Energy Release And Particle Acceleration In The Solar Atmosphere

The conversion of energy generated in the Sun's interior creates its hot corona and a wealth of dynamical phenomena such as flares and mass ejections. Based on recent significant progress in understanding magnetic reconnection and a wealth of new observations of energetic particle signatures from the sun, the present volume reviews the current theoretical and experimental status in the field. Paying attention to both the details and the broader picture, this book addresses both the experienced researcher as well as non-specialist researchers from related areas and postgraduate students.

This volume, together with its two companion volumes, originated in a study commis sioned by the United States National Academy of Sciences on behalf of the National Aeronautics and Space Administration. A committee composed of Tom Holzer, Dimitri Mihalas, Roger Ulrich and myself was asked to prepare a comprehensive review of current knowledge concerning the physics of the sun. We were fortunate in being able to persuade many distinguished scientists to gather their forces for the preparation of 21 separate chapters covering not only. solar physics but also relevant areas of astrophysics and solar-terrestrial relations. In proved necessary to divide the chapters into three separate volumes that cover three different aspects of solar physics. Volumes I and III are concerned with "The Solar Interior" and with "Astrophysics and Solar-Terrestrial Relations." This volume, devoted to "The Solar Atmosphere," covers not only the chromosphere and corona but also the principal phenomena usually referred to as "solar activity." The emphasis is on identifying and analyzing the relevant physical processes, but each chapter also contains a great deal of descriptive material.

Magnetic energy release plays an important role in a wide variety of cosmic objects such as the Sun, stellar coronae, stellar and galactic accretion disks and pulsars. The observed radio, X-ray and gamma-ray emission often directly results from magnetic `flares', implying that these processes are spatially fragmented and of an impulsive nature. A true understanding of these processes requires a combined magnetohydrodynamical and plasma physical approach. Fragmented Energy Release in Sun and Stars: the Interface between MHD and Plasma Physics provides a comprehensive, interdisciplinary summary of magnetic energy release in the Sun and stars, in accretion disks, in pulsar magnetospheres and in laboratory plasmas. These proceedings include papers on both theoretical and observational aspects. Fragmented Energy Release in Sun and Stars: the Interface between MHD and Plasma Physics is for researchers in the fields of solar physics, stellar astrophysics and (laboratory) plasma physics and is a useful resource book for graduate level astrophysics courses.

The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) satellite was launched on 5 February 2002. Its objective is to study the energy release and particle acceleration in solar flares through observations of X-rays and gamma rays. Two novel technologies are combined to obtain both spectra and images over a broad energy range. For the spectroscopy, cooled hyperpure germanium detectors are used to cover the energy range from 3 keV to 17 MeV with unprecedented keV-class resolution. Since focusing optics are not possible for making images with such high energy photons, tungsten and molybdenum absorbing grids are used to modulate the X-rays and gamma-rays coming from the Sun as the spacecraft rotates. This allows the spatial Fourier components of the source to be determined so that images can be made in spectral ranges where astronomical images have never been produced before. These new instrumental techniques require equally innovative software to reconstruct X-ray and gamma-ray spectra and images from the observations. Ample solar activity, abundant observations, and an open data policy have attracted many researchers. Astronomers face in the RHESSI mission an exciting new scientific potential. It has unusually broad possibilities for improving our understanding of the enigmatic solar flare phenomenon that is becoming increasingly important as society depends more and more on space-based technologies. In this volume, the functioning of RHESSI is explained, the data analysis techniques including spectroscopy and image reconstruction are introduced, and the experiences of the first few months of operation are summarized. First scientific results are presented that provide the essential base for more extended studies using RHESSI data and complementary observations by instruments on other spacecraft and at ground-based solar observatories. Scientists and students will find here the latest discoveries in solar flare research, as well as inspiration for future work. The papers will serve as references for the many new discoveries to come from the continuing RHESSI observations.

Short Historical Overview In the 1940s, two phenomena in the ?eld of cosmic rays (CR) forced scientists to think that the Sun is a powerful source of high-energy particles. One of these was discovered because of the daily solar variation of CR, which the maximum number of CR observed near noon (referring to the existence of continuous ?ux of CR from the direction of the Sun); this became the experimental basis of the theory that CR’s ́ originate from the Sun (or, for that matter, from within the solar system) (Alfven 1954). The second phenomenon was discovered when large ?uxes of high energy particles were detected from several solar ?ares, or solar CR. These are the - called ground level events (GLE), and were ?rst observed by ionization chambers shielded by 10 cm Pb (and detected mainly from the secondary muon-component CR that they caused) during the events of the 28th of February 1942, the 7th of March 1942, the 25th of July 1946, and the 19th of November 1949. The biggest such event was detected on the 23rd of February 1956 (see the detailed description in Chapters X and XI of Dorman, M1957). The ?rst phenomenon was investigated in detail in Dorman (M1957), by ?rst correcting experimental data on muon temperature effects and then by using coupling functions to determine the change in particle energy caused by the solar-diurnal CR variation.