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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 17, issue 3
Ann. Geophys., 17, 375–388, 1999
https://doi.org/10.1007/s00585-999-0375-z
© European Geosciences Union 1999
Ann. Geophys., 17, 375–388, 1999
https://doi.org/10.1007/s00585-999-0375-z
© European Geosciences Union 1999

  31 Mar 1999

31 Mar 1999

Stationary magnetospheric convection on November 24, 1981. 2. Small-scale structures in the dayside cusp/cleft

Y. I. Galperin1, J. M. Bosqued2, R. A. Kovrazhkin1, and A. G. Yahnin3 Y. I. Galperin et al.
  • 1Space Research Institute of Russian Academy of Sciences, 117810, Moscow, Russia
  • 2Centre d'Etude Spatiale des Rayonnements, CNRS/UPS, 9, Avenue du Colonel Roche-31028 Toulouse Cedex, France
  • 3Polar Geophysical Institute, Apatity, Murmansk region, 184200, Russia

Abstract. A case study of the dayside cusp/cleft region during an interval of stationary magnetospheric convection (SMC) on November, 24, 1981 is presented, based on detailed measurements made by the AUREOL-3 satellite. Layered small-scale field-aligned current sheets, or loops, superimposed to a narrow V-shaped ion dispersion structure, were observed just equatorward from the region of the "cusp proper". The equatorward sheet was accompanied by a very intense and short (less than 1 s) ion intensity spike at 100 eV. No major differences were noted of the characteristics of the LLBL, or "boundary cusp", and plasma mantle precipitation during this SMC period from those typical of the cusp/cleft region for similar IMF conditions. Simultaneous NOAA-6 and NOAA-7 measurements described in Despirak et al. were used to estimate the average extent of the "cusp proper" (defined by dispersed precipitating ions with the energy flux exceeding 10-3 erg cm-2 s-1) during the SMC period, as ~0.73° ILAT width, 2.6-3.4 h in MLT, and thus the recently merged magnetic flux, 0.54-0.70 × 107 Wb. This, together with the average drift velocity across the cusp at the convection throat, ~0.5 km s-1, allowed to evaluate the cusp merging contribution to the total cross-polar cap potential difference, ~33.8-43.8 kV. It amounts to a quite significant part of the total cross-polar cap potential difference evaluated from other data. A "shutter" scenario is suggested for the ion beam injection/penetration through the stagnant plasma region in the outer cusp to explain the pulsating nature of the particle injections in the low- and medium-altitude cusp region.

Key words. Magnetospheric physics (current systems; magnetopause · cusp · and boundary layers; solar wind-magnetosphere interactions).

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