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GEOPHYSICAL RESEARCH LETTERS, VOL. 27, NO. 4, PAGES 469–472, 2000

Toroidal Ion Distributions Observed at High Altitudes Equatorward of the Cusp

M. M. Huddleston

Southwest Research Institute, San Antonio, Texas


C. J. Pollock

Southwest Research Institute, San Antonio, Texas


M. P. Wüest

Southwest Research Institute, San Antonio, Texas


J. S. Pickett

University of Iowa, Iowa City, Iowa


T. E. Moore

Goddard Space Flight Center, Greenbelt, Maryland


W. K. Peterson

Lockheed Palo Alto Research Lab., Palo Alto, California


Abstract

We examine events where the TIDE and TIMAS ion instruments on board the Polar spacecraft have observed transversely accelerated ions (TAI) at altitudes greater than 20,000 km. We report both H + and O + populations that have been heated perpendicular to the local B field but that also have a sharp low-energy cutoff to the distribution occurring at 20-100 eV. Analysis of an event on 21 April 1996 indicates that the formation of ion toroids may be related to solitary structures or low frequency wave pulses observed during the event. We address some of the implications of using time (as opposed to frequency) domain techniques to analyze wave/particle energization events.

Received 19 July 1999; accepted 3 November 1999.

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Citation: Huddleston, M. M., C. J. Pollock, M. P. Wüest, J. S. Pickett, T. E. Moore, and W. K. Peterson (2000), Toroidal Ion Distributions Observed at High Altitudes Equatorward of the Cusp, Geophys. Res. Lett., 27(4), 469–472.