Programs Integrated Studies of Gamma-Ray Flares Spectroscopy of Hard X Rays and Gamma Rays from Solar Flares Joint Analysis of Gamma-Ray Flares Observed by Yohkoh and Compton Solar Influence on Energetic Particles Impacting the Earth's Atmosphere High-Energy Radiation in the Solar Terrestrial Envrionment Gamma Ray Analysis of HESSI Data Theoretical High Energy Solar Physics Gamma-Ray Spectroscopy of Solar Flares in Cycles 23 with CGRO/OSSE Multi-Spacecraft Observations of Large Solar Energetic Particle Events in Solar Cycle 23 The Limits of Solar Energetic Particle Acceleration in CMEDriven Shocks Modeling Geomagnetic Cutoffs for SEP Hazards on the ISS and Other Spacecraft
	Integrated Studies of Gamma-Ray Flares Significant progress has been made recently in higt-energy flare research based on gamma-ray and neutron observations. We propose to continue oru integrated studies of nuclear emissions and bremsstrahlung in solar flares using both archival data from the SMM/GRS and the Compton Gamma Ray Observatory/OSSE experiments, and new Cycle 23 observations with OSSE. These data will be compared with observations from other instruments including those on CGRO and Yohkoh, where available. These missions represent the onlyu resource for studying high-energy radiation in flares prior to the launch of HESSI. Some of the objectives of this work are: 1) determination of the comostition of accelerated ions impactin the Sun from measurements of broad emmission lines; 2) measurements of the temporal evolution of lines and continua within flares that provide information on changes in the ambient elemental abundances and environment, on the concentration of 3He in the Sun, and on the acceleration and energetics fo electrons and ions; 3)studies relating to the directionality of these acclerated particles; 4) searches for a flare-size cutoff in ion acceleration and for long-lived radioactive nuclei produced in flares; and 5) studies relating to continuous particle acceleration and trapping late in flares. These investigations provide a foundation for planning upcoming observations with HESSI. We also propose continued solar observations by OSSE after launch of HESSI to provide the critical high-energy capability lost when HESP was down-sized to a SMEX mission. Supporting agency: NASA, PI- Gerald Share, Co-I Ronald Murphy, DPR W18995 Up to Program Top
	Spectroscopy of Hard X Rays and Gamma Rays from Solar Flares We propose to perform spectroscopic analyses of solar flares observed by HESSI > 0.05 MeV. We plan to incorporate gamma-ray and neutron observations up to 200 MeV from the OSSE experiment on the Compton Gamma Ray Observatory (CGRO) into these studies. Based on our experience in analyzing over 15 years of spectroscopic data from the Solar Maximum Mission (SMM) and CGRO we propose some key investigations and describe how these may be accomplished using both HESSI and OSSE data. These investigations include: 1) directionality of accelerated protons, alpha particles and heavy ions at the Sun; 2) spectra and energy content of accelerated ions and electrons; 3) composition of accelerated heavy ions and comparison with SEP's observed by ACE and WIND; 4) temperature in the acceleration region; 5) composition of the ambient flare plasma and its association with solar atmospheric density; 6) 3He/4He abundance ratio in photosphere and in accelerated particles; 7) conditions under which ions are accelerated in flares; 9) location where p mesons are produced; and 10) comparing evidence for continuous particle acceleration and trapping late in flares. Supporting agency: NASA, PI-Gerald Share, Co-I Ronald Murphy, DPR W19746 Up to Program Top
	Joint Analysis of Gamma-Ray Flares Observed by Yohkoh and Compton Yohkoh and the Compton Gamma Ray Observatory (CGRO) are likely to be the only satellites to provide measurements of gamma radiation from solar flares up to the peak in activity of Cycle 23. Some surprising discoveries have resulted from recent analyses of g-ray flares: accelerated ions have been found to contain significantly more energy than electrons; the ambient flare plasma on average reflects the elemental abundance of the corona but shows significant variations both within flares and from flare-to-flare; isotropic or fan-beam distributions for the accelerated particles fit the spectroscopic data; temporal variations on the order of 0.1 are observed to energies above 10 MeV; and the accelerated a/proton ratio can approach values of 0.5 and higher. Continued observations of g-ray flares with the spectrometer experiments on these two satellites are important to further these studies and to provide the foundation for observations to be made by HESSI when it is launched in late 2000. This proposal seeks to enhance the flare science achieved with the