Abstract
Abstract. Observations by the ISEE-1 and ISEE-2 spacecraft on 29 September 1978 show large CEP (Cusp Energetic Particle) fluxes while passing through the dayside magnetospheric cusp in near coincident orbits. The event was observed around 11:00 MLT between roughly 12:30 and 13:00 UT by ISEE-1 and 12:00 and 13:00 UT by ISEE-2. During these periods, both electron and ion fluxes increased by more than two orders of magnitude, with the electron flux showing a strong peak at a pitch angle of 90°. The solar wind was ~710 km s−1 and the Dst was ~−200 nT, suggesting the occurrence of a strong geomagnetic storm. The ISEE-1 and ISEE-2 observations, however, show no time-energy dispersion of the CEPs, leading us to believe that these particles could not be the result of substorm processes in the magnetotail. The local magnetic field was depressed and extremely turbulent. Changes in the magnitude of the magnetic field anticorrelate closely to variations of the electron flux. The observations in electron flux peaking at 90° and the close anticorrelation between the local magnetic field strength and electron flux are unique and provide evidence of a potential local source for these energetic particles.
Highlights
Observations from a number of spacecraft have shown the presence of energetic particles in the magnetospheric cusp (Shelly et al, 1976; Kremser et al, 1995; Chen et al, 1997; Pfaff et al, 1998; Savin et al, 2002); their source remains a matter of scientific discussion and debate
Local clock angle should be well correlated within the magnetosheath. This correlation is used as a probe to determine whether International Sun-Earth Explorer-1 (ISEE-1) and ISEE-2 have crossed the magnetopause into the magnetosheath
These conditions are propagated with a time delay (∼27 min) five zones were defined for the ISEE-2 observations (Fig. 9). to the ISEE-1 and ISEE-2 locations, close to 200 RE downZones 1-5 are defined at 12:01–12:18 UT, 12:23–12:32 UT, stream
Summary
Observations from a number of spacecraft have shown the presence of energetic particles in the magnetospheric cusp (Shelly et al, 1976; Kremser et al, 1995; Chen et al, 1997; Pfaff et al, 1998; Savin et al, 2002); their source remains a matter of scientific discussion and debate. Cusp Energetic Particle (CEP) events are characterized by a decreased and turbulent local magnetic field, as well as increased energetic particle flux (Chen et al, 1997, 1998; Fritz et al, 1999). During these events, electrons show large flux enhancements for 100 eV particles and more subtle flux enhancements up to 200 keV. Niehof et al (2005) have used POLAR observations to study the plasma composition and pressure around these CEP events associated with a Cusp Diamagnetic Cavity (CDC). This correlation is used as a probe to determine whether ISEE-1 and ISEE-2 have crossed the magnetopause into the magnetosheath
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