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Author name code: fontenla
ADS astronomy entries on 2022-09-14
author:"Fontenla, Juan"
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Title: Bright Network, UVA, and the Physical Modeling of Solar
Spectral and Total Irradiance in Recent Solar Cycles
Authors: Fontenla, J. M.; Landi, E.
2018ApJ...861..120F Altcode:
In this paper we study the total solar irradiance (TSI) and the spectral
solar irradiance (SSI) by applying the solar disk image decomposition
algorithm (SDIDA) and solar irradiance synthesis algorithm (SISA)
methods. These methods were applied to space-based observations in
previous works, but in this work, they are applied to ground-based
observations from various observatories, which allows for a long-term
determination of TSI and SSI. We discuss the results of the SDIDA
and SISA methods for the areas of solar features and the synthesized
TSI and SSI. We find that SDIDA decompositions based on Ca II K line
images from various sources are all in good agreement between them
and with previous space results when cross-calibration is performed,
and consequently yield essentially the same TSI and SSI when SISA
is applied. This paper shows the synthesized TSI and SSI, as well
as the contributions from various feature types, during the recent
solar cycles 23 and 24 and suggest further work can provide historical
extended coverage using archival ground-based observations. The results
demonstrate the presence of a significant variable bright network
contribution during the cycle maximum, and of a reduced one at solar
minimum, and that such a presence and variability affect both the SSI
and TSI. We also find that all activity features are loosely correlated
over solar cycle variations, but this correlation is nonlinear, and we
show differences between cycles 23 and 24. Furthermore, we find that
the SISA method can be successfully applied to determine the TSI and SSI
for any particular state of the solar disk, and that the results depend
not only on the total areas on the disk for each feature, but also on
the relative distances from disk center of the active region features.
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Title: Solar cycle variations in mesospheric carbon monoxide
Authors: Lee, Jae N.; Wu, Dong L.; Ruzmaikin, Alexander; Fontenla, Juan
2018JASTP.170...21L Altcode:
As an extension of Lee et al. (2013), solar cycle variation of carbon
monoxide (CO) is analyzed with MLS observation, which covers more
than thirteen years (2004-2017) including maximum of solar cycle
24. Being produced primarily by the carbon dioxide (CO<SUB>2</SUB>)
photolysis in the lower thermosphere, the variations of the mesospheric
CO concentration are largely driven by the solar cycle modulated
ultraviolet (UV) variation. This solar signal extends down to the
lower altitudes by the dynamical descent in the winter polar vortex,
showing a time lag that is consistent with the average descent
velocity. To characterize a global distribution of the solar impact,
MLS CO is correlated with the SORCE measured total solar irradiance
(TSI) and UV. As high as 0.8 in most of the polar mesosphere, the
linear correlation coefficients between CO and UV/TSI are more
robust than those found in the previous work. The photochemical
contribution explains most (68%) of the total variance of CO while the
dynamical contribution accounts for 21% of the total variance at upper
mesosphere. The photochemistry driven CO anomaly signal is extended
in the tropics by vertical mixing. The solar cycle signal in CO is
further examined with the Whole Atmosphere Community Climate Model
(WACCM) 3.5 simulation by implementing two different modeled Spectral
Solar Irradiances (SSIs): SRPM 2012 and NRLSSI. The model simulations
underestimate the mean CO amount and solar cycle variations of CO, by a
factor of 3, compared to those obtained from MLS observation. Different
inputs of the solar spectrum have small impacts on CO variation.
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Title: Effects of Ion Magnetization on the Farley-Buneman Instability
in the Solar Chromosphere
Authors: Fletcher, Alex C.; Dimant, Yakov S.; Oppenheim, Meers M.;
Fontenla, Juan M.
2018ApJ...857..129F Altcode:
Intense heating in the quiet-Sun chromosphere raises the temperature
from 4000 to 6500 K but, despite decades of study, the underlying
mechanism remains a mystery. This study continues to explore the
possibility that the Farley-Buneman instability contributes to
chromospheric heating. This instability occurs in weakly ionized
collisional plasmas in which electrons are magnetized, but ions are
not. A mixture of metal ions generate the plasma density in the coolest
parts of the chromosphere; while some ions are weakly magnetized,
others are demagnetized by neutral collisions. This paper incorporates
the effects of multiple, arbitrarily magnetized species of ions to the
theory of the Farley-Buneman instability and examines the ramifications
on instability in the chromosphere. The inclusion of magnetized ions
introduces new restrictions on the regions in which the instability
can occur in the chromosphere—in fact, it confines the instability to
the regions in which heating is observed. For a magnetic field of 30 G,
the minimum ambient electric field capable of driving the instability
is 13.5 V/m at the temperature minimum.
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Title: Solar Cycle Variations as Observed by MLS Carbon Monoxide
Authors: Lee, J. N.; Wu, D. L.; Ruzmaikin, A.; Fontenla, J. M.
2017AGUFMSH43B2813L Altcode:
More than thirteen years (2004-2017) of carbon monoxide (CO)
measurements from the Aura Microwave Limb Sounder (MLS) are analyzed
to better understand impacts of solar cycle 24. The upper mesospheric
CO, produced primarily by the carbon dioxide (CO2) photolysis in the
lower thermosphere, is sensitive to solar irradiance variability. We
find that interannual variations of the mesospheric CO concentration
are largely driven by the solar-cycle modulated ultraviolet (UV)
variation in most of the UV wavelengths (120 to 280 nm) in high
latitude regions. Despite different mean CO abundances in the SH and
NH winters, their solar-cycle dependence appears to be symmetric with
respect to the winter pole. This solar signal extends down to the
lower altitudes by the dynamical descent in the polar vortex, showing
a time lag that is consistent with the average descent velocity. To
characterize a global distribution of the solar influence, Aura MLS CO
is correlated with the Solar Radiation and Climate Experiment (SORCE)
Total Irradiance Monitor (TIM) measured total solar irradiance (TSI)
and with the SORCE Solar-Stellar Irradiance Comparison Experiment
(SOLSTICE) measured UV. As high as 0.8 in most of the polar mesosphere,
the linear correlation coefficients between CO and UV/TSI are more
robust than those found in the previous work, with the extended
analysis period. Different from the result shown in Lee et al. (2013),
the downward propagation of the solar signals is similar in both NH
and SH high latitudes. Effects of solar forcing on mesospheric CO
extend far beyond the polar region. CO is a good tracer to show that
the solar induced CO anomaly seems to follow the global meridional
residual circulation and hemispheric transition from pole to pole in
every six months. WACCM simulation experiment with two different solar
spectral irradiance models, SRPM (Solar Radiation Physical Modeling)
2012 and NRLSSI (Naval Research Laboratory Spectral Solar Irradiance),
shows that the modeled CO variability in the mesosphere over a solar
cycle is weaker by a factor of three than that shown from MLS CO
observation. Two different model inputs for the solar spectrum have
small impacts, not enough to explain the large discrepancy with the
observation. Lacks of strength and variability of the mean meridional
circulation in the model, instead of the model photochemistry, most
likely cause the weak CO variability in the mesosphere.
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Title: Five Years of Synthesis of Solar Spectral Irradiance from
SDID/SISA and SDO/AIA Images
Authors: Fontenla, J. M.; Codrescu, M.; Fedrizzi, M.; Fuller-Rowell,
T.; Hill, F.; Landi, E.; Woods, T.
2017ApJ...834...54F Altcode:
In this paper we describe the synthetic solar spectral irradiance (SSI)
calculated from 2010 to 2015 using data from the Atmospheric Imaging
Assembly (AIA) instrument, on board the Solar Dynamics Observatory
spacecraft. We used the algorithms for solar disk image decomposition
(SDID) and the spectral irradiance synthesis algorithm (SISA) that
we had developed over several years. The SDID algorithm decomposes
the images of the solar disk into areas occupied by nine types of
chromospheric and 5 types of coronal physical structures. With this
decomposition and a set of pre-computed angle-dependent spectra for
each of the features, the SISA algorithm is used to calculate the
SSI. We discuss the application of the basic SDID/SISA algorithm to a
subset of the AIA images and the observed variation occurring in the
2010-2015 period of the relative areas of the solar disk covered by the
various solar surface features. Our results consist of the SSI and total
solar irradiance variations over the 2010-2015 period. The SSI results
include soft X-ray, ultraviolet, visible, infrared, and far-infrared
observations and can be used for studies of the solar radiative forcing
of the Earth’s atmosphere. These SSI estimates were used to drive
a thermosphere-ionosphere physical simulation model. Predictions of
neutral mass density at low Earth orbit altitudes in the thermosphere
and peak plasma densities at mid-latitudes are in reasonable agreement
with the observations. The correlation between the simulation results
and the observations was consistently better when fluxes computed by
SDID/SISA procedures were used.
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Title: Semi-empirical Modeling of the Photosphere, Chromosphere,
Transition Region, and Corona of the M-dwarf Host Star GJ 832
Authors: Fontenla, J. M.; Linsky, Jeffrey L.; Witbrod, Jesse; France,
Kevin; Buccino, A.; Mauas, Pablo; Vieytes, Mariela; Walkowicz,
Lucianne M.
2016ApJ...830..154F Altcode:
Stellar radiation from X-rays to the visible provides the energy
that controls the photochemistry and mass loss from exoplanet
atmospheres. The important extreme ultraviolet (EUV) region (10-91.2
nm) is inaccessible and should be computed from a reliable stellar
model. It is essential to understand the formation regions and
physical processes responsible for the various stellar emission
features to predict how the spectral energy distribution varies with
age and activity levels. We compute a state-of-the-art semi-empirical
atmospheric model and the emergent high-resolution synthetic spectrum
of the moderately active M2 V star GJ 832 as the first of a series
of models for stars with different activity levels. We construct
a one-dimensional simple model for the physical structure of the
star’s chromosphere, chromosphere-corona transition region, and
corona using non-LTE radiative transfer techniques and many molecular
lines. The synthesized spectrum for this model fits the continuum
and lines across the UV-to-optical spectrum. Particular emphasis is
given to the emission lines at wavelengths that are shorter than 300 nm
observed with the Hubble Space Telescope, which have important effects
on the photochemistry of the exoplanet atmospheres. The FUV line ratios
indicate that the transition region of GJ 832 is more biased to hotter
material than that of the quiet Sun. The excellent agreement of our
computed EUV luminosity with that obtained by two other techniques
indicates that our model predicts reliable EUV emission from GJ 832. We
find that the unobserved EUV flux of GJ 832, which heats the outer
atmospheres of exoplanets and drives their mass loss, is comparable
to the active Sun. <P />Based on observations made with the NASA/ESA
Hubble Space Telescope obtained from the Data Archive at the Space
Telescope Science Institute, which is operated by the Association of
Universities for Research in Astronomy, Inc., under NASA contract NAS
AR-09525.01A. These observations are associated with programs #12034,
12035, 12464.
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Title: Photoelectrons and solar ionizing radiation at Mars:
Predictions versus MAVEN observations
Authors: Peterson, W. K.; Thiemann, E. M. B.; Eparvier, Francis G.;
Andersson, Laila; Fowler, C. M.; Larson, Davin; Mitchell, Dave;
Mazelle, Christian; Fontenla, Juan; Evans, J. Scott; Xu, Shaosui;
Liemohn, Mike; Bougher, Stephen; Sakai, Shotaro; Cravens, T. E.;
Elrod, M. K.; Benna, M.; Mahaffy, P.; Jakosky, Bruce
2016JGRA..121.8859P Altcode:
Understanding the evolution of the Martian atmosphere requires
knowledge of processes transforming solar irradiance into thermal
energy well enough to model them accurately. Here we compare Martian
photoelectron energy spectra measured at periapsis by Mars Atmosphere
and Volatile Evolution MissioN (MAVEN) with calculations made using
three photoelectron production codes and three solar irradiance
models as well as modeled and measured CO<SUB>2</SUB> densities. We
restricted our comparisons to regions where the contribution from
solar wind electrons and ions were negligible. The two intervals
examined on 19 October 2014 have different observed incident solar
irradiance spectra. In spite of the differences in photoionization
cross sections and irradiance spectra used, we find the agreement
between models to be within the combined uncertainties associated
with the observations from the MAVEN neutral density, electron flux,
and solar irradiance instruments.
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Title: Semi-empirical Modeling of the Photosphere, Chromosphere,
Transition Region, and Corona of the M-dwarf Host Star GJ 832
Authors: Fontenla, J. M.; Linsky, Jeffrey L.; Witbrod, Jesse;
France, Kevin; Buccino, A.; Mauas, Pablo; Vietes, Mariela; Walkowicz,
Lucianne M.
2016arXiv160800934F Altcode:
Stellar radiation from X-rays to the visible provides the energy
that controls the photochemistry and mass loss from exoplanet
atmospheres. The important extreme ultraviolet (EUV) region
(10--91.2~nm) is inaccessible and should be computed from a reliable
stellar model. It is essential to understand the formation regions and
physical processes responsible for the various stellar emission features
in order to predict how the spectral energy distribution varies with
age and activity levels. We compute a state-of-the-art semi-empirical
atmospheric model and the emergent high-resolution synthetic spectrum
of the moderately active M2~V star GJ~832 as the first of a series
of models for stars with different activity levels. Using non-LTE
radiative transfer techniques and including many molecular lines, we
construct a one-dimensional simple model for the physical structure
of the star's chromosphere, chromosphere-corona transition region, and
corona. The synthesized spectrum for this model fits the continuum and
lines across the UV to optical spectrum. Particular emphasis is given
to the emission lines at wavelengths shorter than 300~nm observed
with {\em HST}, which have important effects on the photochemistry
in the exoplanet atmospheres. The FUV line ratios indicate that the
transition region of GJ~832 is more biased to hotter material than
that of the quiet Sun. The excellent agreement of our computed EUV
luminosity with that obtained by two other techniques indicates that
our model predicts reliable EUV emission from GJ~832. We find that
unobserved EUV flux of GJ~832, which heats the outer atmospheres of
exoplanets and drives their mass loss, is comparable to the active Sun.
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Title: Electron energetics in the Martian dayside ionosphere: Model
comparisons with MAVEN data
Authors: Sakai, Shotaro; Andersson, Laila; Cravens, Thomas E.;
Mitchell, David L.; Mazelle, Christian; Rahmati, Ali; Fowler,
Christopher M.; Bougher, Stephen W.; Thiemann, Edward M. B.; Eparvier,
Francis G.; Fontenla, Juan M.; Mahaffy, Paul R.; Connerney, John E. P.;
Jakosky, Bruce M.
2016JGRA..121.7049S Altcode:
This paper presents a study of the energetics of the dayside ionosphere
of Mars using models and data from several instruments on board the
Mars Atmosphere and Volatile EvolutioN spacecraft. In particular,
calculated photoelectron fluxes are compared with suprathermal electron
fluxes measured by the Solar Wind Electron Analyzer, and calculated
electron temperatures are compared with temperatures measured by the
Langmuir Probe and Waves experiment. The major heat source for the
thermal electrons is Coulomb heating from the suprathermal electron
population, and cooling due to collisional rotational and vibrational
CO<SUB>2</SUB> dominates the energy loss. The models used in this study
were largely able to reproduce the observed high topside ionosphere
electron temperatures (e.g., 3000 K at 300 km altitude) without
using a topside heat flux when magnetic field topologies consistent
with the measured magnetic field were adopted. Magnetic topology
affects both suprathermal electron transport and thermal electron heat
conduction. The effects of using two different solar irradiance models
were also investigated. In particular, photoelectron fluxes and electron
temperatures found using the Heliospheric Environment Solar Spectrum
Radiation irradiance were higher than those with the Flare Irradiance
Spectrum Model-Mars. The electron temperature is shown to affect the
O<SUB>2</SUB><SUP>+</SUP> dissociative recombination rate coefficient,
which in turn affects photochemical escape of oxygen from Mars.
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Title: New atmospheric model of Epsilon Eridani
Authors: Vieytes, Mariela; Fontenla, Juan; Buccino, Andrea; Mauas,
Pablo
2016SPD....47.1105V Altcode:
We present a new semi-empirical model of the atmosphere of the widely
studied K-dwarf Epsilon Eridani (HD 22049). The model is build to
reproduce the visible spectral observations from 3800 to 6800 Angstrom
and the h and k Mg II lines profiles. The computations were carried
out using the Solar-Stellar Radiation Physical Modeling (SSRPM) tools,
which calculate non-LTE population for the most important species in
the stellar atmosphere. We show a comparison between the synthetic
and observed spectrum, obtaining a good agreement in all the studied
spectral range.
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Title: A semi-empirical model for the M star GJ832 using modeling
tools developed for computing semi-empirical solar models
Authors: Linsky, Jeffrey; Fontenla, Juan; France, Kevin
2016SPD....47.0105L Altcode:
We present a semi-empirical model of the photosphere, chromosphere,
transition region, and corona for the M2 dwarf star GJ832, which
hosts two exoplanets. The atmospheric model uses a modification of
the Solar Radiation Physical Modeling tools developed by Fontenla
and collaborators. These computer codes model non-LTE spectral line
formation for 52 atoms and ions and include a large number of lines
from 20 abundant diatomic molecules that are present in the much
cooler photosphere and chromosphere of this star. We constructed the
temperature distribution to fit Hubble Space Telescope observations of
chromospheric lines (e.g., MgII), transition region lines (CII, CIV,
SiIV, and NV), and the UV continuum. Temperatures in the coronal portion
of the model are consistent with ROSAT and XMM-Newton X-ray observations
and the FeXII 124.2 nm line. The excellent fit of the model to the
data demonstrates that the highly developed model atmosphere code
developed to explain regions of the solar atmosphere with different
activity levels has wide applicability to stars, including this M star
with an effective temperature 2200 K cooler than the Sun. We describe
similarities and differences between the M star model and models of
the quiet and active Sun.
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Title: The MUSCLES Treasury Survey. I. Motivation and Overview
Authors: France, Kevin; Loyd, R. O. Parke; Youngblood, Allison;
Brown, Alexander; Schneider, P. Christian; Hawley, Suzanne L.;
Froning, Cynthia S.; Linsky, Jeffrey L.; Roberge, Aki; Buccino,
Andrea P.; Davenport, James R. A.; Fontenla, Juan M.; Kaltenegger,
Lisa; Kowalski, Adam F.; Mauas, Pablo J. D.; Miguel, Yamila; Redfield,
Seth; Rugheimer, Sarah; Tian, Feng; Vieytes, Mariela C.; Walkowicz,
Lucianne M.; Weisenburger, Kolby L.
2016ApJ...820...89F Altcode: 2016arXiv160209142F
Ground- and space-based planet searches employing radial velocity
techniques and transit photometry have detected thousands
of planet-hosting stars in the Milky Way. With so many planets
discovered, the next step toward identifying potentially habitable
planets is atmospheric characterization. While the Sun-Earth system
provides a good framework for understanding the atmospheric chemistry
of Earth-like planets around solar-type stars, the observational
and theoretical constraints on the atmospheres of rocky planets in
the habitable zones (HZs) around low-mass stars (K and M dwarfs) are
relatively few. The chemistry of these atmospheres is controlled by the
shape and absolute flux of the stellar spectral energy distribution
(SED), however, flux distributions of relatively inactive low-mass
stars are poorly understood at present. To address this issue, we
have executed a panchromatic (X-ray to mid-IR) study of the SEDs of
11 nearby planet-hosting stars, the Measurements of the Ultraviolet
Spectral Characteristics of Low-mass Exoplanetary Systems (MUSCLES)
Treasury Survey. The MUSCLES program consists visible observations from
Hubble and ground-based observatories. Infrared and astrophysically
inaccessible wavelengths (EUV and Lyα) are reconstructed using
stellar model spectra to fill in gaps in the observational data. In
this overview and the companion papers describing the MUSCLES survey,
we show that energetic radiation (X-ray and ultraviolet) is present from
magnetically active stellar atmospheres at all times for stars as late
as M6. The emission line luminosities of C IV and Mg II are strongly
correlated with band-integrated luminosities and we present empirical
relations that can be used to estimate broadband FUV and XUV (≡X-ray +
EUV) fluxes from individual stellar emission line measurements. We find
that while the slope of the SED, FUV/NUV, increases by approximately
two orders of magnitude form early K to late M dwarfs (≈0.01-1), the
absolute FUV and XUV flux levels at their corresponding HZ distances
are constant to within factors of a few, spanning the range 10-70 erg
cm<SUP>-2</SUP> s<SUP>-1</SUP> in the HZ. Despite the lack of strong
stellar activity indicators in their optical spectra, several of the
M dwarfs in our sample show spectacular UV flare emission in their
light curves. We present an example with flare/quiescent ultraviolet
flux ratios of the order of 100:1 where the transition region
energy output during the flare is comparable to the total quiescent
luminosity of the star E<SUB>flare</SUB>(UV) ∼ 0.3 L<SUB>*</SUB>Δt
(Δt = 1 s). Finally, we interpret enhanced L(line)/L<SUB>Bol</SUB>
ratios for C IV and N v as tentative observational evidence for the
interaction of planets with large planetary mass-to-orbital distance
ratios (M<SUB>plan</SUB>/a<SUB>plan</SUB>) with the transition regions
of their host stars. <P />Based on observations made with the NASA/ESA
Hubble Space Telescope, obtained from the data archive at the Space
Telescope Science Institute. STScI is operated by the Association
of Universities for Research in Astronomy, Inc. under NASA contract
NAS 5-26555.
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Title: An Empirically-derived non-LTE XUV-Visible Spectral Synthesis
Model of the M1 V Exoplanet Host Star GJ832
Authors: Linsky, Jeffrey; Fontenla, Juan; Witbrod, Jesse; France, Kevin
2016AAS...22712106L Altcode:
GJ832 (HD 204961) is a nearby M1 V host star with two exoplanets:
a Jovian mass planet and a super-Earth. We have obtained near-UV and
far-UV spectra of GJ832 with the STIS and COS instruments on HST as
part of the Cycle 19 MUSCLES pilot program (France et al. 2013). Our
objective is to obtain the first accurate physical model for a
representative M-dwarf host star in order to understand the stellar
radiative emission at all wavelengths and to infer the radiation
environment of their exoplanets that drives their atmospheric
photochemistry.We have calculated a full non-LTE model for GJ 832
including the photosphere, chromosphere, transition region, and
corona to fit the observed emission lines formed over a wide range of
temperatures and the X-ray flux. Our one-dimensional semi-empirical
model uses the Solar-Stellar Physical Modelling tools that are an
offspring of the tools used by Fontenla and collaborators for computing
solar models. For this model of GJ832, we calculate the populations of
52 atoms and ions and 20 molecules with 2 million spectral lines. We
find excellent agreement with the observed H-alpha, CaII, MgII, CII,
SiIV, CIV, and NV lines. Our model for GJ832 has a temperature minimum
in the lower chromosphere much cooler than the Sun and then a steep
temperature rise different from the Sun. The different thermal structure
of GJ832 compared to the Sun results in the formation regions of the
emission lines being different for the two stars. We also compute
theradiative cooling rates as a function of height and temperature in
the atmosphere of GJ832.This work is supported by grants from STScI
to the University of Colorado.
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Title: Comparison of different solar irradiance models for the
superthermal electron transport model for Mars
Authors: Xu, Shaosui; Liemohn, Michael W.; Peterson, W. K.; Fontenla,
Juan; Chamberlin, Phillip
2015P&SS..119...62X Altcode:
As the solar photon fluxes directly control the production of
photoelectrons, it is important to examine the influence of different
solar irradiance models on the photoelectron fluxes. In this study,
we present the implementation of the two recent solar irradiance
models, the Flare Irradiance Spectral Model (FISM) and the Heliospheric
Environment Solar Spectral Radiation (HESSR) model, to our SuperThermal
Electron Transport (STET) model. In addition, we have proposed a new
modification to the Hinteregger-81 model. The resultant photoelectron
fluxes from the three solar irradiance models, the Hinteregger-81 model,
FISM and the HESSR model, are compared and mostly vary within a factor
of 2.
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Title: Electron Energetics in the Martian Ionosphere: Model
Comparisons with MAVEN Data
Authors: Sakai, S.; Rahmati, A.; Cravens, T.; Mitchell, D. L.; Bougher,
S. W.; Mazelle, C. X.; Peterson, W. K.; Eparvier, F. G.; Fontenla,
J. M.; Andersson, L.; Connerney, J. E. P.; Jakosky, B. M.
2015AGUFM.P21A2045S Altcode:
A large part of the solar extreme ultraviolet and soft X-ray radiation
absorbed in planetary upper atmospheres appears as photoelectrons and
some of the energy ends up heating thermal electrons and increasing
the electron temperature. Photoelectrons are important for the
heating related to plasma temperatures, ionization and airglow
production in planetary atmospheres. Measured electron fluxes
provide insight into sources and sinks of energy in the Martian upper
atmosphere. Suprathermal electron fluxes measured by the SWEA (Solar
Wind Electron Analyzer) instrument onboard the MAVEN (Mars Atmosphere
and Volatile EvolutioN) are providing insight into sources and sinks
of energy in the Martian upper atmosphere. A two-stream electron
transport code was used to interpret these observations including Auger
electrons associated with K-shell ionization of carbon, oxygen and
nitrogen. External electron fluxes from the Martian magnetosheath or
tail, are also included. Electron and ion temperatures are found from
numerical solutions of the energy equations and comparisons are made
with the electron temperature measured by the MAVEN Langmuir Probe
(e.g., Ergun et al., 2015). The overall implications of the plasma
energetics for the Martian ionosphere will be discussed.
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Title: Construction of a SORCE-based Solar Spectral Irradiance (SSI)
Record for Input into Chemistry Climate Models
Authors: Harder, J. W.; Fontenla, J. M.
2015AGUFMSH23B2441H Altcode:
We present a research program to produce a solar spectral irradiance
(SSI) record suitable for whole atmosphere chemistry-climate model
(CCM) transient studies over the 2001-2015 time period for Solar
Cycle 23 and 24 (SC23-24). Climate simulations during this time
period are particularly valuable because SC23-24 represents the
best-observed solar cycle in history - both from the perspective of
solar physics and in terms of Earth observation systems. This record
will be based predominantly on the observed irradiance of the SORCE
mission as measured by the SIM and SOLSTICE instruments from April of
2003 to the present time. The SSI data record for this proposed study
requires very broad wavelength coverage (115-100000 nm), daily spectral
coverage, compliance of the integrated SSI record with the TSI, and
well-defined and documented uncertainty estimates. While the majority
of the record will be derived from SORCE observations, extensions back
to the SC23 maximum time period (early 2001) and closure of critical
gaps in the SORCE record will be generated employing the Fontenla et
al. (2015) Solar Radiation Physical Model (SRPMv2). Since SRPM is a
physics-based model, estimates of the SSI for wavelengths outside the
SORCE measurement range can be meaningfully included. This model now
includes non-LTE contributions from metals in the atomic number range
22-28 (i.e. titanium through nickel) as well as important molecular
photo-disassociation contributions from molecules such as NH, molecular
hydrogen, CH, and OH led have led to greatly improved agreement between
the model and the observed 0.1 nm SOLSTICE spectrum. Thus comparative
studies of the SORCE observations with SRPMv2 provide meaningful
insight into the nature of solar variability critical for subsequent
Earth atmospheric modeling efforts.
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Title: Solar Ionizing Radiation at Mars: Predictions vs. MAVEN
Observations
Authors: Peterson, W. K.; Thiemann, E.; Epavier, F.; Andersson,
L.; Larson, D. E.; Mitchell, D. L.; Mazelle, C. X.; Evans, J. S.;
Fontenla, J. M.; Xu, S.; Liemohn, M. W.; Sakai, S.; Cravens, T.
2015AGUFM.P21A2051P Altcode:
The primary source of energy in the Martian upper atmosphere is
solar ionizing radiation. The first of the many processes that
convert solar radiation to thermal energy is the production of
photoelectrons. Observations on the MAVEN spacecraft of both
photoelectrons and broad band solar ionizing radiation allow
quantitative comparison of model calculations of the photoelectron
energy spectra below 200 km with observations. We compare and contrast
photoelectron energy spectra observed before and after an X class solar
flare on October 19, 2014 with calculations from three photoelectron
production and transport codes and solar irradiance spectra derived
from both MAVEN and Earth based observations. We find good agreement
between data and models
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Title: Model insights into energetic photoelectrons measured at Mars
by MAVEN
Authors: Sakai, Shotaro; Rahmati, Ali; Mitchell, David L.; Cravens,
Thomas E.; Bougher, Stephen W.; Mazelle, Christian; Peterson, W. K.;
Eparvier, Francis G.; Fontenla, Juan M.; Jakosky, Bruce M.