Wide Band Spectrometer (WBS) on Yohkoh by performing coordinated observations with the Oriented Scintillation Spectrometer Experiment (OSSE) on CGRO. We first plan on performing simultaneous observations to cross calibrate the two instruments. We then plan on using the unique features of the two instruments to extend the flare observations: performing joint measurements extends flare measurements to times when one of the satellites is either in the radiation belts or is behind the Earth; the WBS is less likely to be saturated than is OSSE, thus providing excellent coverage during the most intense portions of flares; OSSE's high sensitivity and better spectral resolution will permit features observed in WBS spectra to be resolved and understood. The unique capabilities of these instruments will also complement the excellent spectral resolution of HESSI when joint observations are possible in 2000. Supporting Agency: NASA, PI-Gerald Share, Co-I Ronald Murphy, DPR 592690F Up to Program Top
	Solar Influence on Energetic Particles Impacting the Earth's Atmosphere We propose to use gamma-ray lines and continua to study the high-energy effects of solar activity and energetic particles on the earth's atmosphere. Such satellite measurements offer the promise of near real-time determination of latitudinal cut-off for solar energetic particles. Cosmic-ray and solar energetic particles (SEP) interact with the atmosphere to produce gamma-ray lines after direct excitation and nuclear breakup of N and O. Atmospheric emission increased by over three orders of magnitude during the intense particle event of 1989 October 20. We propose to search the SMM database over the period from 1981 to 1989 to acquire observations of additional atmospheric enhancements from SEPs. We also propose to study the latitude dependence of cosmic ray produced gamma rays and its variation over the solar cycle. From this study we will also measure of the latitude dependence and variability of thermal neutrons produced in the atmosphere. The measurements provide data on the spectra of particles incident on the atmosphere; these will be compared with spectra of particles in space using gamma-ray production codes in order to obtain information on transport of particles through the magnetosphere. This will provide real time warning for astronauts and for passengers and crews of commercial and military flights in the polar region. Supporting agency: NASA, PI-Gerald Share, Co-I Ronald Murphy, DPR 76-8167-01 Up to Program Top
	High-Energy Radiation in the Solar Terrestrial Envrionment The objective is to discover and model the physical processes that produce the highly-variable, high-energy (~1 MeV to 10 GeV) particle and g-ray emission in the largest and most powerful coronal mass ejections (CMEs) and solar flares. New results from a fleet of spacecraft [e.g. ACE, Wind, SOHO, Yohkoh (presently operating), CGRO (through June 2000), and HESSI (March 2001 launch)] during the peak of Solar Cycle 23 are already forcing a dramatic re-evaluation of our ideas about the production of penetrating high-energy solar radiation. Thus, the next few years provide an opportunity for substantial progress in understanding the underlying physical phenomena which govern the complexity of solar energetic particle (SEP) events. Because of their episodic nature and large event-to-event variability, SEP events are one of the major radiation hazards affecting the technological utilization of space and constraining the design and operation of DoD/Navy space assets. This research will payoff as the foundation for more accurate, physics-based SEP-hazard models, which are necessitated both by spacecraft-technology trends and by needs for reliable space-weather predictive capabilities. Supporting agency: ONR, NRL Contact-Allan Tylka Up to Program Top
	Gamma Ray Analysis of HESSI Data HESSI, expected to be launched in early 2001, promises major advances in our understanding of the processes involved in solar flares by providing hard X-ray imaging and the first capability for high-resolution spectroscopy of hard X-ray and g-ray emission from flares. The HESSI team has concentrated its software development effort on HESSI's hard X-ray imaging and spectroscopic capabilities. Because of time and budget constraints, a similar-quality g-ray spectroscopic analysis environment will not be in place when the data become available. But it is crucial that the unique information provided by g rays be fully exploited to gain a complete picture of the flare process. We propose to augment and enhance the existing HESSI g-ray analysis environment using our expertise and experience. The HESSI team has expressed interest in our contributions and involvement. We will work closely with them to incorporate into this environment the extensive g-ray analysis strategies and empirical and theoretical models that we have developed through our analysis of almost 20 years of solar-flare g-ray data from both SMM and CGRO/OSSE. We also seek funding for four scientific investigations using HESSI flare data when they become available: (1) a detailed study of the positron annihilation line, (2) a study of the broad-line component, and (3) a study of the >50 keV electron bremsstrahlung spectral shape. We also propose to provide daily solar-flare activity monitoring. Up to Program Top
