLuca, Edward; Tomczyk, Steven; Burkepile,
Joan; Casey, Thomas Anthony; Collier, John; Darrow, Donald DD; Del
Rosso, Dominic; Durda, Daniel D.; Gallagher, Peter; Gascar, Jasmine;
Golub, Leon; Jacyna, Matthew; Johnson, David DJ; Judge, Philip G.;
Klemm, Cary; Laurent, Glenn Thomas; Lewis, Johanna; Mallini, Charles;
Parent, Thomas Duster; Propp, Timothy; Steffl, Andrew; Warner, Jeff;
West, Matthew John; Wiseman, John; Yates, Mallory; Zhukov, Andrei
2018tess.conf31302C Altcode:
Total solar eclipses present rare opportunities to study the complex
solar corona, down to altitudes of just a few percent of a solar
radius above the surface. Studying the corona is critical to gaining
a better understanding of the dominant driver of space weather that
affects human assets on Earth and elsewhere. For example, it is still
poorly understood how the corona is heated to temperatures of 1-2 MK
globally and up to 5-10 MK above active regions, while the underlying
chromosphere is 100 times cooler. The stability of large-scale coronal
structures and the extent of their reach to the middle and outer corona
are also not well known, limited in large part by sensitivities and
fields of view of existing observations. <P />Airborne observations
during a total eclipse provide unique advantages. By flying in the
stratosphere at altitudes of 50 kft or higher, they avoid all weather,
the seeing quality is enormously improved, and additional wavelengths
such as near-IR also become available due to significantly reduced
water absorption. An airborne observatory can also follow the Moon's
shadow, increasing the total observing time by 50% or more. <P />We
present current results of solar coronal measurements from airborne
observations of the 2017 Great American Total Solar Eclipse using two
of NASA's WB-57 high-altitude research aircraft, each equipped with
two 8.7-inch telescopes feeding high-sensitivity visible (green line
and nearby continuum) and medium-wave IR (3-5 μm) cameras operating
at high cadence (30 Hz) with ∼3 arcsec/pixel platescale and ±3
R<SUB>sun</SUB> fields of view. The two aircraft flew along the eclipse
path, separated by ∼110 km, to observe a total of ∼7.5 minutes
of totality in both visible and MWIR. These observations enable
groundbreaking studies of high-speed coherent motion - including
possible Alfvén waves and nanojets - in the lower and middle corona
that could shed light on coronal heating processes and the formation
and stability of coronal structures. Our MWIR observations of a cool
prominence and hot coronal active region plasma will be combined with
spectra from the AIR-Spec instrument, flown concurrently on NCAR's
HIAPER GV. We review the WB-57 eclipse mission and the current results
of analysis on the visible and IR coronal measurements, along with an
outlook for future analysis and missions.
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Title: Chasing the Great American 2017 Total Solar Eclipse: Coronal
Results from NASA's WB-57F High-Altitude Research Aircraft
Authors: Caspi, A.; Tsang, C.; DeForest, C. E.; Seaton, D. B.; Bryans,
P.; Burkepile, J.; Casey, T. A.; Collier, J.; Darrow, D.; DeLuca,
E.; Durda, D. D.; Gallagher, P.; Golub, L.; Judge, P. G.; Laurent,
G. T.; Lewis, J.; Mallini, C.; Parent, T.; Propp, T.; Steffl, A.;
Tomczyk, S.; Warner, J.; West, M. J.; Wiseman, J.; Zhukov, A.
2017AGUFMSH24A..05C Altcode:
Total solar eclipses present rare opportunities to study the complex
solar corona, down to altitudes of just a few percent of a solar
radius above the surface, using ground-based and airborne observatories
that would otherwise be dominated by the intense solar disk and high
sky brightness. Studying the corona is critical to gaining a better
understanding of physical processes that occur on other stars and
astrophysical objects, as well as understanding the dominant driver of
space weather that affects human assets at Earth and elsewhere. For
example, it is still poorly understood how the corona is heated to
temperatures of 1-2 MK globally and up to 5-10 MK above active regions,
while the underlying chromosphere is 100 times cooler; numerous theories
abound, but are difficult to constrain due to the limited sensitivities
and cadences of prior measurements. The origins and stability of coronal
fans, and the extent of their reach to the middle and outer corona,
are also not well known, limited in large part by sensitivities and
fields of view of existing observations. Airborne observations during
the eclipse provide unique advantages; by flying in the stratosphere
at altitudes of 50 kft or higher, they avoid all weather, the seeing
quality is enormously improved, and additional wavelengths such as
near- IR also become available due to significantly reduced water
absorption. For an eclipse, an airborne observatory can also follow the
shadow, increasing the total observing time by 50% or more. We present
results of solar coronal measurements from airborne observations of
the 2017 Great American Total Solar Eclipse using two of NASA's WB-57
high-altitude research aircraft, each equipped with two 8.7" telescopes
feeding high-sensitivity visible (green-line) and medium-wave IR (3-5
μm) cameras operating at high cadence (30 Hz) with 3 arcsec/pixel
platescale and ±3 R_sun fields of view. The aircraft flew along the
eclipse path, separated by 110 km, to observe a summed 7.5 minutes of
totality in both visible and NIR, enabling groundbreaking studies of
high-speed wave motions and nanojets in the lower corona, the structure
and extent of coronal fans, and constraints on a potential primordial
dust ring around the Sun. We review the mission, and the results of
analysis on the visible and IR coronal measurements.
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Title: Multi-wavelength observations of the solar atmosphere from
the August 21, 2017 total solar eclipse
Authors: Tomczyk, S.; Boll, A.; Bryans, P.; Burkepile, J.; Casini,
R.; DeLuca, E.; Gibson, K. L.; Judge, P. G.; McIntosh, S. W.; Samra,
J.; Sewell, S. D.
2017AGUFMSH24A..04T Altcode:
We will conduct three experiments at the August 21, 2017 total
solar eclipse that we call the Rosetta Stone experiments. First,
we will obtain narrow-bandpass images at infrared wavelengths of the
magnetically sensitive coronal emission lines of Fe IX 2855 nm, Mg VIII
3028 nm and Si IX 3935 nm with a FLIR thermal imager. Information on the
brightness of these lines is important for identifying the optimal lines
for coronal magnetometry. These images will also serve as context images
for the airborne AirSpec IR coronal spectroscopy experiment (Samra et
al). Second, we will obtain linear polarization images of the visible
emission lines of Fe X 637 nm and Fe XI 789 nm as well as the continuum
polarization near 735 nm. These will be obtained with a novel detector
with an integral array of linear micro-polarizers oriented at four
different angles that enable polarization images without the need for
liquid crystals or rotating elements. These measurements will provide
information on the orientation of magnetic fields in the corona and
serve to demonstrate the new detector technology. Lastly, we will obtain
high cadence spectra as the moon covers and uncovers the chromosphere
immediately after 2nd contact and before third contact. This so-called
flash spectrum will be used to obtain information about chromospheric
structure at a spatial resolution higher than is possible by other
means. In this talk, we will describe the instrumentation used in these
experiments and present initial results obtained with them. This work
is supported by a grant from NASA, through NSF base funding of HAO/NCAR
and by generous loans of equipment from our corporate partners, FLIR,
4D Technologies and Avantes.
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Title: Digging into the corona: A modeling framework trained with
Sun-grazing comet observations
Authors: Jia, Y. D.; Pesnell, W. D.; Bryans, P.; Downs, C.; Liu, W.;
Schwartz, S. J.
2017AGUFMSH11B2437J Altcode:
Images of comets diving into the low corona have been captured a few
times in the past decade. Structures visible at various wavelengths
during these encounters indicate a strong variation of the ambient
conditions of the corona. We combine three numerical models: a global
coronal model, a particle transportation model, and a cometary plasma
interaction model into one framework to model the interaction of such
Sun-grazing comets with plasma in the low corona. In our framework,
cometary vapors are ionized via multiple channels and then captured
by the coronal magnetic field. In seconds, these ions are further
ionized into their highest charge state, which is revealed by certain
coronal emission lines. Constrained by observations, we apply our
framework to trace back to the local conditions of the ambient corona,
and their spatial/time variation over a broad range of scales. Once
trained by multiple stages of the comet's journey in the low corona,
we illustrate how this framework can leverage these unique observations
to probe the structure of the solar corona and solar wind.
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Title: Surveying the IR corona during the 2017 solar eclipse
Authors: Bryans, P.; Hannigan, J. W.; Sewell, S. D.; Judge, P. G.
2017AGUFMSH13B2479B Altcode:
The spectral emission of the infrared solar corona is the most
promising direct diagnostic of the coronal magnetic field, and
yet remains poorly measured. During the 2017 total solar eclipse,
we will perform the first spectral survey of the IR corona using
the NCAR Airborne Interferometer. This Fourier Transform Infrared
Spectrometer is configured to observe the coronal spectrum from 1.5
to 5.5 microns at R 10,000 from a ground-based site. The location
is atop Casper Mountain, Wyoming (42.73ºN, 106.32ºW, 2400 masl),
8 km from the center-line of totality. In this presentation, we will
outline the need for such measurements, describe the instrument design
and adaptation for the eclipse measurement, observation scheme, and
present preliminary results. We will also discuss implications for
observing infrared coronal lines from the ground, for example with
the upcoming DKIST facility.
---------------------------------------------------------
Title: ASPIRE - Airborne Spectro-Polarization InfraRed Experiment
Authors: DeLuca, E.; Cheimets, P.; Golub, L.; Madsen, C. A.; Marquez,
V.; Bryans, P.; Judge, P. G.; Lussier, L.; McIntosh, S. W.; Tomczyk, S.
