Spatial features observed in the cusp under steady solar wind conditions

Abstract

Multispacecraft studies using Polar, Fast Auroral Snapshot (FAST), and Interball observations revealed that many cusp structures observed during stable solar wind conditions are spatial features. While individual cusp events appear to be very different from each other, multiple observations of the same cusp event during periods of stable solar wind conditions are remarkably similar. These spatial cusp structures have been interpreted as a result of the independent evolution of ion distributions from multiple reconnection sites (X‐lines) in both hemispheres. The location of reconnection sites depends critically on the direction of the interplanetary magnetic field. Thus individual cusp events should have similar cusp structures if they occur in the same magnetic local time sector during comparable solar wind conditions, especially during similar interplanetary magnetic field orientations. Data presented in this paper show just such an effect. For three individual cusp events observed by Polar and FAST, similar stepped ion structures are seen by both satellites passing though these large‐scale spatial structures.