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

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.

Properties of a cusp diamagnetic cavity boundary

“…Walsh et al (2007) and Whitaker et al (2006Whitaker et al ( , 2007 investigated these two events and provided evidence pointing towards a local acceleration source. During both events, the ion PA distributions indicated ions were flowing away from the earth.…”

“…In contrast, only one population of electrons was present, being trapped along the magnetic field line at a PA of 90 • . The electron data for this event is displayed in Walsh et al (2007). The magnitude of the local magnetic field was both depressed and turbulent.…”

“…The ISEE-1 spacecraft measured enhanced energetic particle flux and a depressed and turbulent local magnetic field consistent with a CDC on 29 September 1978 (Walsh et al, 2007) and 30 October 1978 (Whitaker et al, 2006).…”

Reply to S. Fuselier et al.'s comment on "Energetic particle sounding of the magnetospheric cusp with ISEE-1"

“…Although more energetic electron enhancments are observed during the end of the event, the electron flux enhancments are measured during the same time period we see the enhanced energetic ion flux. A similar cusp crossing by ISEE-1 was studied by Walsh et al (2007). During the Walsh et al (2007) event, the spacecraft observed both energetic ions and electrons as well as a depressed and turbulent magnetic field.…”

“…A similar cusp crossing by ISEE-1 was studied by Walsh et al (2007). During the Walsh et al (2007) event, the spacecraft observed both energetic ions and electrons as well as a depressed and turbulent magnetic field. The study showed a strong correlation between enhancments in the energetic electron and ion flux, indicating the two must be from the same source.…”