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GEOPHYSICAL RESEARCH LETTERS, VOL. 27, NO. 10, PAGES 1447–1450, 2000

Multiple Discrete-Energy Ion Features in the Inner Magnetosphere: Observations and Simulations

Xinlin Li

LASP, University of Colorado, Boulder

D. N. Baker

LASP, University of Colorado, Boulder

M. Temerin

Space Sciences Lab., University of California, Berkeley

W. K. Peterson

Lockheed Martin, Palo Alto, California

J. F. Fennell

Aerospace Corporation, Los Angeles, California

Abstract

Recent measurements from the ion composition sensors (CAMMICE/MICS and TIMAS) on the Polar satellite often show multiple discrete-energy peaks in ion-energy spectra, which are seen as multiple bands in energy-time plots. The most striking feature is that these multiple bands occur over a large range of L (L=3-8) and energy (a few keV to hundreds of keV) independent of the mass of the ions. These events are more likely to be observed during quiet times following substorm activity. Using an event observed on Feb. 9, 1998 we interpret the observed ion bands as the result of a time-of-flight effect of the particle’s drift around the Earth. We demonstrate by test-particle simulations that these multiple bands across a large range of L and energy are ion drift echoes that can be injected into the inner magnetosphere from the plasmasheet by a single earthward propagating time-varying field associated with substorm dipolarization. The existence of ion drift echoes even after only moderate substorm activity shows that localized time-varying electric and magnetic fields such as modeled here can and do penetrate deep into the inner magnetosphere.

Received 4 October 1999; accepted 9 February 2000.

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Citation: Li, X., D. N. Baker, M. Temerin, W. K. Peterson, and J. F. Fennell (2000), Multiple Discrete-Energy Ion Features in the Inner Magnetosphere: Observations and Simulations, Geophys. Res. Lett., 27(10), 1447–1450.

Copyright 2000 by the American Geophysical Union.