2017AGUFMSH13B2480D Altcode:
Direct measurements of coronal magnetic fields are critical for
taking the next step in active region and solar wind modeling and
for building the next generation of physics-based space-weather
models. We are proposing a new airborne instrument to make these key
observations. Building on the successful Airborne InfraRed Spectrograph
(AIR-Spec) experiment for the 2017 eclipse, we will design and build a
spectro-polarimeter to measure coronal magnetic field during the 2019
South Pacific eclipse. The new instrument will use the AIR-Spec optical
bench and the proven pointing, tracking, and stabilization optics. A new
cryogenic spectro-polarimeter will be built focusing on the strongest
emission lines observed during the eclipse. The AIR-Spec IR camera,
slit jaw camera and data acquisition system will all be reused. The
poster will outline the optical design and the science goals for ASPIRE.
---------------------------------------------------------
Title: First results from the NASA WB-57 airborne observations of
the Great American 2017 Total Solar Eclipse
Authors: Caspi, Amir; Tsang, Constantine; DeForest, Craig; Seaton,
Daniel B.; Bryans, Paul; Tomczyk, Steven; Burkepile, Joan; Judge,
Phil; DeLuca, Edward E.; Golub, Leon; Gallagher, Peter T.; Zhukov,
Andrei; West, Matthew; Durda, Daniel D.; Steffl, Andrew J.
2017SPD....4810701C Altcode:
Total solar eclipses present rare opportunities to study the complex
solar corona, down to altitudes of just a few percent of a solar
radius above the surface, using ground-based and airborne observatories
that would otherwise be dominated by the intense solar disk and high
sky brightness. Studying the corona is critical to gaining a better
understanding of physical processes that occur on other stars and
astrophysical objects, as well as understanding the dominant driver of
space weather that affects human assets at Earth and elsewhere. For
example, it is still poorly understood how the corona is heated to
temperatures of 1-2 MK globally and up to 5-10 MK above active regions,
while the underlying chromosphere is 100 times cooler; numerous theories
abound, but are difficult to constrain due to the limited sensitivities
and cadences of prior measurements. The origins and stability of coronal
fans, and the extent of their reach to the middle and outer corona,
are also not well known, limited in large part by sensitivities and
fields of view of existing observations.Airborne observations during
the eclipse provide unique advantages; by flying in the stratosphere
at altitudes of 50 kft or higher, they avoid all weather, the seeing
quality is enormously improved, and additional wavelengths such
as near-IR also become available due to significantly reduced water
absorption. For an eclipse, an airborne observatory can also follow the
shadow, increasing the total observing time by 50% or more.We present
the first results from airborne observations of the 2017 Great American
Total Solar Eclipse using two of NASA's WB-57 research aircraft, each
equipped with two 8.7" telescopes feeding high-sensitivity visible
(green-line) and near-IR (3-5 µm) cameras operating at high cadence
(30 Hz) with ~3 arcsec/pixel platescale and ±3 R_sun fields of
view. The aircraft will fly along the eclipse path, separated by ~90
km, to observe a summed ~8 minutes of totality in both visible and
NIR, enabling groundbreaking studies of high-speed wave motions and
nanojets in the lower corona, the structure and extent of coronal fans,
and constraints on a potential primordial dust ring around the Sun.
---------------------------------------------------------
Title: On the Connection between Propagating Solar Coronal
Disturbances and Chromospheric Footpoints
Authors: Bryans, P.; McIntosh, S. W.; De Moortel, I.; De Pontieu, B.
2016ApJ...829L..18B Altcode:
The Interface Region Imaging Spectrograph (IRIS) provides an
unparalleled opportunity to explore the (thermal) interface between the
chromosphere, transition region, and the coronal plasma observed by the
Atmospheric Imaging Assembly (AIA) of the Solar Dynamics Observatory
(SDO). The SDO/AIA observations of coronal loop footpoints show
strong recurring upward propagating signals—“propagating coronal
disturbances” (PCDs) with apparent speeds of the order of 100-120 km
s<SUP>-1</SUP>. That signal has a clear signature in the slit-jaw images
of IRIS in addition to identifiable spectral signatures and diagnostics
in the Mg iih (2803 Å) line. In analyzing the Mg iih line, we are able
to observe the presence of magnetoacoustic shock waves that are also
present in the vicinity of the coronal loop footpoints. We see there is
enough of a correspondence between the shock propagation in Mg iih, the
evolution of the Si IV line profiles, and the PCD evolution to indicate
that these waves are an important ingredient for PCDs. In addition, the
strong flows in the jet-like features in the IRIS Si IV slit-jaw images
are also associated with PCDs, such that waves and flows both appear
to be contributing to the signals observed at the footpoints of PCDs.
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Title: Post Flare Giant Arches and Run-Away Reconnection
Authors: West, Matthew; Seaton, Daniel B.; Savage, Sabrina; Bryans,
Paul
2016SPD....4740206W Altcode:
The nature of post-flare giant arches and their relation to regular
post flare loops has long been debated, especially in the context of
how post-flare giant arches can sustain their growth for such long
periods. In this presentation we discuss how magnetic reconnection can
be sustained to such great heights, and the role the background corona
plays in maintaining this growth. We use observations from 14 October
2014, when the SWAP EUV solar telescope on-board the PROBA2 spacecraft
observed an eruption that led to the formation of perhaps the largest
post-eruptive loop system seen in the solar corona in solar cycle
24. These loops grew to a height of approximately 400000 km (>0.5
solar-radii). We provide evidence of on-going reconnection, through
observations spanning from the chromosphere to the middle corona,
and discuss how only certain conditions can maintain prolonged growth.
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Title: Measuring the IR solar corona during the 2017 eclipse
Authors: Bryans, Paul; Hannigan, James; Philip, Judge; Larson, Brandon;
Sewell, Scott; McIntire, Lauren
2016SPD....4730105B Altcode:
On 21 August 2017 a total solar eclipse will pass across the continental
United States, offering a unique opportunity to conduct scientific
research of the solar atmosphere. With the light from the Sun eclipsed,
the solar corona becomes visible in a way not possible when swamped
by the light from the photosphere. The infrared (IR) spectrum of
the corona, in particular, is predicted to contain some of the most
magnetically sensitive spectral lines. However, no comprehensive survey
of this spectral range has been carried out to date. Here, we describe
a Fourier Transform Spectrometer, currently under construction at NCAR,
to measure the IR spectrum from 2 to 12 microns. We will discuss the
operation of the experiment, which will be deployed along the path of
totality in Wyoming, and the scientific results we hope to obtain.
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Title: On the Absence of EUV Emission from Comet C/2012 S1 (ISON)
Authors: Bryans, Paul; Pesnell, W. Dean
2016ApJ...822...77B Altcode:
When the sungrazing comet C/2012 S1 (ISON) made its perihelion passage
within two solar radii of the Sun’s surface, it was expected to be
a bright emitter at extreme ultraviolet (EUV) wavelengths. However,
despite solar EUV telescopes repointing to track the orbit of the comet,
no emission was detected. This “null result” is interesting in
its own right, offering the possibility of placing limits on the size
and composition of the nucleus. We explain the lack of detection by
considering the properties of the comet and the solar atmosphere that
determine the intensity of EUV emission from sungrazing comets. By
comparing these properties with those of sungrazing comet C/2011 W3
(Lovejoy), which did emit in the EUV, we conclude that the primary
factor resulting in non-detectable EUV emission from C/2012 S1 (ISON)
was an insufficiently large nucleus. We conclude that the radius
of C/2012 S1 (ISON) was at least a factor of four less than that of
C/2011 W3 (Lovejoy). This is consistent with white-light observations
in the days before perihelion that suggested the comet was dramatically
reducing in size on approach.
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Title: Observed Variability of the Solar Mg II h Spectral Line
Authors: Schmit, D.; Bryans, P.; De Pontieu, B.; McIntosh, S.;
Leenaarts, J.; Carlsson, M.
2015ApJ...811..127S Altcode: 2015arXiv150804714S
The Mg ii h&k doublet are two of the primary spectral lines observed
by the Sun-pointing Interface Region Imaging Spectrograph (IRIS). These
lines are tracers of the magnetic and thermal environment that spans
from the photosphere to the upper chromosphere. We use a double-Gaussian
model to fit the Mg ii h profile for a full-Sun mosaic data set taken
on 2014 August 24. We use the ensemble of high-quality profile fits to
conduct a statistical study on the variability of the line profile as
it relates the magnetic structure, dynamics, and center-to-limb viewing
angle. The average internetwork profile contains a deeply reversed
core and is weakly asymmetric at h2. In the internetwork, we find a
strong correlation between h3 wavelength and profile asymmetry as well
as h1 width and h2 width. The average reversal depth of the h3 core
is inversely related to the magnetic field. Plage and sunspots exhibit
many profiles that do not contain a reversal. These profiles also occur
infrequently in the internetwork. We see indications of magnetically
aligned structures in plage and network in statistics associated with
the line core, but these structures are not clear or extended in the
internetwork. The center-to-limb variations are compared to predictions
of semi-empirical model atmospheres. We measure a pronounced limb
darkening in the line core that is not predicted by the model. The
aim of this work is to provide a comprehensive measurement baseline
and preliminary analysis on the observed structure and formation of
the Mg ii profiles observed by IRIS.
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Title: Full-Sun IRIS observations and what they reveal about
chromosphere and transition region variation across the disk
Authors: Bryans, Paul; McIntosh, Scott W.