2015GeoRL..42.8894S Altcode:
Photoelectrons are important for heating, ionization, and airglow
production in planetary atmospheres. Measured electron fluxes provide
insight into the sources and sinks of energy in the Martian upper
atmosphere. The Solar Wind Electron Analyzer instrument on board the
MAVEN (Mars Atmosphere and Volatile EvolutioN) spacecraft measured
photoelectrons including Auger electrons with 500 eV energies. A
two-stream electron transport code was used to interpret the
observations, including Auger electrons associated with K shell
ionization of carbon, oxygen, and nitrogen. It explains the processes
that control the photoelectron spectrum, such as the solar irradiance
at different wavelengths, external electron fluxes from the Martian
magnetosheath or tail, and the structure of the upper atmosphere
(e.g., the thermal electron density). Our understanding of the complex
processes related to the conversion of solar irradiances to thermal
energy in the Martian ionosphere will be advanced by model comparisons
with measurements of suprathermal electrons by MAVEN.
---------------------------------------------------------
Title: Solar Spectral Irradiance, Solar Activity, and the
Near-Ultra-Violet
Authors: Fontenla, J. M.; Stancil, P. C.; Landi, E.
2015ApJ...809..157F Altcode:
The previous calculations of the Solar Spectral Irradiance (SSI)
by the Solar Radiation Physical Modeling, version 2 system, are
updated in this work by including new molecular photodissociation
cross-sections of important species, and many more levels and lines in
its treatment of non-LTE radiative transfer. The current calculations
including the new molecular photodissociation opacities produce a
reduced over-ionizaton of heavy elements in the lower chromosphere and
solve the problems with prior studies of the UV SSI in the wavelength
range 160-400 nm and now reproduce the available observations with much
greater accuracy. Calculations and observations of the near-UV at 0.1
nm resolution and higher are compared. The current set of physical
models includes four quiet-Sun and five active-region components,
from which radiance is computed for ten observing angles. These
radiances are combined with images of the solar disk to obtain the
SSI and Total Solar Irradiance and their variations. The computed SSI
is compared with measurements from space at several nm resolution and
agreement is found within the accuracy level of these measurements. An
important result is that the near-UV SSI increase with solar activity
is significant for the photodissociation of ozone in the terrestrial
atmosphere because a number of highly variable upper chromospheric
lines overlap the ozone Hartley band.
---------------------------------------------------------
Title: Atmospheric Model of a dM Star with Planets
Authors: Vieytes, M. C.; Fontenla, J. M.; Buccino, A. P.; Mauas,
P. J. D.
2015ASPC..496..344V Altcode:
We present our first attempt to model the atmosphere of GJ 876, a weakly
active dM star with planets. We built a photospheric and chromospheric
full NLTE model using the Solar Radiation Physical Modeling code
(SRPM), which was upgraded to take into account molecular features
that become important in the spectrum of a cooler star than the Sun.
---------------------------------------------------------
Title: Characterizing the Habitable Zones of Exoplanetary Systems
with a Large Ultraviolet/Visible/Near-IR Space Observatory
Authors: France, Kevin; Shkolnik, Evgenya; Linsky, Jeffrey; Roberge,
Aki; Ayres, Thomas; Barman, Travis; Brown, Alexander; Davenport,
James; Desert, Jean-Michel; Domagal-Goldman, Shawn; Fleming, Brian;
Fontenla, Juan; Fossati, Luca; Froning, Cynthia; Hallinan, Gregg;
Hawley, Suzanne; Hu, Renyu; Kaltenegger, Lisa; Kasting, James;
Kowlaski, Adam; Loyd, Parke; Mauas, Pablo; Miguel, Yamila; Osten,
Rachel; Redfield, Seth; Rugheimer, Sarah; Schneider, Christian; Segura,
Antigona; Stocke, John; Tian, Feng; Tumlinson, Jason; Vieytes, Mariela;
Walkowicz, Lucianne; Wood, Brian; Youngblood, Allison
2015arXiv150501840F Altcode:
Understanding the surface and atmospheric conditions of Earth-size,
rocky planets in the habitable zones (HZs) of low-mass stars is
currently one of the greatest astronomical endeavors. Knowledge of
the planetary effective surface temperature alone is insufficient
to accurately interpret biosignature gases when they are observed
in the coming decades. The UV stellar spectrum drives and regulates
the upper atmospheric heating and chemistry on Earth-like planets,
is critical to the definition and interpretation of biosignature
gases, and may even produce false-positives in our search for biologic
activity. This white paper briefly describes the scientific motivation
for panchromatic observations of exoplanetary systems as a whole (star
and planet), argues that a future NASA UV/Vis/near-IR space observatory
is well-suited to carry out this work, and describes technology
development goals that can be achieved in the next decade to support
the development of a UV/Vis/near-IR flagship mission in the 2020s.
---------------------------------------------------------
Title: Forecasting the Ionosphere Driven by Solar, Geomagnetic,
and Lower Atmosphere Disturbances
Authors: Fuller-Rowell, T. J.; Codrescu, M.; Fang, T. W.; Wang, H.;
Akmaev, R. A.; Wu, F.; Fedrizzi, M.; Fontenla, J. M.; Retterer, J. M.
2014AGUFMSA12A..03F Altcode:
Ionospheric forecasting has traditionally focused upon, and been
limited by, our ability to forecast magnetospheric drivers one to
two days in advance of a geomagnetic storm. The advances in this area
are significant as physics-based solar wind propagation models have
been transitioned to operations, and provide the time of arrival of a
solar disturbance. Although predicting the magnetic field orientation
and strength is still a challenge, once the solar wind drivers are
forecast, the accuracy of the ionospheric predictions are dependent on
the ability of thermosphere-ionosphere models to correctly capture the
physical processes in the upper atmosphere response to magnetospheric
energy and momentum dissipation. Many of the storm-time thermosphere
responses impacting the ionosphere can be modeled reasonably well,
such as changes in winds, gravity waves, temperature, density, and
composition. However, some of the electric field effects driving
storm enhanced plasma density and the disturbance dynamo are still a
challenge. Under quieter geomagnetic conditions, forecasting solar
extreme ultraviolet radiation becomes more important, as does the
impact of forcing from the lower atmosphere. These two new research
thrusts are also showing promise to provide the drivers of ionospheric
prediction several days in advance. There is also a possibility that
whole atmosphere models could provide the background conditions for
forecasting ionospheric irregularities.
---------------------------------------------------------
Title: First Simulations of a Collisional Two-Stream Instability in
the Chromosphere
Authors: Oppenheim, Meers; Dimant, Yakov; Madsen, Chad Allen;
Fontenla, Juan
2014AAS...22430205O Altcode:
Observations and modeling shows that immediately above the temperature
minimum in the solar atmosphere, a steep rise from below 4,000 K to
over 6,000K occurs. Recent papers show that a collisional two-stream
plasma instability called the Farley-Buneman Instability can develop
at the altitudes where this increase occurs. This instability may
play an important role in transferring energy from turbulent neutral
flows originating in the photosphere to the mid-chromosphere in the
form of heat. Plasma turbulence resulting from this instability could
account for some or most of this intense chromospheric heating. This
paper presents a set of simulations showing the development and
evolution of the Farley-Buneman Instability (FBI) applicable to the
chromosphere. It compares these results with the better-understood
ionospheric FBI. It examines the linear behavior and the dependence
of growth rates for a range of altitudes and driving flows. It also
presents the first study of FBI driven plasma nonlinearities and
turbulence in the chromosphere. This research should help us evaluate
the FBI as a mechanism to convert neutral flow and turbulence energy
into electron thermal energy in the quiet Sun.
---------------------------------------------------------
Title: Theory of Collisional Two-Stream Plasma Instabilities in the
Solar Chromosphere
Authors: Madsen, Chad Allen; Dimant, Yakov; Oppenheim, Meers;
Fontenla, Juan
2014AAS...22432303M Altcode:
The solar chromosphere experiences intense heating just above its
temperature minimum. The heating increases the electron temperature
in this region by over 2000 K. Furthermore, it exhibits little time
variation and appears widespread across the solar disk. Although
semi-empirical models, UV continuum observations, and line emission
measurements confirm the existence of the heating, its source remains
unexplained. Potential heating sources such as acoustic shocks,
resistive dissipation, and magnetic reconnection via nanoflares
fail to account for the intensity, persistence, and ubiquity of the
heating. Fontenla (2005) suggested turbulence from a collisional
two-stream plasma instability known as the Farley-Buneman instability
(FBI) could contribute significantly to the heating. This instability
is known to heat the plasma of the E-region ionosphere which bears many
similarities to the chromospheric plasma. However, the ionospheric
theory of the FBI does not account for the diverse ion species found
in the solar chromosphere. This work develops a new collisional,
two-stream instability theory appropriate for the chromospheric plasma
environment using a linear fluid analysis to derive a new dispersion
relationship and critical E x B drift velocity required to trigger the
instability. Using a 1D, non-local thermodynamic equilibrium, radiative
transfer model and careful estimates of collision rates and magnetic
field strengths, we calculate the trigger velocities necessary to induce
the instability throughout the chromosphere. Trigger velocities as low
as 4 km s^-1 are found near the temperature minimum, well below the
local neutral acoustic speed in that region. From this, we expect the
instability to occur frequently, converting kinetic energy contained
in neutral convective flows from the photosphere into thermal energy
via turbulence. This could contribute significantly to chromospheric
heating and explain its persistent and ubiquitous nature.
---------------------------------------------------------
Title: The Multi-species Farley-Buneman Instability in the Solar
Chromosphere
Authors: Madsen, Chad A.; Dimant, Yakov S.; Oppenheim, Meers M.;
Fontenla, Juan M.
2014ApJ...783..128M Altcode: 2013arXiv1308.0305M
Empirical models of the solar chromosphere show intense electron
heating immediately above its temperature minimum. Mechanisms such as
resistive dissipation and shock waves appear insufficient to account for
the persistence and uniformity of this heating as inferred from both
UV lines and continuum measurements. This paper further develops the
theory of the Farley-Buneman instability (FBI) which could contribute
substantially to this heating. It expands upon the single-ion theory
presented by Fontenla by developing a multiple-ion-species approach
that better models the diverse, metal-dominated ion plasma of the solar
chromosphere. This analysis generates a linear dispersion relationship
that predicts the critical electron drift velocity needed to trigger
the instability. Using careful estimates of collision frequencies and
a one-dimensional, semi-empirical model of the chromosphere, this new
theory predicts that the instability may be triggered by velocities as
low as 4 km s<SUP>-1</SUP>, well below the neutral acoustic speed. In
the Earth's ionosphere, the FBI occurs frequently in situations where
the instability trigger speed significantly exceeds the neutral acoustic
speed. From this, we expect neutral flows rising from the photosphere
to have enough energy to easily create electric fields and electron
Hall drifts with sufficient amplitude to make the FBI common in the
chromosphere. If so, this process will provide a mechanism to convert
neutral flow and turbulence energy into electron thermal energy in
the quiet Sun.
---------------------------------------------------------
Title: Far- and Extreme-UV Solar Spectral Irradiance and Radiance
from Simplified Atmospheric Physical Models
Authors: Fontenla, J. M.; Landi, E.; Snow, M.; Woods, T.
2014SoPh..289..515F Altcode:
This article describes an update of the physical models that we use to
reconstruct the FUV and EUV irradiance spectra and the radiance spectra
of the features that at any given point in time may cover the solar disk
depending on the state of solar activity. The present update introduces
important modifications to the chromosphere-corona transition region of
all models. Also, the update introduces improved and extended atomic
data. By these changes, the agreement of the computed and observed
spectra is largely improved in many EUV lines important for the modeling
of the Earth's upper atmosphere. This article describes the improvements
and shows detailed comparisons with EUV/FUV radiance and irradiance
measurements. The solar spectral irradiance from these models at
wavelengths longer than ≈ 200 nm is discussed in a separate article.
---------------------------------------------------------
Title: The Intrinsic EUV, Lyman-alpha, and UV Emission from Exoplanet
Host Stars
Authors: Linsky, Jeffrey; France, K.; Fontenla, J.
2014AAS...22323002L Altcode:
The chemical composition and mass loss from exoplanet atmospheres
is driven largely by the ultraviolet and extreme ultraviolet (EUV)
radiation from their host stars. In particular, such important
molecules as H2O, CO2, and CH4 are photodissociated primarily by
radiation in the Lyman-alpha line, and planetary exospheres are heated
primarily by EUV radiation from the host star, producing expansion
and mass loss. Unfortunately, most of the host star radiation in the
Lyman-alpha line is removed by hydrogen in the interstellar medium,
and the EUV emission between 400 and 912 Angstroms is absorbed by
interstellar hydrogen. We have developed a variety of techniques for
inferring the intrinsic Lyman-alpha and EUV emission from main sequence
stars with spectral types F5 to M5. We find that the ratios of the
EUV flux to Lyman-alpha and the Lyman-alpha flux to other emission
lines are relatively insensitive to spectral type and activity. We
therefore propose formulae for estimating the intrinsic emission from
exoplanet host stars. We present results from our HST observing program
MUSCLES that provides near-UV and far-UV spectra of M dwarf exoplanet
host stars. We also present a preliminary non-LTE chromosphere model
for an M dwarf host star. This combination of HST spectra, host star
models, and estimated intrinsic Lyman-alpha and EUV emission provides
essential input for the computation of photochemical models of exoplanet
atmospheres. This work is supported by the Space Telescope Science
Institute and NASA grants.
---------------------------------------------------------
Title: The Intrinsic Extreme Ultraviolet Fluxes of F5 V TO M5 V Stars
Authors: Linsky, Jeffrey L.; Fontenla, Juan; France, Kevin
2014ApJ...780...61L Altcode: 2013arXiv1310.1360L
Extreme ultraviolet (EUV) radiations (10-117 nm) from host stars play
important roles in the ionization, heating, and mass loss from exoplanet
atmospheres. Together with the host star's Lyα and far-UV (117-170
nm) radiation, EUV radiation photodissociates important molecules,
thereby changing the chemistry in exoplanet atmospheres. Since stellar
EUV fluxes cannot now be measured and interstellar neutral hydrogen
completely obscures stellar radiation between 40 and 91.2 nm, even
for the nearest stars, we must estimate the unobservable EUV flux
by indirect methods. New non-LTE semiempirical models of the solar
chromosphere and corona and solar irradiance measurements show that the
ratio of EUV flux in a variety of wavelength bands to the Lyα flux
varies slowly with the Lyα flux and thus with the magnetic heating
rate. This suggests and we confirm that solar EUV/Lyα flux ratios
based on the models and observations are similar to the available 10-40
nm flux ratios observed with the Extreme Ultraviolet Explorer (EUVE)
satellite and the 91.2-117 nm flux observed with the Far Ultraviolet
Spectroscopic Explorer (FUSE) satellite for F5 V-M5 V stars. We provide
formulae for predicting EUV flux ratios based on the EUVE and FUSE
stellar data and on the solar models, which are essential input for
modeling the atmospheres of exoplanets.
---------------------------------------------------------
Title: Improving the Ni I Atomic Model for Solar and Stellar
Atmospheric Models
Authors: Vieytes, M. C.; Fontenla, J. M.
2013ApJ...769..103V Altcode: 2013arXiv1303.3528V
Neutral nickel (Ni I) is abundant in the solar atmosphere and is
one of the important elements that contribute to the emission and
absorption of radiation in the spectral range between 1900 and 3900
Å. Previously, the Solar Radiation Physical Modeling (SRPM) models of
the solar atmosphere only considered a few levels of this species. Here,
we improve the Ni I atomic model by taking into account 61 levels and
490 spectral lines. We compute the populations of these levels in full
NLTE using the SRPM code and compare the resulting emerging spectrum
with observations. The present atomic model significantly improves the
calculation of the solar spectral irradiance at near-UV wavelengths,
which is important for Earth atmospheric studies, and particularly
for ozone chemistry.
---------------------------------------------------------
Title: The Ni I lines in the solar spectrum
Authors: Vieytes, Mariela C.; Mauas, Pablo J. D.; Fontenla, Juan M.
2012IAUS..286...93V Altcode:
The stratosphere is the region where the ozone chemistry is important
for the balance of energy, and radiation in the near UV plays a
fundamental role in the creation and destruction of ozone. However,
the radiation in this range of wavelength has not been very well
modeled. One of the most important elements, according to its abundance
in the solar atmosphere, that contribute to the emission and absorption
of radiation in the spectral range between 1900 and 3900 Å, is neutral
nickel (Ni I). In this work we improve the atomic model of this element,
taking into account 490 lines over the spectrum. We solve these lines
in NLTE using the Solar Radiation Physical Modeling (SRPM) program
and compare the results with observation of the quiet sun spectrum.
---------------------------------------------------------
Title: Solar EUV and XUV energy input to thermosphere on solar
rotation time scales derived from photoelectron observations.
Authors: Peterson, W. K. Bill; Solomon, Stanley; Warren, Harry;
Fontenla, Juan; Woods, Thomas; Richards, Phil; Chamberlin, Phillip;
Tobiska, W. Kent
2012cosp...39.1489P Altcode: 2012cosp.meet.1489P
Solar radiation below ~100 nm produces photoelectrons, a substantial
portion of the F region ionization, most of the E region ionization,
and drives chemical reactions in the thermosphere. Unquantified
uncertainties in thermospheric models exist because of uncertainties
in solar irradiance models used to fill spectral and temporal gaps in
solar irradiance observations. We investigate uncertainties in solar
energy input to the thermosphere on solar rotation time scales using
photoelectron observations from the FAST satellite. We compare observed
and modeled photoelectron energy spectra using two photoelectron
production codes driven by five different solar irradiance models. We
observe about 1.7 per cent of the ionizing solar irradiance power in the
escaping photoelectron flux. Most of the code/model pairs used reproduce
the average escaping photoelectron flux over a 109-day interval in
late 2006. The code/model pairs we used do not completely reproduce
the observed spectral and solar cycle variations in photoelectron power
density. For the interval examined, 30 per cent of the variability in
photoelectron power density with equivalent wavelengths between 18
and 45 nm was not captured in the code/model pairs. For equivalent
wavelengths below ~ 16 nm, most of the variability was missed. This
result implies that thermospheric model runs based on the solar
irradiance models we tested systematically underestimate the energy
input from ionizing radiation on solar rotation time scales.
---------------------------------------------------------
Title: Measured and Modeled Trends in Solar Spectral Variability
and Application to Earth Atmospheric Studies
Authors: Harder, J. W.; Fontenla, J. M.; Merkel, A. W.; Woods, T. N.
2012LPICo1675.8096H Altcode:
The Spectral Irradiance Monitor (SIM) and the Solar Stellar
Intercomparison Experiments (SOLSTICE) onboard the Solar Radiation
and Climate Experiment (SORCE) measure solar spectral variability.
---------------------------------------------------------
Title: Solar EUV and XUV energy input to thermosphere on solar
rotation time scales derived from photoelectron observations
Authors: Peterson, W. K.; Woods, T. N.; Fontenla, J. M.; Richards,
P. G.; Chamberlin, P. C.; Solomon, S. C.; Tobiska, W. K.; Warren, H. P.
2012JGRA..117.5320P Altcode: 2012JGRA..11705320P
Solar radiation below ∼100 nm produces photoelectrons, a substantial
portion of the F region ionization, most of the E region ionization,
and drives chemical reactions in the thermosphere. Unquantified
uncertainties in thermospheric models exist because of uncertainties
in solar irradiance models used to fill spectral and temporal gaps
in solar irradiance observations. We investigate uncertainties
in solar energy input to the thermosphere on solar rotation time
scales using photoelectron observations from the FAST satellite. We
compare observed and modeled photoelectron energy spectra using two
photoelectron production codes driven by five different solar irradiance
models. We observe about 1.7% of the ionizing solar irradiance power
in the escaping photoelectron flux. Most of the code/model pairs
used reproduce the average escaping photoelectron flux over a 109-day
interval in late 2006. The code/model pairs we used do not completely
reproduce the observed spectral and solar rotation variations in
photoelectron power density. For the interval examined, 30% of the
variability in photoelectron power density with equivalent wavelengths
between 18 and 45 nm was not captured in the code/model pairs. For
equivalent wavelengths below ∼16 nm, most of the variability was
missed. This result implies that thermospheric model runs based on
the solar irradiance models we tested systematically underestimate
the energy input from ionizing radiation on solar rotation time scales.
---------------------------------------------------------
Title: Far-ultraviolet Continuum Emission: Applying This Diagnostic
to the Chromospheres of Solar-mass Stars
Authors: Linsky, Jeffrey L.; Bushinsky, Rachel; Ayres, Tom; Fontenla,
Juan; France, Kevin
2012ApJ...745...25L Altcode: 2011arXiv1109.5653L
The far-ultraviolet (FUV) continuum flux is recognized as a very
sensitive diagnostic of the temperature structure of the Sun's
lower chromosphere. Until now analysis of the available stellar FUV
data has shown that solar-type stars must also have chromospheres,
but quantitative analyses of stellar FUV continua require far higher
quality spectra and comparison with new non-LTE chromosphere models. We
present accurate far-ultraviolet (FUV, 1150-1500 Å) continuum flux
measurements for solar-mass stars, made feasible by the high throughput
and very low detector background of the Cosmic Origins Spectrograph on
the Hubbble Space Telescope. We show that the continuum flux can be
measured above the detector background even for the faintest star in
our sample. We find a clear trend of increasing continuum brightness
temperature at all FUV wavelengths with decreasing rotational period,
which provides an important measure of magnetic heating rates in stellar
chromospheres. Comparison with semiempirical solar flux models shows
that the most rapidly rotating solar-mass stars have FUV continuum
brightness temperatures similar to the brightest faculae seen on the
Sun. The thermal structure of the brightest solar faculae therefore
provides a first-order estimate of the thermal structure and heating
rate for the most rapidly rotating solar-mass stars in our sample.
---------------------------------------------------------
Title: Far-side imaging tools, front-side imaging, and EUV solar
irradiance forecasting
Authors: Fontenla, J. M.; Quemerais, E.; Lindsey, C. A.
2011AGUFMSH12A..03F Altcode:
Currently we are in an advanced stage of the development of an
application of both far-side and front-side imaging to EUV solar
irradiance forecast. The basic method and its application to one case
were described by Fontenla et al. (2009). This method uses a combination
of several techniques for far-side imaging with front-side images at
various wavelengths, and EUV spectral synthesis. This presentation
shows that all these techniques should be used in concert to produce
a reasonably accurate EUV irradiance forecast at Earth and other
planets. The combination of SOHO/SWAN Ly alpha backscattering, far-side
helioseismic images, and front-side imaging resolves the weaknesses
of each technique by itself. In particular, the presentation will show
how the SOHO/SWAN data plays a very important role in this combination
by supplying unique EUV data (Ly alpha) that is not directly inferred
by helioseismic methods. The SOHO/SWAN data plays a key role in the
combination by allowing us to infer the evolution in EUV brightness of
the active regions on the far-side of the Sun. However, because this
method does not provide a good localization of the emission sources
in the Sun, it needs to me complemented by the good localization
that helioseismology provides. Because the Ly alpha backscattering is
sensitive to active network and plage these images provide essential
information for determining the far-side evolution of components to the
solar flux that are not detected by helioseismology but have important
effects on the EUV irradiance. However, again because of the poor
localization of these features in backscattering images, front side
imaging is also a necessary complement that helps in the localization
on the solar surface of the changes observed in the SOHO/SWAN images.
---------------------------------------------------------
Title: Solar Spectrum Atomic Database Update Comparisons
Authors: Mason, J. P.; Fontenla, J. M.; Woods, T. N.
2011AGUFMGC23A0925M Altcode:
Computations of the solar spectrum from 1 Å to 100 microns are
obtained through the Solar Radiation Physical Modeling (SRPM)
system. However, this presentation examines in detail only the range
1 to 2020 Å. Comparisons are made between the spectra generated by
SRPM including CHIANTI-5 atomic data, the CHIANTI-6 atomic data with no
change to the elemental ionization formulation, and the CHIANTI-6 atomic
data with the new ionization formula used in this version. The extreme
ultraviolet (EUV) part of the spectrum is compared with observations
made by the Solar Dynamics Observatory's EUV Variability Experiment
(SDO/EVE). In addition, the SDO Atmospheric Imaging Assembly (AIA)
data are analyzed for the generation of solar feature masks. These
include photospheric, chromospheric, and coronal layers. Examples are
shown of the routine daily masks and spectra generated.
---------------------------------------------------------
Title: Lyman Alpha Spicule Observatory (LASO)
Authors: Chamberlin, P. C.; Allred, J. C.; Airapetian, V.; Gong, Q.;
Mcintosh, S. W.; De Pontieu, B.; Fontenla, J. M.
2011AGUFMSH33B2064C Altcode:
The Lyman Alpha Spicule Observatory (LASO) sounding rocket will observe
small-scale eruptive events called "Rapid Blue-shifted Events" (RBEs)
[Rouppe van der Voort et al., 2009], the on-disk equivalent of Type-II
spicules, and extend observations that explore their role in the solar
coronal heating problem [De Pontieu et al., 2011]. LASO utilizes a
new and novel optical design to simultaneously observe two spatial
dimensions at 4.2" spatial resolution (2.1" pixels) over a 2'x2' field
of view with high spectral resolution of 66mÅ (33mÅ pixels) across a
broad 20Å spectral window. This spectral window contains three strong
chromospheric and transition region emissions and is centered on the
strong Hydrogen Lyman-α emission at 1216Å. This instrument makes
it possible to obtain new data crucial to the physical understanding
of these phenomena and their role in the overall energy and momentum
balance from the upper chromosphere to lower corona. LASO was submitted
March 2011 in response to the ROSES SHP-LCAS call.
---------------------------------------------------------
Title: Measured and modeled trends in the solar spectral irradiance
variability using the SORCE SIM and SOLSTICE instruments
Authors: Harder, J. W.; Fontenla, J. M.; Rast, M. P.; Snow, M. A.;
Woods, T. N.
2011AGUFMGC22A..06H Altcode:
The Solar Radiation and Climate Experiment (SORCE) Spectral Irradiance
Monitor (SIM) measures solar spectral variability in the 200-2400 nm
range accounting for about 97% of the total solar irradiance (TSI). SIM
concurrently measures ultraviolet variability from 200-310 nm with
the higher spectral resolution Solar-Stellar Irradiance Comparison
Experiment (SOLSTICE). These instruments monitored the descending phase
of solar cycle 23 and are now continuing these observations in the
rising phase of cycle 24. SIM and SOLSTICE observations clearly show
rotational modulation of spectral irradiance due to the evolution of
dark sunspots and bright faculae that respectively deplete and enhance
solar radiation. In addition to this well-known phenomenon, SORCE
observations indicate a slower evolutionary trend in solar spectral
irradiance (SSI) over solar cycle time-scales that are both in and
out of phase with the TSI, with the ultraviolet component indicating
significantly larger UV variability than reported from the UARS era
instruments. Wavelengths where the brightness temperature is less than
Teff = 5770 K are in phase, and where the brightness temperature >
Teff in the visible and infrared, the time series show an anti-solar
cycle trend. This observation is discussed in terms of the Solar
Radiation Physical Modeling (SRPM) program employing solar images from
Precision Solar Photometric Telescope (PSPT) that provides the areas
of active regions on the solar disk as function of time to generate a
modeled SSI time series that is concurrent with the SORCE observations
but extending back to solar maximum conditions. Comparative studies
of the SIM and SOLSTICE will be presented along with analysis of solar
variability derived from SRPM and PSPT.
---------------------------------------------------------
Title: Effects of Radiative Transfer on Helioseismic Signatures in
Active Regions
Authors: Lindsey, C. A.; Fontenla, J. M.
2011AGUFMSH43A1928L Altcode:
Models of active regions based on helioseismology have been
heavily based on acoustics in which compression is assumed to be
adiabatic. Acoustics in the outer atmospheres of the quiet Sun
and active regions are thought to depart strongly from adiabatic
compression, due to radiative-transfer effects. If these departures were
similar in active regions and the quiet Sun, they could plausibly be
ignored. However, this is unlikely, because the radiative environments
in active regions are different from those in the quiet Sun. We
discuss efforts to simulate acoustics in photospheric/chromospheric
media with an account of radiative-transfer effects in both the quiet
Sun and active regions.
---------------------------------------------------------
Title: Photoelectrons as a tool to evaluate solar EUV and XUV model
irradiance spectra
Authors: Peterson, W. K.; Woods, T. N.; Fontenla, J. M.; Richards,
P. G.; Tobiska, W.; Solomon, S. C.; Warren, J.
2011AGUFMSA51C1954P Altcode:
Solar radiation below 50 nm produces a substantial portion of the
F region ionization and most of the E region ionization that drives
chemical reactions in the thermosphere. At times before the launch
of the SDO spacecraft there is a lack of high temporal and spectral
resolution Solar EUV and XUV observations, particularly below 27
nm. To address the space data various solar irradiance models have
been developed. We have developed a technique to use observations of
escaping photoelectron fluxes from the FAST satellite and two different
photoelectron production codes driven by model solar irradiance values
to systematically examine differences between observed and calculated
escaping photoelectron fluxes. We have compared modeled and observed
photoelectron fluxes for the interval from September 14, 2006 to
January 1, 2007. This is an interval included ~ 4 solar rotations
and is characterized by modest solar and geomagnetic activity. Solar
irradiance models included TIMED/SEE data, which is derived from a
model below 27 nm, and the FISM Version 1, the SRPM predictive model
based on solar observation, HEUVAC, S2000, and NRL, solar irradiance
models. We used the GLOW and FLIP photoelectron production codes. Here
we focus on the differences between solar irradiance models and small
differences between photoelectron production code outputs using the
same solar irradiance spectra over this time period.
