Commission 10: Solar Activity (Activité Solaire)

Abstract

The Sun's activity may have declined in the three years since the last report, but the solar community carries on its research at a vigorous pace. During that interval there have been six IAU Symposia/Colloquia sponsored (or co-sponsored) by this commission on topics related to solar activity. Numerous activity-related conferences and workshops supported by other bodies attest to the vibrant interest in, and committement to, research on the wide range of topics which encompass this discipline. Flare research continues as the dominant topic, and is now fueled by a new generation of ground-based instruments and a highly successful solar satellite-Yohkoh (formerly Solar-A). Other recent space missions, although not devoted entirely to solar flares, are likely to have a profound bearing on our understanding of flare issues. They include, among others, the continuing series of sounding rocket flights of the Normal Incidence X-ray Telescope (NIXT), the Compton Gamma Ray Observatory (CGRO), designed to observe energetic phenomena in the Universe, and GRANAT, which is also dedicated to high-energy astronomy. The flare problem spurs research into many related subjects: active-region formation, physical proceses in prominences and filaments, coronal mass ejections, even periodicities in solar activity. This last topic is given separate attention here in order to draw attention to the still obscure link between the Sun's interior and the activity at its surface. It is a pleasure to thank the individual reviewers who took time from their busy schedules to write separate sections of this report. As well as moments of triumph, there have been moments of anxiety, disappointment, and sadness for the solar community. Substantial numbers of solar astronomers and solar physicists in the states of the former Soviet Union live under stressful circumstances as struggles go on to form new political systems in their homelands. Elsewhere ambitious plans for new ground-based or space facilities have been delayed as a worldwide recession continues. And the community has been saddened by the loss of pioneering figures who had a major impact on shaping our discipline: Prof. Keizo Kai, former chief of the solar radio group at the Nobeyama Radio Observatory, Prof. Zenzaburo Suemoto, former director of the Tokyo Astronomical Observatory, Prof. Giuseppe Vaiana, best known in his role as principal investigator of the S054 experiment on Skylab, Dr. Mstislav N. Gnevyshev, founder and director of the Kislovodsk Solar Station of the Central Astronomical Observatory of the Russian Academy of Sciences. They will remain alive in our memory and in our work, which builds upon their considerable achievements. New devices under construction include a continuous face-plate mirror with 218 mm clear aperture and 61 actuators (Dunn et al. 1991), and a coronagraph with adaptive optics using a membrane mirror with 91 actuators (Clampin et al. 1991).