2015TESS....120313B Altcode:
The recent launch of the Interface Region Imaging Spectrometer
(IRIS) has resulted in the first high-resolution spectroscopy of the
chromosphere and transition region. The wavelength range sampled by IRIS
allows us to measure emission and absorption lines across a range of
heights in the lower solar atmosphere. However, the IRIS field-of-view
is limited to 175 arcsec<SUP>2</SUP>, so simultaneous observations of
these spectral lines is not possible across the entire disk. To overcome
this problem we have performed full-disk mosaics, where we build up
observations of the entire Sun using 184 different IRIS pointings. An
analysis of these mosaics has highlighted interesting variations in
the spectral line profiles across the disk. In this presentation we
will summarize these findings and speculate on what physical insights
they reveal.
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Title: Coronal Diagnostics from Cometary Emission
Authors: Bryans, Paul; Pesnell, William D; Seaton, Daniel B; West,
Matthew J
2014AAS...22442203B Altcode:
The extreme ultraviolet (EUV) emission observed from sungrazing comets
as they pass through the solar atmosphere can be used to infer the
properties of the corona. In this paper we will discuss several of these
properties that can be estimated from the EUV observations of Comet
Lovejoy from AIA/SDO and SWAP/PROBA2. The longevity of the emission
allows us to constrain the coronal electron density through which
the comet passes. We will also discuss how dispersion of the emitting
cometary material we can be used to estimate the local Alfven speed in
the corona. Finally, measuring the deformation of the magnetic field
as it is impacted by the comet can be used to estimate the magnetic
field strength in this location. In the absence of the comet, none
of these parameters are directly measurable in the corona. Sungrazing
comets are thus unique probes of the solar atmosphere.
---------------------------------------------------------
Title: The Time-dependent Chemistry of Cometary Debris in the
Solar Corona
Authors: Pesnell, W. D.; Bryans, P.
2014ApJ...785...50P Altcode:
Recent improvements in solar observations have greatly progressed the
study of sungrazing comets. They can now be imaged along the entirety
of their perihelion passage through the solar atmosphere, revealing
details of their composition and structure not measurable through
previous observations in the less volatile region of the orbit further
from the solar surface. Such comets are also unique probes of the solar
atmosphere. The debris deposited by sungrazers is rapidly ionized and
subsequently influenced by the ambient magnetic field. Measuring the
spectral signature of the deposited material highlights the topology
of the magnetic field and can reveal plasma parameters such as the
electron temperature and density. Recovering these variables from the
observable data requires a model of the interaction of the cometary
species with the atmosphere through which they pass. The present paper
offers such a model by considering the time-dependent chemistry of
sublimated cometary species as they interact with the solar radiation
field and coronal plasma. We expand on a previous simplified model by
considering the fully time-dependent solutions of the emitting species'
densities. To compare with observations, we consider a spherically
symmetric expansion of the sublimated material into the corona and
convert the time-dependent ion densities to radial profiles. Using
emissivities from the CHIANTI database and plasma parameters derived
from a magnetohydrodynamic simulation leads to a spatially dependent
emission spectrum that can be directly compared with observations. We
find our simulated spectra to be consistent with observation.
---------------------------------------------------------
Title: What EUV Observations of Comet ISON Reveal About the Solar
Corona
Authors: Bryans, P.; Pesnell, W. D.
2013AGUFM.P31A1787B Altcode:
Recent advances in space-based solar observations have greatly
progressed the study of sungrazing comets. They can now be imaged along
the entirety of their perihelion passage, revealing details of their
composition, structure, and size. Such comets are also unique probes
of the solar corona. The debris deposited by sungrazers is rapidly
ionized and subsequently forced to follow the ambient magnetic field. In
this paper we present preliminary results from EUV observations of
Comet ISON. We estimate the size of the comet nucleus based on the
EUV radiance and compare with independent estimates. The variation
of the EUV emission with wavelength provides limits on the density of
the ambient corona, and the motion of ionized debris will be used to
infer the coronal magnetic field structure.
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Title: Time-dependent chemisty of outgassed cometary detritus in
the solar corona
Authors: Bryans, Paul; Pesnell, W. D.
2013SPD....44...32B Altcode:
Recent observations of sungrazing comets have opened an exciting novel
methof of probing the solar atmosphere. As well as providing valuable
insight on the magnetic field of the lower corona, sungrazing comets
also promise the potential of measuring the solar wind as their detritus
follows the open field lines of the corona. In this work, we model the
chemisty of the material sublimated from comets as they skim across
the Sun. This material, largely water ice, is rapidly dissociated and
ionized by the solar radiation field and coronal electrons. We track
the evolution of the ionizing material as it expands into the corona
using a generalized Haser-like model. Based on these results, we have
predicted the emission resulting from these ions in different regions
of the corona and compared the results with SDO/AIA observations.
---------------------------------------------------------
Title: What Will Comet ISON Debris Teach Us About the Sun?
Authors: Pesnell, W. D.; Bryans, P.
2013SPD....44...34P Altcode:
Comet ISON is a large sun-grazing comet due to pass perihelion on
November 28, 2013. It will go through the corona 2.7 Rsun above
the surface, much higher than earlier EUV comets. We will use our
time-dependent models of cometary debris to discuss how the trail of
Comet ISON can be used to probe the solar corona. The debris trail left
behind as a sun-grazing comet passes by the Sun undergoes different
chemical processes at different distances from the Sun. Near the Sun
the material is rapidly converted to atomic ions and becomes part of
the solar corona. Far from the Sun the evaporated material can remain in
molecular form for a long time, while the grains of asteroidal material
can exist long enough to become meteors in planetary atmospheres. The
larger fragments may survive as independent comets, until the next
perihelion passage. In between those limits the material moves in the
solar wind acceleration region. The debris could become entrained in
the solar wind and be measured by satellites far from the Sun. This
material would be observed as abundance anomalies in the solar wind. We
will describe the fate of the cometary debris trail left by Comet ISON
and what the trail can tell us about the solar corona and solar wind.
---------------------------------------------------------
Title: EUV Emission from Sungrazing Comets
Authors: Bryans, Paul; Pesnell, W. Dean
2013enss.confE..33B Altcode:
The EUV emission resulting from comets' passage through the solar
atmosphere has opened many exciting avenues of study. The observations
show the sublimated cometary material to interact with ambient magnetic
field and highlight magnetic features that are not normally visible with
EUV telescopes. The first step, however, is to explain why the comet
produces the EUV emission. In this talk, I will outline a model that
describes the interaction of the cometary atmosphere with the quiescent
solar background and results in such emission. In particular, the model
accurately predicts the temporal and wavelength response of the emission
detected by SDO/AIA. After describing the emission process, I will go on
to discuss what we can learn about the corona from these observations.
---------------------------------------------------------
Title: Can we use comets as solar probes?
Authors: Bryans, P.
2012AGUFMSH13B2251B Altcode:
The EUV emission resulting from comets' passage through the solar
atmosphere has opened many exciting avenues of study. The observations
show the sublimated cometary material to interact with ambient magnetic
field and highlight magnetic features that are not normally visible with
EUV telescopes. The first step, however, is to explain why the comet
produces the EUV emission. In this talk, I will outline a model that
describes the interaction of the cometary atmosphere with the quiescent
solar background and results in such emission. In particular, the model
accurately predicts the temporal and wavelength response of the emission
detected by SDO/AIA. After describing the emission process, I will go on
to discuss what we can learn about the corona from these observations.
---------------------------------------------------------
Title: Investigating Coronal Activity by Release Using Sublimation
Authors: Moore, T. E.; Bryans, P.; Pesnell, W. D.; Thompson, B. J.
2012AGUFMSH21D..05M Altcode:
Plasma tails left by sun-grazing comets are visible in EUV, expanding
their traditional role as "windsocks" into the low corona and serving
as natural "chemical release" experiments. SDO obtained spectrally
resolved video imagery of passages as close as 0.15 Rs to the solar
photosphere at 12 sec frame cadence. Vaporized cometary materials
form sublimation trails or "subtrails" that persist as long as 20
min. in 13.1 and 17.1 nm channels. Striation along local magnetic flux
tubes implies filamentation of the visible plasma, and the subtrails
exhibit substantial deviations from the comet orbital track. These
reveal coronal winds and shears with velocities that are comparable to
the comet velocity of up to 600 km/s. We analyze the likely origins
and directionality of these winds and their implications for coronal
heating in the altitude range where ion-neutral collision mean free
paths are longer than the gyro radius but shorter than the atmospheric
scale height, that is, the solar transition region. With active impact
or photo-ionization, and charge exchange, the inferred super-thermal,
sub-Alfvenic ion-neutral relative velocities will lead to ion pick-up
distributions that decay or relax into "kappa" distributions with
super-thermal power law tails that are relevant to the formation of
the corona.
---------------------------------------------------------
Title: Time-dependent Chemistry of Detritus from Sun-grazing Comets
Authors: Pesnell, W. D.; Bryans, P.
2012AGUFMSH13B2253P Altcode:
As a sun-grazing comet passes the Sun at perihelion it leaves behind
a trail of water vapor and detritus. The latter are grains of stony
material that rapidly heat and vaporize in the intense radiation field
of the solar photosphere. A large amount of O is produced from both the
water and the stony material. The atomic material does not continue
along the comet's orbital path but appears to move along the ambient
magnetic field. This requires an ionization mechanism that rapidly
converts the neutral atoms into ions. We propose two models of the
time-dependent chemistry that can be used to calculate the ionization
balance of O and Fe. One is an extension of the Haser model to include
many stages of ionization but without recombination. The advantage
is that an analytic solution can be derived for an arbitrary numbers
of ionization stages. Once the time dependence is known it can be
converted to the radial profile in either spherical or cylindrical
symmetry. The other model integrates in time the equations describing
ionization/recombination balance. Both types of solutions can be
numerically inverted to estimate the radiance profiles. The models give
the same sequence to the ionization stages, but the time dependence
and radial profiles are shown to differ. Although we concentrate on
the O and Fe chemistry because it is observed from SDO/AIA, any atom
can be considered.