---------------------------------------------------------
Title: High-resolution solar spectral irradiance from extreme
ultraviolet to far infrared
Authors: Fontenla, J. M.; Harder, J.; Livingston, W.; Snow, M.;
Woods, T.
2011JGRD..11620108F Altcode:
This paper presents new extremely high-resolution solar spectral
irradiance (SSI) calculations covering wavelengths from 0.12 nm to
100 micron obtained by the Solar Irradiance Physical Modeling (SRPM)
system. Daily solar irradiance spectra were constructed for most of
Solar Cycle 23 based on a set of physical models of the solar features
and non-LTE calculations of their emitted spectra as function of viewing
angle, and solar images specifying the distribution of features on
the solar disk. Various observational tests are used to assess the
quality of the spectra provided here. The present work emphasizes
the effects on the SSI of the upper chromosphere and full-non-LTE
radiative transfer calculation of level populations and ionizations
that are essential for physically consistent results at UV wavelengths
and for deep lines in the visible and IR. This paper also considers the
photodissociation continuum opacity of molecular species, e.g., CH and
OH, and proposes the consideration of NH photodissociation which can
solve the puzzle of the missing near-UV opacity in the spectral range
of the near-UV. Finally, this paper is based on physical models of
the solar atmosphere and extends the previous lower-layer models into
the upper-transition-region and coronal layers that are the dominant
source of photons at wavelengths shorter than ∼50 nm (except for
the He II 30.4 nm line, mainly formed in the lower-transition-region).
---------------------------------------------------------
Title: The impact of solar spectral irradiance variability on middle
atmospheric ozone
Authors: Merkel, Aimee W.; Harder, Jerald W.; Marsh, Daniel R.; Smith,
Anne K.; Fontenla, Juan M.; Woods, Thomas N.
2011GeoRL..3813802M Altcode:
This study presents the impact of solar spectral irradiance (SSI)
variability on middle atmospheric ozone over the declining phase
of solar cycle 23. Two different types of spectral forcing are
applied to the Whole Atmosphere Community Climate Model (WACCM) to
simulate the ozone response between periods of quiet and high solar
activity. One scenario uses the solar proxy reconstructions model
from the Naval Research Laboratory (NRLSSI), and the other is based
on SSI observations from the Solar Radiation and Climate Experiment
(SORCE). The SORCE observations show 3-5 times more variability in
ultraviolet (UV) radiation than predicted by the proxy model. The NRLSSI
forcing had minimal impact on ozone, however, the higher UV variability
from SORCE induced a 4% reduction in ozone concentration above 40 km
at solar active conditions. The model result is supported by 8 years
(2002-2010) of ozone observations from the Sounding of the Atmosphere
using Broadband Emission Radiometry (SABER) instrument. The SABER
ozone variations have greater similarity with the SORCE SSI model
simulations. The model and satellite data suggests that the ozone
response is due to enhanced photochemical activity associated with
larger UV variability.
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Title: Lyman Alpha Spicule Observatory (LASO)
Authors: Chamberlin, Phillip C.; Allred, J.; Airapetian, V.; Gong,
Q.; Fontenla, J.; McIntosh, S.; de Pontieu, B.
2011SPD....42.1506C Altcode: 2011BAAS..43S.1506C
The Lyman Alpha Spicule Observatory (LASO) sounding rocket will observe
small-scale eruptive events called "Rapid Blue-shifted Events” (RBEs),
the on-disk equivalent of Type-II spicules, and extend observations that
explore their role in the solar coronal heating problem. LASO utilizes
a new and novel optical design to simultaneously observe two spatial
dimensions at 4.2" spatial resolution (2.1” pixels) over a 2'x2'
field of view with high spectral resolution of 66mÅ (33mÅ pixels)
across a broad 20Å spectral window. This spectral window contains three
strong chromospheric and transition region emissions and is centered on
the strong Hydrogen Lyman-α emission at 1216Å. This instrument makes
it possible to obtain new data crucial to the physical understanding
of these phenomena and their role in the overall energy and momentum
balance from the upper chromosphere to lower corona. LASO was submitted
March 2011 in response to the ROSES SHP-LCAS call.
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Title: Application of Solar Spectral Irradiance Variability in a
Earth Atmospheric Model
Authors: Harder, J. W.; Merkel, A.; Fontenla, J.; Marsh, D.; Woods,
T. N.
2010AGUFMGC13E..02H Altcode:
The Spectral Irradiance Monitor (SIM) measures solar spectral
variability in the 200-2400 nm range, accounting for about 97% of
the total solar irradiance (TSI). SIM monitored the descending phase
of solar cycle 23 and is now continuing these observations into the
rising phase of cycle 24. The SIM observations indicate a slower
evolutionary trend in solar spectral irradiance (SSI) over solar
cycle times periods that are both in and out of phase with the TSI. To
estimate the atmospheric response to the solar variability implied by
these observations, quiet sun and active solar reference spectra were
created as input into the Whole Atmosphere Community Climate Model
(WACCM). The SIM observations were combined with the SORCE SOLSTICE
instrument in the 110-240 nm range and SRPM (Solar Radiation Physical
Modeling) estimates in the infrared beyond the 2400 nm measurement limit
of SIM to generate the reference spectra. The model output suggest a
very different response in ozone than from atmospheric forcing from
semi-empirical models of SSI. The model predicts a reduction in lower
mesosphere at higher solar activity and a large increase in mid-
to upper stratosphere. This structure can be explained by enhanced
production of HOx,, and O3 self-healing effect. This structure is
commensurate with contemporaneous observations of O3 from AURA-MLS
and SABER.
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Title: Forecasting Solar EUV Irradiance, Validation and Automation
Authors: Fontenla, J. M.; Gonzalez Hernandez, I.; Quémerais, E.;
Lindsey, C.; Mason, J. P.
2010AGUFMSM51A1751F Altcode:
A new forecasting technique of the EUV solar irradiance was developed
and a test case tried. This method is based on physical semi-empirical
models of the solar atmosphere that are essentially different from
empirical proxies based only on mathematical correlation. The physics
based forecast can readily incorporate the large body of solar physics
and radiative transfer knowledge, and any future developments in the
understanding of the physical processes that operate in the solar
atmosphere. In this paper it is shown how this forecast method is
applied to a wide range of wavelengths and produces indices related to
Earth upper atmospheric processes that can be correlated to observed
patterns, as well as full spectra in the range 0.2 nm to 12 micron that
can be utilized in GCM models. It is also shown how the forecast method
is now in the process of being automated and applied to the onset of the
solar activity cycle 24. In addition to the GONG and SWAN helioseismic
and Ly alpha backscattering data, respectively, and the ground-based
PSPT data, new measurements by SDO instruments (AIA and EVE) are being
used to feed current data into the forecast technique. Furthermore,
SDO/EVE data is starting to being used to validate the forecast in a
substantial part of the UV range, from 6 to 100 nm.
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Title: Photoelectrons as a tool to evaluate spectral and temporal
variations of solar EUV and XUV irradiance models over solar rotation
and solar cycle time scales
Authors: Peterson, W. K.; Woods, T. N.; Fontenla, J. M.; Richards,
P. G.; Tobiska, W.; Solomon, S. C.; Warren, H. P.
2010AGUFMSA33B1766P Altcode:
Solar radiation below 50 nm produces a substantial portion of the F
region ionization and most of the E region ionization that drives
chemical reactions in the thermosphere. Because of a lack of high
temporal and spectral resolution Solar EUV and XUV observations,
particularly below 27 nm, various solar irradiance models have
been developed. We have developed a technique to use observations of
escaping photoelectron fluxes from the FAST satellite and two different
photoelectron production codes driven by model solar irradiance values
to systematically examine differences between observed and calculated
escaping photoelectron fluxes. We have compared modeled and observed
photoelectron fluxes from the start of TIMED/SEE data availability
(2002) to the end of FAST photoelectron observations (2009). Solar
irradiance inputs included TIMED/SEE data, which is derived from a model
below 27 nm, and the FISM Version 1, the SRPM predictive model based on
solar observation, HEUVAC, S2000, and NRL, solar irradiance models. We
used the GLOW and FLIP photoelectron production codes. We find that
model photoelectron spectra generated using the HEUVAC solar irradiance
model have the best overall agreement with observations. Photoelectron
spectra generated with the the TIMED/SEE based FISM model best agree
with the observations on solar cycle time scales. Below ~27 nm all but
the HEUVAC solar irradiance model produces photoelectron fluxes that are
systematically below observations. We also noted systematic differences
in the photoelectron energy spectra below 25 eV produced by the GLOW
and FLIP photoelectron production codes for all solar irradiance inputs.
---------------------------------------------------------
Title: The SORCE SIM Solar Spectrum: Comparison with Recent
Observations
Authors: Harder, J. W.; Thuillier, G.; Richard, E. C.; Brown, S. W.;
Lykke, K. R.; Snow, M.; McClintock, W. E.; Fontenla, J. M.; Woods,
T. N.; Pilewskie, P.
2010SoPh..263....3H Altcode: 2010SoPh..tmp...72H
The Spectral Irradiance Monitor (SIM) on board the NASA SORCE satellite
(Solar Radiation and Climate Experiment) was launched on 25 January
2003 and has been making twice-daily measurements of solar variability
in the 220 to 1630 nm range and daily measurements in the 1600 to 2400
nm range. This study presents preflight and postlaunch calibration
activities of the SIM instrument and its flight spare components
as well as in-flight comparisons with the ATLAS 3 composite spectrum
(Atmospheric Laboratory for Applications and Science) in the ultraviolet
(UV), visible, and near infrared (NIR) as well as comparisons with
the SOLSTICE (Solar Stellar Irradiance Comparison Experiment) in the
UV. In the 258 to 1350 nm range, the SIM agrees with ATLAS 3 with a
fractional difference of −0.021±0.021 (k=1, estimated standard
deviation) and with the additional corrections discussed herein
the agreement improves to −0.008±0.021 (k=1). In the ultraviolet
(220-307 nm) the agreement between all the instruments in this study
is better than 5%, but fractional differences reveal other instrument-
and calibration-related differences. In the 1350 to 2400 nm range the
agreement between SIM and ATLAS 3 is about 8%, so these SIM data are
corrected to agree with ATLAS 3 in this range.
---------------------------------------------------------
Title: First Accurate, and Surprising, Observations of Solar Spectral
Irradiance by the SIM/SORCE Instrument
Authors: Fontenla, Juan; Harder, J.; Woods, T.
2010AAS...21631304F Altcode: 2010BAAS...41Q.888F
It has been long speculated by the solar irradiance community that
the observed Total Solar Irradiance (TSI) variations during the last
few cycles were due to the active regions present on the solar disk
at times of maximum sunspot index. Although sunspots darkness reduces
the TSI, it was surmised that brightening in the surrounding facular
and plage regions could over-compensate the sunspot effect. <P />The
first accurate observations of Solar Spectral Irradiance (SSI) during
the decay of solar cycle 23, by the SIM/SORCE instrument, showed
larger changes in the solar spectrum that are not simply described
by TSI variations. <P />These observations show much larger variation
of the visible and IR ranges and of the opposite phase to those that
were inferred from TSI proxies. Instead, the near-UV varies in phase
with the TSI proxy but with amplitude much larger than was expected
and the visible-IR power changes nearly compensate the UV leaving
the residual small changes of the TSI. These solar cycle trends are
much larger than the 27-day modulation due to the solar rotation,
and cannot be fully explained by the passage of plage and sunspot on
the disk. <P />Therefore, a paradigm change is needed in our study of
SSI variations that requires a significant decrease in the photospheric
temperature gradient at times of maximum solar activity. To explain the
observations such a decrease must be relatively small but occur over
areas of the solar surface much more extended than observed active
regions. Increased energy transport efficiency in the active Sun's
photosphere can explain this temperature gradient change.
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Title: Long-term measurements of solar spectral irradiance
variability: toward the establishment of a climate record
Authors: Richard, Erik; Harder, Jerald; Pilewskie, Peter; Fontenla,
Juan; Woods, Thomas; Brown, Steven; Lykke, Keith
2010cosp...38.1691R Altcode: 2010cosp.meet.1691R
Knowledge of the top of the atmosphere (TOA) solar spectral irradiance
(SSI) is crucial in interpreting the spectrally dependent radiative
processes throughout Earth's climate system. Where this energy is
deposited into the atmosphere and surface, how the climate responds
to solar variability, and the mechanisms of climate response, are
highly dependent on how the incident solar radiation is distributed
with wavelength. In order to advance understanding of how natural and
anthropogenic process affect Earth's climate system there is a strong
scientific imperative to maintain accurate, long-term records of climate
forcing and response. The contin-uation of SSI measurements provides
a unique opportunity to characterize poorly understood wavelength
dependent climate processes. Coupled chemistry-climate models require
realistic assessments of the magnitudes and long-term trends in
SSI for the interpretation and quantifi-cation of solar forcing in
climate change scenarios. This places stringent requirements on the
absolute calibration of the instrument (tied directly to international
standards) and the ability to maintain that calibration on-orbit
(long-term stability). The Spectral Irradiance Monitor (SIM) is a
solar spectral radiometer that continuously monitors the SSI from 200
nm -2400 nm, a wavelength region encompassing 96% of the total solar
irradiance. The SIM instrument is included as part of the Total and
Spectral Solar Irradiance Sensor (TSIS) to continue the mea-surement
of SSI, which began with the SOlar Radiation and Climate Experiment
(SORCE), launched in 2003. SORCE SIM measurements have characterized
SSI variability during the descending phase of Solar Cycle (SC) 23,
but the determination of multi-solar cycle dependen-cies remains a key
climatic uncertainty. Analysis of the measured spectral irradiance
variability during the SORCE mission has resulted in a number of
instrument design refinements central to maintaining, on-orbit, the
long-term absolute calibration to the International System of Units
(SI) irradiance standards (0.2% absolute) and achieve the necessary
measurement precision and long-term reproducibility (0.05 -0.01%
relative per year) to meet the needs for establishing a climate record
of solar spectral irradiance. We will review the findings from the SORCE
SIM observations over the past 7 years, a time period encompassing the
declining phase of SC 23 and the start of SC 24, and how these results
guided performance enhancements that will be applied to the TSIS SIM
instrument to meet the needs for climate monitoring of solar spectral
irradiance into the future.
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Title: Radiative emission of solar features in Ca II K
Authors: Criscuoli, S.; Ermolli, I.; Fontenla, J.; Giorgi, F.; Rast,
M.; Solanki, S. K.; Uitenbroek, H.
2010MmSAI..81..773C Altcode: 2010arXiv1002.0244C
We investigated the radiative emission of different types of solar
features in the spectral range of the Ca II K line. We analyzed
full-disk 2k × 2k observations from the Precision Solar Photometric
Telescope (PSPT). The data were obtained by using three narrow-band
interference filters that sample the Ca II K line with different pass
bands. Two filters are centered in the line core, the other in the red
wing of the line. We measured the intensity and contrast of various
solar features, specifically quiet Sun (inter-network), network,
enhanced network, plage, and bright plage (facula) regions. Moreover,
we compared the results obtained with those derived from the numerical
synthesis performed for the three PSPT filters with a widely used
radiative code on a set of reference semi-empirical atmosphere models.
---------------------------------------------------------
Title: Measured and modeled trends in solar spectral irradiance
variability in the visible and infrared
Authors: Harder, Jerald; Fontenla, Juan; Rast, Mark; Pilewskie, Peter;
Woods, Thomas
2010cosp...38...16H Altcode: 2010cosp.meet...16H
The Spectral Irradiance Monitor (SIM) measures solar spectral
variability in the 200-2400 nm range, accounting for about 97%
of the total solar irradiance (TSI). This instrument monitored
the descending phase of solar cycle 23 and is now continuing these
observations in the rising phase of cycle 24. The SIM observations
clearly show rotational modulation of spectral irra-diance due to
the evolution of dark sunspots and bright faculae that respectively
deplete and enhance solar radiation. In addition to this well-known
phenomenon, SIM observations indicate a slower evolutionary trend in
solar spectral irradiance (SSI) over solar cycle times periods that are
both in and out of phase with the TSI. Wavelengths where the brightness
temperature is less than Teff = 5770 K are in phase, and where the
brightness temperature ¿ Teff in the vis-ible and infrared, the time
series show an anti-solar cycle trend. This observation is discussed
in terms of the Solar Radiation Physical Modeling (SRPM) program and
solar images from Precision Solar Photometric Telescope (PSPT) that
provides the areas of active regions on the solar disk as function of
time to generate a modeled SSI time series that is concurrent with the
SIM observations. The findings from SIM also suggest a very different
solar forcing for the stratosphere than has been previously considered.
---------------------------------------------------------
Title: Semiempirical Models of the Solar Atmosphere. III. Set of
Non-LTE Models for Far-Ultraviolet/Extreme-Ultraviolet Irradiance
Computation
Authors: Fontenla, J. M.; Curdt, W.; Haberreiter, M.; Harder, J.;
Tian, H.
2009ApJ...707..482F Altcode:
Semiempirical atmospheric models of solar surface features as observed
at moderate resolution are useful tools for understanding the observed
solar spectral irradiance variations. Paper I described a set of models
constructed to reproduce the observed radiance spectrum for solar
surface features at ~2 arcsec resolution that constitute an average
over small-scale features such as granulation. Paper II showed that a
revision of previous models of low-chromospheric inter-network regions
explains the observed infrared CO lines in addition to the UV and radio
continuum from submillimeter to centimetric wavelengths. The present
paper (1) shows that the Ca II H and K line wing observations are
also explained by the new quiet-Sun-composite model, (2) introduces
new low-chromospheric models of magnetic features that follow the
ideas in Paper II, (3) introduces new upper chromospheric structures
for all quiet-Sun and active-region models, and (4) shows how the new
set of models explains EUV/FUV observations of spectral radiance and
irradiance. This paper also discusses the chromospheric radiative-loss
estimates in each of the magnetic features. The new set of models
provides a basis for the spectral irradiance synthesis at EUV/FUV
wavelengths based on the features observed on the solar surface.
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Title: Calculation of the Solar UV/EUV Spectrum in Spherical Symmetry
Authors: Haberreiter, Margit; Fontenla, Juan
2009AIPC.1171..355H Altcode: 2009arXiv0906.2011H
We present work in progress concerning spectral synthesis calculations
of the solar UV/EUV in spherical symmetry carried out with the Solar
Radiation Physical Modeling (SRPM) project. We compare the synthetic
irradiance spectrum for the quiet Sun with the recent solar minimum
spectrum taken with the EVE rocket instrument. The good agreement of
the synthetic spectrum with the observation shows that the employed
atmosphere structures are suitable for UV/EUV irradiance calculations.
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Title: Particle diffusion, flows, and NLTE calculations
Authors: Fontenla, J. M.; Avrett, E.
2009AIPC.1171...61F Altcode:
Particle diffusion plays an important role in the transition-region
between the chromosphere and the corona of the Sun and solar-type
stars. Also, mass flows are often observed and these in combination
with diffusion make it necessary to perform physically consistent
calculations to determine the elemental ionization and atom/ion level
populations. Such calculations require the solution of NLTE radiative
transfer equations to determine the ionization and level populations,
and need to include the effects of particle transport processes. This
paper discusses the basis and implementation of the method used in
the Solar Radiation Physical Modeling (SRPM) project, also implemented
for H and He in the PANDORA code.
---------------------------------------------------------
Title: Solar irradiance forecast and far-side imaging
Authors: Fontenla, J. M.; Quémerais, E.; González Hernández, I.;
Lindsey, C.; Haberreiter, M.
2009AdSpR..44..457F Altcode:
This paper presents a new approach to forecasting short-term Lyα solar
irradiance variations due to the presence and evolution of magnetically
heated regions in the Sun's outer atmosphere. This scheme is based
on images of the solar disk at key wavelengths, currently Ca II K
filtergrams, maps of backscattered solar Lyα from the interplanetary
medium, and helioseismic images of large far-side active regions. The
combination of these resources allows accurate forecasts of the
UV solar irradiance several days in advance. The technique takes
into consideration the evolution of recently observed activity on
the Sun's near surface as well as active regions on the Sun's far
side. The far-side helioseismic maps and the Lyα backscattering are
very important, because of the long period of time features spend on
the Sun's far side compared with their typical evolution time and their
relatively sudden appearance on the near side. We describe the basics
of the forecasting technique and apply it to a case study that shows
how the technique dramatically improves Lyα irradiance forecasting. An
extension of the technique described here promises realistic forecasts
of the entire FUV/EUV solar spectral irradiance spectrum.
---------------------------------------------------------
Title: Tools For Understanding And Forecasting Solar Spectral
Irradiance Variations
Authors: Fontenla, Juan; Haberreiter, M.; Harder, J.
2009SPD....40.1601F Altcode:
We describe the application and current status of the Solar
Radiation Physical Modeling (SRPM) project for understanding the
nature of the solar spectral irradiance (SSI) variations from EUV
to IR wavelengths. These tools enable up to a few weeks forecast of
variations of the spectrum of the solar irradiance at any location
in the Heliosphere. These methods are been also developed for very
detailed estimates of the EUV solar irradiance changes on the Earth
and planetary atmospheres. We show first results comparing visible
and IR SRPM computations with SORCE observations during the last few
years. Also, we show first results of the EUV irradiance computations
compared with some observations by SOHO/SUMER, SORCE/SOLSTICE, and
EVE rocket flight.
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Title: Solar UV/EUV Spectral Synthesis in Spherical Symmetry
Authors: Haberreiter, Margit; Fontenla, J.
2009SPD....40.3504H Altcode:
We present recent progress in the calculation of the solar coronal
spectrum in spherical symmetry, which allows us to correctly
account for the contribution of the extended corona to the irradiance
spectrum. With the Solar Radiation Physical Modeling (SRPM) system we
solve the full NLTE for the most abundant elements from H to Fe up to
ion charge 2. For higher ionization states the statistical equation
is solved in the optically thin approach. Presently, a total number
of 14,000 atomic levels and 170,000 spectral lines are included. The
calculations are based on 1D atmosphere structures for the chromosphere
and transition region for different solar surface features and various
coronal temperature structures for coronal features such as coronal
holes, the quiet and active corona. The results are compared with
the SOHO/EIT observations and the spectrum taken with the EVE rocket
instrument on April 14, 2008. These results are important for the
interpretation of the observations taken with the EVE instrument on
board the Solar Dynamics Observatory (SDO) expected to launch this year.
---------------------------------------------------------
Title: The Solar Radiation and Climate Experiment (SORCE): Measuring
the Sun's influence on climate from space
Authors: Harder, J.; Snow, M.; Kopp, G.; Fontenla, J.; Pilewskie,
P.; Richard, E.; Woods, T.
2009EGUGA..11.3317H Altcode:
The NASA Solar Radiation and Climate Experiment, launched in January
of 2003, is a suite of instruments that measures the variability of
both the Sun's total solar irradiance (TSI) and its solar spectral
irradiance (SSI) over the 110-2400 nm spectral range thereby accounting
for more the 97% of the sun's radiant output. The SORCE spectrometers
decompose the TSI signal into its spectral components, and the solar
cycle trends in the 300-2400 nm have been measured for the first
time. The SORCE instruments have revealed a number of important
findings that have significance to the earth-climate system. 1) The
Total Irradiance Monitor (TIM) measures the TSI with a precision of
about1.0 part per million (ppm) and very small degradation that is
correctable to about 10 ppm. Furthermore, recent laboratory studies
support the absolute calibration of the instrument's reported Solar
Cycle 23 solar minimum irradiance value of 1360.75 Wm-2, an important
finding for Earth radiation budget analyses. 2) The time series from
the Spectral Irradiance Monitor (SIM) shows that the observed TSI
trends are the sum of offsetting spectral irradiance trends rather
than the quasi-uniform change predicted from proxy/solar atmospheric
models. These observed spectral irradiance changes will enable more
realistic investigations of the mechanisms of climate responses to
solar forcing. 3) The Solar Stellar Irradiance Comparison Experiment
(SOLSTICE) is an ultraviolet spectrometer that was also onboard UARS
satellite; the combined missions have a continuous observational record
extending back to 1992 encompassing two solar minimum time periods. In
the FUV portion of the spectrum (112-180 nm), the SOLSTICE data shows
a lower spectral irradiance during the minimum of Solar Cycle 23 than
during the minimum period of Solar Cycle 22 by about 5%.
---------------------------------------------------------
Title: Trends in solar spectral irradiance variability in the visible
and infrared
Authors: Harder, Jerald W.; Fontenla, Juan M.; Pilewskie, Peter;
Richard, Erik C.; Woods, Thomas N.
2009GeoRL..36.7801H Altcode: 2009GeoRL..3607801H
The Spectral Irradiance Monitor (SIM) on-board the Solar Radiation
and Climate Experiment (SORCE) satellite provides the first multi-year
continuous measurements of solar spectral irradiance (SSI) variability
from 200-2400 nm, accounting for about 97% of the total solar irradiance
(TSI). In addition to irradiance modulation from active region passage,
the SSI values for wavelengths with a brightness temperature greater
than 5770 K show a brightening with decreasing solar activity, whereas
those with lower brightness temperatures show a dimming. These results
demonstrate that different parts of the solar atmosphere contribute
differently to the TSI with the behavior in the deep photospheric layers
giving an opposing and nearly compensating trend to that in the upper
photospheric and lower chromospheric layers. These findings need to
be incorporated into Earth-climate assessments since the solar forcing
induced by these differential trends are inherently different from the
relatively flat spectral contributions employed in the IPCC assessments.
---------------------------------------------------------
Title: Solar Irradiance Reference Spectra (SIRS) for the 2008 Whole
Heliosphere Interval (WHI)
Authors: Woods, Thomas N.; Chamberlin, Phillip C.; Harder, Jerald W.;
Hock, Rachel A.; Snow, Martin; Eparvier, Francis G.; Fontenla, Juan;
McClintock, William E.; Richard, Erik C.
2009GeoRL..36.1101W Altcode:
The IHY2007 Whole Heliosphere Interval (WHI) for solar Carrington
Rotation 2068 (20 March to 16 April 2008) has been very successful
in obtaining a wide variety of solar, heliospheric, and planetary
observations during times of solar cycle minimum conditions. One of
these efforts is the generation of solar irradiance reference spectra
(SIRS) from 0.1 nm to 2400 nm using a combination of satellite
and sounding rocket observations. These reference spectra include
daily satellite observations from TIMED Solar Extreme ultraviolet
Experiment (SEE) and Solar Radiation and Climate Experiment (SORCE)
instruments. The extreme ultraviolet range is also improved with
higher spectral resolution observations using the prototype SDO
Extreme ultraviolet Variability Experiment (EVE) aboard a sounding
rocket launched on 14 April 2008. The SIRS result is an important
accomplishment in that it is the first data set to have simultaneous
measurements over the full spectral coverage up to 2400 nm during
solar cycle minimum conditions.
---------------------------------------------------------
Title: SORCE Solar Irradiance Data Products
Authors: Lindholm, D. M.; Pankratz, C. K.; Knapp, B. G.; Meisner,
R.; Fontenla, J.; Harder, J. W.; McClintock, W. E.; Kopp, G.; Snow,
M.; Woods, T. N.
2008AGUFMSM11B1623L Altcode:
The Laboratory for Atmospheric and Space Physics (LASP) at the
University of Colorado manages the SOlar Radiation and Climate
Experiment (SORCE) Science Data System. This data processing system
routinely produces Total Solar Irradiance (TSI) and Spectral Solar
Irradiance (SSI) data products, which are formulated using measurements
from the four primary instruments on board the SORCE spacecraft. The TIM
instrument provides measurements of the TSI, whereas the SIM, SOLSTICE,
and XPS instruments collectively provide measurements of the solar
irradiance spectrum from 1 nm to 2400 nm (excluding 31-115 nm, which
is measured by the SEE instrument on NASA's TIMED mission). Derived
products, such as the Magnesium II Core-to-Wing Index which can be
used for space weather applications, are also produced. The SORCE
Science Data System utilizes raw spacecraft and instrument telemetry,
calibration data, and other ancillary information to produce a
variety of solar irradiance data products that have been corrected
for all known instrumental and operational factors. Since launch of
the SORCE spacecraft in January 2003, science processing algorithms
have continued to mature, instrument calibrations (e.g. degradation
corrections) have improved, and regularly updated versions of data
products have been released. "Level 3" data products (time-averaged over
daily and six-hourly periods and/or spectrally re-sampled onto uniform
wavelength scales) are routinely produced and delivered to the public
via the SORCE web site (http://lasp.colorado.edu/sorce/data/), and
are archived at the Goddard Earth Sciences (GES) Data and Information
Services Center (DISC). Native resolution "Level 2" products are also
available for scientific studies. This poster provides an overview
of the SORCE data processing system, summarizes the present state of
the processing algorithms, describes the quality of the current SORCE
data products, provides details on how to access SORCE science data,
and presents future plans.
