New advances in thermal plasma research

Abstract

It has been a decade since the comprehensive measurements made by the Ogo 5 satellite and by ground‐based whistler techniques have given us a picture of the plasmasphere as a dynamically changing region of ionospherically produced plasma. This image was at once comforting in its completeness and misleading in its simplicity. We found it easy to think of the plasmasphere as a region full of ‘cold’ plasma which was modulated by the magnetospheric convection electric field. At that same time, however, theory was predicting complex plasma distributions along the field lines which combined polar wind flow and diffusive equilibrium and which involved shock fronts and two‐stream instabilities. Today, with data from the Isee and Geos spacecraft we can begin to measure these complex distributions. The plasma is sometimes cold, but at times it is warm, and the influence of plasma flows combined with the effects of magnetic field line guidance opens an intriguing new world of thermal plasma studies. Such studies will be an essential element in the understanding of mass and energy interchange within the magnetosphere.