Magnetospheric physics: Magnetic fields

Progress in magnetospheric physics during the last quadrennium was not achieved through any one or a number of significant new discoveries or breakthroughs. Rather the advance was manifested more in gradual changes in the collective magnetospheric consciousness: the spreading acceptance that the magnetosphere is indeed ‘open,’ the increasing awareness of the key role of magnetospheric dynamics (substorms) in governing the various magnetospheric processes, a deeper appreciation of the role of electric fields and currents parallel to the magnetic field, the unfolding of the complexities of the earth's bow shock and associated phenomena, a strengthening attack on the merging process via theoretical and laboratory work, and the generation by several groups of magnetospheric magnetic field models based on observational data. The quadrennium also appears to have marked the end of the exploratory phase of magnetospheric studies with the launching of spacecraft into the last unexplored reaches of the magnetosphere and the resultant discovery and investigation of the polar cusp, at the boundary between the closed and open field lines over the day side magnetosphere, and the plasma mantle, a boundary layer of flowing plasma in the high‐latitude magnetotail. New records for closest boundary positions were established during this period. Previously, the magnetopause had been observed at synchronous orbit on ATS 1. However, in March 1970, even the shock crossed synchronous orbit, and solar wind plasma was detected at synchronous orbit. Then in August 1972, Explorer 45 crossed the magnetopause at 5.2 R E . If it is assumed that the magnetopause and shock surface simply changed scale sizes, the ATS 5 observation of solar wind represents the greater magnetospheric distortion.