Energetic particle sounding of the magnetospheric cusp with ISEE-1

Abstract

Abstract. Observations on 30October 1978 show the ISEE-1 spacecraft passing though the high-altitude dayside northern magnetospheric cusp region from roughly 16:00 to 18:30 UT, during a slow solar wind period (∼380 km/s). More than two orders of magnitude enhancements of the cusp energetic particle (CEP) fluxes were observed along with a depressed and turbulent local magnetic field. The observed variations of the pitch angle distributions (PAD) provide a unique opportunity to determine the structure of the cusp and the origin of the CEP. Through a boundary sounding technique, the location and orientation of the cusp poleward (or backside) boundary was observed for almost 10 min during which time it appeared initially to be stationary in the GSM/GSE X-direction and then moved sunward about 0.12 Earth radii (R E ). The orientation remained approximately perpendicular to the GSM/GSE X-axis until it was observed to rotate by 60 degrees in ∼3 min before ISEE-1 was fully inside the cusp cavity. The cavity itself was filled with CEP fluxes displaying large anisotropies, indicative of their source being located below (Earthward) of the satellite location. The spacecraft entered from the backside of the cusp, then traveled ∼4 R E through the cavity, and exited through the "top" of the cavity leaving a region of energetic ions below. The PADs demonstrate that the bow shock cannot be the main source of the observed CEPs. The CEP fluxes were measured at about 8.5 h MLT when the IMF had both an 8-10 nT duskward and southward component.

Energetic particles observed by ISEE-1 and ISEE-2 in a cusp diamagnetic cavity on 29 September 1978

“…8 show similar enhanced flux and PA distributions. Proton observations of a similar event on 30 October 1978 agree with this result, showing an increased flux with PA of 180 • to 90 • for close to 2 h (Whitaker et al, 2006(Whitaker et al, , 2007.…”

“…In addition to the event studied in this paper, there have been two other reports on the occurrance of such an ISEE pass through the cusp occurring (Phillips et al, 1993;Whitaker et al, 2006Whitaker et al, , 2007.…”

Properties of a cusp diamagnetic cavity boundary

“…A similar sounding technique has been used on a single energy channel for this event by Whitaker et al (2007), but the event is being revisited to look for trends over multiple energy channels. The same boundary sounding analysis done with the 29 September 1978 observations was repeated with the data from the 30 October 1978 event.…”

“…Previous work has been done sounding boundaries from distances of up to 2 gyroradii from an absorbing boundary (Williams et al, 1979;Fritz and Fanhnensteil, 1982). Whitaker et al (2007) used ISEE-1 to sound an emitting boundary of a CDC in order to measure its motion and orientation. A similar method to that used by Whitaker et al (2007) is used in this paper with improvements to the process of identifying the angles φ 1 and φ 2 .…”

“…Whitaker et al (2007) used ISEE-1 to sound an emitting boundary of a CDC in order to measure its motion and orientation. A similar method to that used by Whitaker et al (2007) is used in this paper with improvements to the process of identifying the angles φ 1 and φ 2 . This paper also utilizes multiple energy channels to sound particles of a variety of energies to further probe the properties of the cavity.…”