Zdenek Svestka - Böcker

The SOLAR-A spacecraft was launched by the Institute of Space and Astronautical Science, Japan (ISS) in August 1991, and, following and ISAS tradition, was renamed YOHKOH. This mission is dedicated principally to the study of solar flares, especially of high-energy phenomena observed in the X-ray and gamma-ray ranges. With a co-ordinated set of instruments including hard X-ray and soft X-ray imaging telescopes as well as spectrometers with advanced capabilities, it is expected to reveal new aspects of flares and help better understand their physics, supporting international collaborations with ground-based observatories as well as theoretical investigations. An overview of this mission, including the stallite, its scientific instruments, and its operation is given in this book.

The aim of the VIRGO investigation (Variability of solar IRradiance and Gravity Oscillations) on SOHO (SOlar and Heliospheric Observatory) is to determine the characteristics of pressure and internal gravity oscillations by observing irradiance and radiance variations, to measure the solar total and spectral irradiance and to quantify their variability over periods of days to the duration of the mission. VIRGO contains two different active-cavity radiometers for monitoring the sol- ar 'constant' (DIARAD and PM06-V), two three-channel sunphotometers (SPM) for the measurement of the spectral irradiance at 402, 500, and 862 nm with a bandwidth of 5 nm, and a low-resolution imager (Luminosity Oscillation Imager, LOI) with 12 'scientific' and 4 guiding pixels, for measuring the radiance dis- tribution over the solar disk: at 500 nm. The instrumentation has been described in detail by Frohlich et al. (1995). In addition, the observed in-flight performance and operational aspects of the irradiance observations are described by Frohlich et al. (1997), and those of the LOI by Appourchaux et al. (1997).

This text focuses on the advances in our understanding of solar convection and activity, and on new methods and results of helioseismic diagnostics of the internal structures and dynamics of solar convection and active regions. The methods of local helioseismology (time-distance tomography, ring-diagram analysis, acoustic imaging, and holography) have provided promising results on the deep structure of large-scale convection and flows, emerging active regions, and sunspots. The book includes reviews and contributed papers presented at the SOHO-9 Workshop held on July 12-15, 1999, at Stanford University, California, USA. It provides a comprehensive overview of the current status of the field and presents new ideas and approaches to helioseismic diagnostics and theoretical modelling of the physical processes inside the Sun. The book is recommended for graduate students and specialists in solar physics, astrophysics, and geophysics.

This is an exhaustive survey of present-day solar research including both theory and observations. It deals with eruptive flares, filament eruption in x-rays and radio waves, energy release and transport, and terrestrial response to solar flares. Details of the most recent SOLAR-A project (launched shortly after the conference) are also presented.

This book is the first part of the originally planned publication by Z. Svestka and L. D. de Feiter 'Solar High Energy Photon and Particle Emission'. The second part, with the original title, was to be published by de Feiter in about one year from now. However, to the deep sorrow of all of us, Dr de Feiter died suddenly and unexpectedly when the present book was in print. Thus, unfortunately, de Feiter's second part may not appear. Due to the fact that the originally planned publication was divided into two parts, the present book is mainly descriptive and concerned with the flare morphology. It was expected that theoretical interpretations would be extensively developed in the second part, prepared by de Feiter. In particular, this refers to the theoretical back­ grounds of radio emissions, particle acceleration and particle propagation in space. Only in Chapter II, concerning the 'low-temperature' flare, do we go deeper into the theoretical interpretations, anticipating that de Feiter would have been concerned mainly with the 'high-energy' physics. Still, the book includes discussions on all important aspects of flares and thus can present the reader with a complete picture of the complex flare phenomenon. It is clear that many observed data on flares can be interpreted in different ways.

This Catalog originated as a common enterprise of solar physicists and space scientists under the auspices of the Second Working Group of the Inter-Union Commission of Solar Terrestrial Physics (IUCSTP). It is a pleasure to acknowledge the support we received from the IUCSTP president, Dr H. Friedman, and the IUCSTPSecretary, Dr E. R. Dyer during the several years we have spent on this project. The aim of our work has been to assemble all observations of particle events from the first PCA observation in 1955 through two solar cycle maxima up to the end of 1969, in order to preserve these data from the first epoch of the space era in a concise form for use in the future. Because the techniques of observation have very much improved in the present solar cycle, there is a tendency to consider the observations before 1964 as incomplete and out-of-date; one must not forget, however, that the 19th solar cycle greatly differed from cycle No. 20 in the level of its activity, and also may have been the last cycle of strong activity for many decades to come. Therefore, the particle event observations before 1964 'should be compiled in a consistent manner for comparison with later observations, and we believe that the Catalog achieves this. The rapid development of the exploration techniques necessarily results in a significant amount of inhomogeneity in the Catalog, as increasingly smaller events were detected.

Most papers in this book were presented at the SOHO-9 Workshop 'Helioseismic Diagnostics of Solar Convection and Activity', held on 12-15 July 1999 at Stanford University, California, U.S.A. Some papers which were not presented at the work­ shop have been added, after authors had been invited in Solar News to contribute to this book. All papers submitted to this book have been refereed, and only those of high scientific quality were accepted for publication. The book focuses on the recent advances in our understanding of solar con­ vection and activity, and on methods and results of helioseismic diagnostics of the internal structures and dynamics of solar convection and active regions. The methods of local helioseismology (time-distance tomography, ring-diagram analy­ sis, acoustic imaging and holography), intensively developed in the past few years, have provided promising results on the deep structure of large-scale convection and flows, emerging active regions, and sunspots. Along with the traditional 'global' helioseismology based on frequencies of resonant oscillation modes, the local-area techniques have become increasingly important for studying the solar interior and the mechanisms of solar activity. The new high-resolution helioseismology projects 'Solar Oscillation Investiga­ tionlMichelson Doppler Imager' (SOIlMDI) on board SOHO, and ground-based 'Global Oscillation Network Group' (GONG) have provided a tremendous amount of solar oscillation data. Extracting from these data the information about the in­ ternal properties and dynamics of the Sun, and using this information in theoretical models and space weather forecasts are new challenges in solar physics.

The aim of the VIRGO investigation (Variability of solar IRradiance and Gravity Oscillations) on SOHO (SOlar and Heliospheric Observatory) is to determine the characteristics of pressure and internal gravity oscillations by observing irradiance and radiance variations, to measure the solar total and spectral irradiance and to quantify their variability over periods of days to the duration of the mission. VIRGO contains two different active-cavity radiometers for monitoring the sol- ar 'constant' (DIARAD and PM06-V), two three-channel sunphotometers (SPM) for the measurement of the spectral irradiance at 402, 500, and 862 nm with a bandwidth of 5 nm, and a low-resolution imager (Luminosity Oscillation Imager, LOI) with 12 'scientific' and 4 guiding pixels, for measuring the radiance dis- tribution over the solar disk: at 500 nm. The instrumentation has been described in detail by Frohlich et al. (1995). In addition, the observed in-flight performance and operational aspects of the irradiance observations are described by Frohlich et al. (1997), and those of the LOI by Appourchaux et al. (1997).