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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 112, A10216, doi:10.1029/2007JA012544, 2007

Observations of dipolarization at geosynchronous orbits and its response in the polar cap convection during extreme southward interplanetary magnetic field conditions

P. T. Jayachandran

Physics Department, University of New Brunswick, Fredericton, New Brunswick, Canada


J. W. MacDougall

Department of Physics and Astronomy, University of Western Ontario, London, Ontario, Canada


A. M. Hamza

Physics Department, University of New Brunswick, Fredericton, New Brunswick, Canada


M. G. Henderson

Los Alamos National Laboratory, Los Alamos, New Mexico, USA


Abstract

Analysis of the polar cap convection and geosynchronous magnetic field measurements, in the context of dipolarization events, during extreme southward interplanetary magnetic field (IMF) conditions is presented in the paper. Clear dipolarization events at geosynchronous orbits are always followed by an increase in the polar cap convection with a time delay. The distribution of the time delay between the onset of dipolarization at geosynchronous orbit and polar cap convection response varied between 6 and 15 min with an average of 9 min. The polar cap convection response to the dipolarization events enabled the deduction of the dipolarization timescales at geosynchronous orbits and in the ionosphere. A comparison of these two timescales revealed that the timescales of dipolarization events deduced from geosynchronous magnetic field measurements were always shorter (average 11 min) than the timescales deduced from the polar cap convection measurements (average 33 min).

Received 15 May 2007; accepted 10 September 2007; published 19 October 2007.

Keywords: polar cap convection; dipolarization; substorms.

Index Terms: 2776 Magnetospheric Physics: Polar cap phenomena; 2730 Magnetospheric Physics: Magnetosphere: inner; 2760 Magnetospheric Physics: Plasma convection (2463); 2790 Magnetospheric Physics: Substorms; 2736 Magnetospheric Physics: Magnetosphere/ionosphere interactions (2431).

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Citation: Jayachandran, P. T., J. W. MacDougall, A. M. Hamza, and M. G. Henderson (2007), Observations of dipolarization at geosynchronous orbits and its response in the polar cap convection during extreme southward interplanetary magnetic field conditions, J. Geophys. Res., 112, A10216, doi:10.1029/2007JA012544.