---------------------------------------------------------
Title: TSIS: The Total Solar Irradiance Sensor
Authors: Sparn, T.; Pilewskie, P.; Harder, J.; Kopp, G.; Richard,
E.; Fontenla, J.; Woods, T.
2008AGUFM.A51F0165S Altcode:
The Total Solar Irradiance Sensor (TSIS) is a dual-instrument
package that will acquire solar irradiance in the next decade on the
National Polar-orbiting Operational Environmental Satellite System
(NPOESS). Originally de-manifested during the 2006 NPOESS restructuring,
TSIS was restored following a decision by the NPOESS Executive Committee
earlier this year because of its critical role in determining the
natural forcings of the climate system and the high priority given it by
the 2007 Earth Science Decadal Survey. TSIS is comprised of the Total
Irradiance Monitor, or TIM, which measures the total solar irradiance
(TSI) that is incident at the boundaries of the atmosphere; and the
Spectral Irradiance Monitor, or SIM, which measures solar spectral
irradiance (SSI) from 200 nm to 2400 nm (96 percent of the TSI). The
TSIS TIM and SIM are heritage instruments to those currently flying
on the NASA Solar Irradiance and Climate Experiment (SORCE). Both were
selected as part of the TSIS because of their unprecedented measurement
accuracy and stability, and because both measurements are essential to
constraining the energy input to the climate system and interpreting the
response of climate to external forcing. This paper will describe those
attributes of TSIS which uniquely define its capability to continue the
30-year record of TSI and to extend the new 5-year record of SSI. The
role of the solar irradiance data record in the present climate state,
as well as in past and future climate change, will also be presented.
---------------------------------------------------------
Title: Solar Spectral Variability as measured by the SORCE SIM
Instrument
Authors: Harder, J. W.; Fontenla, J.; Pilewskie, P.; Richard, E.;
Woods, T.
2008AGUFMSH23A1630H Altcode:
The Spectral Irradiance Monitor (SIM) on-board the Solar Radiation and
Climate Experiment (SORCE) satellite provides the first comprehensive
measurements of solar spectral irradiance (SSI) variability from
200-2400 nm, accounting for about 97 percent of the total solar
irradiance (TSI) incident at the top of the Earth's atmosphere. SIM
observations indicate that, in addition to modulation due to active
region passage, the SSI values for wavelengths with a brightness
temperature greater than 5770 K show a brightening with decreasing solar
activity, whereas below this value there is a dimming. These results
demonstrate that different parts of the solar atmosphere contribute
differently to the TSI with the behavior in the deep photospheric
layers giving an opposing and nearly compensating solar cycle trend
to that in the upper photospheric and lower chromospheric layers that
produce the ultraviolet contributions. We will show these results
over the last 4.5 years of the mission during the descending phase
of Solar Cycle 23 that includes the solar minimum time period of the
Whole Heliosphere Interval (WHI).
---------------------------------------------------------
Title: Understanding and forecasting solar EUV and UV irradiance
variations
Authors: Haberreiter, M.; Fontenla, J.; Gonzalez-Hernandez, I.;
Lindsey, C.; Quemerais, E.
2008AGUFMSA24A..02H Altcode:
We describe the application and current status of the Solar Radiation
Physical Modeling (SRPM) project for understanding the nature of the
solar EUV and UV irradiance variations and building tools to forecast
short and medium term variations of the solar irradiance spectrum at
any location in the Heliosphere. These methods can be used for very
detailed estimates of the EUV solar irradiance changes on the Earth and
planetary atmospheres. Reliable EUV estimates are an important input
for the modeling of the physical parameters of the thermosphere. In
the presentation we show the current status, the solar atmospheric
models, the synthetic EUV and UV spectra and the performance of the
forecasting tool.
---------------------------------------------------------
Title: Modeling the UV/EUV Spectrum with SRPM
Authors: Haberreiter, M.; Fontenla, J.; Curdt, W.; Tian, H.
2008ESPM...12.3.12H Altcode:
We present a new set of semi-empirical solar atmosphere structures
for different features on the solar disk that is consistent with the
latest inter- network model by Fontenla et al. (2007), which reproduces
the CO lines in the IR as well as the UV and radio continua. The
intensity distribution of SUMER observations is used to define a set
of solar disk features that accounts for the observed range of upper
chromospheric heating. Using these models the UV/EUV (as well as longer
wavelengths) radiance spectra are computed with SRPM in full-NLTE using
the latest available atomic data and considering 24 elements up to high
ionization stages with a total of approximately 14000 atomic levels
and approximately 170000 line transitions. The radiance spectra of
the new atmosphere structures allow us to study in detail the varying
contributions of these features to the solar spectral irradiance. The
synthetic spectra are compared with SUMER data and EUV irradiance
observations obtained with the EVE rocket-instrument during a recent
rocket flight.
---------------------------------------------------------
Title: Chromospheric heating by the Farley-Buneman instability
Authors: Fontenla, J. M.; Peterson, W. K.; Harder, J.
2008A&A...480..839F Altcode:
Context: Chromospheric heating produces UV emissions that can only
occur in an enhanced electron temperature medium. In the quiet Sun the
radiative losses are orders of magnitude larger than those in the much
hotter corona. Chromospheric heating mechanisms considered previously
(e.g. shock waves and nanoflares) have failed to account for the
observed persistency and uniformity of UV lines and continua. Also,
resistive magnetic free-energy dissipation is not efficient enough in
the highly electrically conductive solar atmosphere. <BR />Aims: In this
paper we consider plasma effects in the low chromosphere and propose
that the Farley-Buneman (hereafter FB) plasma-instability mechanism
provides the mechanism for dissipating the energy of convectively driven
motions of neutral atoms into chromospheric heating in the Sun and other
cool stars that have a partially ionized chromosphere. <BR />Methods:
Analysis of the ion acoustic sound speed and consideration of recent
measurements of magnetic field in the quiet, inter-network, solar
low chromosphere are carried out in the context of understanding the
characteristics and onset of chromospheric heating. The FB instability
is triggered by the cross-field motion of the partially ionized gas at
velocities in excess of the ion acoustic velocity. The ions acquire
their cross-field velocities through collisions with the much denser
chromospheric neutral atoms. Estimates of cross-field velocities are
obtained from consideration of both spectral line widths and convection
numerical simulations that indicate values from a few to several km
s<SUP>-1</SUP> at the top of the practically radiative-equilibrium low
chromosphere. <BR />Results: The FB instability is triggered by the
cross-field motion of the neutral component of the partially ionized gas
at velocities in excess of the ion acoustic velocity. This instability
occurs in the solar chromosphere because electrons become strongly
magnetized just above the photosphere, while heavy ions and protons
remain unmagnetized, and only at the very top of the chromosphere do
they become magnetized. <BR />Conclusions: We find that convective
overshoot motions are drivers of the FB instability and provide enough
energy to account for the upper chromospheric radiative losses in the
quiet-Sun internetwork and network lanes.
---------------------------------------------------------
Title: Tools for understanding and forecasting solar EUV and UV
irradiance variations
Authors: Fontenla, Juan; Haberreiter, Margit; Quemerais, E.
2008cosp...37..911F Altcode: 2008cosp.meet..911F
We describe the application and current status of the Solar Radiation
Physical Modeling (SRPM) project for understanding the nature of the
solar EUV and UV irradiance variations and building tools to forecast
short and medium term variations of the spectrum of the solar irradiance
irradiance at any location in the Heliosphere. These methods can be
used for very detailed estimates of the EUV solar irradiance changes
on the Earth and planetary atmospheres.
---------------------------------------------------------
Title: Solar Spectral Irradiance Variability in the Near Infrared
and Correlations to the Variability of Total Solar Irradiance During
the Declining Phase of Solar Cycle 23
Authors: Richard, E. C.; Harder, J. W.; Fontenla, J.; Pilewskie, P.;
Kopp, G.; Woods, T. N.
2007AGUFMGC31B0349R Altcode:
The Spectral Irradiance Monitor (SIM) as part of the NASA EOS SORCE
mission continuously monitors the solar spectral irradiance (SSI)
across the wavelength region spanning the ultraviolet, visible and
near infrared (a region encompassing >97% of the TSI measured by
the SORCE Total Irradiance Monitor, TIM). These are the first daily
measurements from space with the required precision to detect real
changes in SSI. The record of TSI measured from space tracks changes
in solar total energy output and establishes the baseline for energy
input for the Earth. Where this radiative energy is deposited into
the Earth system, how the climate responds to solar variability,
and the mechanisms of climate response, are determined by how
the incident solar radiation is distributed with wavelength, the
SSI. For the near IR region in particular, spectral decomposition of
the TSI variability provides TOA constraints on the direct input for
atmospheric heating simulations. We present here the first long-term,
continuous measurements of the near infrared variability of solar
spectral irradiance and establish quantitative correlations of near
infrared variability across the spectral region of the solar H minus
opacity minimum with TSI variability. The unprecedented precision of
the SIM near-infrared measurements provide a direct determination
of the wavelength dependence of the facular and sunspot contrasts
and serve to refine solar atmospheric models of the solar magnetic
features that produce irradiance variability in emission from the
deepest photospheric layers.
---------------------------------------------------------
Title: Variation of Atmospheric Heating Rates Derived from SORCE
Solar Spectra and the SRPM Model
Authors: Fontenla, J.; Pilewskie, P.; Harder, J.; Snow, M.; Richard,
E.; Woods, T.
2007AGUFMGC31B0343F Altcode:
Measurements from the SOLSTICE and SIM instruments on board the Solar
Radiation and Climate Experiment (SORCE) cover the 200-2400 nm region
and span a time frame from August 2003 to the present and are able
to characterize the solar spectral irradiance variability during the
descending phase of Solar Cycle 23. Because absorption and scattering
processes in the Earth's atmosphere are highly spectrally dependent,
the spectral distribution and variability of the Sun's radiative energy
is an important boundary condition for quantifying Earth's radiation
budget as well as the vertical deposition of solar radiation in the
atmosphere. The SORCE observations allow for the very first time the
derivation of spectral atmospheric heating rates from measured spectral
variability. The variability in spectral irradiance exhibited in the
plage- versus sunspot-dominated cases leads to significant differences
in atmospheric heating compared to the Quiet Sun, particularly evident
in the mid-visible ozone Chappuis continuum and in the near infrared
water bands. When integrated over the visible and near-infrared spectral
bands these differences are on the order of 0.1 K per day. The findings
from the SORCE observations and results derived from Solar Radiation
Physical Modeling (SRPM) project will be presented in this study.
---------------------------------------------------------
Title: SORCE Solar Irradiance Data Products
Authors: Lindholm, D. M.; Pankratz, C. K.; Knapp, B. G.; Meisner,
R.; Fontenla, J.; Harder, J. W.; McClintock, W. E.; Kopp, G.; Snow,
M.; Woods, T. N.
2007AGUFMSH13A1105L Altcode:
The Laboratory for Atmospheric and Space Physics (LASP) at the
University of Colorado manages the SOlar Radiation and Climate
Experiment (SORCE) Science Data System. This data processing system
routinely produces Total Solar Irradiance (TSI) and Spectral Solar
Irradiance (SSI) data products, which are formulated using measurements
from the four primary instruments on board the SORCE spacecraft. The TIM
instrument provides measurements of the TSI, whereas the SIM, SOLSTICE,
and XPS instruments collectively provide measurements of the solar
irradiance spectrum from 1 nm to 2400 nm (excluding 31-115nm, which
is measured by the SEE instrument on NASA's TIMED mission). The SORCE
Science Data System utilizes raw spacecraft and instrument telemetry,
calibration data, and other ancillary information to produce a variety
of solar irradiance data products that have been corrected for all
known instrumental and operational factors. Since launch of the SORCE
spacecraft in January 2003, science processing algorithms have continued
to mature, and "Level 3" data products (time-averaged and/or spectrally
resampled onto uniform wavelength scales) are routinely being produced
and delivered to the public via the SORCE web site, and are archived at
the Goddard Earth Sciences (GES) Data and Information Services Center
(DISC, formerly DAAC). This poster provides an overview of the SORCE
data processing system, summarizes the present state of the processing
algorithms and future plans, describes the quality of the current SORCE
data products, and provides details on how to access SORCE science data.
---------------------------------------------------------
Title: The LASP Interactive Solar IRradiance Datacenter (LISIRD)
Authors: Pankratz, C. K.; Lindholm, D. M.; Snow, M.; Knapp, B.;
Woodraska, D.; Templeman, B.; Woods, T. N.; Eparvier, F. G.; Fontenla,
J.; Harder, J.; McClintock, W. E.
2007AGUFMIN22A..08P Altcode:
The Laboratory for Atmospheric and Space Physics (LASP) has been
making space-based measurements of solar irradiance for many decades,
and thus has established an extensive catalog of past and ongoing
space- based solar irradiance measurements. In order to maximize the
accessibility and usability of solar irradiance data and information
from multiple missions, LASP is developing the LASP Interactive
Solar IRradiance Datacenter (LISIRD) to better serve the needs of
researchers, educators, and the general public. This data center is
providing interactive and direct access to a comprehensive set of solar
spectral irradiance measurements from the soft X-ray (XUV) at 0.1 nm
up to the near infrared (NIR) at 2400 nm, as well as state-of-the-art
measurements of Total Solar Irradiance (TSI). LASP researchers are
also responsible for an extensive set of solar irradiance models
and historical solar irradiance reconstructions, which will also be
accessible via this data center over time. LISIRD currently provides
access to solar irradiance data sets from the SORCE, TIMED-SEE,
UARS-SOLSTICE, and SME instruments, spanning 1981 to the present,
as well as a Lyman Alpha composite that is available from 1947 to
the present. LISIRD also provides data products of interest to the
space weather community, whose needs demand high time cadence and near
real-time data delivery. This poster provides an overview of the LISIRD
system, summarizes the data sets currently available, describes future
plans and capabilities, and provides details on how to access solar
irradiance data through LISIRD's various interfaces.
---------------------------------------------------------
Title: Semiempirical Models of the Solar Atmosphere. II. The Quiet-Sun
Low Chromosphere at Moderate Resolution
Authors: Fontenla, J. M.; Balasubramaniam, K. S.; Harder, J.
2007ApJ...667.1243F Altcode:
We present a new, one-dimensional model of the solar
atmosphere (called SRPM 305) at moderate angular resolution
(~1<SUP>”</SUP>-2<SUP>”</SUP>). Key characteristics of the SRPM 305
model include (1) a minimum temperature of ~3800 K at a gas pressure
of ~80 dyne cm<SUP>-2</SUP> and (2) a rapid temperature rise above the
temperature-minimum layer that results in substantial overionization
of most elements when compared with LTE calculations. The model
calculations reproduce the ~4300 K minimum brightness temperature of
the UV continuum (between 1400-1500 Å) observed by SUMER and the ~4400
K observed minimum radio-continuum brightness temperature (between
wavelengths 0.01 and 100 mm). Neither the UV nor the radio continuum
bear on the low-temperature minimum value because their broad intensity
contribution functions cause the higher temperatures of the upper
chromospheric layers to effectively hide the low minimum temperature
region. The SRPM 305 model reproduces the observed intensities of CO
lines at 4.466 μm, at both the disk center and near the limb, by using
C and O abundances consistent with recent literature low values. The
model also reproduces observed intensities of C I spectral lines at
5381 and 8337 Å, CH lines at about 4306 Å, the CN band head at 3883
Å, and the O I lines at 7772, 7774, and 7776 Å, respectively. Using
the SRPM 305 model, we find no significant abundance variations
between the photosphere and the low chromosphere. Consequently,
the single-component model presented here matches several apparently
contradictory observations and thereby resolves the controversy about
the temperature minimum value.
---------------------------------------------------------
Title: Log-normal intensity distribution of the quiet-Sun FUV
continuum observed by SUMER
Authors: Fontenla, J. M.; Curdt, W.; Avrett, E. H.; Harder, J.
2007A&A...468..695F Altcode:
We analyse observations of the quiet-Sun far ultraviolet (FUV)
continuum at various wavelengths near 1430 Å obtained by the SUMER
instrument on SOHO. According to semi-empirical atmospheric models
this continuum originates from the layers in the chromosphere where
the temperature rises from low values at near-radiative equilibrium
to a plateau of about 6000 K. We study raster images and intensity
distribution histograms and find that a single log-normal distribution
matches these observations very well, and that the spatial structure
observed corresponds to a mixture of features at supergranular and
smaller scales that probably correspond to granular clusters. Also,
a log-normal distribution was found in the literature to correspond
to other chromospheric features and we compare here with histograms
obtained from a H i Ly-α quiet-Sun image. Because the continuum around
1430 Å is mainly produced by Si i recombination it is expected to
respond well to deep chromospheric heating and not be directly affected
by velocities. The data suggest that chromospheric heating originates
through dissipation of magnetic free-energy fields of small size and
magnitude in underlying photospheric intergranular lanes. It has been
suggested that such fields can be produced by photospheric dynamos
at the intergranular scale and/or by complex fields emerging in a
“magnetic carpet”. Such fields are expected to have sufficient
free-energy to power the chromospheric heating. Plasma instabilities,
such as the Farley-Buneman instability, would allow this free-energy
to be dissipated in the chromosphere.
---------------------------------------------------------
Title: Chromospheric Heating and Low-Chromosphere Modeling
Authors: Fontenla, J. M.; Balasubramaniam, K. S.; Harder, J.
2007ASPC..368..499F Altcode:
Updated modeling of the “quiet” Sun low chromosphere based on existing
observations show that at least all the data we examined in detail
is consistent with a single model that has a very low temperature
minimum and a sharp temperature increase above it. Such a model
explains simultaneously the deep CO lines observed on the disk and
off the limb, as well as the UV and radio continua and thus solves
the controversy regarding the minimum temperature without resorting
to “bifurcation”. This results simply from considering both: the
spatial extent of the intensity contribution functions, and non-LTE. The
model also shows that the structure of the low-chromosphere cannot be
unambiguously inferred from any simple diagnostic but rather needs
to be examined by forward modeling with consideration of full-NLTE
radiative transfer and observations at many wavelengths. In addition,
the characteristics of this model are consistent with the magnetic
heating of the chromosphere. The mechanism proposed consists of small
scale magnetic fields and sudden triggering of their free-energy
dissipation by a plasma instability starting at the base of the
chromospheric plateau. As a result of such a mechanism a complex spatial
structure would result in the upper chromosphere that can hardly be
explained in terms of shocks but instead shows magnetic patterns.
---------------------------------------------------------
Title: Using the MODTRAN5 radiative transfer algorithm with NASA
satellite data: AIRS and SORCE
Authors: Anderson, Gail P.; Berk, Alexander; Chetwynd, James H.,
Jr.; Harder, Jerald; Fontenla, Juan M.; Shettle, Eric P.; Saunders,
Roger; Snell, Hilary E.; Pilewskie, Peter; Kindel, Bruce C.; Gardner,
James A.; Hoke, Michael L.; Felde, Gerald W.; Lockwood, Ronald B.;
Acharya, Prabhat K.
2007SPIE.6565E..1OA Altcode: 2007SPIE.6565E..57A
Testing MODTRA <SUP>TM</SUP>5 (MOD5) capabilities against NASA
satellite state-of-the-art radiance and irradiance measurements has
recently been undertaken. New solar data have been acquired from
the SORCE satellite team, providing measurements of variability
over solar rotation cycles, plus an ultra-narrow calculation for a
new solar source irradiance, extending over the full MOD5 spectral
range. Additionally, a MOD5-AIRS analysis has been undertaken with
appropriate channel response functions. Thus, MOD5 can serve as
a surrogate for a variety of perturbation studies, including two
different modes for including variations in the solar source function,
Io: (1) ultra-high spectral resolution and (2) with and without
solar rotation. The comparison of AIRS-related MOD5 calculations,
against a suite of 'surrogate' data generated by other radiative
transfer algorithms, all based upon simulations supplied by the AIRS
community, provide validation in the Long Wave Infrared (LWIR). All
~2400 AIRS instrument spectral response functions (ISRFs) are expected
to be supplied with MODTRAN <SUP>TM</SUP>5. These validation studies
show MOD5 replicates line-by-line (LBL) brightness temperatures (BT)
for 30 sets of atmospheric profiles to approximately -0.02°K average
offset and <1.0°K RMS.
---------------------------------------------------------
Title: Atmospheric Sensitivity to Spectral Top-of-Atmosphere Solar
Irradiance Perturbations, Using MODTRAN-5 Radiative Transfer Algorithm
Authors: Anderson, G.; Berk, A.; Harder, G.; Fontenla, J.; Shettle,
E.; Pilewski, P.; Kindel, B.; Chetwynd, J.; Gardner, J.; Hoke, M.;
Jordan, A.; Lockwood, R.; Felde, G.; Archarya, P.
2006AGUFM.A11C..05A Altcode:
The opportunity to insert state-of-the-art solar irradiance measurements
and calculations, with subtle perturbations, into a narrow spectral
resolution radiative transfer model has recently been facilitated
through release of MODTRAN-5 (MOD5). The new solar data are from:
(1) SORCE satellite measurements of solar variability over solar
rotation cycle, & (2) ultra-narrow calculation of a new solar
source irradiance, extending over the full MOD5 spectral range,
from 0.2 um to far-IR. MODTRAN-5, MODerate resolution radiance and
TRANsmittance code, has been developed collaboratively by Air Force
Research Laboratory and Spectral Sciences, Inc., with history dating
back to LOWTRAN. It includes approximations for all local thermodynamic
equilibrium terms associated with molecular, cloud, aerosol and surface
components for emission, scattering, and reflectance, including multiple
scattering, refraction and a statistical implementation of Correlated-k
averaging. The band model is based on 0.1 cm-1 (also 1.0, 5.0 and 15.0
cm-1 statistical binning for line centers within the interval, captured
through an exact formulation of the full Voigt line shape. Spectroscopic
parameters are from HITRAN 2004 with user-defined options for additional
gases. Recent validation studies show MOD5 replicates line-by-line
brightness temperatures to within ~0.02ºK average and <1.0ºK
RMS. MOD5 can then serve as a surrogate for a variety of perturbation
studies, including the two modes for the solar source function,
Io. (1) Data from the Solar Radiation and Climate Experiment (SORCE)
satellite mission provide state-of-the-art measurements of UV, visible,
near-IR, plus total solar radiation, on near real-time basis. These
internally consistent estimates of Sun's output over solar rotation
and longer time scales are valuable inputs for studying effects of
Sun's radiation on Earth's atmosphere and climate. When solar rotation
encounters bright plage and dark sunspots, relative variations are
expected to be very small in visible wavelengths, although absolute
power is substantial. SORCE's Spectral Irradiance Monitor measurements
are readily included in comparative MOD5 calculations. (2) The embedded
solar irradiance within MOD5 must be compatible with the chosen band
model resolution binning. By matching resolutions some issues related
to the correlated-k band model parameterizations can be tested. Two
high resolution solar irradiances, the MOD5 default irradiance (Kurucz)
and a new compilation associated with Solar Radiation Physical Modeling
project (Fontenla), are compared to address the potential impact of
discrepancies between any sets of irradiances. The magnitude of solar
variability, as measured and calculated, can lead to subtle changes
in heating/cooling rates throughout the atmosphere, as a function of
altitude and wavelength. By holding chemical & dynamical responses
constant, only controlled distributions of absorbing gases, aerosols
and clouds will contribute to observed 1st order radiative effects.
---------------------------------------------------------
Title: Solar Radiation Physical Modeling project update
Authors: Fontenla, Juan
2006SPD....37.0205F Altcode: 2006BAAS...38..221F
In this presentation we describe the current status of the Solar
Radiation Physical Modeling (SRPM) project and compare its current
results with observations. We discuss the current state of the
quantitative physical modeling of the solar chromosphere and transition
region in regard to the available spectral observations. We show
how SRPM intends to contribute to developing more up to date models
that take into account dynamics and better address the energy balance
issues in the solar chromosphere and transition region. This research
is needed to understand the observations from ground and space and also
relate to the recent advances in photospheric modeling and simulations.
---------------------------------------------------------
Title: Semiempirical Models of the Solar Atmosphere. I. The Quiet-
and Active Sun Photosphere at Moderate Resolution
Authors: Fontenla, J. M.; Avrett, E.; Thuillier, G.; Harder, J.
2006ApJ...639..441F Altcode:
In this paper we study and modify previous semiempirical models of
the solar photosphere as observed at moderate spatial and temporal
resolution (~3" and ~30 minutes, respectively) in the main quiet- and
active Sun component features. Our present models are constructed to
match the relevant available observations at this resolution for which a
one-dimensional and time-independent stratification is reasonable. The
models do not describe the fine structure and temporal variability
observed in high-resolution images but correspond to a “radiation
averaging” over the fine-structure and p-mode variations. We use
the observed limb darkening in the range 0.3-2.4 μm, as well as the
absolute intensities and details of the spectral continua and lines
in this range, to validate and adjust the models. Using the method
described in a previous paper, we compute the emergent radiation
from our models in full detail for the visible and IR continuum and
the lines in the interval 0.3-5 μm for which we have atomic data from
NIST (~13,000 lines used) and molecular data from HITRAN and Gray &
Corbally (~480,000 molecular lines used). The observations, abundances,
and atomic/molecular data are improved over previous work and yield
models that better fit the observations. In addition, we construct a new
penumbra model. The visible and IR detailed spectra computed from these
models provide insight for understanding the effects of magnetic fields
on the solar irradiance and are useful tools for computing synthetic
spectral irradiances in different solar activity configurations.
---------------------------------------------------------
Title: The Solar Radiation Physical Modeling Project
Authors: Fontenla, J.; Dasgupta, S.
2005AGUFMSH41B1135F Altcode:
The Solar Radiation Physical Modeling (SRPM) project is a computing
system for quantitative evaluation of physical processes modeling
in the context of high spectral resolution solar observations. The
forward-computation modular design is based on a set of components
that permit the researcher to compute the high-resolution spectrum
of the solar atmosphere at any wavelength based on given physical
processes and parameters. The SRPM object-oriented design allows for
either internally computing or using externally generated parameters
(e.g., atmospheric models, level populations, etc.) and computing
very detailed radiative losses and emitted spectrum. The computed
data and the input atomic data are stored in relations databases
that are accessed via SQL. The atomic data is often updated with the
latest from NIST, TOPBASE, CHIANTI, etc. Current modules include: H and
other elements NLTE with PRD calculations, computation of coronal loop
footpoints transition region energy balance and H particle diffusion,
and computation of the entire solar spectrum for 1-dimensional models
with either LTE or provided ionization and level populations. A set
of semi-empirical 1-dimensional models is being developed for quiet
and active solar features to fit much of the observed spectra. New
modules and algorithms under construction are 3-dimensional NLTE
radiative transfer for chromospheric and prominence applications,
convection-diffusion equation for studying flows and particle diffusion
in coronal loops and their footpoints, and MHD simulation coupled with
the NLTE radiative-transfer.
---------------------------------------------------------
Title: SORCE Solar Irradiance Data Products
Authors: Pankratz, C. K.; Knapp, B. G.; Fontenla, J. M.; Rottman,
G. J.; Woods, T. N.; Harder, J. W.; Kopp, G.; McClintock, W. E.;
Snow, M.
2005AGUFMSM43B1219P Altcode:
The SORCE Science Data System produces Total Solar Irradiance
(TSI) and Spectral Solar Irradiance (SSI) data products on a daily
basis, which are formulated using measurements from the four primary
instruments on board the SORCE spacecraft. The TIM instrument provides
measurements of the TSI, whereas the SIM, SOLSTICE, and XPS instruments
collectively provide measurements of the solar irradiance spectrum from
1 nm to 2700 nm (excluding 31-115 nm, which is measured by the TIMED
SEE experiment). The Science Data System utilizes raw spacecraft and
instrument telemetry, calibration data, and other ancillary information
to produce a variety of data products that have been corrected for
all known instrumental and operational factors. Since launch of
the SORCE spacecraft in January 2003, science processing algorithms
have continued to mature, and "Level 3" data products are routinely
being produced and delivered to the public via the SORCE web site and
the Goddard Earth Sciences (GES) Distributed Active Archive Center
(DAAC). This poster provides an overview of the SORCE data processing
system, summarizes the present state of the processing algorithms and
future plans, describes the quality of the current SORCE data products,
and provides details on how to access SORCE science data. The NPOESS
TSIS instrument package will also include TIM and SIM instruments,
having direct flight heritage from the SORCE mission, and will produce
data products similar to those produced by the existing SORCE Science
Data System.
---------------------------------------------------------
Title: The spectral composition of TSI as measured by the SORCE SIM
solar spectral radiometer
Authors: Harder, J. W.; Fontenla, J.; Kopp, G.; Richard, E.; Woods, T.