---------------------------------------------------------
Title: The Extreme-ultraviolet Emission from Sun-grazing Comets
Authors: Bryans, P.; Pesnell, W. D.
2012ApJ...760...18B Altcode: 2012arXiv1209.5708B
The Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory
has observed two Sun-grazing comets as they passed through the solar
atmosphere. Both passages resulted in a measurable enhancement of
extreme-ultraviolet (EUV) radiance in several of the AIA bandpasses. We
explain this EUV emission by considering the evolution of the cometary
atmosphere as it interacts with the ambient solar atmosphere. Molecules
in the comet rapidly sublimate as it approaches the Sun. They are
then photodissociated by the solar radiation field to create atomic
species. Subsequent ionization of these atoms produces a higher
abundance of ions than normally present in the corona and results in
EUV emission in the wavelength ranges of the AIA telescope passbands.
---------------------------------------------------------
Title: The Journey of Sungrazing Comet Lovejoy
Authors: Bryans, Paul; A'Hearn, M.; Battams, K.; Biesecker, D.;
Bodewits, D.; Boice, D.; Brown, J.; Caspi, A.; Chodas, P.; Hudson,
H.; Jia, Y.; Jones, G.; Keller, H. U.; Knight, M.; Linker, J.; Lisse,
C.; Liu, W.; McIntosh, S.; Pesnell, W. D.; Raymond, J.; Saar, S.;
Saint-Hilaire, P.; Schrijver, C.; Snow, M.; Tarbell, T.; Thompson,
W.; Weissman, P.; Comet Lovejoy Collaboration Team
2012AAS...22052507B Altcode:
Comet Lovejoy (C/2011 W3) was the first sungrazing comet, observed
by space-based instruments, to survive perihelion passage. First
observed by ground-based telescopes several weeks prior to perihelion,
its journey towards the Sun was subsequently recorded by several solar
observatories, before being observed in the weeks after perihelion by
a further array of space- and ground-based instruments. Such a surfeit
of wide-ranging observations provides an unprecedented insight into
both sungrazing comets themselves, and the solar atmosphere through
which they pass. This paper will summarize what we have learnt from the
observations thus far and offer some thoughts on what future sungrazing
comets may reveal about comets, the Sun, and their interaction.
---------------------------------------------------------
Title: The EUV Emission from Sun-Grazing Comets
Authors: Bryans, Paul; Pesnell, W. D.
2012AAS...22042305B Altcode:
The Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory
(SDO) has, to date, viewed two Sun-grazing comets as they passed
through the solar corona. Both passages resulted in the significant
enhancement of Extreme Ultraviolet (EUV) emission in several of
the AIA bandpasses. We explain this EUV emission by considering the
evolution of the cometary atmosphere as it interacts with the ambient
solar atmosphere. Water ice in the comet rapidly sublimates as it
approaches the Sun. This water vapor is then photodissociated by
the solar radiation field to create atomic H and O. Other molecules
present in the comet also evaporate and dissociate to give atomic
Fe and other metals. Subsequent ionization of these atoms produces a
high abundance of ions not normally present at the temperature of the
corona and results in EUV emission in the wavelength ranges of the
AIA telescopes. Understanding the EUV emission places constraints on
the cometary composition and provides valuable insight to the nature
of the upper solar atmosphere.
---------------------------------------------------------
Title: The EUV Emission in Comet-Solar Corona Interactions
Authors: Bryans, P.; Pesnell, W. D.; Schrijver, C. J.; Brown, J. C.;
Battams, K.; Saint-Hilaire, P.; Liu, W.; Hudson, H. S.
2011AGUFMSH34B..05B Altcode:
The Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory
(SDO) viewed a comet as it passed through the solar corona on 2011 July
5. This was the first sighting of a comet by a EUV telescope. For 20
minutes, enhanced emission in several of the AIA wavelength bands marked
the path of the comet. We explain this EUV emission by considering
the evolution of the cometary atmosphere as it interacts with the
ambient solar atmosphere. Water ice in the comet rapidly sublimates
as it approaches the Sun. This water vapor is then photodissociated,
primarily by Ly-α, by the solar radiation field to create atomic H and
O. Other molecules present in the comet also evaporate and dissociate
to give atomic Fe and other metals. Subsequent ionization of these
atoms can be achieved by a number of means, including photoionization,
electron impact, and charge exchange with coronal protons and other
highly-charged species. Finally, particles from the cometary atmosphere
are thermalized to the background temperature of the corona. Each step
could cause emission in the AIA bandpasses. We will report here on
their relative contribution to the emission seen in the AIA telescopes.
---------------------------------------------------------
Title: New Collisional Ionization Equilibrium Calculations for
Optically Thin Plasmas
Authors: Savin, D. W.; Bryans, P.; Mitthumsiri, W.; Badnell, N. R.;
Gorczyca, T. W.; Laming, J. M.
2011nlaw.confC...5S Altcode:
Reliably interpreting spectra from electron-ionized laboratory and
cosmic plasmas requires accurate ionization balance calculations for
the plasma in question. However, much of the atomic data needed for
these calculations have not been generated using modern theoretical
methods and their reliability are often highly suspect. We have carried
out state-of-the-art calculations of dielectronic recombination (DR)
rate coefficients for the hydrogenic through Mg-like ions of all
elements from He to Zn as well as for Al- like to Ar-like ions of
Fe. We have also carried out state-of-the-art radiative recombination
(RR) rate coefficient calculations for the bare through Na-like ions
of all elements from H to Zn. Using our data and the most recently
recommended electron impact ionization data, we present improved
collisional ionization equilibrium (CIE) calculations. Here, as an
example, we present our calculated fractional ionic abundances for
iron using these data and compare them with those from the previously
recommended CIE calculations.
---------------------------------------------------------
Title: Comparison of Vector Magnetograms from the Solenoidal and
Irrotational Components of the Magnetic Field
Authors: Bryans, Paul; Pesnell, W. D.
2011SPD....42.2108B Altcode: 2011BAAS..43S.2108B
According to the Helmholtz Theorem, the solar magnetic field can be
defined in terms of an irrotational and a solenoidal component. We will
discuss the partitioning of the field into these components as a means
of attributing elements of the magnetic field to its vorticity and
divergence. We will then discuss the advantages of this decomposition
as a metric for comparing vector magnetograms of varying spatial and
temporal resolution.
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Title: Properties of a Polar Coronal Hole During the Solar Minimum
in 2007
Authors: Hahn, M.; Bryans, P.; Landi, E.; Miralles, M. P.; Savin, D. W.
2010ApJ...725..774H Altcode: 2010arXiv1010.4277H
We report measurements of a polar coronal hole during the recent
solar minimum using the Extreme Ultraviolet Imaging Spectrometer on
Hinode. Five observations are analyzed that span the polar coronal hole
from the central meridian to the boundary with the quiet-Sun corona. We
study the observations above the solar limb in the height range of
1.03-1.20 R <SUB>sun</SUB>. The electron temperature T <SUB>e</SUB>
and emission measure (EM) are found using a geometric mean emission
measure method. The EM derived from the elements Fe, Si, S, and Al
are compared in order to measure relative coronal-to-photospheric
abundance enhancement factors. We also studied the ion temperature
T <SUB>i</SUB> and the non-thermal velocity v <SUB>nt</SUB> using the
line profiles. All these measurements are compared to polar coronal hole
observations from the previous (1996-1997) solar minimum and to model
predictions for relative abundances. There are many similarities in the
physical properties of the polar coronal holes between the two minima at
these low heights. We find that the electron density, T <SUB>e</SUB>,
and T <SUB>i</SUB> are comparable in both minima. T <SUB>e</SUB> shows
a comparable gradient with height. Both minima show a decreasing T
<SUB>i</SUB> with increasing charge-to-mass ratio q/M. A previously
observed upturn of T <SUB>i</SUB> for ions above q/M>0.25 was not
found here. We also compared relative coronal-to-photospheric elemental
abundance enhancement factors for a number of elements. These ratios
were ~1 for both the low first ionization potential (FIP) elements Si
and Al and the marginally high FIP element S relative to the low FIP
element Fe, as is expected based on earlier observations and models
for a polar coronal hole. These results are consistent with no FIP
effect in a polar coronal hole.
---------------------------------------------------------
Title: Properties of the Solar Corona above a Polar Coronal Hole
during the Solar Minimum in 2007
Authors: Hahn, Michael; Landi, E.; Bryans, P.; Miralles, M. P.; Savin,
D. W.
2010shin.confE.150H Altcode:
Observations have shown that the latest solar minimum differs from the
previous one in 1996-1997. Here we present the analysis of EUV spectra
of the north polar coronal hole observed during the recent minimum 16
November 2007. The data were taken using the Extreme ultraviolet Imaging
Spectrometer (EIS) on Hinode. Five observations span the coronal hole
in the longitudinal direction from the center to the boundary with
the quiet sun corona and extend radially from the solar disk to about
1.2 Rsun. We use the geometric mean emission measure (GEM) approach to
determine the plasma emission measure (EM) and electron temperature. The
GEM analysis shows that the observations are nearly isothermal, but
there are indications of a small contribution from higher temperature
plasma along the line of sight. To investigate the temperature structure
in more detail we are performing a differential emission measure (DEM)
analysis. The upper and lower bounds on the ion temperature are also
measured using line widths. Our results are compared to spectroscopic
measurements of polar coronal holes obtained from observations carried
out during the previous solar minimum in 1996-1997.