	Theoretical High Energy Solar Physics We propose a broad research program centered upon the study of the gamma ray, neutron and secondary charged particle signatures of energy release and particle acceleration in solar flares. We have developed in the past computational tools that we have used for the analysis of SMM/GRS, CGRO/OSSE, EGRET, COMPTEL, BATSE, GRANAT/PHEBUS, and GAMMA-1 data, as well as data from several accelerated particle detectors. The anticipation of much improved gamma ray spectroscopic and imaging data from HESSI, as well as the potential of significantly improved analysis of archival gamma ray and neutron data (SMM/GRS and CGRO/OSSE). point to the need for updating. expansion and refinement of our computational tools. We thus propose to update, further develop and unify the following codes: nuclear deexcitation line: positron production and annihilation, neutron production and 2.223 MeV line emission, pion decay radiation, transport of the accelerated ions and the products of the nuclear interactions. We also propose to develop a code for the production of energetic secondary particles (H-2. H-3, Li, Be, B) that will be applied to ACE data to study the escape of charged particles from the flare accelerated particle interaction region. These efforts will allow us to more rigorously explore line ratios, line shapes and the structure of the continuum, to search for weaker lines that could carry important information, and to apply ion transport calculations to the interpretation of new imaging data. By applying the improved codes to HESSI and archival data we will investigate many exciting topics including the energy content in flare accelerated ions, ambient solar atmospheric abundances both in the chromosphere (e.g. He) and photosphere (He-3), and accelerated particle abundances (e.g. He-3 and heavy ions). As we have shown in past research, these impact several important issues in space physics and astrophysics. ranging from solar atmospheric dynamics, solar wind and flare particle acceleration to Galactic chemical evolution. Up to Program Top
	Gamma-Ray Spectroscopy of Solar Flares in Cycles 23 with CGRO/OSSE The Oriented Scintillation Spectrometer Experiment (OSSE) on the Compton Gamma Ray Observatory (CGRO) is the most sensitive instrument in orbit for measuring solar g-ray lines and continua during Cycle 23. We propose to fully exploit its potential for high-energy solar science demonstrated in the detailed analysis of the 1991 June 4 flare which has provided exciting new information about the accelerated-particle spectra and composition and about the ambient plasma at the flare site. We plan to perform the detailed analyses of all flares observed by OSSE during Cycles 22 and 23 in order to confirm these new results, place them in context with other measurements (e.g. from ACE, WIND, SOHO, SAMPEX, Ulysses, and TRACE), compare them with flare models, and provide the basis for future high-resolution spectral measurements. (Potential funding under current and future CGRO GI programs is only adequate for low-level data processing and archiving.) During the first year covered by this proposal, we plan to focus our efforts on Cycle 22 archive data. As the rate of flares increases, we will perform timely analyses of the new data and distribute high-level data products to the solar research community. During the first year of this effort we plan to study: (1) the variation in depth of the interaction site during individual flares and from flare-to-flare using the positron annihilation line and continuum; (2) the composition and angular distribution of the accelerated particles using both the alpha-alpha fusion lines and the de-excitation lines; (3) a new method for unambiguously determining the accelerated alpha/proton ratio; (4) high-energy gamma-ray and neutron emission in the 1991 June flares; and (5) whether there is a threshold for ion acceleration in flares. Up to Program Top
	Multi-Spacecraft Observations of Large Solar Energetic Particle Events in Solar Cycle 23 Up to Program Top
	The Limits of Solar Energetic Particle Acceleration in CMEDriven Shocks Up to Program Top
	Modeling Geomagnetic Cutoffs for SEP Hazards on the ISS and Other Spacecraft Up to Program Top