Temporal versus spatial interpretation of cusp ion structures observed by two spacecraft

Abstract

A series of nearly simultaneous cusp crossings by the Polar and Fast Auroral Snapshot (FAST) spacecraft are used to investigate the development of cusp structures such as sudden changes in the energy of cusp precipitating ions. While such changes are generally interpreted as temporal signatures, recent investigations show evidence that such features can also be interpreted as spatial structures. Our analysis of four events during stable solar wind conditions confirms that cusp structures observed by one satellite are remarkably similar to cusp features observed up to several hours later by a second satellite. Using the spatial separation of the Polar and FAST spacecraft, the cusp features could also be traced over several hours in magnetic local time. These similarities led to the conclusion that large-scale cusp structures are spatial structures related to global ionospheric convection pattern set up by magnetic merging and not the result of temporal variations in reconnection parameters. Copyright 2002 by the American Geophysical Union.