Alfvén boundaries: noses and zippers

Abstract

On April 15, 1996, POLAR was in a noon-midnight meridional plane and observed an atypical energetic particle distribution, characterized by a band of nearly monochromatic 90° ions at 60 keV, and a second, nearly monochromatic band of of field-aligned ions around 40 keV. These ions persisted from L=7−3.5. Below L∼3.5 the bands vanished, but reappeared as the spacecraft exited the magnetosphere. The upper band is identified as a “nose” event, first described by Smith and Hoffman (1974). The bimodal distribution is reminiscent of “zipper” events discussed by Fennell et al. (1981), though this may be the most energetic zipper event ever described. After examining the solar wind monitor and ground stations, we develop a scenario to explain this distribution, where the nose ions injected from the plasmasheet produce a parallel electric field that extracts oxygen from the ionosphere. Although we lack the Dst, we hypothesize that we were observing a classical ∼−100 Dst magnetic storm, albeit from a new perspective. We generalize this observation by proposing that all storm injections involve intense nose events that produce parallel electric fields that populate the ring current with ionospheric oxygen.

Department

Physics

Publication Date

12-31-1997

Journal Title

Advances in Space Research

Publisher

Elsevier

Digital Object Identifier (DOI)

10.1016/S0273-1177(97)00708-4

Document Type

Article

Rights

Copyright © 1997, Elsevier

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