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© European Geosciences Union 2005
Interhemispheric asymmetries in the occurrence of magnetically conjugate sub-auroral polarisation streams
1Department of Physics, La Trobe University, Victoria 3086, Australia
2British Antarctic Survey, Natural Environment Research Council, Cambridge CB3 0ET, UK
3Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UK
4Department of Electronic Engineering, La Trobe University, Victoria 3086, Australia
5Space Sciences Laboratory, University of California, Berkeley, CA 94720–7450, USA
6Communications Research Laboratory, 4-2-1 Nukuikita, Koganei, Tokyo 184–8795, Japan
Abstract. Earthward injections of energetic ions and electrons mark the onset of magnetospheric substorms. In the inner magnetosphere (L
4),
the energetic ions drift westward and the electrons eastward, thereby
enhancing the equatorial ring current. Wave-particle interactions can
accelerate these particles to radiation belt energies. The ions are injected
slightly closer to Earth in the pre-midnight sector, leading to the
formation of a radial polarisation field in the inner magnetosphere. This
maps to a poleward electric field just equatorward of the auroral oval in
the ionosphere. The poleward electric field is subsequently amplified by
ionospheric feedback, thereby producing auroral westward flow channels
(AWFCs). In terms of electric field strength, AWFCs are the strongest
manifestation of substorms in the ionosphere. Because geomagnetic flux tubes
are essentially equi-potentials, similar AWFC signatures should be observed
simultaneously in the Northern and Southern Hemispheres. Here we present
magnetically conjugate SuperDARN radar observations of AWFC activity
observed in the pre-midnight sector during two substorm intervals including
multiple onsets during the evening of 30 November 2002. The Northern
Hemisphere observations were made with the Japanese radar located at King
Salmon, Alaska (57
, and the Southern Hemisphere observations
with the Tasman International Geospace Environment Radar (TIGER) located at
Bruny Island, Tasmania (
55. LANL geosynchronous satellite
observations of energetic ion and electron fluxes monitored the effects of
substorms in the inner magnetosphere (L6). The radar-observed AWFC
activity was coincident with activity observed at geosynchronous orbit, as
well as westward current surges in the ionosphere observed using
ground-based magnetometers. The location of AWFCs with respect to the
auroral oval was inferred from FUV auroral images recorded on board the
IMAGE spacecraft. DMSP SSIES ion drift measurements confirmed the presence
of AWFCs equatorward of the auroral oval. Systematic asymmetries in the
interhemispheric signatures of the AWFCs probably arose because the magnetic
flux tubes were distorted at L shells passing close to the substorm
dipolarisation region. Transient asymmetries were attributed to the
development of nearby field-aligned potential drops and currents.Full Article (PDF, 2512 KB)
Citation: Parkinson, M. L., Pinnock, M., Wild, J. A., Lester, M., Yeoman, T. K., Milan, S. E., Ye, H., Devlin, J. C., Frey, H. U., and Kikuchi, T.: Interhemispheric asymmetries in the occurrence of magnetically conjugate sub-auroral polarisation streams, Ann. Geophys., 23, 1371-1390, 2005. Bibtex EndNote Reference Manager
