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Ann. Geophys., 17, 1602-1610, 1999
www.ann-geophys.net/17/1602/1999/
© European Geosciences Union 1999

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

R. Nakamura¹, G. Haerendel¹, W. Baumjohann¹, A. Vaivads¹, H. Kucharek¹, B. Klecker¹, E. Georgescu^1,2, J. Birn³, L. M. Kistler⁴, T. Mukai⁵, S. Kokubun⁶, P. Eglitis^7,8, L. A. Frank⁹, and J. B. Sigwarth^9
1Max-Planck-Institut für extraterrestrische Physik, Garching, Germany
²Institut for Space Sciences, Bucharest, Romania
³Los Alamos National Laboratory, USA
⁴Space Science Center, University of New Hampshire, USA
⁵Institut for Space and Astronautical Science, Sagamihara, Japan
⁶Solar-Terrestrial-Environment Laboratory, Nagoya University, Japan
⁷Swedish Institute of Space Physics, Uppsala, Sweden
⁸Finnish Meteorological Institute, Helsinki, Finland
⁹Department of Physics and Astronomy, University of Iowa, USA

Abstract. 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.

Key words. Magnetospheric physics (magnetospheric configuration and dynamics; plasma sheet; storms and substorms)

Full Article (PDF, 491 KB)

Citation: Nakamura, R., Haerendel, G., Baumjohann, W., Vaivads, A., Kucharek, H., Klecker, B., Georgescu, E., Birn, J., Kistler, L. M., Mukai, T., Kokubun, S., Eglitis, P., Frank, L. A., and Sigwarth, J. B.: Substorm observations in the early morning sector with Equator-S and Geotail, Ann. Geophys., 17, 1602-1610, 1999.   Bibtex   EndNote   Reference Manager