2005AGUFMSH41A1113H Altcode:
The SORCE (Solar Radiation and Climate Experiment) SIM (Spectral
Irradiance Monitor) instrument is a satellite-borne prism spectrometer
that measures the solar spectrum from 200-2700 nm with a cadence of
at least 2 spectra per day and a wavelength dependent resolution
of 1-33 nm. This instrument provides the temporal evolution of
solar irradiance in the ultraviolet, visible, and infrared spectral
regions. At some wavelengths in the ultraviolet, the SIM measurements
exhibit variations similar to the Mg II core-to-wing ratio, and in the
visible and IR they show similarities to the total solar irradiance
(TSI) record, but with differing wavelength dependent amplitudes,
phases, and shapes. Furthermore, the observed TSI variations can be
examined in the context of the integral of the spectral irradiance
over discrete spectral bands in the 200-1600 nm region showing the
spectral contributions of solar active regions. Further insight into
the solar variability observed by the SIM can be gained from analyzing
the distribution of solar features as measured by the Precision Solar
Photometric Telescope in conjunction with spectral decomposition (ApJ,
1999, 518, 480).
---------------------------------------------------------
Title: The LASP Interactive Solar IRradiance Datacenter (LISIRD)
Authors: Snow, M.; Woods, T. N.; Eparvier, F. G.; Fontenla, J.;
Harder, J.; McClintock, W. E.; Pankratz, C.; Richard, E.; Windnagel,
A.; Woodraska, D.
2005AGUFMIN33B1180S Altcode:
LASP has created an online resource for combined solar irradiance
datasets from the SORCE, TIMED, UARS, and SME missions. The LASP
Interactive Solar IRradiance Datacenter (LISIRD) not only provides
unified access to the individual datasets, but also combines them for
ease of use by scientists, educators, and the general public. In
particular, LISIRD makes available composite spectra and time
series. The TIMED SEE, SORCE SOLSTICE, and SORCE SIM instruments
produce spectra that together cover the solar spectrum from 1 to 2700
nm. Through the LISIRD interface, the user can get data that bridges
the various missions in both wavelength and time. LISIRD also hosts
data products of interest to the space weather community. They have
slightly different needs than the atmospheric modelers that are the
typical users of irradiance data. For space weather applications, high
time cadence and near real-time data delivery are key. For these users,
we make our observations available shortly after spacecraft contact,
and append the observations to a single data file which they can
retrieve using anonymous ftp every few hours. The third component
of LISIRD is the Solar Physical Radiation Model (SPRM) results of
Fontenla et al. It provides a model of current solar activity, the
synthetic spectral irradiance, and tools that permit one to model the
solar activity source of the spectral irradiance variations.
---------------------------------------------------------
Title: Chromospheric plasma and the Farley-Buneman instability in
solar magnetic regions
Authors: Fontenla, J. M.
2005A&A...442.1099F Altcode:
We study the plasma parameters in recent models of the observed magnetic
features in the solar atmosphere and find that electrons are strongly
magnetized in the chromosphere but protons are unmagnetized up to the
transition region. Considering the magnetization and the classical
Pedersen conductivity we find that magnetic diffusion is too small
for effectively affecting propagating MHD waves of periods of a few
minutes. However, the chromospheric-plasma parameters suggest a scenario
in which upward-propagating fast-mode MHD waves of mHz frequencies
would trigger the Farley-Buneman plasma instability at chromospheric
layers where horizontal magnetic fields are present. We show that,
because of the collisions between charged particles and neutral H atoms,
the conditions in the chromosphere meet the instability criteria if
the MHD wave velocity amplitude is lower but near the adiabatic sound
speed. The instability growth is much faster than the wave frequency
and the instability would quickly saturate. The electrostatic plasma
waves resulting from the instability are expected to produce anomalous
resistivity and wave energy dissipation that would heat the chromosphere
as well as absorb the p-modes in magnetic regions.
---------------------------------------------------------
Title: The Spectral Irradiance Monitor: Scientific Requirements,
Instrument Design, and Operation Modes
Authors: Harder, Jerald; Lawrence, George; Fontenla, Juan; Rottman,
Gary; Woods, Thomas
2005SoPh..230..141H Altcode:
The Spectral Irradiance Monitor (SIM) is a dual Fèry prism
spectrometer that employs 5 detectors per spectrometer channel to
cover the wavelength range from 200 to 2700 nm. This instrument is
used to monitor solar spectral variability throughout this wavelength
region. Two identical, mirror-image, channels are used for redundancy
and in-flight measurement of prism degradation. The primary detector
for this instrument is an electrical substitution radiometer (ESR)
designed to measure power levels ∼1000 times smaller than other
radiometers used to measure TSI. The four complementary focal plane
photodiodes are used in a fast-scan mode to acquire the solar spectrum,
and the ESR calibrates their radiant sensitivity. Wavelength control
is achieved by using a closed loop servo system that employs a linear
charge coupled device (CCD) in the focal plane. This achieves 0.67
arcsec control of the prism rotation angle; this is equivalent to
a wavelength positioning error of δλ/λ = 150 parts per million
(ppm). This paper will describe the scientific measurement requirements
used for instrument design and implementation, instrument performance,
and the in-flight instrument operation modes.
---------------------------------------------------------
Title: The Spectral Irradiance Monitor: Measurement Equations and
Calibration
Authors: Harder, Jerald W.; Fontenla, Juan; Lawrence, George; Woods,
Thomas; Rottman, Gary
2005SoPh..230..169H Altcode:
The Spectral Irradiance Monitor (SIM) is a satellite-borne spectrometer
aboard the Solar Radiation and Climate Experiment (SORCE) that measures
solar irradiance between 200 and 2700 nm. This instrument employs
a Fèry prism as a dispersing element, an electrical substitution
radiometer (ESR) as the primary detector, and four additional photodiode
detectors for spectral scanning. Assembling unit level calibrations
of critical components and expressing the sensitivity in terms of
interrelated measurement equations supplies the instrument's radiant
response. The calibration and analysis of the spectrometer's dispersive
and transmissive properties, light aperture metrology, and detector
characteristics provide the basis for these measurement equations. The
values of critical calibration parameters, such as prism and detector
response degradation, are re-measured throughout the mission to correct
the ground-based calibration.
---------------------------------------------------------
Title: The SORCE Science Data System
Authors: Pankratz, Christopher K.; Knapp, Barry G.; Reukauf, Randy A.;
Fontenla, Juan; Dorey, Michael A.; Connelly, Lillian M.; Windnagel,
Ann K.
2005SoPh..230..389P Altcode:
The SORCE Science Data System produces total solar irradiance (TSI)
and spectral solar irradiance (SSI) data products on a daily basis,
which are formulated using measurements from the four primary
instruments onboard the SORCE spacecraft. The Science Data System
utilizes raw spacecraft and instrument telemetry, calibration data,
and other ancillary information to produce and distribute a variety
of data products that have been corrected for all known instrumental
and operational effects. SORCE benefits from a highly optimized
object-oriented data processing system in which all data are stored
in a commercial relational database system, and the software itself
determines the versions of data products at run-time. This unique
capability facilitates optimized data storage and CPU utilization
during reprocessing activities by requiring only new data versions to be
generated and stored. This paper provides an overview of the SORCE data
processing system, details its design, implementation, and operation,
and provides details on how to access SORCE science data products.
---------------------------------------------------------
Title: The Spectral Irradiance Monitor (SIM): Early Observations
Authors: Rottman, Gary; Harder, Jerald; Fontenla, Juan; Woods, Thomas;
White, Oran R.; Lawrence, George M.
2005SoPh..230..205R Altcode:
This paper presents and interprets observations obtained by the Spectral
Irradiance Monitor (SIM) on the Solar Radiation and Climate Experiment
(SORCE) over a time period of several solar rotations during the
declining phase of solar cycle 23. The time series of visible and
infrared (IR) bands clearly show significant wavelength dependence
of these variations. At some wavelengths the SIM measurements are
qualitatively similar to the Mg II core-to-wing ratio, but in the
visible and IR they show character similar to the Total Solar Irradiance
(TSI) variations. Despite this overall similarity, different amplitudes,
phases, and temporal features are observed at various wavelengths. The
TSI can be explained as a complex sum of the various wavelength
components. The SIM observations are interpreted with the aid of solar
images that exhibit a mixture of solar activity features. Qualitative
analysis shows how the sunspots, faculae, plage, and active network
provide distinct contributions to the spectral irradiance at different
wavelengths, and ultimately, how these features combine to produce the
observed TSI variations. Most of the observed variability appears to
be qualitatively explained by solar surface features related directly
to the magnetic activity.
---------------------------------------------------------
Title: SORCE Solar Irradiance Data Products
Authors: Pankratz, C. K.; Knapp, B. G.; Fontenla, J. M.; Rottman,
G. J.; Woods, T. N.; Harder, J. W.; Kopp, G.; McClintock, W. E.;
Snow, M.
2005AGUSMSH51B..03P Altcode:
The SORCE Science Data System produces Total Solar Irradiance
(TSI) and Spectral Solar Irradiance (SSI) data products on a daily
basis, which are formulated using measurements from the four primary
instruments on board the SORCE spacecraft. The TIM instrument provides
measurements of the TSI, whereas the SIM, SOLSTICE, and XPS instruments
collectively provide measurements of the solar irradiance spectrum from
1 nm to 3000 nm (excluding 31-115nm, which is covered by the TIMED
SEE experiment). The Science Data System utilizes raw spacecraft and
instrument telemetry, calibration data, and other ancillary information
to produce a variety of data products that have been corrected for
all known instrumental and operational factors. Since launch of
the SORCE spacecraft in January 2003, science processing algorithms
have continued to mature, and "Level 3" data products are routinely
being produced and delivered to the public via the SORCE web site and
the Goddard Earth Sciences (GES) Distributed Active Archive Center
(DAAC). This poster provides an overview of the SORCE data processing
system, summarizes the present state of the processing algorithms and
the quality of the current SORCE data products, and provides details
on how to access SORCE science data.
---------------------------------------------------------
Title: Solar spectral irradiance variability comparisons of the SORCE
SIM instrument with monitors of solar activity and spectral synthesis
Authors: Harder, J.; Fontenla, J.; White, O.; Rottman, G.; Woods, T.
2005MmSAI..76..735H Altcode:
The SORCE (Solar Radiation and Climate Experiment) SIM (Spectral
Irradiance Monitor) instrument is a satellite-borne prism spectrometer
that measures the solar spectrum from 200-2700 nm with a cadence of at
least 2 spectra per day with a resolution of 1-33 nm. The nearly 800-day
long data set provides the temporal evolution of solar irradiance
throughout ultraviolet, visible and infrared spectral regions. At some
wavelengths in the ultraviolet, the SIM measurements exhibit variations
similar to Mg II index, and in the visible and IR they show similarities
to Total Solar Irradiance (TSI) record, but with differing amplitudes,
phases, and shapes relative to the monitors. The TSI can be explained
as a complex mix of the various wavelength components observed by
SIM. Further insight into the solar variability observed by SIM can
be gained from comparing an analysis of the distribution of solar
features as measured by PSPT (Precision Solar Photometric Telescope)
in conjunction with spectral synthesis. Most of the observed behavior
appears to be qualitatively explained by the observed solar surface
features that directly relate to the magnetic activity but some IR
variations are not readily explained as was noted by \citet{fontenla2}.
---------------------------------------------------------
Title: Physical modeling of spectral irradiance variations
Authors: Fontenla, J.; Harder, G.
2005MmSAI..76..826F Altcode:
In this paper we introduce the Solar Radiation Physical Modeling (SRPM)
methods and show its application to the modeling of spectral irradiance
variations observed by the Spectral Irradiance Monitor (SIM) onboard
SORCE. For the modeling we produce a set of seven physical models for
features observed on the solar atmosphere. These models account for the
available mid spatial and temporal-resolution observations of the main
quiet-Sun and active-region features at visible and IR wavelengths. The
computed, very high spectral resolution, spectra from each of these
models at ten different positions on the disk are used together with
image analysis of Precision Solar Photometric Telescope (PSPT) images
to produce an image mask and the absolute spectral irradiance that
corresponds to each set of PSPT images. After convolving the spectra
with the specific instrumental profile one can directly compare these
synthetic spectra with spectral irradiance observations. The combination
of the models matches the observed solar irradiance measured by SOLSPEC
within the combined observational and computational accuracy, but it
is on the high side. Also, the spectral irradiance visible and IR are
computed and convolved to SIM resolution for comparison or irradiance
variations.
---------------------------------------------------------
Title: Solar irradiance variability during the October 2003 solar
storm period
Authors: Woods, Thomas N.; Eparvier, Francis G.; Fontenla, Juan;
Harder, Jerald; Kopp, Greg; McClintock, William E.; Rottman, Gary;
Smiley, Byron; Snow, Martin
2004GeoRL..3110802W Altcode:
The extraordinary solar storms between 18 October 2003 and 5 November
2003 include over 140 flares, primarily from two different large
sunspot groups. There were 11 large X-class flares during this period,
including an X17 flare on 28 October 2003 and an X28 flare on 4 November
2003. The X28 flare is the largest flare since GOES began its solar
X-ray measurements in 1976. The solar (full-disk) irradiance during
these flares was observed by the instruments aboard the NASA Solar
Radiation and Climate Experiment (SORCE) spacecraft and the NASA
Thermosphere, Ionosphere, Mesosphere, Energetics, and Dynamics (TIMED)
spacecraft. The total solar irradiance (TSI) dropped by unprecedented
0.34% during this period due to the dark, large sunspots. In addition,
the TSI increased by 270 ppm during the X17 (4B optical) flare on 28
October, the first definitive measurement of a TSI flare event. The
ultraviolet (UV) variations for this X17 flare range from a factor
of about 50 shortward of 10 nm to about 10% for the Mg II 280 nm
emission. One interesting result for the UV flare variations is that
the broad wings of the H I Lyman-α (121.6 nm) emission increased by
more than a factor of 2 during the X17 flare while the core of the
Lyman-α emission only increased by 20%. Another interesting result is
the time profile of the Si III 120.6 nm emission, which shows a sharp
1-minute long increase by a factor of 17 during the impulsive phase.
---------------------------------------------------------
Title: Solar Irradiance Variations in the Visible and
Infrared:Comparison of the SORCE SIM instrument to the RISE model
Authors: Harder, J.; Davis, S.; Fontenla, J.; Rottman, G.; White, O.
2004AAS...204.7107H Altcode: 2004BAAS...36Q.798H
The Spectral Irradiance Monitor, SIM, is now providing the first
continuous record of solar irradiance variations throughout the
visible and near infrared. This instrument is aboard the Solar
Radiation and Climate Experiment, SORCE, which was launched in January
2003. SIM is a prism spectrometer that makes precise measurements
of the solar irradiance four times a day over the entire spectral
range 200-2700 nm. The SIM data provide important new information on
both the mechanisms of solar variability and on how the changing Sun
influences our terrestrial environment. The SIM observations will be
compared with concurrent computations of the solar spectral irradiance
generated from the RISE (Radiative Inputs from the Sun to the Earth)
synthesis code with decompositions of PSPT (Precision Solar Photometric
Telescope) images. This irradiance synthesis directly accounts for
the distribution and evolution of features on the Sun that contribute
to irradiance variations. The RISE method uses seven solar atmospheric
models (Fontenla, Avrett, and Loeser, ApJ, 406, 319, 1993) to represent
sunspots, plage, network, and quiet atmosphere. The contributions
of these seven atmospheric models are then weighted according to the
decomposition of the solar images. Time series comparisons at visible
wavelengths between the model and the SIM observations indicate good
agreement. However, current models of IR spectral irradiance are
inaccurate at long wavelengths; this behavior is due to the fact
that, contrary to the current model assumptions, the presence of
active regions on the solar disk increase the spectral irradiance
at all wavelengths even near the opacity minimum at 1.6 microns in
a manner similar to the observed TSI. Consequently, calculations of
solar spectral irradiance at wavelengths near 1.6 microns need to be
revised to match the observed solar irradiance.
---------------------------------------------------------
Title: Irradiance Observations of the October 28, 2003 X-17 Flare
Authors: Rottman, G.; Woods, T.; Kopp, G.; McClintock, W.; Snow, M.;
Fontenla, J.; Harder, J.
2004AGUSMSH31B..02R Altcode:
The Solar Radiation and Climate Experiment, SORCE, carries four
instruments that measure solar irradiance -- both total solar
irradiance, TSI, and spectral irradiance from soft X-rays, ultraviolet,
visible and near infrared. During the X-17 flare at 11:00 UT on October
28, 2003 the SORCE instruments were in ideal configurations to record
increases in TSI and at most observed wavelengths. The X-ray and UV
irradiance originating in the transition region and corona increased
by factors as large as fifty. This large flare also provided the first
measurement of an increase in TSI, a unique measurement that places an
important new constraint on the energy release during the flare. This
report is a survey and interpretation of the irradiance variations
observed during this X-17 flare.
---------------------------------------------------------
Title: The Signature of Solar Activity in the Infrared Spectral
Irradiance
Authors: Fontenla, J. M.; Harder, J.; Rottman, G.; Woods, T. N.;
Lawrence, G. M.; Davis, S.
2004ApJ...605L..85F Altcode:
The effects of solar activity on the spectral irradiance have
been studied using atmospheric semiempirical models developed
from observations of the various surface features observed on the
Sun. From these models, it has been the long-standing belief that the
contributions of active regions to solar irradiance at wavelengths in
the range of 1.2-3 μm is negative; that is, their net effect reduces
the overall solar irradiance at these wavelengths by a small amount. For
verifying the validity of the current modeling, we use the observed
plage areas to compute the solar irradiance variations at two bands
(centered at 0.516 and 1.553 μm wavelength). We compare in detail the
predictions of the models by Fontenla et al. with measurements of the
solar spectral irradiance variations obtained by the Spectral Irradiance
Monitor instrument aboard the Solar Radiation and Climate Experiment
spacecraft. The data comparison extends over a 6 month period in 2003
that covers several solar rotations. The comparison indicates that
the variations in the short wavelength display good agreement between
models and observations but also that the current models of IR spectral
irradiance are inaccurate at the long wavelength. This disagreement
in the IR may be due to the fact that, contrary to the current model
assumptions, the presence of active regions on the disk increases the
spectral irradiance at all wavelengths, even near 1.6 μm. Consequently,
the modeling of solar spectral irradiance at wavelengths in the range
around 1.6 μm has to be revised to match the new observations.
---------------------------------------------------------
Title: The SunRISE solar synthesis model
Authors: Fox, P.; White, O. R.; Fontenla, J. M.
2004cosp...35.2337F Altcode: 2004cosp.meet.2337F
We present a spectral synthesis approach to making quantitative
estimates of UV and EUV spectral variability. We combine the
identification of solar surface structures from the analysis of images
from the PSPT and spectromagnetograms from NSO/KP, with the theory
for emission, absorption, and transfer of radiation in the solar
atmosphere. We will present the latest results from the spectral
synthesis model and compare them to related observations and comment
on their accuracy and applicability to use in terrestrial atmoshpere
studies. NCAR is sponsored by the National Science Foundation. This
work is partly sponsored by the NSF RISE program.
---------------------------------------------------------
Title: Chromospher-corona transition region line emissions
Authors: Fontenla, J.; Judge, P.
2004cosp...35..668F Altcode: 2004cosp.meet..668F
We study the effects of diffusion and flows on the transition region
trace-species emission lines and the radiative losses produced by
them and compare them with observations. We find that mass flows can
have dramatic effects on the line emissions through the effect on
non-local ionization and in this way completely alter the radiative
losses and the structure of the transition regions. Also, in static
cases thermal diffusion can have a very significant effect on the
elemental abundance variation that in turn affects the line emissions
and radiative losses leading to reduced abundances of trace species at
temperatures around 10^5 K, and the details this effect is dependent on
the first-ionization-potential. This is due to the combination of large
temperature gradient and increased mean free path and is expected to
occur for all species. However, the mass flows would reduce this effect
and especially in the case of downflows the thermal diffusion can have
complex results. Also, species diffusion flows can arise from specific
boundary conditions and may not be directly related to a simultaneous
mass flow. We discuss several scenarios that may arise in typical
dynamic cases that have been observed. We show that the transition
region emissions have the large fluctuations in space and time, much
more than the chromospheric emissions, and that the radiated energy
can be easily explained in terms of the downward energy flow from the
corona coupled with enthalpy and ionization energy carried by the up
and down mass flows often observed.
---------------------------------------------------------
Title: Solar irradiance variability - comparison of models and
observations
Authors: Fox, P. A.; Fontenla, J. M.; White, O. R.
2004AdSpR..34..231F Altcode:
Over the past decade, regular measurement programs for parts of the
solar spectrum have been established. In recent years substantial
progress has also been made on the physical understanding of these
measurements. To refine our understanding and to make quantitative
estimates of this variability requires a study of the entire solar
spectrum. Our approach to this requirement is to combine empirical
image analysis with the theory for emission, absorption, and transfer
of radiation in the solar atmosphere. The goal is the successful
combination of observed solar images with semi-empirical models and
theory for calculation of a mixed line + continuum spectrum emitted from
realistic representations of the observed solar disk. We present the
latest results from the SunRISE spectral synthesis model in specific
spectral bands in the UV, visible, and near-IR, and compare them to
related observations.
---------------------------------------------------------
Title: Solar irradiance variations in the visible and infrared -
observations and model calculations
Authors: Harder, J.; Fontenla, J.; Davis, S.; Rottman, G.; Woods,
T.; White, O.
2004cosp...35.1901H Altcode: 2004cosp.meet.1901H
The Spectral Irradiance Monitor, SIM, is now providing the first
continuous record of solar irradiance variations throughout the visible
and near infrared. This instrument is aboard the Solar Radiation and
Climate Experiment, SORCE, which was launched in January 2003. SIM
is a prism spectrometer that makes precise measurements of the solar
irradiance four times a day over the entire spectral range 200-2700
nm. The SIM data provide important new information on both the
mechanisms of solar variability and on how the changing Sun influences
our terrestrial environment. One important new finding has resulted
from a comparison of SIM observations with corresponding spectral
irradiance time series synthesized by the model of Fontenla, White,
Fox, Avrett, and Kurucz (ApJ, 1999, 518, 480). Their model directly
accounts for the distribution and evolution of features on the Sun
that contribute to irradiance variations. This SUNRISE model uses seven
semi-empirical spectral models to represent sunspots, plage, network,
and quiet atmosphere, and these models are then combined according
to a decomposition of solar images. The comparison of the model and
observations indicate good agreement at visible wavelengths, but in
the infrared the model and observations differ significantly. The
models assume that in the infrared, near the peak of the H- opacity
at about 1600 nm, the active regions are somewhat dark relative to
the quite Sun decreasing the irradiance when they are present. The
IR disagreements between the SIM observations and the models indicate
that the "dark plage" assumptions used in the model(s) will need to be
adjusted. The models must incorporate "bright plage" at all wavelengths
so that the infrared irradiance will vary in a manner similar to the
shorter wavelength visible and ultraviolet wavelength.
---------------------------------------------------------
Title: Solar Spectral Irradiance Variability in the Visible and
Infrared During the SORCE Mission
Authors: Harder, J. W.; Fontenla, J.; Smiley, B.; Rottman, G.;
Lawrence, G.; Woods, T.
2003AGUFMSH12A1158H Altcode:
The Spectral Irradiance Monitor (SIM) is a dual prism spectrometer
onboard the SORCE (Solar Irradiance and Climate Experiment) satellite
that was launched in January 2003. SIM covers the wavelength region
200- 2700 nm with a spectral resolution varying from 0.25 to 34 nm over
this range. The primary detector for this instrument is an electrical
substitution radiometer (ESR), and three additional photodiode detectors
complement the ESR measurement and span the spectral range from 308 to
1600 nm; these photodiodes provide the bulk of the data used to study
solar variability. The ESR calibrates the radiant sensitivities of
the photodiodes in flight, and pre-flight measurements of the prism
transmission and the spectral response function give the absolute
calibration of the instrument. The SIM solar spectrum is in good
agreement with other standard solar spectra such as the SOLSPEC spectrum
(Thuillier et al. Metrologia, 35, 689, 1998) and the Davos World
Radiation Center Reference Spectrum (Wehrli, C., World Radiation Center
(WRC) Publication No. 615, Davos-Dorf, Switzerland, July 1985). SIM
is able to detect short-term spectral irradiance variability of about
0.1% in the of 27-day solar rotation period induced by the appearance
and varying intensity of solar structural features (such as sun spots
and plage) relative to the quiet sun. A comparative study of the SIM
solar spectrum relative to other standard spectra and an analysis of
short-term solar variability as measured by SIM will be presented.
---------------------------------------------------------
Title: Modeling Solar Irradiance With the PSPT Solar Disk Observations
and RISE Solar Spectrum Synthesis
Authors: Davis, S. M.; Fontenla, J.; Harder, J.; Rottman, G.;
Meisner, R.
2003AGUFMSH12A1159D Altcode:
The PSPT (Precision Solar Photometric Telescope) at the Mauna Loa
Solar Observatory produces full disk solar images in the Ca II-K
spectral line (393 nm +/- 0.15 nm), blue (409.3 nm +/- 0.15 nm)
continuum, and red (607.2 nm +/- 0.15 nm) continuum, with ∼0.1%
photometric precision and 1 arc sec pixels. The RISE (Radiative Inputs
of the Sun to Earth) spectral synthesis calculation is based on 7 solar
atmosphere models corresponding to quiet and active solar features, and
currently calculates the emitted intensity as a function of wavelength
from 0.5 to 10 micron for 10 positions in the solar disk. We use the
RISE-derived center-to-limb variation functions for each surface feature
in the instrument spectral band to extract the feature distribution
on the solar surface corresponding to each PSPT image. The average
disk intensity as a function of wavelength is then constructed using
the RISE calculated spectra for each feature and position on the
disk. We present the results of a preliminary study of solar irradiance
calculations and comparisons with measurements from the Solar Radiation
and Climate Experiment (SORCE) satellite. These comparisons are made
with the Spectral Irradiance Monitor (SIM), which measures spectral
irradiance (200 nm - 2700 nm). In addition to the preliminary results,
we present future plans for comparisons with SIM data.
---------------------------------------------------------
Title: Physical Synthesis of the Solar Radiance, a Tool for
Understanding Spectral Irradiance
Authors: Fontenla, J. M.; White, O. R.; Evrett, E. H.; Rottman, G.;
Fox, P.; Harder, J.; Davis, S.
2003AGUFMSH12A1157F Altcode:
In this paper we summarize the current status of our physical modeling
of the solar radiation and briefly describe the key improvements
in the methods we use to compute synthetic solar spectrum. We use 7
solar atmosphere models for summarizing the features observed on the
solar disk, and we compute the emitted spectrum at 10 positions on
the disk. These models and disk positions are intended to cover the
significant features of quiet and active Sun that are linked with solar
irradiance variations. The calculation is extremely detailed and each
of the many thousands of spectral lines is fully resolved so that the
spectra can be convolved with any instrument function and compared with
observations at high or low spectral resolution. Our version 1 code
and models provide very good agreement with observations of spectral
irradiance between ∼450 and ∼1000 nm, but is not accurate outside
that range. We describe the basic procedures used in Version 1 and
the differences with the procedures that will be used in Version 2
for improving the synthesis accuracy over a more extended wavelength
range. We expect that version 2 will be a major step in understanding
the solar spectral irradiance and its variations beyond what is
currently available from any solar irradiance models.
---------------------------------------------------------
Title: Pre-Launch and On-Orbit Calibration of the Spectral Irrandiance
Monitor (SIM) on SORCE
Authors: Smiley, B. D.; Harder, J.; Fontenla, J.; Lawrence, G.;
Rottman, G.
2003AGUFMSH12A1160S Altcode:
The Spectral Irradiance Monitor (SIM) aboard the Solar Radiation
and Climate Experiment (SORCE) satellite measures the solar spectral
irradiance from 200 - 2700 nm. SIM is a Féry prism spectrometer that
uses an electrical substitution radiometer (ESR) to monitor the absolute
irradiance calibration throughout operation. The two SIM instruments
on SORCE are mirror images of each other, mounted side-by-side in
the same package. Since the prism transmission coefficient is a
term that appears directly in the instrument's measurement equation,
laboratory measurements are required for data analysis. Ratiometric
laboratory measurements of the prism transmission as a function of
wavelength and polarization will be presented, along with experiment
descriptions. Furthermore, on-orbit experiments monitor changes in
prism transmission to maintain the pre-launch calibration. Each SIM
can calibrate the other. During an on-orbit transmission measurement,
one SIM directs monochromatic light into the second via a periscope
mechanism. The second SIM then uses internal optics to measure its
prism transmission ratiometrically. Preliminary results from the
ongoing prism degredation analysis will also be presented.
---------------------------------------------------------
Title: Physical Modeling of the Solar Radiation, Current Status
and Prospects
Authors: Fontenla, J. M.; Avrett, E. H.; Goodman, M.; White, O. W.;
Rottman, G.; Fox, P.; Harder, J.