---------------------------------------------------------
Title: Multiple Component Outflows in an Active Region Observed with
the EUV Imaging Spectrometer on Hinode
Authors: Bryans, P.; Young, P. R.; Doschek, G. A.
2010ApJ...715.1012B Altcode: 2010arXiv1004.5085B
We have used the Extreme Ultraviolet Imaging Spectrometer on the
Hinode spacecraft to observe large areas of outflow near an active
region. These outflows are seen to persist for at least 6 days. The
emission line profiles suggest that the outflow region is composed of
multiple outflowing components, Doppler-shifted with respect to each
other. We have modeled this scenario by imposing a double-Gaussian fit
to the line profiles. These fits represent the profile markedly better
than a single-Gaussian fit for Fe XII and XIII emission lines. For
the fastest outflowing components, we find velocities as high as 200
km s<SUP>-1</SUP>. However, there remains a correlation between the
fitted line velocities and widths, suggesting that the outflows are
not fully resolved by the double-Gaussian fit and that the outflow
may be comprised of further components.
---------------------------------------------------------
Title: Properties of the Solar Corona above a Polar Coronal Hole
during the Recent Solar Minimum
Authors: Hahn, Michael; Landi, E.; Bryans, P.; Miralles, M.; Savin, D.
2010AAS...21640105H Altcode: 2010BAAS...41..857H
Recent observations have shown that the latest solar minimum differs
from the previous one in 1996-1997. Here we present the analysis of
EUV spectra of the north polar coronal hole observed in November 2007,
during the current minimum. The data were taken using the Extreme
Ultraviolet Imaging Spectrometer (EIS) on Hinode. Five observations
span the coronal hole in the longitudinal direction from the center
to the boundary with the quiet sun corona and extend radially from
the solar disk to about 1.2 solar radii to. We use the geometric mean
emission measure (GEM) approach to determine the plasma emission measure
(EM) and electron temperature. From the EM we estimate the relative
elemental abundances. We also determine upper and lower bounds on the
ion temperature using measured line widths. We then compare our results
to spectroscopic measurements of polar coronal holes obtained from
observations carried out during the previous solar minimum in 1996-1997.
---------------------------------------------------------
Title: Coronal Active Region Loop Variability Observed with Hinode/EIS
Authors: Bryans, Paul
2010AAS...21640720B Altcode:
Using the Extreme Ultraviolet Spectrometer (EIS) on the Hinode
spacecraft, we have studied the properties of active region loops
along their length. Here, we present results of the variation of the
temperature, density and filling factor with respect to height in
the loop. In particular, we find differences in the electron density
between loop footpoints that provide important constraints on models
used to explain coronal loop heating.
---------------------------------------------------------
Title: Updated Collisional Ionization Equilibrium Calculated for
Optically Thin Plasmas
Authors: Savin, Daniel Wolf; Bryans, P.; Badnell, N. R.; Gorczyca,
T. W.; Laming, J. M.; Mitthumsiri, W.
2010HEAD...11.1504S Altcode: 2010BAAS...42..678S
Reliably interpreting spectra from electron-ionized cosmic plasmas
requires accurate ionization balance calculations for the plasma
in question. However, much of the atomic data needed for these
calculations have not been generated using modern theoretical methods
and their reliability are often highly suspect. We have carried out
state-of-the-art calculations of dielectronic recombination (DR) rate
coefficients for the hydrogenic through Na-like ions of all elements
from He to Zn as well as for Al-like to Ar-like ions of Fe. We have
also carried out state-of-the-art radiative recombination (RR) rate
coefficient calculations for the bare through Na-like ions of all
elements from H to Zn. Using our data and the recommended electron
impact ionization data of Dere (2007), we present improved collisional
ionization equilibrium calculations (Bryans et al. 2006, 2009). We
compare our calculated fractional ionic abundances using these data
with those presented by Mazzotta et al. (1998) for all elements from
H to Ni. This work is supported in part by the NASA APRA and SHP
SR&T programs.
---------------------------------------------------------
Title: Deriving the coronal hole electron temperature: electron
density dependent ionization / recombination considerations
Authors: Doyle, John Gerard; Chapman, Steven; Bryans, Paul;
Pérez-Suárez, David; Singh, Avninda; Summers, Hugh; Savin,
Daniel Wolf
2010RAA....10...91D Altcode: 2009arXiv0909.3195D
Comparison of appropriate theoretically derived line ratios with
observational data can yield estimates of a plasma's physical
parameters, such as electron density or temperature. The usual practice
in the calculation of the line ratio is the assumption of excitation
by electrons/protons followed by radiative decay. Furthermore, it
is normal to use the so-called coronal approximation, i.e. one only
considers ionization and recombination to and from the ground-state. A
more accurate treatment is to include ionization/recombination to and
from metastable levels. Here, we apply this to two lines from adjacent
ionization stages, Mg IX 368 Å and Mg X 625 Å, which has been shown to
be a very useful temperature diagnostic. At densities typical of coronal
hole conditions, the difference between the electron temperature derived
assuming the zero density limit compared with the electron density
dependent ionization/recombination is small. This, however, is not
the case for flares where the electron density is orders of magnitude
larger. The derived temperature for the coronal hole at solar maximum
is around 1.04 MK compared to just below 0.82 MK at solar minimum.
---------------------------------------------------------
Title: Multiple Component Outflows in Active Regions observed by EIS
Authors: Bryans, Paul; Doschek, G. A.; Young, P. R.
2009SPD....40.1221B Altcode:
We have used the Extreme Ultraviolet Imaging Spectrometer (EIS) on
the Hinode spacecraft to observe large areas of outflow near an active
region. These outflows are seen to persist for a number of days. The
emission line profiles suggest that the outflow region is composed of
multiple outflowing components, Doppler-shifted with respect to each
other. We have modelled this scenario by imposing a double-Gaussian fit
to the line profiles; these fits represent the profile markedly better
than a single Gaussian fit. For the fastest outflowing components,
we find velocities as high as 200 km/s. However, there remains a
correlation between the fitted line velocities and widths, suggesting
that the outflows are not fully resolved by the double-Gaussian fit
and that the outflow may be comprised of further components.
---------------------------------------------------------
Title: Molecular Cloud Chemistry and the Importance of Dielectronic
Recombination
Authors: Bryans, P.; Kreckel, H.; Roueff, E.; Wakelam, V.; Savin, D. W.
2009ApJ...694..286B Altcode: 2008arXiv0809.4504B
Dielectronic recombination (DR) of singly charged ions is a
reaction pathway that is commonly neglected in chemical models of
molecular clouds. In this study we include state-of-the-art DR data
for He<SUP>+</SUP>, C<SUP>+</SUP>, N<SUP>+</SUP>, O<SUP>+</SUP>,
Na<SUP>+</SUP>, and Mg<SUP>+</SUP> in chemical models used to simulate
dense molecular clouds, protostars, and diffuse molecular clouds. We
also update the radiative recombination (RR) rate coefficients
for H<SUP>+</SUP>, He<SUP>+</SUP>, C<SUP>+</SUP>, N<SUP>+</SUP>,
O<SUP>+</SUP>, Na<SUP>+</SUP>, and Mg<SUP>+</SUP> to the current
state-of-the-art values. The new RR data have little effect on the
models. However, the inclusion of DR results in significant differences
in gas-grain models of dense, cold molecular clouds for the evolution
of a number of surface and gas-phase species. We find differences of
a factor of 2 in the abundance for 74 of the 655 species at times
of 10<SUP>4</SUP>-10<SUP>6</SUP> yr in this model when we include
DR. Of these 74 species, 16 have at least a factor of 10 difference
in abundance. We find the largest differences for species formed on
the surface of dust grains. These differences are due primarily to the
addition of C<SUP>+</SUP> DR, which increases the neutral C abundance,
thereby enhancing the accretion of C onto dust. These results may
be important for the warm-up phase of molecular clouds when surface
species are desorbed into the gas phase. We also note that no reliable
state-of-the-art RR or DR data exist for Si<SUP>+</SUP>, P<SUP>+</SUP>,
S<SUP>+</SUP>, Cl<SUP>+</SUP>, and Fe<SUP>+</SUP>. Modern calculations
for these ions are needed to better constrain molecular cloud models.
---------------------------------------------------------
Title: A New Approach to Analyzing Solar Coronal Spectra and
Updated Collisional Ionization Equilibrium Calculations. II. Updated
Ionization Rate Coefficients
Authors: Bryans, P.; Landi, E.; Savin, D. W.
2009ApJ...691.1540B Altcode: 2008arXiv0805.3302B
We have re-analyzed Solar Ultraviolet Measurement of Emitted
Radiation (SUMER) observations of a parcel of coronal gas using new
collisional ionization equilibrium (CIE) calculations. These improved
CIE fractional abundances were calculated using state-of-the-art
electron-ion recombination data for K-shell, L-shell, Na-like, and
Mg-like ions of all elements from H through Zn and, additionally, Al-
through Ar-like ions of Fe. They also incorporate the latest recommended
electron impact ionization data for all ions of H through Zn. Improved
CIE calculations based on these recombination and ionization data are
presented here. We have also developed a new systematic method for
determining the average emission measure (EM) and electron temperature
(T<SUB>e</SUB> ) of an isothermal plasma. With our new CIE data and
a new approach for determining average EM and T<SUB>e</SUB> , we have
re-analyzed SUMER observations of the solar corona. We have compared
our results with those of previous studies and found some significant
differences for the derived EM and T<SUB>e</SUB> . We have also
calculated the enhancement of coronal elemental abundances compared to
their photospheric abundances, using the SUMER observations themselves
to determine the abundance enhancement factor for each of the emitting
elements. Our observationally derived first ionization potential factors
are in reasonable agreement with the theoretical model of Laming.
