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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 111, A09311, doi:10.1029/2006JA011646, 2006

Optical observations of the development of secondary instabilities on the eastern wall of an equatorial plasma bubble

J. J. Makela

Department of Electrical and Computer Engineering, University of Illinois, Urbana, Illinois, USA


M. C. Kelley

School of Electrical and Computer Engineering, Cornell University, Ithaca, New York, USA


M. J. Nicolls

School of Electrical and Computer Engineering, Cornell University, Ithaca, New York, USA


Abstract

Optical evidence is presented for the growth of a local secondary plasma instability on the eastern wall of an equatorial plasma bubble observed from the Haleakala Volcano, Hawaii (geographic: 20.71 N, 203.83 E; geomagnetic: 21.31 N, 271.45 E). Typically, only the western wall of depletions at tropical latitudes are susceptible to secondary structuring. This event occurs during a minor geomagnetic storm when the plasma bubble is observed to be drifting to the west, rather than with the typical eastward drift velocity. The data are interpreted in terms of the generalized E × B instability with an anomalous wind directed westward and toward the equator. This wind drives the eastern wall of the depletion region unstable. The anomalous wind is associated with an equatorward propagating neutral wind surge caused by an ongoing geomagnetic storm. The observations of the growth of these instabilities in the local tropical ionosphere are in stark contrast to the typical development of secondary instabilities on equatorial plasma bubbles, which grow near the equatorial plane on the western wall of the primary depletion and map along the magnetic field lines to off-equatorial latitudes.

Received 1 February 2006; accepted 16 June 2006; published 21 September 2006.

Index Terms: 2439 Ionosphere: Ionospheric irregularities; 2443 Ionosphere: Midlatitude ionosphere; 2415 Ionosphere: Equatorial ionosphere; 2435 Ionosphere: Ionospheric disturbances.

Subscriber Access to Full Article (Nonsubscribers may purchase for $9.00, Includes print PDF, file size: 1042729 bytes)

Citation: Makela, J. J., M. C. Kelley, and M. J. Nicolls (2006), Optical observations of the development of secondary instabilities on the eastern wall of an equatorial plasma bubble, J. Geophys. Res., 111, A09311, doi:10.1029/2006JA011646.