2003SPD....34.0301F Altcode: 2003BAAS...35..808F
Physical models that include full NLTE radiative transfer as well as
particle transport and MHD processes are the key to understanding the
solar radiative output and also are essential to our understanding
of heating and the dynamics of the solar atmosphere, in particular
for chromospheric layers. SOHO observations show that chromospheric
emission lines do not vary dramatically in time and that chromospheric
heating, even in the quiet Sun, is not simply due to, p-modes induced,
strong shock waves passing through the chromosphere. The physics of
the chromospheric heating is more complicated and remains elusive. The
chromospheric and coronal heating are likely closely related to the
dynamics in these regions as well as in the thin chromosphere-corona
transition region since they are a coupled system. Solar atmospheric
heating and dynamics are strongly affected by the magnetic fields and
MHD mechanisms must be considered. Models for the upper photosphere
and chromosphere should also consider NLTE radiative transfer and
radiative losses as well as particle transport processes including
tensor electric resistivity with magnetic field. Models for the
transition region and coronal layers must also consider particle
diffusion. In this paper we show schematically: 1) the current state
of our research on modeling observed features of the solar structure
and their radiative signatures; 2) the application of this modeling
to the Earth solar irradiance and comparisons with observations; 3)
the key achievements and the needed improvements of the modeling; 4)
our plans for future research starting from ab initio semi-empirical
models based on observations, and, while maintaining the agreement with
relevant observations, moving towards physically consistent models that
include key MHD processes thereby replacing empirical constraints by
physically consistent processes and boundary conditions.
---------------------------------------------------------
Title: Influence of Mass Flows on the Energy Balance and Structure
of the Solar Transition Region
Authors: Avrett, E. H.; Fontenla, J. M.
2003ASPC..288..279A Altcode: 2003sam..conf..279A
We have extended our previous modeling of energy balance in the
chromosphere-corona transition region to include the effects of particle
and mass flows. We consider quasi-steady cases satisfying the momentum
and energy balance equations throughout the transition region and low
corona. We include particle diffusion as well as flows in the non-LTE
equations for H, HeI, and HeII. Mass flows substantially affect the
ionization and radiative losses of H and He thereby affecting the
structure and extent of the transition region. We find that the H and
He line profiles are greatly affected by flows, and that line shifts
are much less important than the changes in line intensity and central
reversal due to the effects of flows on atmospheric structure. The
profiles we compute can generally explain the range of observed high
spectral and spatial resolution Lyman alpha profies from the quiet
Sun. A full account of this work appears in a paper by Fontenla,
Avrett, and Loeser submitted to The Astrophysical Journal.
---------------------------------------------------------
Title: Energy Balance in the Solar Transition Region. IV. Hydrogen
and Helium Mass Flows with Diffusion
Authors: Fontenla, J. M.; Avrett, E. H.; Loeser, R.
2002ApJ...572..636F Altcode: 2001astro.ph..9416F
In this paper we extend our previous modeling of energy balance in
the chromosphere-corona transition region to cases with particle and
mass flows. The cases considered here are quasi-steady and satisfy
the momentum and energy balance equations in the transition region. We
assume one-dimensional geometry and include the flow velocity terms in
all equations, but we neglect the partial derivatives with respect to
time. We present a complete and physically consistent formulation and
method for solving the non-LTE and energy balance equations in these
situations, including both particle diffusion and flows of H and He. Our
calculations include partial frequency redistribution in the Lyα and
Lyβ lines. Our results show quantitatively how mass flows affect
the ionization and radiative losses of H and He, thereby affecting
the structure and extent of the transition region. Furthermore,
our computations show that the H and He line profiles are greatly
affected by flows. We find that line shifts are much less important
than the changes in line intensity and central reversal as a result
of the influence of flows on the excitation and ionization. In this
paper we use fixed conditions at the base of the transition region
and in the underlying chromosphere. Our intent is to show the physical
effects of flows on the transition region, not to match any particular
observations. However, our computed Lyα profiles can account for
the range of observed high spectral and spatial resolution from the
quiet Sun. We suggest that dedicated modeling of specific sequences
of observations based on physically consistent methods like those
presented here will substantially improve our understanding of the
energy balance in the chromosphere and corona.
---------------------------------------------------------
Title: Calculation of Solar Irradiances. I. Synthesis of the Solar
Spectrum
Authors: Fontenla, Juan; White, Oran R.; Fox, Peter A.; Avrett,
Eugene H.; Kurucz, Robert L.
1999ApJ...518..480F Altcode:
Variations in the total radiative output of the Sun as well as
the detailed spectral irradiance are of interest to terrestrial
and solar-stellar atmosphere studies. Recent observations provide
measurements of spectral irradiance variations at wavelengths in the
range 1100-8650 Å with improved accuracy, and correlative studies
give procedures for estimating the spectral irradiance changes from
solar activity records using indicators such as those derived from
Ca II K and Mg II indices. Here we describe our approach to physical
modeling of irradiance variations using seven semiempirical models to
represent sunspots, plage, network, and quiet atmosphere. This paper
gives methods and details, and some preliminary results of our synthesis
of the variations of the entire irradiance spectrum. Our calculation
uses object-oriented programming techniques that are very efficient
and flexible. We compute at high spectral resolution the intensity
as a function of wavelength and position on the disk for each of the
structure types corresponding to our models. These calculations include
three different approximations for the line source function: one suited
for the very strong resonance lines where partial redistribution
(PRD) is important, another for the most important nonresonance
lines, and another approximation for the many narrow lines that are
provided in Kurucz's listings. The image analysis and calculations
of the irradiance variation as a function of time will be described
in a later paper. This work provides an understanding of the sources
of variability arising from solar-activity surface structures. We
compute the Lyα irradiance to within 3% of the observed values. The
difference between our computations and the Neckel & Labs data is 3%
or less in the near-IR wavelengths at 8650 Å, and less than 1% in the
red at 6080 Å. Near 4100 Å we overestimate the irradiance by 9%-19%
because of opacity sources missing in our calculations. We also compute
a solar cycle variability of 49% in the Lyα irradiance, which is very
close to observed values. At wavelengths between 4100 Å and 1.6 μm,
we obtain spectral irradiance variations ranging from -0.06% to 0.46%
in the visible--the higher values correspond to the presence of strong
lines. The variability in the IR between 1.3 and 2.2 μm is ~-0.15%.
---------------------------------------------------------
Title: The Gradual Phase of Flares
Authors: Svestka, Z. F.; Poletto, G.; Fontenla, J.; Hick, P.; Kopp,
R. A.; Sylwester, B.; Sylwester, J.
1999mfs..conf..409S Altcode:
Heating and Cooling in the Gradual Phase Emission Measure-Temperature
Diagrams Flaring Arches Gradual Phase of Eruptive Flares Postflare
Giant Arches Giant Arches: Modeling and Interpretation
---------------------------------------------------------
Title: Velocity determination of the mass of the prominence from
the calculation of ionization states of different atoms.
Authors: Rovira, M. G.; Costa, A.; Fontenla, J. M.
1998larm.confE..14R Altcode:
We calculated the ionization curves for different states taking
into account diffusion and center of mass velocities of different
atoms. Comparing the profiles calculated with observations made witn
the SUMER instrument on board SOHO satellite, we can estimate the
velocity of the mass of the prominence.
---------------------------------------------------------
Title: Microflares and active filaments
Authors: Schmieder, B.; Fontenla, J.; Tandberg-Hanssen, E.
1998PAICz..88...63S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Ultraviolet Events Observed in Active Regions. II. An
Interpretation of Flaring Arches and Associated Small Flares
Authors: Fontenla, J.; Rovira, M.; Tandberg-Hanssen, E.
1997ApJ...491..925F Altcode:
We analyze Hα, UV, and X-ray emissions in and around the spectacular
arch system seen in the corona on 1980 March 27 during the Solar Maximum
Mission. The flaring of the arch plasma is studied, and its dependence
on triggering mechanisms related to the observed small limb flare in
the arch footpoint is analyzed. To drive these events, we propose a
mechanism in which small electric current circuits and the localized
magnetic free energy are continuously generated at a magnetic null by
a pressure gradient, which then compress or expand the plasma. This
free energy dissipates by Joule effect and upward transport.
---------------------------------------------------------
Title: Efecto de la difusión y la velocidad en la ionización del
átomo de Carbono
Authors: Rovira, M. G.; Fontenla, J. M.
1997BAAA...41...59R Altcode:
The equations of statistical equilibrium for all ionization states
of the atom are solved. The effects of diffusion and center of mass
velocity are included. In order to estimate the modifications of the
ionization curves, they were applied to the Carbon atom. To solve
these equations, solar prominences' models obtained in a previous
paper were adopted. They were extended to reach a temperature of
1.5 × 10<SUP>6</SUP> K and the complete model of the prominence
was calculated. Ionization curves for different values of velocity,
diffusion and medium models were obtained. The different models
represent structures with different densities. Considerable
modifications due to these effects are found.
---------------------------------------------------------
Title: Measuring storage and release of magnetic free-energy
Authors: Fontenla, Juan M.
1996SPIE.2804..194F Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Ultraviolet Spectrum of a 3B Class Flare Observed with
SOLSTICE
Authors: Brekke, P.; Rottman, G. J.; Fontenla, J.; Judge, P. G.
1996ApJ...468..418B Altcode:
An observation of the ultraviolet spectrum (1200-1800 Å) during the
impulsive phase of a very extended 3B-X3 class solar flare on 1992
February 27 was obtained with the Solar-Stellar Irradiance Comparison
Experiment (SOLSTICE). This observation is combined with ground-based
Hα, magnetogram, and microwave data as well as hard X-ray measurements
from the Ulysses spacecraft. This flare shows a dramatic enhancement of
lines formed in the solar transition region. The irradiance (emitted
flux density from the entire solar disk) of the resonance lines of
C iv and Si iv increased by a factor of 12-13 during the impulsive
phase of the flare. These irradiance enhancements are comparable
with those measured during stellar flares. By taking into account the
emitting flare area we infer that the radiance (specific intensity)
of the flaring plasma was at least a factor of 15,000 brighter than the
average solar disk radiance just prior to the event. Assuming the flare
site's initial radiance was that of a typical active region, it then
must have brightened by a factor of at least 3400. Such enhancement
far exceeds previous published values (e.g., OSO 8, Skylab, and SMM)
and indicates that many observations were affected by limited dynamic
range. Thus, the SOLSTICE observation may be the first measurement of
the true UV enhancement during the impulsive phase of very bright solar
flares. <P />The Si III multiplet near 1295 Å also shows remarkable
enhancement, but other allowed lines of C II, Si III (1206 Å), N V,
and He II show more moderate enhancements, the weakest being H I Lyα,
the irradiance of which increases only 6%. Some of the differences
between the various enhancements are certainly caused by the timing of
the observations since the scanning spectrometer observed different
spectral features over periods of 4 minutes. Other differences due
to line formation processes are being investigated but are consistent
with density effects in the line emission coefficients. The inferred
Lyα radiance enhancement is consistent with current post-impulsive
phase flare models. However, the formation of the C IV and Si IV lines,
formed during the impulsive phase of the flare, remains unknown. During
the impulsive phase of the flare the strong transition region lines
are systematically redshifted by 50 km s<SUP>-1</SUP>.
---------------------------------------------------------
Title: Prominence Thread Models Including Ambipolar Diffusion
Authors: Fontenla, J. M.; Rovira, M.; Vial, J. -C.; Gouttebroze, P.
1996ApJ...466..496F Altcode:
We present a study of the modeling of prominence slabs. Our models
consider a collection of threads in energy balance with the surrounding
corona and submitted to illumination from the underlying chromospheric
layers. The models are isobaric, but temperature variations within
the slab occur as a result of the energy balance constraint. We
compute the non-LTE radiative transfer for a hydrogen model atom
with five bound levels. The ionization is treated consistently with
non-LTE radiative transfer and ambipolar diffusion (AD). The AD
also affects the energy balance because of the transport of hydrogen
ionization energy. We compute the emitted Lyman and Balmer spectra of
our models and compare them with the observations. We find that the
consideration of ambipolar diffusion increases the emission in Lyβ
(and higher members of the Lyman series) as compared with the other
lines. This contrasts with isothermal models that yield Lyβ emission
that is too low. However, the AD models give excessive Lyβ emission,
viz., too small a Lyα/Lyβ ratio compared with observations. We also
compute models that include a cold core in which mechanical energy is
dissipated. These models increase the Hα/Lβ ratio to values similar to
the observed values for a moderate number of threads along the line of
sight. However, these models still give too low a Lyα/Lyβ ratio. We
conclude that the prominence observations in Lyβ show intensities
that are not compatible with a steady state, field-aligned interface
between the cold prominence and the hot coronal material. Also, the
observations are not consistent with an isothermal slab isolated from
the corona. Consequently, we suggest that at the prominence-corona
interface, there is a substantial angle between the temperature gradient
and the field, although this angle is significantly smaller than 90°.
---------------------------------------------------------
Title: Subflares and surges in AR 2744 during the Solar Maximum
Mission.
Authors: Schmieder, B.; Rovira, M.; Simnett, G. M.; Fontenla, J. M.;
Tandberg-Hanssen, E.
1996A&A...308..957S Altcode:
Active region NOAA 2744, which was at S25, had its central meridian
passage on Oct 23 1980 and was relatively quiet according to Hα, UV
and X-ray observations made by the Solar Maximum Mission (SMM). The
region was also observed by the Marshall Space Flight Center (MSFC)
vector magnetograph. During its disk passage only subflares and surges
were detected. Their locations appeared to be governed by the magnetic
topology. On October 21 a miniflare occurred close to the separator
between the two main sunspots. On October 22 the emergence of a small
region of parasitic polarity in the existing magnetic field appeared
to be responsible for three subflares and subsequent surges. We discuss
the energy budget for plasmas at temperatures in the 10^4^K, 10^5^K and
10^6^K ranges in the context of surge-trigger mechanisms. On October
21 the energy deposition driving the surges did not produce a high
temperature plasma. By October 22 the active region had evolved and the
surges were now associated with some high temperature plasma. However,
the energy radiated at transition region temperatures would be larger
than that estimated in X-rays depending on the dilution factor. This
would imply a continuous influx of energy in order to sustain the
long duration surge (30min) rather than a simple, impulsive energy
input. If the electron density in the 10^4^-10^5^K plasma is taken
as ~10^12^cm^-3^ the diameter of individual surge loops should only
be ~40km. The relevance of our results to (a) reconnection and (b)
gradient pressure driven models for surges is discussed.
---------------------------------------------------------
Title: Ultraviolet (1200 to 1800 Angstroms) Emission during the
Impulsive Phase of a Class 3B-X3 Solar Flare Observed with SOLSTICE
Authors: Brekke, P.; Rottman, C. J.; Fontenla, J.; Judge, P. G.
1996mpsa.conf..213B Altcode: 1996IAUCo.153..213B
No abstract at ADS
---------------------------------------------------------
Title: The UV "sun as a star" flare spectrum observed with SOLSTICE
Authors: Brekke, P.; Rottman, G. J.; Fontenla, J.; Judge, P. G.
1996ASPC..109..111B Altcode: 1996csss....9..111B
No abstract at ADS
---------------------------------------------------------
Title: Electric Currents and Magnetic Shear Variations during Some
Flares of M- and X-Class
Authors: Ambastha, A.; Fontenla, J. M.; Hagyard, M. J.
1996mpsa.conf..533A Altcode: 1996IAUCo.153..533A
We study the magnetic field evolution during flares of M and
X-class using overlays of cotemporal halpha filtergrams and
magnetograms.Significant decrease in the area-averaged magnetic
shear was found in some cases around the flare onset-time, increasing
subsequently as the flare progressed. However, the changes were less
pronounced for relatively smaller M-class flares. Strong Lorentz forces
were found to exist at the photosphere, acting against the observed
motions of sunspots. Extrapolated potential field indicated presence
of a magnetic null at the upper chromosphere/lower coronal height,
directly above a large Halpha flare.
---------------------------------------------------------
Title: The Solar LY alpha Line Profile
Authors: Woods, Thomas N.; Rottman, Gary J.; White, O. R.; Fontenla,
Juan; Avrett, E. H.
1995ApJ...442..898W Altcode:
Solar Ly-alpha irradiance measurements from the SOLar STellar Irradiance
Comparison Experiment (SOLSTICE) on the Upper Atmosphere Research
Satellite (UARS) have been made since 1991 October with a spectral
resolution of 0.1 nm. The uniqueness of the small molecular oxygen cross
section near Ly-alpha permits the Ly-alpha radiation to penetrate much
deeper into the atmosphere than the other emissions near Ly-alpha. We
have taken advantage of this phenomenon by performing solar occultation
experiments near the Ly-alpha to evaluate precisely the instrument
scattered light contribution. After correcting for scattered light,
the broad wings of the solar Ly-alpha line can be extracted out to 5
nm from line center with a typical accuracy of +/-20%. The variability
in the Ly-alpha wings near 2 nm from line center is about one-half
that of the Ly-alpha core emission, defined within 0.1 nm from line
center. These Ly-alpha profile measurements are found to be consistent
with the Skylab radiance measurements and theoretical models of the
Ly-alpha line profiles computed using partial redistribution of photons
in the source function.
---------------------------------------------------------
Title: Calculation of Absolute Solar Irradiances and Their Variation
with Solar Activity
Authors: White, O. R.; Fontenla, J.; Fox, P.; Avrett, E. H.; Harvey, K.
1995SPD....26..308W Altcode: 1995BAAS...27..954W
No abstract at ADS
---------------------------------------------------------
Title: The Magnetic Evolution of AR 6555 Which LED to Two Impulsive,
Relatively Compact, X-Type Flares
Authors: Fontenla, J. M.; Ambastha, A.; Kalman, B.; Csepura, Gy.
1995ApJ...440..894F Altcode:
We study the evolution of the vector magnetic field and the sunspot
motions observed in AR 6555 during 1991 March 23-26. This region
displays two locations of large magnetic shear that were also sites
of flare activity. The first location produced two large (X-class)
flares during the period covered by our observations. The second
location had larger magnetic shear than the first but produced only
small (M- and C-class) flares during our observations. We study the
evolution of the photospheric magnetic field in relation to the large
flares in the first location. These flares occurred around the same
included polarity and have very similar characteristics (soft X-ray
light curves, energies, etc.). However, the whole active region has
changed substantially in the period between them. We found several
characteristics of the region that appear related to the occurrence of
these flares: (1) The flares occurred near regions of large magnetic
"shear," but not at the locations of maximum shear or maximum field. (2)
Potential field extrapolations of the observed field suggest that the
topology changed, prior to the first of the two flares, in such a way
that a null appeared in the coarse magnetic field. (3) This null was
located close to both X-class flares and remained in that location for
a few days while the two flares were observed. (4) The flaring region
has a pattern of vector field and sunspot motions in which material
is "squeezed" along the polarity inversion line. This pattern is very
different from that usually associated with shearing arcades, but it is
similar to that suggested previously by Fontenla and Davis. The vertical
electric currents, inferred from the transverse field, are consistent
with this pattern. (5) A major reconfiguration of the longitudinal
field and the vertical electric currents occurred just prior to the
first of the two flares. Both changes imply substantial variations of
the magnetic structure of the region. On the basis of the available
data we suggest that these changes made the flaring possible, and we
develop a scenario that can explain the origin of the magnetic free-
energy that was released in these flares.
---------------------------------------------------------
Title: Simultaneous Ultraviolet and X-Ray Observations of Solar
Microflares
Authors: Porter, J. G.; Fontenla, J. M.; Simnett, G. M.
1995ApJ...438..472P Altcode:
We present a comparison of observations of a solar active region
obtained with the Ultraviolet Spectrometer and Polarimeter (UVSP) and
the Hard X-ray Imaging Spectrometer (HXIS) on board the Solar Maximum
Mission (SMM). The data show many subflares and smaller events during
a 9 hr period in which there were no major flares. This activity is
associated with areas of complex, evolving magnetic fields. Events
substantially smaller than subflares, identified in C IV 1548 A emission
(T = 10<SUP>5</SUP> K), are found to have impulsive counterparts
in 3.5-5.5 keV X-ray emission characteristic of T approximately
10<SUP>7</SUP> K. These 'microflares' are therefore true members of
the flare family, reaching temperatures greater than that of the
ambient solar corona. Plots of X-ray versus UV emission show that
the emission from the smaller microflares is softer than that from
the larger microflares and subflares. Distributions of solar flares
with energy that are based on hard X-ray fluxes can be corrected using
this X-ray/UV relationship. The corrected distributions suggest that
microflares play a larger role in coronal heating than was indicated
by analysis of the original distributions.
---------------------------------------------------------
Title: The problem of the MG II resonance lines and the constraints
on turbulent transport in the upper chromosphere
Authors: Fontenla, J. M.
1994ESASP.373...47F Altcode: 1994soho....3...47F
No abstract at ADS
---------------------------------------------------------
Title: Microflares and their Related Events
Authors: Schmieder, B.; Fontenla, J.; Tandberg-Hanssen, E.; Simnett,
G. M.
1994kofu.symp..339S Altcode:
We have studied in detail two series of events that occur in two
separate active regions on October 9 and June 15, 1980 during the
period of SMM observations. These events can be considered as typical
of a class of solar compact subflares. The events have been studied
using simultaneous UVSP (C IV) and Meudon (H_alpha) data, and for the
brighter event we also use X-ray data from HXIS. Characteristics of
microflares are derived. The simplest microflare may be composed of
a large number of small events, some of which appear to be triggered
by earlier events in the same series.
---------------------------------------------------------
Title: FNAS UAH UVSP and complimentary data analysis and modeling
Authors: Fontenla, Juan M.
1994alab.reptQ....F Altcode:
Several data sets obtained by the UVSP and HXIS instruments on board
SMM were studied. From these data, several events of sequences of
events were selected that are specially representative of the plethora
of active region energetic phenomena that was simultaneously observed
by UVSP and HXIS. The selection criteria was to have available both
types of observations in active region flares that are not so bright
that the UVSP instrument was switched off for protection, and at the
same time flares that are not so dim in X-Rays that HXIS will have
collected significant data. Another criteria of secondary importance
was to select events where auxiliary optical data is available.
---------------------------------------------------------
Title: Time Evolution of a Miniflare as Seen in H alpha , UV Lines,
and X-Rays
Authors: Fontenla, J.; Schmieder, B.; Simnett, G. M.; Tandberg-Hanssen,
E.
1994ApJ...424.1022F Altcode:
A miniflare that occurred in active region Hale 16896 on 1980 June 15
was observed in H-alpha, UV lines, and soft X-rays. These data allow us
to analyze the flare emission and derive the energetics and dynamics
of the chromospheric plasma involved. Our results indicate that the
energy released by the miniflare was about 10<SUP>28</SUP> ergs, about
four orders of magnitude smaller than that of a large flare. However,
hard X-rays (5.5-8.0 keV) were observed which indicated a plasma with
temperature as high as 27 x 10<SUP>6</SUP> K. The H-alpha wings, C
IV, and X-rays all showed a short-lived and compact (3 sec x 3 sec)
brightening in a location near the leading sunspot. At this location,
small-scale changes in the magnetic field were observed from about 2 hr
before to about 6 hr after the miniflare. Only very small velocities
seem to have been associated with most of the event in H-alpha. The
data are consistent with short and dense loops at temperatures above
10<SUP>7</SUP> K which lost a large fraction of their energy via
downward conduction through regions at the footpoints. Several secondary
events appear to have been triggered by the miniflare along an arch
filament which itself was not greatly affected. A number of much less
energetic (10<SUP>25</SUP>-10<SUP>26</SUP> erg) events preceded and
followed the mini-flare. One of these occurred 11 minutes after the
mini-flare and displayed a highly Doppler-shifted signature from the
foot-point of a C IV arch. This arch delineates the connection that
existed between the location of the mini-flare and the location of
secondary events triggered by the flare.
---------------------------------------------------------
Title: Formation of the Solar 10830 Angstrom Line
Authors: Avrett, E. H.; Fontenla, J. M.; Loeser, R.
1994IAUS..154...35A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Formation of the solar 10830 A line
Authors: Avrett, E. H.; Fontenla, J. M.; Loeser, R.
1994isp..book...35A Altcode:
One-dimensional hydrostatic-equilibrium models are shown here for faint,
average, and bright components of the quiet Sun, and for a plage region,
describing in each case how the atmosphere is stratified through the
photosphere, chromosphere, and transition region up to a temperature
of 10^5 K. The observed coronal line radiation is assumed to be
the inward incident radiation at the 10^5 K boundary. This coronal
radiation penetrates into the upper chromosphere causing sufficient
helium ionization to populate the lower level of the He I 10830 A line,
producing optically-thin absorption of the photospheric continuum at
10830 A. The amount of absorption, which is proportional to the optical
thickness of the upper chromosphere in the 10830 line, depends on 1)
the strength of the coronal lines at wavelengths in the He I 504 A
ionizing continuum, and 2) the density and geometrical thickness of
the upper chromosphere. The computed 10830 A line is shown for the four
atmospheric models and for three values of the coronal illumination. The
calculated off-limb 10830 intensity distribution shows a minimum
in the low chromosphere and a maximum at roughly 2000 km above the
photosphere, in general agreement with observations, indicating that
this is the predominant height of the transition region over most of
the solar surface.
---------------------------------------------------------
Title: Effects of Ambipolar Diffusion on Prominence Thread Models
Authors: Rovira, M. G.; Fontenla, J. M.; Vial, J. -C.; Gouttebroze, P.
1994scs..conf..315R Altcode: 1994IAUCo.144..315R
The authors have improved previous model calculations of the
prominence-corona transition region including the effect of the
ambipolar diffusion in the statistical equilibrium and energy balance
equations. They show its influence on the different parameters that
characterize the resulting prominence theoretical structure. They
take into account the effect of the partial frequency redistribution
in the line profiles and total intensities calculations.
---------------------------------------------------------
Title: Generation of Electric Currents in Two-dimensional Magnetic
Nulls
Authors: Fontenla, Juan M.
1993ApJ...419..837F Altcode:
We present detailed calculations and results for a model case of
two-dimensional small distortions of static, current-free equilibrium
around a null-line magnetic configuration. This setup has been
studied for fast energy release in flares, but has not been studied
before in the context of the magnetic energy buildup that precedes the
flare. Our analytical results are new because they include gas pressure
and provide explicit formulae for the expressions of all quantities
(and especially the electric current) and energy storage as functions
of the values of boundary conditions. A general solution is shown as
a combination of eigenfunctions, with coefficients resulting from the
boundary conditions. These boundary conditions are given in terms of
any arbitrary plasma acceleration at a boundary enclosing the domain
we study. The approach used here studies the MHD evolution of the
electric current and plasma density variations driven by external
forces. We find that both pressure and Lorentz forces are important,
and that their boundary values select between a wide range of solutions,
many of which have been found previously in numerical simulations. Most
of the modes we find display strong current sheets, velocities, and
pressure variations at the separatrices Also we find that Joule and
other dissipative terms are not important for typical cases, except at
an extremely narrow inner core, and near the separatrices We discuss
our results and their relationship to numerical MHD simulations.
---------------------------------------------------------
Title: Microflare distributions and coronal heating.
Authors: Porter, J. G.; Fontenla, J. M.; Simnett, G. M.
1993BAAS...25.1202P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Microflare Distributions and Coronal Heating
Authors: Porter, J. G.; Fontenla, J. M.; Simnett, G. M.
1993SPD....24.1513P Altcode: 1993BAAS...25R1202P
No abstract at ADS
---------------------------------------------------------
Title: Energy Balance in the Solar Transition Region. III. Helium
Emission in Hydrostatic, Constant-Abundance Models with Diffusion
Authors: Fontenla, J. M.; Avrett, E. H.; Loeser, R.
1993ApJ...406..319F Altcode:
In our previous papers we described the mathematical formalism and
the computed results for energy-balance hydrostatic models of the
solar transition region. In this paper we discuss in some detail
the limitations of the hydrostatic and one-dimensional assumptions
used. Then we analyze the determination of helium emission when
diffusion is included. We use transport coefficients estimated
from kinetic theory to determine the helium departures from local
ionization balance. We calculate the helium spectra for each of our
models and evaluate the role of helium in the energy transport. Also,
we investigate the effects of coronal illumination on the structure
of the transition region and upper chromosphere, and show how
coronal illumination affects various EUV lines and the He I 10830
A line. Comparing with both absolute intensities and detailed line
profiles, we show that our models are consistent not only with the
observed hydrogen spectra but also with the available helium spectra.
---------------------------------------------------------
Title: Measurement of p-Mode Energy Propagation in the Quiet Solar
Photosphere
Authors: Fontenla, J. M.; Rabin, D.; Hathaway, D. H.; Moore, R. L.
1993ApJ...405..787F Altcode:
We have measured and analyzed the p-mode oscillations in the profile
of the Mg I 4571 A line in a quiet region near disk center. The
oscillations are found to be mostly standing waves, in agreement with
previous work. However, a small propagating component is measured, and
we determine the direction, magnitude, and vertical variation of the
energy propagation. The work integral indicates an upward energy flow of
about 2 x 10 exp 7 ergs/sq cm/s at a height of 50 km above the base of
the photosphere for waves with frequencies of 2-16 mHz. This energy flow
decreases exponentially with height and drops below 10 exp 5 ergs/sq
cm/s in the uppermost photosphere. The energy flow leaving the upper
photosphere is at least an order of magnitude too small to constitute a
significant source of heating for the chromosphere. However, the p-mode
damping in the lower photosphere approaches levels large enough to
account for the measured p-mode line widths. The relative amplitudes
and phases of the thermodynamic quantities indicate that the p-mode
are neither adiabatic nor isothermal in the photosphere.