---------------------------------------------------------
Title: VizieR Online Data Catalog: Plasma Recombination rate
coefficients (Bryans+, 2006)
Authors: Bryans, P.; Badnell, N. R.; Gorczyca, T. W.; Laming, J. M.;
Mitthumsiri, W.; Savin, D. W.
2008yCat..21670343B Altcode:
Reliably interpreting spectra from electron-ionized cosmic plasmas
requires accurate ionization balance calculations for the plasma in
question. However, much of the atomic data needed for these calculations
have not been generated using modern theoretical methods and are often
highly suspect. This translates directly into the reliability of the
collisional ionization equilibrium (CIE) calculations. We make use
of state-of-the-art calculations of dielectronic recombination (DR)
rate coefficients for the hydrogenic through Na-like ions of all
elements from He up to and including Zn. Where measurements exist,
these published theoretical DR data agree with recent laboratory work
to within typically 35% or better at the temperatures relevant for
CIE. We also make use of state-of-the-art radiative recombination
(RR) rate coefficient calculations for the bare through Na-like ions
of all elements from H through to Zn. Here we present improved CIE
calculations for temperatures from 104 to 109 K using our data and the
recommended electron impact ionization data of Mazzotta et al. (1998,
Cat. ) for elements up to and including Ni and Mazzotta (2000, private
communication) for Cu and Zn. DR and RR data for ionization stages
that have not been updated are also taken from these two additional
sources. <P />(2 data files).
---------------------------------------------------------
Title: The Status of Collisional Ionization Equilibrium Calculations
and a New Approach to Emission Eeasure Determinations
Authors: Bryans, Paul; Laming, J. M.; Landi, E.; Savin, D. W.
2008AAS...212.0302B Altcode: 2008BAAS...40Q.184B
We have calculated improved collisional ionization equilibrium (CIE)
fractional abundances using state-of-the-art dielectronic recombination
(DR) and radiative recombination (RR) rate coefficients for K-shell,
L-shell, Na-like, and Mg-like ions of all elements from H through Zn and
M-shell ions of Fe. These data have been compared with other published
state-of-the-art DR and RR data and found to agree within 35% and 10%,
respectively, in the temperature range where the ion forms in CIE. Where
DR measurements exist, theory and experiment agree to within 35% in this
temperature range. We have also investigated recent improvements to
the recommended electron impact ionization rate coefficient database,
concluding that differences of up to a factor of 4 between recent
compilations implies that significant additional <P />experimental
and theoretical work is required. Using our new CIE calculations we
have re-analyzed solar coronal observations of an isothermal parcel
of coronal gas. We have also developed a mathematically rigorous
method for determining the average emission measure and temperature
of the emitting plasma. Using our new CIE data and our new approach
to determining the average emission measure, we use the observations
to quantify the first ionization potential effect on the coronal
abundances of the emitting elements. We present the results of this
analysis and compare our conclusions with those of previous works.
---------------------------------------------------------
Title: Electron-Impact Ionization of Be-like C III, N IV, and O V
Authors: Fogle, M.; Bahati, E. M.; Bannister, M. E.; Vane, C. R.; Loch,
S. D.; Pindzola, M. S.; Ballance, C. P.; Thomas, R. D.; Zhaunerchyk,
V.; Bryans, P.; Mitthumsiri, W.; Savin, D. W.
2008ApJS..175..543F Altcode:
We present recent measurements of absolute electron-impact ionization
cross sections for Be-like C III, N IV, and O V forming Li-like C IV,
N V, and O VI. The measurements were taken using the crossed-beams
apparatus at Oak Ridge National Laboratory. A gas cell beam attenuation
method was used to independently measure the metastable fractions
present in the ion beams. The measured ionization cross sections were
compared with calculations using the R-matrix with pseudostates and
distorted-wave theoretical methods. Best agreement is found with the
R-matrix with pseudostates cross sections results that account for the
metastable fractions inferred from the gas attenuation measurements. We
present a set of recommended rate coefficients for electron-impact
single ionization from the ground state and metastable term of each ion.
---------------------------------------------------------
Title: The Status of Collisional Ionization Equilibrium Calculations
and a New Approach to Emission Measure Determinations
Authors: Bryans, Paul; Laming, J. M.; Landi, E.; Savin, D. W.
2008HEAD...10.1313B Altcode:
We have calculated improved collisional ionization equilibrium (CIE)
fractional abundances using state-of-the-art dielectronic recombination
(DR) and radiative recombination (RR) rate coefficients for K-shell,
L-shell, Na-like, and Mg-like ions of all elements from H through Zn and
M-shell ions of Fe. These data have been compared with other published
state-of-the-art DR and RR data and found to agree within 35% and 10%,
respectively, in the temperature range where the ion forms in CIE. Where
DR measurements exist, theory and experiment agree to within 35% in this
temperature range. We have also investigated recent improvements to
the recommended electron impact ionization rate coefficient database,
concluding that differences of up to a factor of 5 between recent
compilations implies that significant additional experimental and
theoretical work is required. Using our new CIE calculations we
have re-analyzed solar coronal observations of an isothermal parcel
of coronal gas. We have also developed a mathematically rigorous
method for determining the average emission measure and temperature
of the emitting plasma. Using our new CIE data and our new approach
to determining the average emission measure, we use the observations
to quantify the first ionization potential effect on the coronal
abundances of the emitting elements. We present the results of this
analysis and compare our conclusions with those of previous works.
---------------------------------------------------------
Title: Implications for Atomic Physics from New Ionization Balance
Calculations and Solar Physics Observations
Authors: Bryans, Paul; Landi, Enrico; Savin, Daniel
2007APS..DMP.R1107B Altcode:
We have used state-of-the-art electron-ion recombination data
for K-shell, L-shell, and Na-like ions of H through Zn to calculate
improved collisional ionization equilibrium (CIE) fractional abundances
for ions of all these elements. We present the implications of these
new CIE results for observations of the solar atmosphere and discuss
a number of atomic systems showing puzzling discrepancies between
observations and solar models. These discrepancies suggest errors in
the underlying atomic data. Based on this, we highlight those atomic
processes that require improved theoretical or experimentally-derived
rate coefficients.
---------------------------------------------------------
Title: Collisional Ionization Equilibrium for Optically Thin
Plasmas. I. Updated Recombination Rate Coefficients for Bare through
Sodium-like Ions
Authors: Bryans, P.; Badnell, N. R.; Gorczyca, T. W.; Laming, J. M.;
Mitthumsiri, W.; Savin, D. W.
2006ApJS..167..343B Altcode: 2006astro.ph..4363B
Reliably interpreting spectra from electron-ionized cosmic plasmas
requires accurate ionization balance calculations for the plasma in
question. However, much of the atomic data needed for these calculations
have not been generated using modern theoretical methods and are often
highly suspect. This translates directly into the reliability of the
collisional ionization equilibrium (CIE) calculations. We make use
of state-of-the-art calculations of dielectronic recombination (DR)
rate coefficients for the hydrogenic through Na-like ions of all
elements from He up to and including Zn. Where measurements exist,
these published theoretical DR data agree with recent laboratory work
to within typically 35% or better at the temperatures relevant for
CIE. We also make use of state-of-the-art radiative recombination
(RR) rate coefficient calculations for the bare through Na-like ions
of all elements from H through to Zn. Here we present improved CIE
calculations for temperatures from 10<SUP>4</SUP> to 10<SUP>9</SUP>
K using our data and the recommended electron impact ionization data
of Mazzotta et al. for elements up to and including Ni and Mazzotta
for Cu and Zn. DR and RR data for ionization stages that have not
been updated are also taken from these two additional sources. We
compare our calculated fractional ionic abundances using these data
with those presented by Mazzotta et al. for all elements from H to
Ni. The differences in peak fractional abundance are up to 60%. We
also compare with the fractional ionic abundances for Mg, Si, S, Ar,
Ca, Fe, and Ni derived from the modern DR calculations of Gu for the
H-like through Na-like ions, and the RR calculations of Gu for the bare
through F-like ions. These results are in better agreement with our
work, with differences in peak fractional abundance of less than 10%.
---------------------------------------------------------
Title: Updated Ionization Balance Calculations for Collisionally
Ionized Plasmas
Authors: Bryans, Paul; Badnell, N. R.; Gorczcya, T. W.; Laming, J. M.;
Mitthumsiri, W.; Savin, D. W.
