Author name code: fontenla ADS astronomy entries on 2022-09-14 author:"Fontenla, Juan" ------------------------------------------------------------------------ Title: Bright Network, UVA, and the Physical Modeling of Solar Spectral and Total Irradiance in Recent Solar Cycles Authors: Fontenla, J. M.; Landi, E. Bibcode: 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. Title: Solar cycle variations in mesospheric carbon monoxide Authors: Lee, Jae N.; Wu, Dong L.; Ruzmaikin, Alexander; Fontenla, Juan Bibcode: 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 (CO2) 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. 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. Bibcode: 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. Title: Solar Cycle Variations as Observed by MLS Carbon Monoxide Authors: Lee, J. N.; Wu, D. L.; Ruzmaikin, A.; Fontenla, J. M. Bibcode: 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. 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. Bibcode: 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. 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. Bibcode: 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.

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. 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 Bibcode: 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 CO2 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. 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. Bibcode: 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. 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. Bibcode: 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 CO2 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 O2+ dissociative recombination rate coefficient, which in turn affects photochemical escape of oxygen from Mars. Title: New atmospheric model of Epsilon Eridani Authors: Vieytes, Mariela; Fontenla, Juan; Buccino, Andrea; Mauas, Pablo Bibcode: 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. 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 Bibcode: 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. 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. Bibcode: 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-2 s-1 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 Eflare(UV) ∼ 0.3 L*Δt (Δt = 1 s). Finally, we interpret enhanced L(line)/LBol ratios for C IV and N v as tentative observational evidence for the interaction of planets with large planetary mass-to-orbital distance ratios (Mplan/aplan) with the transition regions of their host stars.

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. 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 Bibcode: 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. 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 Bibcode: 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. 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. Bibcode: 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. Title: Construction of a SORCE-based Solar Spectral Irradiance (SSI) Record for Input into Chemistry Climate Models Authors: Harder, J. W.; Fontenla, J. M. Bibcode: 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. 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. Bibcode: 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 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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 Bibcode: 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 Bibcode: 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. Bibcode: 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-1, 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Title: Lyman Alpha Spicule Observatory (LASO) Authors: Chamberlin, Phillip C.; Allred, J.; Airapetian, V.; Gong, Q.; Fontenla, J.; McIntosh, S.; de Pontieu, B. Bibcode: 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. 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. Bibcode: 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. Title: Forecasting Solar EUV Irradiance, Validation and Automation Authors: Fontenla, J. M.; Gonzalez Hernandez, I.; Quémerais, E.; Lindsey, C.; Mason, J. P. Bibcode: 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. 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. Bibcode: 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. Bibcode: 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. Bibcode: 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.

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.

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.

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. 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 Bibcode: 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. 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Title: Calculation of the Solar UV/EUV Spectrum in Spherical Symmetry Authors: Haberreiter, Margit; Fontenla, Juan Bibcode: 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. Title: Particle diffusion, flows, and NLTE calculations Authors: Fontenla, J. M.; Avrett, E. Bibcode: 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. Bibcode: 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. Bibcode: 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. Title: Solar UV/EUV Spectral Synthesis in Spherical Symmetry Authors: Haberreiter, Margit; Fontenla, J. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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.
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.
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-1 at the top of the practically radiative-equilibrium low chromosphere.
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.
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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 2007ApJ...667.1243F Altcode: We present a new, one-dimensional model of the solar atmosphere (called SRPM 305) at moderate angular resolution (~1''-2''). Key characteristics of the SRPM 305 model include (1) a minimum temperature of ~3800 K at a gas pressure of ~80 dyne cm-2 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. Bibcode: 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. Bibcode: 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. Bibcode: 2007SPIE.6565E..1OA Altcode: 2007SPIE.6565E..57A Testing MODTRA TM5 (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 TM5. 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 × 106 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. Bibcode: 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. Bibcode: 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.

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-1. Title: Prominence Thread Models Including Ambipolar Diffusion Authors: Fontenla, J. M.; Rovira, M.; Vial, J. -C.; Gouttebroze, P. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 = 105 K), are found to have impulsive counterparts in 3.5-5.5 keV X-ray emission characteristic of T approximately 107 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 1028 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 106 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 107 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 (1025-1026 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1993BAAS...25.1202P Altcode: No abstract at ADS Title: Microflare Distributions and Coronal Heating Authors: Porter, J. G.; Fontenla, J. M.; Simnett, G. M. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 104 to 105K. 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 = 104K) 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 (107 K), hot (106 K), mild (105 K), and cool (104 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. Bibcode: 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. Bibcode: 1991BAAS...23..935P Altcode: No abstract at ADS Title: Considerations for Flare Related Magnetic Field Measurements Authors: Davis, J. M.; Fontenla, J. M. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 etaHeI for T greater than 35,000 K and decreases etaHeI (while increasing eta(sub(HeII)) between 9,000 and 25,000 K. Including the effects of diffusion also increases etaHeIII 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1989BAAS...21.1021F Altcode: No abstract at ADS Title: Oscillations in Stellar Atmospheres Authors: Costa, A.; Fontenla, J. M.; Ringuelet, A. E. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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 1012 cm -3. From measured widths of higher Balmer lines the density at the tops of the loops was found to be 4 x 1012 cm -3 if no non-thermal motions were present, or 5 × 1011 cm -3 for a turbulent velocity of ~ 12 km s -1. Title: High Resolution Ly Alpha Line Observations Authors: Fontenla, J. M.; Reichmann, E.; Tandberg-Hanssen, E. Bibcode: 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. Bibcode: 1987BAAS...19Q.931F Altcode: No abstract at ADS Title: Stability of solar protuberances Authors: Hernaiz, A. F.; Fontenla, J. M. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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 1012 cm-3. From measured widths of higher Balmer lines the density at the loops of the loops was found to be 4 × 1012 cm-3 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 107 K to 104 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 Bibcode: 1986PhDT........69F Altcode: No abstract at ADS Title: Numerical evaluations in radiative transfer. Authors: Fontenla, J. M.; Rovira, M. G. Bibcode: 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. Bibcode: 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 Te = 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 1013 y 1010 cm-3 y temperaturas del orden de 103-104 K. Title: Formación de líneas espectrales fuera de equilibrio termodinámico en la atmósfera solar Authors: Fontenla, J. M.; Molnar, H. Bibcode: 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, [Te(h), ne(h), MA.(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. Bibcode: 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. Title: Cálculo de poblaciones y líneas del He I en la cromósfera solar Authors: Molnar, H.; Fontenla, J. M. Bibcode: 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. Title: Modelos de vientos estelares en la región fotosférica Authors: Fontenla, J. M.; Verga, A. D. Bibcode: 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. Title: Estudio de espectros de protuberancias Authors: Fontenla, J. M.; Rovira de Miceli, M. Bibcode: 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 D3 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. Title: Ultraviolet observations of 27 Canis Majoris, pi Aquarii and 48 Librae. Authors: Ringuelet, A. E.; Fontenla, J. M.; Rovira, M. Bibcode: 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. Bibcode: 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. Bibcode: 1979SoPh...64..177F Altcode: Intensities and profiles of the Hα, Hβ, Hγ, K, and D3 lines are measured in a solar prominence. From the profiles of these lines we estimate T = 6400 K and υt = 5.7 km s−1. We construct a simple isothermal model which explains the Hα intensity and profile for an assumed total particle density nT = 3 × 1011 cm−3, and a filling factor, α = 1/6.