Solar wind and interplanetary magnetic field

Abstract

A brief history is presented of some of our ideas regarding the solar wind. The basic physical principles of supersonic expansion are discussed. An analogy is drawn with the flow of an ideal gas through a rocket‐engine nozzle. Supersonic expansion of a stellar corona requires a stellar and coronal temperature lower than a specified maximum. For temperatures above this maximum, subsonic expansion should result. The thermal structure of the sun is such that only supersonic expanion occurs although subsonic expansion is, in principal, allowed. The present status of relevant experiments and theory regarding the solar wind and interplanetary magnetic field is discussed. In particular, attention is drawn to a comparison between theoretical predictions and actual measurements. It is concluded that measurements are consistent with theory for the component of field projected on the ecliptic plane. However, a serious discrepancy is noted between theory and experiment with regard to a possible component perpendicular to the sun's equatorial plane. Wave motion in the solar wind is discussed briefly. It is shown that, under certain conditions, relative wave amplitudes should grow with increasing heliocentric distance. Finally, ideas concerning the ultimate fate of the supersonic solar wind are reviewed.