2006HEAD....9.1835B Altcode: 2006BAAS...38R.387B
Reliably interpreting spectra from electron-ionized cosmic plasmas
requires accurate ionization balance calculations for the plasma
in question. However, much of the atomic data needed for these
calculations have not been generated using modern theoretical methods
and their reliability are often highly suspect. We have carried out
state-of-the-art calculations of dielectronic recombination (DR)
rate coefficients for the hydrogenic through Na-like ions of all
elements from He to Zn. We have also carried out state-of-the-art
radiative recombination (RR) rate coefficient calculations for the
bare through Na-like ions of all elements from H to Zn. Using our data
and the recommended electron impact ionization data of [1], we present
improved collisional ionization equilibrium calculations. We compare
our <P />calculated fractional ionic abundances using these data with
those presented <P />by [1] for all elements from H to Ni, and with the
fractional abundances derived from the modern DR and RR calculations of
[2] for Mg, Si, S, Ar, Ca, Fe, and Ni. <P />[1] Mazzotta, P. et al.,
1998, A&AS, 133, 403 <P />[2] Gu, M. F., 2003a, ApJ, 590, 1131;
2003b, 589, 1085; 2004, 153, 389 <P />This work is supported in part
by NASA.
---------------------------------------------------------
Title: Updated Coronal Equilibrium Calculations
Authors: Bryans, Paul; Badnell, N. R.; Gorczyca, T. W.; Laming, J. M.;
Mitthumsiri, W.; Savin, D. W.
2006SPD....37.0101B Altcode: 2006BAAS...38..215B
Reliably interpreting solar spectra requires accurate ionization
balance calculations. However, much of the atomic data needed for
these calculations have not been generated using modern theoretical
methods and are often highly suspect. This translates directly
into the reliability of the collisional ionization equilibrium
(CIE) calculations. We make use of state-of-the-art calculations of
dielectronic recombination (DR) rate coefficients for the hydrogenic
through Na-like ions of all elements from He through to Zn. We
also make use of state-of-the-art radiative recombination (RR)
rate coefficient calculations for the bar e through Na-like ions of
all elements from H to Zn. Here we present improved CIE calculations
for temperatures from 1e4 to 1e9 K using our data and the recommended
electron impact ionization data of Mazzotta et al. (1998, A&AS, 133,
403) for elements up through Ni and Mazzotta (private communication)
for Cu and Zn. DR and RR data for ionization stages that have not
been updated are also taken from these two additional sources. We
compare our calculated fractional ionic abundances using these data
with those presented by Mazzotta et al. for all elements from H to
Ni. The differences in peak fractional abundance are up to 60%. We
also compare with the fractional ionic abundances for Mg, Si, S, Ar,
Ca, Fe, and Ni derived from the modern DR calculations of Gu (2003a,
ApJ, 590, 1131; 2004, ApJ, 153, 389) for the H-like through Na-like
ions, and the RR calculations of Gu (2003b, ApJ, 589, 1085) for the
bare through F-like ions. These results are in better agreement with
our work, with differences in peak fractional abundance of less than
10%. <P />This work was supported in part by the NASA Solar SR&T
and LWS programs, theOffice of Naval Research, and PPARC.
---------------------------------------------------------
Title: A Plasma Mechanism explaining the Asymmetric X-ray Emission
from the Supernova
Authors: Kellett, B. J.; Bingham, R.; Bryans, P.; Torney, M.; Summers,
H.; Shapiro, V.; Spicer, Ds
2006sgrb.confE..31K Altcode:
The interaction of the expanding shock from a supernova explosion
with thesurrounding environment is a powerful source of radiation in
variousspectral bands at different stages in the development of the
supernovaremnant. Studying the X-rays generated by such objects is
therefore likelyto reveal details of these on going interactions. For
example, the X-rayemission from the relatively old supernova remnant
PKS1209-52 is highlyasymmetric - 75% of the total emission arises from
the eastern side of theshock. We describe a possible model that can
explain this extra emissionfrom the eastern lobe of the remnant as
resulting from a recent encounterbetween the shock front and a small,
dense, interstellar cloud. Theparticular mechanism is a plasma streaming
instability known as themodified two-stream instability. The presence
of the cloud makes itpossible to extract some of the kinetic energy
of the shock wave andconvert this into X-ray emission via high-energy
electrons generated fromlower hybrid waves in the plasma interaction
region. We have carried out2-D fluid simulation of the interaction
which agrees very well with theobserved geometry of the source. Finally,
the neutron star remnant of theoriginal supernova explosion is seen to
generate cyclotron absorptionfeatures in its X-ray emission spectrum
that reveal the detailed dynamicsof the magnetic field of the neutron
star itself. Planned laboratoryexperiments to study the results will
be outlined.
---------------------------------------------------------
Title: Collisional Ionization Equilibrium for Optically Thin Plasmas
Authors: Bryans, P.; Mitthumsiri, W.; Savin, D. W.; Badnell, N. R.;
Gorczyca, T. W.; Laming, J. M.
2006nla..conf..166B Altcode:
Reliably interpreting spectra from electron-ionized cosmic plasmas
requires accurate ionization balance calculations for the plasma in
question. However, much of the atomic data needed for these calculations
have not been generated using modern theoretical methods and their
reliability are often highly suspect. We have utilized state-of-the-art
calculations of dielectronic recombination (DR) rate coefficients
for the hydrogenic through Na-like ions of all elements from He to
Zn. We have also utilized state-of-the-art radiative recombination
(RR) rate coefficient calculations for the bare through Na-like ions
of all elements from H to Zn. Using our data and the recommended
electron impact ionization data of tet{Mazz98a}, we have calculated
improved collisional ionization equilibrium calculations. We compare
our calculated fractional ionic abundances using these data with those
presented by tet{Mazz98a} for all elements from H to Ni, and with the
fractional abundances derived from the modern DR and RR calculations
of tet{Gu03a,Gu03b,Gu04a} for Mg, Si, S, Ar, Ca, Fe, and Ni.
---------------------------------------------------------
Title: Evidence for explosive event activity originating in the
chromosphere
Authors: Doyle, J. G.; Ishak, B.; Ugarte-Urra, I.; Bryans, P.; Summers,
H. P.
2005A&A...439.1183D Altcode:
We report on a joint SUMER, CDS, TRACE study, concentrating on
a region which shows prolonged EUV explosive event (EE) activity
in the transition region line N v 1238 Å, yet little evidence of
such activity in another transition region line O v 629 Å (formed
at a similar temperature) which was observed simultaneously. A
possible explanation for the lack of major activity in the O v line
in several explosive events could be that they originate in the lower
chromosphere. This is consistent with the enhancements in the C i 1249
Å line and with the findings of another study which reported time
delays between the chromospheric and transition region lines in some
EE's using high cadence observations (10 s exposure time) obtained
with the SUMER spectrometer in H i Ly 6 (20 000 K) and S vi (200 000
K). Using the generalized collisional-radiative picture, including
the population of metastable levels, we derive the density dependent
contribution function for both N v 1238 and O v 629 for four values
of the electron density; 10<SUP>6</SUP> cm<SUP>-3</SUP> representing
the low density limit, 10<SUP>9</SUP> cm<SUP>-3</SUP> for a typical
quiet Sun electron density plus 10<SUP>11</SUP> cm<SUP>-3</SUP> and
10<SUP>12</SUP> cm<SUP>-3</SUP> for an active region. These calculations
show that with increasing electron density, both lines shift to slightly
lower temperatures. However, the major difference is in the relative
increase in the line flux with increasing density. For N v, increasing
the density to 10<SUP>11</SUP> cm<SUP>-3</SUP> results in a 60%
increase in the line flux, while O v shows a 30% decrease. Increasing
the electron density to 10<SUP>12</SUP> cm<SUP>-3</SUP> results in a
factor of two decrease in the O v flux, thus making it difficult to
detect explosive event activity in this line if the event is formed
in the chromosphere. Other explosive events which show simultaneous
activity in both lines are probably formed in the transition region. In
one such event, activity is observed in both N v and O v, yet nothing
in C i. In this event we also observe an increase in the TRACE 173
emission, delayed by ≈40 s compared to the transition region lines.
---------------------------------------------------------
Title: X-Ray Emission from Comets and Nonmagnetic Planets. Theory
and Comparison with CHANDRA Observations
Authors: Shapiro, V. D.; Bingham, R.; Kellett, B. J.; Quest, K.;
Mendis, D. A.; Bryans, P.; Torney, M.; Summers, H. P.
2005PhST..116...83S Altcode:
Mass loading of the solar wind by newly created cometary photoions as
well as counterstreaming fluxes of protons in the mantle regions at
the ionospheric boundaries of nonmagnetic planets Mars, Venus result in
the modified two stream instability MTSI and excitation of the intense
lower hybrid wave turbulence. Electrons are efficiently energized by
these waves in the magnetic field aligned direction up to KeV energies
confirmed by in situ observations and interacting with cometary
or planetary atmospheres producing X-Ray emission by combination
of Bremsstrahlung and line K-shell radiation. Analytical study of
the nonlinear evolution of MTSI as well as numerical simulations
of instability development in the mantle regions of nonmagnetic
planets has been performed and it basically confirms the scenario of
electron acceleration. Using the above described mechanism of X-ray
emission produced in impacts of energetic electrons with ions and
neutrals we employed ADAS atomic data code to analyze X-ray spectrum
emitted by comet Linear and obtained a good fit with recent CHANDRA
observations. The theoretical model also predicts strong x-ray emission
from nonmagnetic planets such as Mars and Venus.
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Title: The effect of metastable level populations on the ionization
fraction of Li-like ions
Authors: Doyle, J. G.; Summers, H. P.; Bryans, P.
