Physics Of The Solar Corona And Transition Region

Solar Physics publishes up to two Topical Issues per year that focus on areas of especially vigorous and active research. The present Topical Issue contains papers of recent results on the solar corona, as well as on the transition region and low solar wind. The majority of these papers, which were all refereed in accordance with the standards of Solar Physics, were presented in August 1999 at a workshop held in Monterey, California. The authors were offered the opportunity to present relevant parts of their contributions on an accompanying CD ROM of this Topical Issue. The Sun's magnetic field is responsible for the spectacularly dynamic and intri cate phenomenon that we call the corona. The past decade has seen an enormous increase in our understanding of this part of the solar outer atmosphere, both as a result of observations and because of rapid advances in numerical studies. The Yohkoh satellite has observed the Sun now for over eight years, producing spectac ular sequences of images that convey the complexity of the corona. The imaging and spectroscopic instruments on SOHO have added information on the cooler part of the corona. And since April of 1998 TRACE has given us very high resolution images of the 1-2 MK corona, at cadences that allow detailed observations of field oscillations, loop evolution, mass ejecta, etc.

Proceedings of the Monterey Workshop, held in Monterey, California, August 1999

The solar transition region, which spans the temperature range from about 20,000 to 1,000,000 K, separates the chromosphere from the corona. All the energy that heats the corona and powers the solar wind must pass through this part of the solar atmosphere. This book summarizes recent ultraviolet and extreme ultraviolet observations of the transition region, the empirical models derived from them, and the physical models that try to explain both the observations and the empirical models. The observational focus is on quiet solar transition region observations made with Skylab and subsequent rocket and satellite experiments. The book also presents a unified discussion of the analysis of ultraviolet and extreme ultraviolet spectroscopic data, including the determination of the emission measure and density and temperature diagnostics. This will be useful to astrophysicists who are confronting high-resolution ultraviolet and extreme ultraviolet data from astrophysical plasmas for the first time.

A thorough introduction to solar physics based on recent spacecraft observations. The author introduces the solar corona and sets it in the context of basic plasma physics before moving on to discuss plasma instabilities and plasma heating processes. The latest results on coronal heating and radiation are presented. Spectacular phenomena such as solar flares and coronal mass ejections are described in detail, together with their potential effects on the Earth.

Proceedings of the Monterey Workshop, held in Monterey, California, August 1999

Proceedings of the NATO Advanced Institute on Physics of the Solar Corona, held in Cavouri-Vouliagmeni, Athens, Greece, 6-17 September 1970

The widespread tendency in solar physics to divide the solar atmosphere into separate layers and to distinguish phenomena of solar activity from phenomena of the quiet Sun emphasizes the wide ranging diversity of physical conditions and events occurring in the solar atmosphere. This diversity spans the range from a neutral, essentially quiescent atmosphere to a highly ionized, violently convective atmosphere; from a domain in which magnetic field effects are unimportant to a domain in which the magnetic pressure exceeds the gas pressure, and from a domain in which the particle motions are Maxwellian to a domain in which an appreciable fraction of the particles is accelerated to relativistic energies. It is now widely recognized that the chromosphere and corona have a common origin in the mechanical energy flux generated in the hydrogen convection zone lying beneath the photosphere. Furthermore, magnetic field phenomena appear to be as vital to the structure of th~ quiet Sun as to the active Sun. For these reasons it appears desirable to present a unified treatment of the entire solar atmosphere, both active and quiet, in a single volume. On the other hand, such a treatise must be very long if it is to avoid being superficial, and it is very difficult for a single author to write authoritatively on such a wide range of topics.