Ionosphere‐magnetosphere coupling: 1. Thermal plasma

The past four years have seen a continued increasing interest in the basic processes which connect the thermal plasma population of the ionosphere with that of the outer magnetosphere. Measurement techniques have improved, and we are now able to observe the dynamics of the ionization in these regions as well as their detailed morphology. Although the specific reasons for the formation of the light ion trough and its connection with the plasmapause still elude us, we are beginning to grasp the nature of the many interchange flow processes which seem to play a basic role in the shaping of the well‐known plasmapause and light ion trough features. The thermal plasma population of the magnetosphere has also grown in importance. In addition to attracting the interest of scientists studying the ionosphere and plasmasphere the distribution of thermal plasma has also been found to affect the energetic particle population of the magnetosphere. This interaction between the hot and cold plasma has drawn the attention of workers studying the energetic particles of the radiation belts, the ring current, and the plasma sheet and has further emphasized the tight coupling within the magnetosphere‐ionosphere system.