---------------------------------------------------------
Title: Effects of hydrogen and electron diffusion on trace species
diffusion in the solar atmosphere.
Authors: Fontenla, Juan M.; Avrett, E. H.
1992ESASP.348..335F Altcode: 1992cscl.work..335F
The authors study the effects of the diffusion of neutral hydrogen,
protons, and electrons, on the diffusion of heavy species in the
lower transition-region. This layer has large temperature and
hydrogen-ionization gradients as the temperature changes from
10<SUP>4</SUP> to 10<SUP>5</SUP>K. Hydrogen diffusion induces an
abundance gradient opposed to the hydrogen ionization gradient. Thermal
diffusion counteracts this effect for ionized particles. The low FIP
species (fully ionized in the lower transition region) experience
both effects. The high FIP species (neutral at T = 10<SUP>4</SUP>K)
are practically affected by only the hydrogen-diffusion effect. The
result is the enhancement of the abundance of the low-FIP elements with
respect to the high-FIP elements at the top of the models. However, the
rate at which this process occurs is critical and large departures from
the equilibrium abundances are expected because of the slow relaxation
rates at the top of the chromosphere.
---------------------------------------------------------
Title: FNAS: The magnetic configuration leading to solar flares
Authors: Fontenla, Juan M.
1992alab.rept.....F Altcode:
We present a method for solving plasma magnetohydrodynamic (MHD)
problems arising from the interaction of plasmas with magnetic fields
in stellar atmospheres. Our approach, in contrast to previous methods,
is not based on solving equations for the magnetic field and plasma
velocity but rather studies the evolution of the electric current and
density (and the related gas pressure). We have applied the method
to several studies involving linearized departures from static,
current-free equilibria. The applications show explicit solutions for
cases found in astrophysics and to problems encountered with earlier
studies where the gas pressure was neglected. The method is particularly
well suited for studying situations which involve a transition between
high and low plasma-beta regions. It shows precisely how electric
currents, and magnetic free-energy, build up in the plasma as a result
of the slow stressing of a potential magnetic field configuration. The
method also demonstrates how transverse-current waves, a mix of Alfven
and magneto-acoustic modes, propagate in a low-beta plasma for any
density stratification and background field geometry.
---------------------------------------------------------
Title: Book Review: Mechanisms of chromospheric and coronal heating /
Springer, 1991
Authors: Fontenla, J. M.; Mullan, D. J.; Fontenla, J. M.
1992SoPh..139..409F Altcode: 1992SoPh..139..409U
No abstract at ADS
---------------------------------------------------------
Title: The Dynamics of Electric Currents in High Conductivity Plasma
Authors: Fontenla, J. M.
1992AAS...180.5505F Altcode: 1992BAAS...24..819F
A new method for solving plasma MHD problems arising from the
interaction of plasmas with magnetic fields is presented. The
approach is based on studying directly the coupled evolution of
electric current and plasma density (and related pressure). This
contrasts with previous studies based on velocity and magnetic field
and in which the electric current is found from derivatives of the
field. The method presented here shows that transverse-current waves
(a mix of Alfven and magneto-acoustic modes) propagate in a low-beta
plasma at the Alfven speed. The origin and distribution of the magnetic
free-energy in the plasma results directly from the currents without
resorting to calculating differences between global quantities. The
expressions presented show that the approach of using the “inductance”
is good in some cases, but may be misleading in other cases. The method
proposed is well suited for studying the slow buildup of magnetic
stressed configurations leading to dynamic phenomena such as flares
and prominence eruptions. This occurs because the method can accurately
treat the coupling between plasma (gravity and pressure effects), and
magnetic field (Lorentz forces). This coupling is critical as the plasma
changes from high- to low-beta regimes in the solar chromosphere. Two
examples are shown in detail for typical two-dimensional cases of
small departures from the current-free case. For these the analytical
expressions of the general solutions are derived. A full solution for
these simple cases using observable boundary conditions is found. The
method presented is specially interesting for more complicated 3D
cases where the electric currents can not only displace, but also
realign themselves.
---------------------------------------------------------
Title: Klein-Gordon equation and reflection of Alfvén waves in
nonuniform media
Authors: Musielak, Z. E.; Fontenla, J. M.; Moore, R. L.
1992PhFlB...4...13M Altcode:
A new analytical approach is presented for assessing the reflection
of linear Alfven waves in smoothly nonuniform media. The general
one-dimensional case in Cartesian coordinates is treated. It is
shown that the wave equations, upon transformation into the form
of the Klein-Gordon equation, display a local critical frequency for
reflection. At any location in the medium, reflection becomes strong as
the wave frequency descends past this characteristic frequency set by
the local nonuniformity of the medium. This critical frequecy is given
by the transformation as an explicit function of the Alfven velocity
and its first and second derivatives, and hence as an explicit spatial
function. The transformation thus directly yields, without solution
of the wave equations, the location in the medium at which an Alfven
wave of any given frequency becomes strongly reflected and has its
propagation practically cut off.
---------------------------------------------------------
Title: A microflare-related activation of a filament observed in
H-alpha and C IV lines
Authors: Schmieder, B.; Fontenla, J.; Tandberg-Hanssen, E.
1991A&A...252..343S Altcode:
A filament in active region AR 2717 was observed in two lines formed
at different temperatures (H-alpha at 10 exp 4 K and C IV at 10 exp
5 K) with the multichannel-double-pass (MSDP) spectrograph and the
ultraviolet spectrometer and polarimeter (UVSP). The partial disparition
brusque (DB) of the filament as observed in H-alpha was due to the
heating of a filament section in the vicinity of a bright point. A
propagating disturbance followed this event. A detailed analysis of C
IV rasters shows that this disturbance was not a passive perturbation,
but was itself triggering active phenomena at various locations along
its path, resulting in energy releases. It is suggested that this
propagation of brightness was due to fast successive reconnections
between fine looplike structures of the filament.
---------------------------------------------------------
Title: Energy Balance in the Solar Transition Region. II. Effects
of Pressure and Energy Input on Hydrostatic Models
Authors: Fontenla, J. M.; Avrett, E. H.; Loeser, R.
1991ApJ...377..712F Altcode:
The radiation of energy by hydrogen lines and continua in hydrostatic
energy-balance models of the transition region between the solar
chromosphere and corona is studied using models which assume that
mechanical or magnetic energy is dissipated in the hot corona and is
then transported toward the chromosphere down the steep temperature
gradient of the transition region. These models explain the average
quiet sun and also the entire range of variability of the Ly-alpha
lines. The relations between the downward energy flux, the pressure
of the transition region, and the different hydrogen emission are
described.
---------------------------------------------------------
Title: Polarimetry of extreme ultraviolet lines in solar astronomy.
Authors: Fineschi, Silvano; Hoover, Richard B.; Fontenla, Juan M.;
Walker, Arthur B. C., Jr.
1991OptEn..30.1161F Altcode:
Several mechanisms can induce a detectable amount of linear polarization
in spectral lines emitted by the outer solar atmosphere at EUV/FUV
wavelengths: (1) Polarization in FUV lines (up to 20%) can be
originated by resonance scattering of radiation anisotropically
illuminating the emitting atoms. (2) Impact line polarization can
arise from anisotropic collisional excitation of the EUV-emitting
atoms by particles (electrons, protons) with non-Maxwellian velocity
distributions. The authors suggest how new technological developments
in the production of ultrasmooth, low-scatter flow-polished mirror
substrates and high-quality multilayer and interference film coatings
can make possible some new optical instruments for the observation of
these polarization effects. They describe several FUV/EUV polarimeter
designs based on these polarization optics.
---------------------------------------------------------
Title: Imaging polarimeters for solar extreme ultraviolet astronomy.
Authors: Hoover, Richard B.; Fineschi, Silvano; Fontenla, Juan M.;
Walker, Arthur B. C., Jr.
1991OptEn..30.1169H Altcode:
The authors describe new EUV/FUV (100Å ≤ λ ≤ 1500Å) polarimeter
instrument concepts for solar research. These instruments are
designed to observe linear polarization in EUV/FUV spectral lines
originating in the outer solar atmosphere, specifically: (1) a new
coronagraph/polarimeter operating at 1215.7Å (neutral hydrogen Lyman
α), which could observe this line in the near solar corona and lead to
the first direct measurements of both strength and direction of coronal
magnetic fields and (2) a new multilayer EUV imaging polarimeter,
operating at wavelengths of strong helium emission lines (e.g.,
304Å, 584Å), which could observe impact polarization phenomena and
provide information concerning the relative importance of thermal and
nonthermal processes in solar flares. The authors discuss several
instrument configurations and provide theoretical calculations and
performance predictions.
---------------------------------------------------------
Title: Flaring Arches - Part Three
Authors: Fontenla, Juan M.; Svestka, Zdenek; Farnik, Frantisek; Tang,
Frances Y.
1991SoPh..134..145F Altcode:
We show detailed observations in X-rays, UV lines, and Hα of an
extended arch, about 300000 km long, which developed as a consequence
of a compact subflare. This subflare occurred in an `included' magnetic
polarity of relatively low magnetic field strength (compared to that of
the sunspots). The apparition of this big arch was preceded by that of a
smaller arch, about 30000 km long, which masked the polarity inversion
line filament in the early phase of the subflare. The big arch which
developed later, around the time of the main X-ray and UV spike of the
subflare, connected the included polarity and the main leading sunspot
of the region, and became fully developed in a few minutes. The fact
that both arches were simultaneously observed in all spectral domains as
well as their fine structure in Hα can only be explained by considering
the arch as composed of several unresolved portions of material
having widely different temperatures. The Hα observations can be
interpreted as showing the appearance of this cool material as a result
of condensation, but a more appealing interpretation is that there
was almost simultaneous ejection of superhot (10<SUP>7</SUP> K), hot
(10<SUP>6</SUP> K), mild (10<SUP>5</SUP> K), and cool (10<SUP>4</SUP>
K) material from the subflare site along previously existing magnetic
tubes of much lower density. The termination of the subflare was marked
by a rather hard X-ray and UV spike which appeared to originate in a
different structure than that of the main spike. The material in the
arch gradually cooled and drained down after the end of the subflare.
---------------------------------------------------------
Title: Diffusion of Helium in the Solar Transition Region
Authors: Avrett, E. H.; Fontenla, J. M.
1991BAAS...23.1029A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Simultaneous UV and X-ray Observations of Solar Microflares
Authors: Porter, J. G.; Fontenla, J. M.; Moore, R. L.; Simnett, G. M.
1991BAAS...23..935P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Considerations for Flare Related Magnetic Field Measurements
Authors: Davis, J. M.; Fontenla, J. M.
1991BAAS...23.1055D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Non-Maxwellian Electron Distributions in Models of the Solar
Atmosphere
Authors: MacNeice, P.; Fontenla, J.; Ljepojevic, N. N.
1991ApJ...369..544M Altcode:
In this paper, the solar models of Fontenla et al. (1990) are extended
to coronal temperatures using optically thin radiative losses and a
semicircular loop geometry. The effects of a non-Maxwellian high-energy
tail of the electron distribution function is tested by performing
a Fokker-Planck calculation of the tail. The results show that the
downward conductive heat flux is very clsoe to that given by Braginskii
(1965) for small departures from a Maxwellian distribution. The
effects of the high-energy tail of the electron distribution on
element ionization are computed and found to be negligible for all
ionization states of O, Ne, and Si. It is concluded that, for quiet
sun loop models in stationary energy balance, the ionization state of
all elements is not significantly affected by the non-Maxwellian tail
of the electron velocity distribution, and that the heat flux can be
computed by considering only small first-order departures from the
Maxwellian distribution.
---------------------------------------------------------
Title: The X-Ray Counterparts of UV Microflares
Authors: Porter, J. G.; Fontenla, J. M.; Moore, R. L.; Simnett, G. M.
1991BAAS...23.1027P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the Direction of the Currents at Magnetic Neutral Points
Authors: Fontenla, J. M.; Davis, J. M.
1991BAAS...23Q1067F Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Solar EUV/FUV line polarimetry. Pt. 1. Observational parameters
and theoretical considerations.
Authors: Fineschi, Silvano; Hoover, Richard B.; Fontenla, Juan M.;
Walker, Arthur B. C., Jr.
1991SPIE.1343..376F Altcode:
Several mechanisms can induce a detectable amount of linear polarization
(≥1%) in spectral lines emitted by the outer solar atmosphere at
EUV/FUV wavelengths (100 Å ≤ λ ≤ 1500 Å). The authors suggest
how new technological developments associated with the production of
ultra-smooth, low scatter, flow-polished mirror substrates and high
quality multilayer and interference film coatings can make possible
some exciting new optical instruments which should permit observations
of these polarization effects. They describe some new types of EUV/FUV
polarimeters based on these polarization optics.
---------------------------------------------------------
Title: Solar EUV/FUV line polarimetry: instruments and methods
Authors: Hoover, Richard B.; Fineschi, Silvano; Fontenla, Juan M.;
Walker, Arthur B.
1991SPIE.1343..389H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Electron Impact Polarization Expected in Solar EUV Lines from
Flaring Chromospheres/Transition Regions
Authors: Fineschi, S.; Fontenla, J. M.; MacNeice, P.; Ljepojevic, N. N.
1991max..conf...95F Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The 3-D description of vertical current sheets with application
to solar flares
Authors: Fontenla, Juan M.; Davis, J. M.
1991deas.reptQ....F Altcode:
Following a brief review of the processes which have been suggested for
explaining the occurrence of solar flares we suggest a new scenario
which builds on the achievements of the previous suggestion that the
current sheets, which develop naturally in 3-D cases with gravity
from impacting independent magnetic structures (i.e., approaching
current systems), do not consist of horizontal currents but are instead
predominantly vertical current systems. This suggestion is based on the
fact that as the subphotospheric sources of the magnetic field displace
the upper photosphere and lower chromosphere regions, where plasma beta
is near unity, will experience predominantly horizontal mass motions
which will lead to a distorted 3-D configurations of the magnetic
field having stored free energy. In our scenario, a vertically flowing
current sheet separates the plasma regions associated with either of the
subphotospheric sources. This reflects the balanced tension of the two
stressed fields which twist around each other. This leads naturally to
a metastable or unstable situation as the twisted field emerges into a
low beta region where vertical motions are not inhibited by gravity. In
our flare scenario the impulsive energy release occurs, initially,
not by reconnection but mainly by the rapid change of the magnetic
field which has become unstable. During the impulsive phase the field
lines contort in such way as to realign the electric current sheet into
a minimum energy horizontal flow. This contortion produces very large
electric fields which will accelerate particles. As the current evolves
to a horizontal configuration the magnetic field expands vertically,
which can be accompanied by eruptions of material. The instability of
a horizontal current is well known and causes the magnetic field to
undergo a rapid outward expansion. In our scenario, fast reconnection
is not necessary to trigger the flare, however, slow reconnection would
occur continuously in the current layer at the locations of potential
flaring. During the initial rearrangement of the field strong plasma
turbulence develops. Following the impulsive phase, the final current
sheet will experience faster reconnection which we believe responsible
for the gradual phase of the flare. The reconnection will dissipate
part of the current and will produce sustained and extended heating
in the flare region and in the postflare loops.
---------------------------------------------------------
Title: The role of particle diffusion in the lower transition region:
Revised interpretation of emission measures
Authors: Avrett, Eugene H.; Fontenla, Juan M.
1991deas.rept.....A Altcode:
Our energy-balance models of the lower transit ion region were
presented in a previous paper (New Models of the Chromosphere and
Transition Region). Here we show the influence of particle diffusion
on the calculated hydrogen and helium number densities for a given
temperature-density model (model C in the preceding paper). We have also
solved the statistical equilibrium and radiative transfer equations for
a 13-level He I atom (22 radiative transitions) and a 6-level He II ion
(15 radiative transitions) together with He III. The resulting He I and
He II level-1 number densities and He III density are shown as functions
of temperature. Diffusion substantially increases eta<SUB>HeI</SUB>
for T greater than 35,000 K and decreases eta<SUB>HeI</SUB> (while
increasing eta(sub(HeII)) between 9,000 and 25,000 K. Including the
effects of diffusion also increases eta<SUB>HeIII</SUB> for T less
than 60,000 K.
---------------------------------------------------------
Title: Electron impact polarization expected in solar EUV lines from
flaring chromospheres/transition regions
Authors: Fineschi, S.; Fontenla, Juan M.; MacNeice, P.; Ljepojevic,
N. N.
1991deas.reptR....F Altcode:
We have evaluated lower bounds on the degree of impact Extreme
Ultraviolet/Ultraviolet (EUV/UV) line polarization expected during
solar flares. This polarization arises from collisional excitation by
energetic electrons with non-Maxwellian velocity distributions. Linear
polarization was observed in the S I 1437 A line by the Ultraviolet
Spectrometer and Polarimeter/Solar Maximum Mission (UVSP/SMM) during a
flare on 15 July 1980. An early interpretation suggested that impact
excitation by electrons propagating through the steep temperature
gradient of the flaring transition region/high chromosphere produced
this polarization. Our calculations show that the observed polarization
in this UV line cannot be due to this effect. We find instead that,
in some flare models, the energetic electrons can produce an impact
polarization of a few percent in EUV neutral helium lines (i.e.,
lambda lambda 522, 537, and 584 A).
---------------------------------------------------------
Title: The Role of Particle Diffusion in the Lower Transition Region:
Revised Interpretation of Emission Measures (With 2 Figures)
Authors: Avrett, E. H.; Fontenla, J. M.
1991mcch.conf..100A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Energy Balance in the Solar Transition Region. I. Hydrostatic
Thermal Models with Ambipolar Diffusion
Authors: Fontenla, J. M.; Avrett, E. H.; Loeser, R.
1990ApJ...355..700F Altcode:
The energy balance in the lower transition region is analyzed by
constructing theoretical models which satisfy the energy balance
constraint. The energy balance is achieved by balancing the radiative
losses and the energy flowing downward from the corona. This energy flow
is mainly in two forms: conductive heat flow and hydrogen ionization
energy flow due to ambipolar diffusion. Hydrostatic equilibrium
is assumed, and, in a first calculation, local mechanical heating
and Joule heating are ignored. In a second model, some mechanical
heating compatible with chromospheric energy-balance calculations is
introduced. The models are computed for a partial non-LTE approach in
which radiation departs strongly from LTE but particles depart from
Maxwellian distributions only to first order. The results, which apply
to cases where the magnetic field is either absent, or uniform and
vertical, are compared with the observed Lyman lines and continuum
from the average quiet sun. The approximate agreement suggests that
this type of model can roughly explain the observed intensities in
a physically meaningful way, assuming only a few free parameters
specified as chromospheric boundary conditions.
---------------------------------------------------------
Title: Impact Line Polarization in Hot Solar Plasmas with
Non-Maxwellian Electron Distributions
Authors: Fineschi, S.; Fontenla, J. M.; MacNeice, P.; Ljepojevic, N. N.
1990BAAS...22..826F Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Formation of the He I Resonance Lines in the Solar Transition
Region
Authors: Avrett, E. H.; Fontenla, J. M.
1990BAAS...22..816A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Measurement of Dissipation or Pumping of P-Modes in the
Solar Photosphere
Authors: Fontenla, J. M.; Hathaway, D. H.; Rabin, D.; Moore, R.
1990BAAS...22..856F Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Effect of Radiative Transfer on Convection in the Deep
Photosphere of Late-Type Dwarfs
Authors: Fontenla, J. M.; Musielak, Z. E.; Moore, R. L.
1990ASPC....9...82F Altcode: 1990csss....6...82F
A method is proposed to eliminate the compressional instability of a
shallow layer in the upper part of stellar convective zones in standard
mixing-length models. By equating the radiative cooling time of mixing
eddies to their convective turnover time, the effective sizes of the
eddies are assumed to be the smallest of those which are not eliminated
by radiative transfer. Computations of the models with this assumption
leads to smooth temperature profiles in the previously unstable layers
and reductions of the convective velocity above its maximum value.
---------------------------------------------------------
Title: Multi-Thread Structure as a Possible Solution for the L-Beta
Problem in Solar Prominences
Authors: Vial, J. -C.; Rovira, M.; Fontenla, J.; Gouttebroze, P.
1990LNP...363..282V Altcode: 1990IAUCo.117..282V; 1990doqp.coll..282V
Following the pioneering works of Heasley, Mihalas, Milkey and Poland
(see e.g. Heasley and Milkey, 1983) who built non LTE onedimensional
models of solar prominence, much attention has been paid to the
spectral signatures of the Lyman lines as observed with OSO 8 (Vial,
1982a). In spite of a better treatment of the frequency redistribution
and boundary conditions, one-dimensional low-pressure models lead to
Lyman intensities much lower than observed ones (Heinzel, Gouttebroze
and Vial, 1987). Different atomic processes of formation of hydrogen
lines (Cooper, Ballagh and Hubeny, 1988) or the inclusion of a
Prominence Corona Transition Region or PCTR (Heinzel, Gouttebroze and
Vial, 1988) have been proposed to explain this discrepancy. We present
here a different approach where the filamentary nature of prominences
which provides the hydrogen lines with different opacities, offers
their photons different escaping possibilities. The thread models
we use derive from an energy equation where radiative losses are
balanced by conductive flux (Foutenla and Rovira, 1983, 1985). We
show that no superposition of threads gives good values of Lyman a,
and H a intensities for too high and too low pressures. Solutions are
found for pressure around 0.05-0.1 dyn/cm2 and a number of threads
between 100 and 400. Two improvements have been performed: first, the
inclusion of Partial Redistribution leads to a decrease of L (and L)
intensity and models now require a higher number of threads; second,
the inclusion of the ambipolar diffusion along the steep temperature
gradient which changes the hydrogen ionization in the lower regions
(Foutenla, Avrett and Loeser, 1990). The new run of temperature and
density implies more material at low temperatures and hydrogen lines
intensities increase. A solution for the L problem can be found for
a pressure of about 0.1 dyn cm-t2. However the H intensity appears to
be rather high. Moreover, the number of threads required (about 200)
is far larger than the number derived by Zirker and Koutchmy (this
issue) and Mein (this issue) from observed H profiles. Our neglect
of the radiative interaction between threads may explain our results
(Heinzel, this issue). To conclude, these computations of non-lte
radiative transfer in realistic geometrical and physical models, appear
to be a promising path for the investigation of solar prominences.
---------------------------------------------------------
Title: Driving of the Solar P-modes by Radiative Pumping in the
Upper Photosphere
Authors: Fontenla, Juan M.; Emslie, A. G.; Moore, Ronald L.
1990AIPC..198..218F Altcode: 1989AIPC..198..218F; 1990asan.conf..218F
It is shown that one viable driver of the solar p-modes is radiative
pumping in the upper photosphere where the opacity is dominated by
the negative hydrogen ion. This new option is suggested by the similar
magnitudes of two energy flows that have been evaluated by independent
empirical methods. The similarity indicates that the p-modes are
radiatively pumped in the upper photosphere and therefore provide the
required nonradiative cooling.
---------------------------------------------------------
Title: Why DA and DB White Dwarfs Do Not Show Coronal Activity and
p-Mode Oscillations
Authors: Musielak, Z. E.; Fontenla, J. M.
1989ApJ...346..435M Altcode:
The problems of nonradiative heating of outer atmospheric layers and
p-mode oscillations in white dwarfs caused by acoustic waves generated
in convective zones are discussed. These effects have been studied
by calculating the cutoff periods for adiabatic and isothermal waves
propagating in atmospheres of DA and DB stars with Teff greater than
or equal 20,000 K and log g = 6-9. The obtained cutoff periods are
approximately bounded by 0.01 and 40 sec for high- and low-gravity
white dwarfs, respectively. Expected amplitudes of p-mode oscillations
corresponding to trapped acoustic waves with small angular wave numbers
are estimated, indicating that the amplitudes could be observed
as Doppler shifts of spectral lines which might be detectable if
adequate spectral resolution were available. The luminosity variations
corresponding to these amplitudes are unlikely to be observable when
all damping processes are accounted for. Results also indicate that
the present theory of convection predicts some irregularities in the
behavior of physical parameters.
---------------------------------------------------------
Title: Flaring Arches - Part Two
Authors: Svestka, Zdenek; Farnik, Frantisek; Fontenla, Juan M.;
Martin, Sara F.
1989SoPh..123..317S Altcode:
We discuss first the development of the coronal arch-shaped structure of
∼ 57000 km length which was born at or before 08:00 UT on 6 November,
1980 and became the site of 13 quasi-periodic brightenings in hard
X-rays from 10:00 to 14:30 UT. The same structure became the site
of a series of 17 flaring arches between 15:30 and 24:00 UT on that
day. The periodicity of ∼ 19 min, defined well for the quasi-periodic
variations, seems to be partly retained during the occurrence of the
flaring arches.
---------------------------------------------------------
Title: Ultraviolet Events Observed in Active Regions. I. Observations
and Scenario
Authors: Fontenla, J. M.; Tandberg-Hanssen, E.; Reichmann, E. J.;
Filipowski, Sharon
1989ApJ...344.1034F Altcode:
UV line data obtained in solar active regions on and near the limb,
taken with the Ultraviolet Spectrometer and Polarimeter experiment on
the Solar Maximum Mission are examined. The study provides insight
into the physical processes behind sudden localized brightenings
(or microflares) that occur within these active regions and their
relation to surging activity. Time sequences of rasters and rasters
through the line (taken in Ly-alpha and N V lines simultaneously) and
C IV dopplergrams are the core of these data. They show the brightening
events on the disk and Doppler shifts in dynamic events on the disk and
above the limb. The study suggests, for the events, a localized energy
deposition in a region of the chromosphere that heats the material and
produces a pressure pulse. This mechanism explains the brightenings
in transition region lines and also the observed surging behavior and
jet-like events.
---------------------------------------------------------
Title: Non-Maxwellian Electron Distributions in a Model of the Quiet
Solar Atmosphere
Authors: MacNeice, P.; Fontenla, J.; Ljepojevic, N.
1989BAAS...21.1112M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Do Any White Dwarfs Have X-ray Coronae?
Authors: Musielak, Z. E.; Fontenla, J. M.; Moore, R. L.
1989BAAS...21.1222M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Wave energy leakage and heating of white dwarf atmospheres.
Authors: Fontenla, J. M.; Musielak, Z. E.
1989BAAS...21.1021F Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Oscillations in Stellar Atmospheres
Authors: Costa, A.; Fontenla, J. M.; Ringuelet, A. E.
1989ApJ...339..314C Altcode:
Atmospheric excitation and propagation of oscillations are analyzed for
typical pulsating stars. The linear, plane-parallel approach for the
pulsating atmosphere gives a local description of the phenomenon. From
the local analysis of oscillations, the minimum frequencies are
obtained for radially propagating waves. The comparison of the
minimum frequencies obtained for a variety of stellar types is in good
agreement with the observed periods of the oscillations. The role of
the atmosphere in the globar stellar pulsations is thus emphasized.
---------------------------------------------------------
Title: UV and X-Ray Flaring Arch of June 27, 1980
Authors: Fontenla, J. M.
1989BAAS...21..850F Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Eruption of a Quiescent Prominence as Observed in
Ultraviolet Lines
Authors: Fontenla, J. M.; Poland, A. I.
1989SoPh..123..143F Altcode:
We compare observations of an eruptive and a quiescent prominence
in order to better understand the energetic processes in an eruptive
prominence. Observations of an eruptive prominence were obtained in
Hα, several UV emission lines (1215-1640 Å), and coronal white light
at approximately 19:00 UT on September 20, 1980. The data we present
shows the development of the eruption in the Hα and UV emission lines
and is compared with the intensities from similar observations of a
quiescent prominence. While the event is coincident with some coronal
changes, above 1.2 and up to 1.5 solar radii, it does not result in
a true coronal mass ejection event.
---------------------------------------------------------
Title: Arches showing UV flaring activity
Authors: Fontenla, J. M.
1988fnsm.work..141F Altcode:
The UVSP data obtained in the previous maximum activity cycle show the
frequent appearance of flaring events in the UV. In many cases these
flaring events are characterized by at least two footpoints which
show compact impulsive non-simultaneous brightenings and a fainter
but clearly observed arch developes between the footpoints. These
arches and footpoints are observed in line corresponding to different
temperatures, as Lyman alpha, N V, and C IV, and when observed above
the limb display large Doppler shifts at some stages. The size of the
arches can be larger than 20 arcsec.
---------------------------------------------------------
Title: Arches Showing UV Flaring Activity
Authors: Fontenla, J. M.
1988BAAS...20..913F Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Lyman-Alpha Line in Various Solar Features. I. Observations
Authors: Fontenla, J.; Reichmann, E. J.; Tandberg-Hanssen, E.
