Multipoint observations of the magnetopause: Results from ISEE and AMPTE

Abstract

Multiple spacecraft observations of the magnetopause have allowed us to infer boundary motion and structure, and to compare these with theoretical expectations. The results of the ISEE mission indicate the magnetopause is thicker than expected, often ten magnetosheath ion gyroradii or more, and that its characteristic radial motion is usually sub-Alfvénic. With small spacecraft separations it is possible to infer considerable small-scale magnetic structure within the current layer, suggesting filamentary currents much smaller than an ion gyroradius. Such micro-structure may be important in particle diffusion and, hence, reconnection. There are also phenomena on much larger scales, the highly variable boundary layer, flux transfer events and surface waves due to dynamic pressure variations, the structure of which can be best determined when spacecraft separations are large. The dynamics of these large scale disturbances at the magnetopause constitutes an important link in the chain of energy transfer from the solar wind into the magnetosphere and ionosphere. No matter what the scale of spacecraft separation, whether small or large compared to the magnetopause current sheet thickness, important phenomena can be studied by multiple spacecraft.