Properties of a cusp diamagnetic cavity boundary

Abstract. While crossing through the high-altitude dayside cusp on 29 September 1978 and again on 30 October 1978, the ISEE-1 spacecraft observed enhanced energetic particle flux and a depressed and turbulent magnetic field, the signature characteristics of a cusp diamagnetic cavity. As ISEE-1 approached the cavity during each event, a boundary sounding technique was used to measure properties of an emitting boundary. Sounding over multiple energy channels reveals an energy dependent boundary with lower energy particles filling a larger cavity than higher energy particles. Relative motion of the boundary as well as boundary orientation are also measured. The two cusp events were measured at different locations and during different geomagnetic and solar wind conditions; however, they show similar results.