Scope of the article and previous reviews

1.1 Scope of the article and previous reviews

The kinetic physics of the solar corona and solar wind is reviewed, whereby emphasis is placed on the progress made in the theoretical understanding of the properties of thermal particles and plasma waves as measured in situ in the solar wind. Also, new results on the kinetic state of the corona will be addressed, which were obtained through remote-sensing solar observations and by means of visible-light and VUV/EUV (Vacuum/Extreme Ultraviolet) spectroscopy and imaging, capabilities provided especially by the optical instruments on SOHO (Solar and Heliospheric Observatory). Measurements, theories and numerical simulations will be discussed.

Several books and reviews (Hundhausen, 1970 ; Hollweg, 1975 , 1978 ; Schwartz, 1980 ; Marsch, 1991a ,b ; Feldman and Marsch, 1997 ) were written in the past, which partly covered kinetic aspects of solar wind and coronal physics. Some of them were even fully devoted to this subject. Here, some previous material is cursorily covered, however, selected key results, and theories which are still valid or relevant, will anew be discussed if the scientific context requires that. The many solar and heliospheric missions of the past decades have greatly enhanced our knowledge and understanding, as compared with the early days of solar wind physics, the state of which then was reviewed by Parker (1963 ) and Hundhausen (1972 ) in their classical monographs. An early review of kinetic and exospheric physics was provided by Fahr and Shizgal (1983 ). A comprehensive account of solar wind phenomenology and the properties of the interplanetary medium was given by Schwenn (1990 ) after completion of the Helios mission.

In coronal physics, kinetic processes have always played a major role in the interpretation of the non-thermal radio and X-ray emissions, in particular during flares in association with suprathermal ions and electrons. The corresponding literature is very comprehensive. We cannot address the related physics issues here, but must refer the reader to the books of Benz (1993 ) and Aschwanden (2002 ), or the modern textbook of Aschwanden (2004 ) and the many references therein. In this review, we will concentrate on the thermal and suprathermal particles that constitute the bulk and beam populations of the coronal and solar wind plasma, and on the various plasma waves occurring in the kinetic domain at the natural scales of a warm plasma.

Waves in the solar corona and solar wind is a rather wide and mature research field. Because of the lack of space and size of this subject, here we cannot deal with magnetohydrodynamic waves (and turbulence), but must at the outset of this article refer to the existing reviews for the details and in depth discussions. MHD structures, waves and turbulence in the solar wind, including observations and models, have in the past been reviewed extensively by Marsch (1991b ), Mangeney et al. (1991 ) and Tu and Marsch (1995 ), with emphasis on the Helios observations in the ecliptic plane and inner heliosphere. The Ulysses observations at high latitudes and radial distances between $1 AU$ and about $5 AU$ are described by Horbury and Tsurutani (2001 ), and observations made in the outer heliosphere mostly by the Voyagers are contained in the book of Burlaga (1995 ) and the review of Goldstein et al. (1997 ), which also includes some numerical simulation results.

Recently in this journal, two modern and comprehensive reviews have become available, by Bruno and Carbone (2005 ) on the solar wind as a turbulence laboratory, an article which partly covers kinetic issues as well, and by Nakariakov and Verwichte (2005 ) on the novel subject of coronal waves and oscillations.