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Ann. Geophys., 20, 341-347, 2002
www.ann-geophys.net/20/341/2002/
© European Geosciences Union 2002
Plasma sheet fast flows and auroral dynamics during substorm: a case study
N. L. Borodkova1, A. G. Yahnin2, K. Liou3, J.-A. Sauvaud4, A. O. Fedorov4,*, V. N. Lutsenko1, M. N. Nozdrachev1, and A. A. Lyubchich2
1Space Research Institute, Russian Academy of Sciences, Moscow, Russia
2Polar Geophysical Institute, Apatity, Russia
3Applied Physics Laboratory, Johns Hopkins University, Laurel, USA
4Centre d’Etude Spatiale des Rayonnements, Toulouse, France
*On leave from the Space Research Institute, Moscow
Correspondence to: J.-A. Sauvaud (sauvaud@cesr.cnes.fr)
Abstract. Interball-1 observations
of a substorm development in the mid-tail on 16 December 1998 are compared with
the auroral dynamics obtained from the Polar UV imager. Using these data, the
relationship between plasma flow directions in the tail and the location of the
auroral activation is examined. Main attention is given to tailward and
earth-ward plasma flows, interpreted as signatures of a Near Earth Neutral Line
(NENL). It is unambiguously shown that in the mid-plasma sheet the flows were
directed tailward when the auroral bulge developed equatorward of the
spacecraft ionospheric footprint. On the contrary, when active auroras moved
poleward of the Interball-1 projection, earthward fast flow bursts were
observed. This confirms the concept that the NENL (or flow reversal region) is
the source of auroras forming the poleward edge of the auroral bulge. The
observed earthward flow bursts have all typical signatures of Bursty Bulk Flows
(BBFs), described by Angelopolous et al. (1992). These BBFs are related to
substorm activations starting at the poleward edge of the expanded auroral
bulge. We interpret the BBFs as a result of reconnection pulses occurring
tail-ward of Interball-1. In addition, some non-typically observed phenomena
were detected in the plasma sheet during this substorm: (i) tailward/earthward
flows were superimposed on a very strong duskward flow, and (ii) wavy
structures of both magnetic field and plasma density were registered. The
latter observation is probably linked to the filamentary structure of the
current sheet.
Key words. Magnetospheric physics (auroral
phenomena; plasma sheet; storms and substorms)
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