2005A&A...430L..29D Altcode:
Lines from Li-like ions have been known to produce theoretical
intensities under-estimated compared to lines of a similar formation
temperature. Here we investigate this anomalous behaviour whereby the
ionization fractions are calculated using the ADAS code considering
the electron density dependence of dielectronic recombination coupled
with collisional ionization from metastable levels. For the lines
investigated, the line contribution functions show a clear dependence
with increasing electron density. For example, C IV 1548 Å shows
over a factor of three enhancement for N<SUB>e</SUB> = 10<SUP>12</SUP>
cm<SUP>-3</SUP>. The increase in the higher temperature lines is lower,
but are still in the range of 30 to 60%. Furthermore, all the lines have
their peak contribution shifted to lower temperature. Calculating the
total radiative power output at an electron density of 10<SUP>11</SUP>
cm<SUP>-3</SUP>, we find that the difference in the transition region
is 10-15% while above 10<SUP>6</SUP> K the difference is around 30%
compared to the low density value.
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Title: A New Mechanism Explaining the Asymmetric X-Ray Emission from
Supernova Remnant PKS 1209-52
Authors: Bingham, R.; Kellett, B. J.; Bryans, P.; Summers, H. P.;
Torney, M.; Shapiro, V. D.; Spicer, D. S.; O'Brien, M.
2004ApJ...601..896B Altcode:
The interaction of a supernova remnant with its surrounding environment
is a powerful source of radiation in various spectral regions and at
different stages in its development. The study of these emissions can
therefore help to investigate the interstellar medium surrounding a
supernova. For example, the highly asymmetric X-ray emission from PKS
1209-52 has previously been described as resulting from the supernova
shock front on the eastern side of the remnant interacting with a small,
dense interstellar cloud (or cloud core). In this paper we describe a
possible mechanism through which the kinetic energy of the expanding
shock is converted to energetic electrons. The particular interaction
is a plasma streaming instability known as the modified two-stream
instability that creates plasma waves in the lower hybrid frequency
range that can then go on to accelerate electrons to high energy. A
Fokker-Planck equation describing the diffusion of the electrons
to high energies by lower hybrid waves is solved for both Gaussian
and Lorentzian wave spectral distributions. We also simulate the
interaction between the supernova remnant with the dense interstellar
cloud using a two-dimensional fluid code. The nonthermal electrons
can then generate X-ray emission via bremsstrahlung and also line
radiation through interactions with the ambient medium. The maximum
energy of these electrons is limited to the few keV energy range and
therefore does not lead to any synchrotron radio emission that would
otherwise lead to a radio asymmetry in the remnant that is not seen.
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Title: X-ray Emission From Planets Venus and Mars: Theoretical Model
and Numerical Simulations
Authors: Bryans, P.; Quest, K. B.; Shapiro, V. D.; Bingham, R.;
Tourner, M.
2003AGUFMSM31C1122B Altcode:
Recently X-ray emission from non-magnetic planets Venus and Mars
have been discovered by Chandra X-ray telescopes [1,2]. Analysis
of observational data shows that either charge exchange model or
fluorescent scattering of solar x-rays cannot explain the whole
set of observational data. The premise of this paper is that x-ray
emission of both planets is a combination of line k-shell radiation
and Bremmstrahlung produced by energetic electrons interacting
with planetary atmospheres. Due to the absence of their planetary
magnetospheres, planetary bow shocks are located quite close to the
ionospheres and on both planets their ionospheres are directly exposed
to the shocked solar wind flow. In situ observations revealed the
existence at the ionospheric boundaries of strongly turbulent layer --
the so-called plasma mantle. Previous hybrid simulations (kinetic ions
and hydro dynamical electrons) have shown that mantle turbulence is
produced by interaction of counterstreaming ion populations of the solar
wind and planetary ionospheres. Recently developed particle in cell
(fully kinetic) code demonstrated that mantle turbulence is responsible
for electron acceleration in an agreement with in-situ observations
that revealed the presence in mantle electrons with energies up to
several hundred eV.[3] In the present paper we incorporated energetic
electron distribution obtained by numerical simulations into ADAS
code [4] and compared results with observations. <P />1. K. Dennerl
et.al. A&A 286, 319 (2002). 2. K. Dennerl, A&A 394, 1119-1128
(2002). 3. K. Szego et.al. J6R 112, 2175 (1997) 4. http: adas.phystretch
ac.uk
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Title: X-ray Emission from Planets Venus and Mars. Theoretical Model
and Numerical Simulations.
Authors: Bryans, Paul; Quest, Kevin; Shapiro, Vitali; Bingham, Robert;
Torney, Martin
2003APS..DPPGP1136B Altcode:
Recently X-ray emission from non-magnetic planets Venus and Mars
have been discovered by Chandra X-ray telescopes [1,2]. Analysis
of observational data shows that either charge exchange model or
fluorescent scattering of solar x-rays cannot explain the whole
set of observational data. The premise of this paper is that x-ray
emission of both planets is a combination of line k-shell radiation
and Bremmstrahlung produced by energetic electrons interacting
with planetary atmospheres. Due to the absence of their planetary
magnetospheres, planetary bow shocks are located quite close to the
ionospheres and on both planets their ionospheres are directly exposed
to the shocked solar wind flow. In situ observations revealed the
existence at the ionospheric boundaries of strongly turbulent layer --
the so-called plasma mantle. Previous hybrid simulations (kinetic ions
and hydro dynamical electrons) have shown that mantle turbulence is
produced by interaction of counterstreaming ion populations of the solar
wind and planetary ionospheres. Recently developed particle in cell
(fully kinetic) code deomonstrated that mantle turbulence is responsible
for electron acceleration in an agreement with in-situ observations
that revealed the presence in mantle electrons with energies up to
several hundred eV.[3] In the present paper we incorporated energetic
electron distribution obtained by numerical simulations into ADAS code
and compared results with observations. 1. K. Dennerl et. al. A, 286,
319 (2002) 2. K. Dennerl et. al. A, 394, 1119-1128 (2002 3. K. Szego
et. al., JGR, 112, 2175 (1997) 4. http: adas.phystretch ac.uk
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Title: A Plasma Mechanism Explaining the Asymmetric X-ray Emission
from the Supernova Remnant PKS1209-52.
Authors: Kellett, Barry; Bingham, Robert; Bryans, Paul; Torney,
Martin; Summers, Hugh; Shapiro, Vitali; Spicer, Daniel
2003APS..DPPGP1149K Altcode:
The interaction of the expanding shock from a supernova explosion with
the surrounding environment is a powerful source of radiation in various
spectral bands at different stages in the development of the supernova
remnant. Studying the X-rays generated by such objects is therefore
likely to reveal details of these on going interactions. For example,
the X-ray emission from the relatively old supernova remnant PKS1209-52
is highly asymmetric - 75arises from the eastern side of the shock. We
describe a possible model that can explain this extra emission from
the eastern lobe of the remnant as resulting from a recent encounter
between the shock front and a small, dense, interstellar cloud. The
particular mechanism is a plasma streaming instability known as the
modified two-stream instability. The presence of the cloud makes it
possible to extract some of the kinetic energy of the shock wave and
convert this into X-ray emission via high-energy electrons generated
from lower hybrid waves in the plasma interaction region. We have
carried out 2-D fluid simulation of the interaction which agree very
well with the observed geometry of the source. Finally, the neutron
star remnant of the original supernova explosion is seen to generate
cyclotron absorption features in its X-ray emission spectrum that reveal
the detailed dynamics of the magnetic field of the neutron star itself.
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Title: Coronal dimming and the coronal mass ejection onset
Authors: Harrison, R. A.; Bryans, P.; Simnett, G. M.; Lyons, M.
2003A&A...400.1071H Altcode:
A set of five observations of extreme-ultraviolet (EUV) coronal dimming
associated with coronal mass ejection (CME) activity is examined. Using
spectroscopic data, plasma characteristics across a broad range of
temperatures from 20 000 K to 2 million K are determined. The dimming
events are found to coincide in time, and to coincide spatially, with
the projected onset times and locations of the associated CMEs. The
spectral data confirm that the dimming is due to mass-loss, and not
temperature variations. The actual mass-loss calculated from the degree
of dimming, using two different methods, shows that the extracted
mass in each case, is of the same order as the mass of the associated
CME. In some cases, the EUV observations are limited to relatively small
regions under the CME events and it is expected that we do not witness
the mass-loss associated with the entire event, for these. However,
we believe that this analysis has provided a method for locating the
source region of the trigger for a CME eruption, and that the dimming
characteristics can be used to distinguish between onset processes of
the CME. In particular, the gradual nature of the dimming process,
which takes place over several hours, suggests that either the CME
has a continuous driver rather than a sudden impulsive onset, or the
low coronal response to a CME extends over a long period.
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Title: EUV Sprays: Jet-like eruptive activity on the solar limb
Authors: Harrison, R. A.; Bryans, P.; Bingham, R.
2001A&A...379..324H Altcode:
Jet-like eruptive events have been detected in the extreme ultraviolet
(EUV) observations from the Solar and Heliospheric Observatory
(SOHO) spacecraft. Some jet-like events are shown and for one event,
that of January 22 2000, we provide a detailed analysis of the EUV
observations. The January 22 observation was part of an on-going
campaign to observe the onset of coronal mass ejections (CMEs) using
extreme ultraviolet spectroscopy. A high-temperature fan-like jet
was first detected in emission lines from plasmas at one million K
and over, and it appears to be the onset of a narrow mass ejection
identified later in coronagraph data. This was followed by a dramatic
jet or finger of cool (<=250 000 K), rotating plasma which extended
vertically, high into the corona. It extended well beyond the field of
view of the instrument and appears to relate to a small ejected cloud
which is detected in subsequent coronagraph data. The spectroscopic
characteristics are used to provide plasma diagnostic information for
these two events, and this combined with images for a wide range of
temperatures allows a thorough investigation of the processes leading
to such eruptions. A simple accreting magnetic field model is used to
descibe the basic features of the jet activity.