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Volume 16, issue 11
Ann. Geophys., 16, 1423–1433, 1998
https://doi.org/10.1007/s00585-998-1423-9
© European Geosciences Union 1998
Ann. Geophys., 16, 1423–1433, 1998
https://doi.org/10.1007/s00585-998-1423-9
© European Geosciences Union 1998

  30 Nov 1998

30 Nov 1998

Study of the longitudinal expansion velocity of the substorm current wedge

A. Belehaki1, I. Tsagouri2,1, and H. Mavromichalaki2 A. Belehaki et al.
  • 1National Observatory of Athens, Institute of Ionospheric and Space Research, Metaxa and Vas. Pavlou str., Palaia Penteli 152 36, Greece
  • 2Nuclear and Particle Physics Section, Physics Department, University of Athens, Solonos 104, 10680 Athens, Greece

Abstract. In this work we examine simultaneous observations from the two geosynchronous satellites GOES-5 and GOES-6 located at 282°E and 265°E respectively, and from middle and low latitude ground observatories located within 250°E and 294°E geographic longitude, during isolated substorms of moderate activity. The spatial distribution of our observation points allows us to make a detailed study of the azimuthal expansion of the substorm current wedge. The data analysis shows evidence that the substorm initiation and development mechanism include the cross-tail current diversion/ disruption, the substorm current wedge formation and the azimuthal expansion of the inner plasma sheet. The triggering mechanism is initially confined in a longitudinally narrow sector, estimated to be less than 15° and located very close to local midnight to the east or to the west. The current disruption region expands both eastward and westward in the magnetotail, so that the location of major field-aligned currents flowing into the ionosphere shifts successively eastward, and the location of the currents flowing out of the ionosphere shifts successively westward. Evidence was found that the perturbation travels toward the west with velocities greater than those expanding the wedge eastward. The drastic decrease of the velocity with the azimuthal distance from the location of the disturbance initiation, i.e., the onset sector, indicates that the energy release is a very localized phenomenon. Finally, the transient D perturbation observed by the geosynchronous satellites suggests that the field-aligned currents forming the wedge have a longitudunally limited extent.

Key words. Magnetospheric physics (current systems; magnetosphere-ionosphere interactions)

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