Substorm observations in the early morning sector with Equator-S and Geotail

R. Nakamura (1) , G. Haerendel (1) , W. Baumjohann (1) , A. Vaivads (1) , H. Kucharek (1) , B. Klecker (1) , E. Georgescu (1, 2) , J. Birn (3) , L. M. Kistler (4) , T. Mukai (5) , S. Kokubun (6) , P. Eglitis (7, 8) , L. A. Frank (9) , J. B. Sigwarth (9)

1 MPE - Max-Planck-Institut für Extraterrestrische Physik
2 ISS - Institute of Space Science [Bucharest-Măgurele]
3 LANL - Los Alamos National Laboratory
4 SSC - UNH Space Science Center [Durham]
5 ISAS - Institute of Space and Astronautical Science
6 STEL - Solar-Terrestrial Environment Laboratory [Nagoya]
7 IRF - Swedish Institute of Space Physics [Kiruna]
8 FMI - Finnish Meteorological Institute
9 Department of Physics and Astronomy [Hanover]

Data from Equator-S and Geotail are used to study the dynamics of the plasma sheet observed during a substorm with multiple intensifications on 25 April 1998, when both spacecraft were located in the early morning sector (03?04 MLT) at a radial distance of 10?11 R_E. In association with the onset of a poleward expansion of the aurora and the westward electrojet in the premidnight and midnight sector, both satellites in the morning sector observed plasma sheet thinning and changes toward a more tail-like field configuration. During the subsequent poleward expansion in a wider local time sector (20?04 MLT), on the other hand, the magnetic field configuration at both satellites changed into a more dipolar configuration and both satellites encountered again the hot plasma sheet. High-speed plasma flows with velocities of up to 600 km/s and lasting 2?5 min were observed in the plasma sheet and near its boundary during this plasma sheet expansion. These high-speed flows included significant dawn-dusk flows and had a shear structure. They may have been produced by an induced electric field at the local dipolarization region and/or by an enhanced pressure gradient associated with the injection in the midnight plasma sheet.

Domaines: Océan, Atmosphère; Sciences de la Terre

R. Nakamura, G. Haerendel, W. Baumjohann, A. Vaivads, H. Kucharek, et al.. Substorm observations in the early morning sector with Equator-S and Geotail. Annales Geophysicae, 1999, 17 (12), pp.1602-1610. ⟨hal-00316727⟩