1988ApJ...329..464F Altcode:
The authors give an overview of the main features of the solar
atmosphere as observed in the Lyα line by the Ultraviolet Spectrometer
and Polarimeter on the SMM. The authors use high spectral and
spatial resolution data as well as broad-band spectroheliograms to
characterize the various features, and they present the values which
theoretical models have to explain. It is shown that on the disk
(quiet Sun and active regions) the central reversal of the line is
highly variable in depth and frequently shifted, leading to asymmetric
profiles. Observations above the limb reveal the appearance of a
dynamic layer (cloud layer) overlying the limb. The authors present
its Lyα profile and show that it can be responsible for distorting the
background profile of the line and leading to the observed asymmetric
profiles.
---------------------------------------------------------
Title: Hydrogen Ionization and Energy Balance in the Solar Transition
Region
Authors: Avrett, E. H.; Fontenla, J. M.
1988BAAS...20..721A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Detection of Microflares with the Present UVSP
Authors: Porter, J. G.; Moore, R. L.; Reichmann, E. J.; Fontenla, J. M.
1988BAAS...20..711P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Photospheric Radiative Pumping of the Solar Global p-Mode
Oscillations
Authors: Fontenla, J. M.; Moore, R. L.
1988BAAS...20..684F Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Lyman alpha SMM/UVSP absolute calibration and geocoronal
correction
Authors: Fontenla, Juan M.; Reichmann, Edwin J.
1987STIN...8812446F Altcode:
Lyman alpha observations from the Ultraviolet Spectrometer Polarimeter
(UVSP) instrument of the Solar Maximum Mission (SMM) spacecraft were
analyzed and provide instrumental calibration details. Specific values
of the instrument quantum efficiency, Lyman alpha absolute intensity,
and correction for geocoronal absorption are presented.
---------------------------------------------------------
Title: Multi-thermal observations of newly formed loops in a
dynamic flare
Authors: Švestka, Zdeněk F.; Fontenla, Juan M.; Machado, Marcos E.;
Martin, Sara F.; Neidig, Donald F.; Poletto, Giannina
1987SoPh..108..237S Altcode:
The dynamic flare of 6 November, 1980 (max ≈ 15:26 UT) developed a
rich system of growing loops which could be followed in Hα for 1.5
hr. Throughout the flare, these loops, near the limb, were seen in
emission against the disk. Theoretical computations of deviations from
LTE populations for a hydrogen atom reveal that this requires electron
densities in the loops close to, or in excess of 10<SUP>12</SUP>
cm <SUP>-3</SUP>. From measured widths of higher Balmer lines the
density at the tops of the loops was found to be 4 x 10<SUP>12</SUP>
cm <SUP>-3</SUP> if no non-thermal motions were present, or 5 ×
10<SUP>11</SUP> cm <SUP>-3</SUP> for a turbulent velocity of ~ 12 km
s <SUP>-1</SUP>.
---------------------------------------------------------
Title: High Resolution Ly Alpha Line Observations
Authors: Fontenla, J. M.; Reichmann, E.; Tandberg-Hanssen, E.
1987BAAS...19..930F Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Energy Balance at the Base of the Solar Transition Region
Authors: Fontenla, J. M.; Avrett, E. H.; Loeser, R.
1987BAAS...19Q.931F Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Stability of solar protuberances
Authors: Hernaiz, A. F.; Fontenla, J. M.
1987BAAA...33...67H Altcode:
This method of stability analysis was developed for stellar envelopes
and it is extended to solar protuberances taking into account the
boundary conditions of this case. This is a first approximation to the
study of the stability of solar protuberances because this chemical
compositions have been simplified. Only hydrogen in its fundamental
state and ionized hydrogen have been considered. In the optically
thick case, the instability depends on the incident radiation coming
from the photosphere and chromosphere.
---------------------------------------------------------
Title: Análisis de modos de oscilación atmosféricos
Authors: Costa, A.; Fontenla, J. M.; Ringuelet, A. E.
1987BAAA...32...79C Altcode:
Se analiza la respuesta atmosférica de estrellas pulsantes a las
oscilaciones que se propagan en ellas. El estudio analítico de la
propagación de ondas en medios estratificados se hace sobre la base
de datos obtenidos de los modelos atmosféricos de Kurucz. De este
análisis se obtienen los modos propio de oscilación,y la región de
excitación de oscilaciones. Se definen las impedancias complejas Zww
que dan la absorción o disipación y la excitación y las impedancias
Zww' que dan información sobre la interacción de distintos modos.
---------------------------------------------------------
Title: Consistent Transport Theory in Astrophysics
Authors: Fontenla, J. M.
1986BAAS...18.1004F Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The hydrogen Balmer, Paschen, and Brackett series lines in
quiescent prominences
Authors: Rovira, Marta G.; Fontenla, Juan Manuel
1986SoPh..106..315R Altcode:
To calculate the Balmer, Paschen, and Brackett line intensities, we
solved the statistical equilibrium equations for a twenty level plus
continuum atom of hydrogen.
---------------------------------------------------------
Title: Consistent transport coefficients in astrophysics
Authors: Fontenla, Juan M.; Rovira, M.; Ferro Fontan, C.
1986STIN...8824560F Altcode:
A consistent theory for dealing with transport phenomena in stellar
atmospheres starting with the kinetic equations and introducing three
cases (LTE, partial LTE, and non-LTE) was developed. The consistent
hydrodynamical equations were presented for partial-LTE, the transport
coefficients defined, and a method shown to calculate them. The method
is based on the numerical solution of kinetic equations considering
Landau, Boltzmann, and Focker-Planck collision terms. Finally a set
of results for the transport coefficients derived for a partially
ionized hydrogen gas with radiation was shown, considering ionization
and recombination as well as elastic collisions. The results obtained
imply major changes is some types of theoretical model calculations
and can resolve some important current problems concerning energy and
mass balance in the solar atmosphere. It is shown that energy balance
in the lower solar transition region can be fully explained by means
of radiation losses and conductive flux.
---------------------------------------------------------
Title: A dynamic flare with anomalously dense flare loops
Authors: Svestka, Z.; Fontenla, J. M.; Machado, M. E.; Martin, S. F.;
Neidig, D. F.; Poletto, G.
1986AdSpR...6f.253S Altcode: 1986AdSpR...6..253S
The dynamic flare of 6 November 1980 (max. ~ 15:26 UT) developed a
rich system of growing loops which could be followed in Hα for 1.5
hours. Throughout the flare, these loops, near the limb, were seen in
emission against the disk. Theoretical computations of b-values for
a hydrogen atom reveal that this requires electron densities in the
loops to be close to 10<SUP>12</SUP> cm<SUP>-3</SUP>. From measured
widths of higher Balmer lines the density at the loops of the loops
was found to be 4 × 10<SUP>12</SUP> cm<SUP>-3</SUP> if no non-thermal
motions were present. It is now general knowledge that flare loops
are initially observed in X-rays and become visible in Hα only after
cooling. For such a high density a loop would cool through radiation
from 10<SUP>7</SUP> K to 10<SUP>4</SUP> K within a few minutes so that
the dense Hα loops should have heights very close to the heights of
the X-ray loops. This, however, contradicts the observations obtained by
the HXIS and FCS instruments on board SMM which show the X-ray loops at
much higher altitudes than the loops in Hα. Therefore, the density must
have been significantly smaller when the loops were formed and the flare
loops were apparently both shrinking and becoming denser while cooling.
---------------------------------------------------------
Title: Transporte en atmósferas estelares
---------------------------------------------------------
Title: Transporte en
atmósferas estelares
---------------------------------------------------------
Title: Transport in stellar atmospheres;
Authors: Fontenla, Juan Manuel
1986PhDT........69F Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Numerical evaluations in radiative transfer.
Authors: Fontenla, J. M.; Rovira, M. G.
1985JQSRT..34..389F Altcode:
The authors compare different methods of calculating the monochromatic
mean intensity and flux divergence for different dependences of the
source function on the optical depth. They consider a semi-infinite
plane-parallel atmosphere and a plane-parallel symmetric slab. The
authors show that in some cases the methods commonly used are quite
inaccurate, and propose another which gives consistent values for both
the flux divergence and the mean intensity, even in extreme cases of
high and small optical depths.
---------------------------------------------------------
Title: Simultaneous IUE and ground-based observations of 48 Librae.
Authors: Rovira, M.; Ringuelet, A. E.; Fontenla, J. M.; Sahade, J.;
Kondo, Y.
1985RMxAA..10..245R Altcode:
IUE and ground-based observations of 48 Librae were carried out
simultaneously in July, 1981. The main results are: (1) no progression
was observed in the Balmer lines; (2) the photographic metallic lines
have radial velocities around +30 km/s; (3) the radial velocities of the
UV lines formed in the cool envelope are grouped around the value +20
km/s with a higher dispersion than the photographic metallic lines;
(4) the lines originating in the transition region yield negative
velocities; (5) the continuum energy distribution corresponds to
T<SUB>e</SUB> = 16000K and log g = 4.5, and (6) Ca II λ3933 Å has
no chromospheric components.
---------------------------------------------------------
Title: Quiescent Prominence Threads Models
Authors: Fontenla, J. M.; Rovira, M.
1985SoPh...96...53F Altcode:
We have calculated prominence thread models for different values of
the center temperature and pressure. We have simultaneously solved
the radiative transfer, statistical equilibrium and ionization
equilibrium equations assuming a three-level atom plus continuum. We
have also computed the energy balance equation including the hydrogen
radiative losses from our calculations, plus other radiative losses
and heat conduction. Some models have been calculated assuming possible
variations in thermal conductivity and heating terms. We computed the
lines and continua emitted by a number of threads, in order to compare
with the observations and evaluate how the different values of the
parameters affect the profiles and absolute intensities of Lα, Lβ,
Hα, and Ly continuum.
---------------------------------------------------------
Title: Kinetic Equations and Departures from LTE
Authors: Fontenla, J. M.
1985RMxAA..10..413F Altcode:
We present a method for the numerical solution of the kinetic
equations for a gas composed by photons, electrons, atoms and
ions. The gas is assumed to satisfy the statistical hypothesis. We
show the integro-diferential equations that determine the distribution
functions, for situations departing from thermodynarnical equilibrium
as in stellar atmospheres. These functions differ from Boltzrnann'
s and even from Maxwell's function. We give the equations for a
one-dimensional problem and propose the use of the Newton-Raphson method
to solve the equations for given boundary conditions. We also show how
to compute first order devia tions from Maxwell's distribution, and,
from these departures, how to compute the transport coefficients and
their range of aplicability. We further suggest correction procedures
for saturated fluxes.
---------------------------------------------------------
Title: Perturbaciones a primer orden en la solución formal de las
ecuaciones de transporte radiativo
Authors: Hernaiz, A. F.; Fontenla, J. M.
1985BAAA...31..281H Altcode:
En este trabajo se exponen modificaciones al método desarrollado por
Fontenla para la resolución simultánea de las ecuaciones de transporte
radiativo y equilibrio estadístico. Mediante dichas modificaciones
se lleva el método al tipo de Newton-Raphson generalizado, hecho que
mejoraría las condiciones de convergencia, particularmente en los
casos de grandes espesores ópticos.
---------------------------------------------------------
Title: Estudio hidrodinámico de atmósferas estelares II
Authors: Costa, A.; Fontenla, J. M.; Ringuelet, A. E.
1985BAAA...31..280C Altcode:
En este trabajo se estudian las frecuencias propias de oscilación
de la atmósfera de una estrella pulsante, la interacción de los
distintos modos de oscilación y las limitaciones que la atmósfera
impone a la pulsación.
---------------------------------------------------------
Title: Coeficientes de transporte en astrofísica
Authors: Fontenla, J. M.
1985BAAA...31..287F Altcode:
Se exponen aquí los primeros resultados obtenidos para los coeficientes
de transporte (conductividades térmica y eléctrica y otros) en
condiciones típicas en astrofísica.
---------------------------------------------------------
Title: Cálculo de las intensidades de la línea de Balmer, Paschen
y Brackett para las protuberancias quiescente
Authors: Rovira, M. G.; Fontenla, J. M.
1985BAAA...31..284R Altcode:
Con el objeto de calcular las intensidades de las líneas de las
series de Balmer, Paschen y Brackett en protuberancias solares se
resolvieron las ecuaciones de equilibrio estadístico para un átomo
de hidrógeno de 20 niveles más continuo. A partir de los valores de
temperatura, ionización y las poblaciones de los tres primeros niveles
de los modelos de protuberancias deducidos en un trabajo anterior,
se calcularon las poblaciones de los 20 niveles y las intensidades
integradas de las líneas correspondientes a las tres series antes
mencionadas. El método también fue aplicado a los modelos teóricos
de Heasley y Mihalas.
---------------------------------------------------------
Title: IUE low dispersion observations of symbiotic objects.
Authors: Sahade, J.; Brandi, E.; Fontenla, J. M.
1984A&AS...56...17S Altcode:
The results of the study of low dispersion IUE ultraviolet spectra
of 20 symbiotic stars and of the binary RY Scuti are presented in
tables and graphs. The continuous and the line spectra are analyzed
and discussed. Variations in line intensity and in the continuum
are reported.
---------------------------------------------------------
Title: Análisis de la estabilidad de la ionización del hidrógeno
en estrellas B
Authors: Hernaiz, A. F.; Fontenla, J. M.
1984BAAA...30...23H Altcode:
Se estudia la estabilidad y relajación en el tiempo de la ionización,
para un gas de hidrógeno puro en el caso una envoltura de estrella
B. Para ello se utiliza un modelo con un solo nivel y el continuo y se
resuelven simultáneamente las ecuaciones de equilibrio estadístico,
teniendo en cuenta el término dependiente del tiempo y las ecuaciones
de transporte radiativo en forma detallada.
---------------------------------------------------------
Title: Estudio hidrodinámico de atmósferas estelares
Authors: Costa, A.; Fontenla, J. M.; Ringuelet, A. E.
1984BAAA...30...26C Altcode:
Analizando la propagación de ondas en medios estratificados y sobre
la base de modelos de Mihalas y Kurucz, se obtienen resultados
cuantitativos que permiten su comparación con observaciones de
atmósferas de estrellas pulsantes.
---------------------------------------------------------
Title: Simultaneous IUE and ground-based observations of V923 Aquilae.
Authors: Ringuelet, A. E.; Sahade, J.; Rovira, M.; Fontenla, J. M.;
Kondo, Y.
1984A&A...131....9R Altcode:
Simultaneous IUE and ground-based observations of V 923 Aquilae
carried out in July 1981 are used to propose a model of the extended
envelope of this Be star with a transition region relatively close to
the star, where the highly ionized species would be formed. The shell
photographic and ultraviolet lines of Fe II and the photographic lines
of Ca II and Na I would originate in regions exterior to the transition
zone. As for the faint Fe II and Ni II emissions that are displayed
by the photographic spectrum, the possible regions where they could
form are considered. The zone of temperature rise between the star
and the transition region appears as more likely; plans to check this
model numerically are being formulated. The star is characterized by
variable mass-ejection, and is not a cyclic V/R variable.
---------------------------------------------------------
Title: Funciones de distribución en No-Lte
Authors: Fontenla, J. M.
1984BAAA...28..171F Altcode:
Se están desarrollando método para resolver numéricamente las
ecuaciones de Maxwell y las de Boltzmann en casos de interés en
astrofísica, como: a) vientos estelares, donde la distribución de la
materia está dominada por la radiación. b) regiones de transición
cromosfera - corona y prominencia - corona donde la temperatura varía
fuertemente respecto al "libre camino" de las partículas.
---------------------------------------------------------
Title: Observaciones desde Tierra y desde el IUE de V923 Aquilae
Authors: Ringuelet, A. E.; Sahade, J.; Rovira, M.; Fontenla, J. M.;
Kondo, K.
1984BAAA...28...79R Altcode:
En base a observaciones simultáneas desde tierra y desde satélites
se elabora un modelo semi-empírico de la envoltura de V923 Aquilae
que explica los perfiles de las líneas observadas en el UV y en la
región fotográfica.
---------------------------------------------------------
Title: The Lyman alpha line in solar prominences.
Authors: Fontenla, J. M.; Rovira, M.
1983SoPh...85..141F Altcode:
We present simplified models for the region where Lα is formed, in
the boundary between prominences and corona. The models were calculated
by solving the radiation transfer in the line and the energy equation
considering conductive flux. We calculate the absolute intensities and
profiles of the Lα line given by the models, and compare them with
observed values. From the comparison there results that temperature
gradient starts increasing in the region of formation of Lyman continuum
and reaches a steep gradient in the region where the central core of
Lα is formed. We find general agreement and we show the influence of
the different parameters on models and on the emerging intensities.
---------------------------------------------------------
Title: Formación de la línea Lyman α en la región de transición
protuberancia-corona
Authors: Fontenla, J. M.; Rovira, M.
1982BAAA...27...11F Altcode:
Se presentan modelos de las capas de la región de transición
protuberancia-corona en las cuales se forma el núcleo de la
línea Ly α. Para calcular estos modelos se tiene en cuenta el
balance de energía entre la radiación y la conducción suponiendo
presión constante y balance de ionización. Además, se resuelven
simultáneamente las ecuaciones de equilibrio estadístico y transporte
radiativo fuera de equilibrio termodinámico local. A partir de estos
modelos se calculan las líneas emitidas y los flujos totales y se
establece un método para evaluar parámetros de esa región.
---------------------------------------------------------
Title: El espectro ultravioleta de la estrella simbiótica RW Hydrae
Authors: Sahade, J.; Brandi, E.; Fontenla, J. M.
1982BAAA...27..152S Altcode:
La comparación de espectros de RW Hydrae tomados con el IUE en enero
y en julio de 1979, ha permitido detectar variaciones en la intensidad
de varias líneas de emisión así como variaciones en el espectro
continuo. El espectro continuo de julio de 1979 se corresponde con el
modelo de Kurucz para una temperatura efectiva de 20000 K y log g=4,
mientras que el espectro de enero de mismo año parece provenir de
una fuente más fría pero sin que pueda hacerse corresponder con
ningún modelo de atmósfera estelar. Las líneas de emisión han
sido agrupadas tentativamente en cinco grupos y se sugiere un modelo
de atmósfera extendida en que se ubican las distintas regiones donde
se originarían dichas líneas.
---------------------------------------------------------
Title: Observaciones de estrellas simbióticas con el
IUE. II. Variaciones en el espectro
Authors: Sahade, J.; Brandi, E.; Fontenla, J.
1982BAAA...27..151S Altcode:
Uno de los objetivos del programa de observación de estrellas
simbióticas con el IUE consistía en la detección de posibles cambios
de los espectros en función del tiempo. Diez de las estrellas del
programa fueron observados en dos épocas de 1979, con un intervalo
de seis meses entre las mismas. Hasta septiembre de 1981 se habían
analizado las observaciones de siete de esas estrellas, a saber:
R Aquarii, T Coronae Borealis, AX Persei, AG Pegasi, HD 4174, Z
Andromedae y RW Hydrae. Todas estas estrellas muestran variaciones en
la intensidad de varias líneas de emisión que, en los casos de Z And,
R Aqr, AG Peg y RW Hya, incluyen las de resonancia del MG II. En RW
Hya hemos encontrado una variación notable en el continuo. En julio de
1979 el espectro continuo se corresponde con el modelo de Kurucz para
una temperatura efectiva de 20000 K y log g=4, mientras que el espectro
de enero del mismo año parece provenir de una fuente más fría, pero
que no se puede hacer corresponder con ningún modelo. Las líneas de
emisión han sido agrupadas tentativamente en cinco grupos y se sugiere
un modelo de atmósfera extendida en el que se ubican los distintos
regiones donde se originarían dichas líneas. Hemos encontrado
también cambios en el espectro continuo de T CrB y, posiblemente,
en Z And. El trabajo será publicado in extenso en otra parte.
---------------------------------------------------------
Title: Variations in the ultraviolet spectrum of the symbiotic star
Z And.
Authors: Sahade, J.; Brandi, E.; Fontenla, J. M.
1981RMxAA...6..201S Altcode:
Variations in line intensity detected on low-resolution lUE spectra
of Z Andromedae, taken in January and in July, 1979, are reported. The
lines, all of which appear in emission, are classified in 5 groups and
a very tentative model of the envelope, that will be re-examined later,
is proposed.
---------------------------------------------------------
Title: Transition region models for Be stars
Authors: Fontenla, J. M.; Rovira, M.; Ringuelet, A. E.
1981RMxAA...6..209F Altcode:
A preliminary model that reproduces the general characteristics
of equivalent widths and profiles of ultraviolet spectral lines
corresponding to ions such as C IV, Si IV, and N V which frequently
exhibit asymmetric profiles and which are particularly observed in early
type objects undergoing mass loss, is presented. The model considers
terms due to kinetic and potential energies as well as radiative losses
in solving for the energy balance equation. In a first approximation,
it is shown how the kinetic energy can account for the heating of
the material up to temperatures compatible with the formation of ions
like C IV and Si IV by collisional processes. Agreement, at least as
to the order of magnitude, between the model and the observations is
found if the existence of some kind of braking mechanism is postulated.
---------------------------------------------------------
Title: Ultraviolet continuum of a sample of Be stars.
Authors: Ringuelet, A. E.; Rovira, M.; Fontenla, J. M.
1981RMxAA...6..215R Altcode:
IUE spectra obtained in the low dispersion mode were used to analyze
the energy distributions in the UV of Alpha Draconis, Tau Orionis, 53
Persei, 48 Librae, Pi Aquarii, and 27 Canis Majoris. Absolute fluxes
were determined. The effective temperatures and gravity of the model
atmospheres which provide the best fit to the spectra of these stars
are presented. Alpha Dra and Tau Ori show no discrepancies with regard
to the effective temperature and gravity, while the continuum of 53
Per may be variable. 48 Lib fits the log g = 4 or 4.5 and effective
temperature 18,000 K model. Pi Aqr and 27 CMa fit models with effective
temperature of 30,000 K and log g = 5.
---------------------------------------------------------
Title: Ultraviolet observations of 27 CMa, pi AQR and 48 Lib.
Authors: Ringuelet, A. E.; Fontenla, J. M.; Rovira, M.
1981A&A...100...79R Altcode:
An analysis of 27 CMa, Pi Aqr, and 48 Lib, Be stars and V/R variables
is discussed to determine the physical conditions and the gaseous
structure surrounding the stars. On the basis of two different types
of absorption lines the narrow and deep, and the broad and shallow
profiles, the gaseous structure is divided into two regions: (1) a
geometrically thin region that rotates with the stars, and exhibits
higher ionization temperatures than the temperature of the radiation
field of the stars, and expands with velocities not higher than the
escape velocity of a normal star; and (2) an extended cold region which
does not rotate with the star, with expansion velocities decreasing
to the values of the radial velocities of the interstellar line.
---------------------------------------------------------
Title: Ultraviolet observations of 27 Canis Majoris, Pi Aquarii and
48 Librae
Authors: Ringuelet, A. E.; Fontenla, J. M.; Rovira, M.
1981A&A....99..386R Altcode:
An analysis of 27 CMa, Pi Aqr, and 48 Lib, Be stars and V/R variables
is discussed to determine the physical conditions and the gaseous
structure surrounding the stars. On the basis of two different types
of absorption lines the narrow and deep, and the broad and shallow
profiles, the gaseous structure is divided into two regions: (1) a
geometrically thin region that rotates with the stars, and exhibits
higher ioinization temperatures than the temperature of the radiation
field of the stars, and expands with velocities not higher than the
escape velocity of a normal star; and (2) an extended cold region which
does not rotate with the star, with expansion velocities decreasing
to the values of the radial velocities of the interstellar line.
---------------------------------------------------------
Title: Método de cálculo de poblaciones y líneas de hidrógeno
fuera del equilibrio termodinámico local
Authors: Fontenla, J. M.
1981BAAA...21..243F Altcode: 1981BAAA...20..243F
Se presenta un programa de cálculo que permite resolver las ecuaciones
de equilibrio estadístico para las poblaciones de los tres primeros
niveles del átomo de hidrógeno y protones. El programa se ha
construido para una atmósfera de hidrógeno irradiada por una fuente
de radiación externo. El método se ha comprobado para densidades
entre 10<SUP>13</SUP> y 10<SUP>10</SUP> cm<SUP>-3</SUP> y temperaturas
del orden de 10<SUP>3</SUP>-10<SUP>4</SUP> K.
---------------------------------------------------------
Title: Formación de líneas espectrales fuera de equilibrio
termodinámico en la atmósfera solar
Authors: Fontenla, J. M.; Molnar, H.
1981BAAA...20..146F Altcode:
Es sabido que para obtener perfiles de líneas fuera de equilibrio
termodinámico, es necesario resolver en forma auto-consistente las
ecuaciones de equilibrio estadístico y de transporte radiativo en la
atmósfera. El programa que se presenta resuelve este problema en forma
iterativa en base al método de Skumanich y Domenico. Las variables
de entrada son el modelo, [T<SUB>e</SUB>(h), n<SUB>e</SUB>(h),
M<SUB>A</SUB>.(h)] y la radiación incidente externa. Además de
los perfiles de línea, se obtiene información complementaria sobre
transformación de energía, opacldades, etc.
---------------------------------------------------------
Title: Cálculo de modelos de "Zonas de Transición" en estrellas B
Authors: Fontenla, J. M.; Rovira, M.; Ringuelet, A. E.
1981BAAA...26..169F Altcode:
Se ha desarrollado un método para el cálculo de modelos de las
regiones interiores de las atmósferas extendidas de estrellas B, por el
cual se resuelven numéricamente las ecuaciones de impulso y energía,
teniendo en cuenta simetría esférica o cilíndrica y rotación. Las
pérdidas de energía por radiación se aproximan por los cálculos
de Cox y Tucker y para la opacidad se tienen en cuenta las líneas de
la región ultravioleta del espectro, que dan origen a esa pérdida
de energía. Se obtienen así modelos que muestran diferentes formas
de variación de la velocidad y temperatura con la distancia a la
estrella. En los mismos, se aprecia que los parámetros considerados
no responden a una ley simple de variación. A partir de esos modelos
se calculan los perfiles de líneas de absorción y se comparan con
algunos observados en la región ultravioleta para estrellas Be.
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Title: Cálculo de poblaciones y líneas del He I en la cromósfera
solar
Authors: Molnar, H.; Fontenla, J. M.
1981BAAA...20...63M Altcode: 1981BAAA...19...63M
Se está desarrollando un programa de computación para poblaciones de
los niveles del He I fuera de equilibrio termodinámico, para diversas
condiciones de densidad, temperatura y geometría. Estas poblaciones se
emplearán en el cálculo de las lineas del He I para obtener modelos
aplicable a cromósfera, protuberancias y flares solares.
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Title: Modelos de vientos estelares en la región fotosférica
Authors: Fontenla, J. M.; Verga, A. D.
1981BAAA...26..173F Altcode:
Es conocido, a partir de diversas observaciones astronómicas, que las
atmósferas de las estrellas presentan frecuentemente movimientos de
expansión en sus capas externas, como se manifiesta principalmente en
las estrellas de tipos tempranos. En este trabajo se plantea el problema
de cómo ese flujo de materia, al considerarse en las capas profundas
de la fotosfera, modifica fundamentalmente la estructura de las mismas.
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Title: Estudio de espectros de protuberancias
Authors: Fontenla, J. M.; Rovira de Miceli, M.
1981BAAA...20...51F Altcode: 1981BAAA...19...51F
Se midieron los anchos Doppler de las líneas H y K del Ca II, Hɛ,
Hα y en dos casos la D<SUB>3</SUB> de He I. A partir de ellos se
estimó la temperatura y la turbulencia de las regiones que emitirían
esas líneas, suponiendo que se formaron en regiones de la misma
microturbulencia. Se obtuvieron valores diferentes para diversas
líneas y se encontró una relación entre el tipo de protuberancia
y las diferencias de temperatura.
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Title: Ultraviolet observations of 27 Canis Majoris, pi Aquarii and
48 Librae.
Authors: Ringuelet, A. E.; Fontenla, J. M.; Rovira, M.
1980ESASP.157..143R Altcode: 1980IUE2n......143R
No abstract at ADS
---------------------------------------------------------
Title: Estudio de las condiciones de visibilidad para la observación
solar en algunos puntos del país
Authors: Peretti-Hollemaert, A. L.; Marquevich, E. A.; Fontenla,
J. M.; Estol, R. C.
1980BAAA...18...82P Altcode:
A los efectos de encontrar un sitio apropiado para la ubicación de un
telescopio solar de gran resolución, se ha encarado el estudio de las
condiciones de visibilidad ("seeing") imperantes en varios lugares. Se
detallan las líneas de tratamiento del tema y los métodos a emplear.
---------------------------------------------------------
Title: A Prominence Model Based on Spectral Observations
Authors: Fontenla, J. M.
1979SoPh...64..177F Altcode:
Intensities and profiles of the Hα, Hβ, Hγ, K, and D<SUB>3</SUB>
lines are measured in a solar prominence. From the profiles of
these lines we estimate T = 6400 K and υ<SUB>t</SUB> = 5.7 km
s<SUP>−1</SUP>. We construct a simple isothermal model which explains
the Hα intensity and profile for an assumed total particle density
n<SUB>T</SUB> = 3 × 10<SUP>11</SUP> cm<SUP>−3</SUP>, and a filling
factor, α = 1/6.
