Energetic particle sounding of the magnetospheric cusp with ISEE-1

• Published in: Annales geophysicae (1988) Vol. 25; no. 5; pp. 1175 - 1182
• Main Authors: WHITAKER, K. E, FRITZ, T. A, CHEN, J, KLIDA, M
• Format: Journal Article
• Language: English
• Published: Katlenburg-Lindau European Geophysical Society 04-06-2007; Copernicus GmbH; European Geosciences Union; Copernicus Publications
• Subjects: Earth Sciences; Earth, ocean, space; Exact sciences and technology; External geophysics; Magnetic fields; Ocean, Atmosphere; Physics of the ionosphere; Physics of the magnetosphere; Sciences of the Universe; Energetics; High altitude; cusp; magnetic field; precipitating; Magnetopause; boundary layer; anisotropy; Magnetopause; Pitch angle; and boundary layers; Magnetospheric configuration and dynamics; ISEE satellite; Magnetospheric physics (Energetic particles; solar wind; Particle flux; dynamics; Local field; Angular distribution; Relativistic particle; Magnetospheric shock wave
• ISSN: 0992-7689; 1432-0576; 1432-0576
• DOI: 10.5194/angeo-25-1175-2007

Observations on 30 October 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 (RE). 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 RE 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.