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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 17, issue 4
Ann. Geophys., 17, 443–454, 1999
https://doi.org/10.1007/s00585-999-0443-4
© European Geosciences Union 1999
Ann. Geophys., 17, 443–454, 1999
https://doi.org/10.1007/s00585-999-0443-4
© European Geosciences Union 1999

  30 Apr 1999

30 Apr 1999

Conjugate observations of the day-side reconnection electric field: A GEM boundary layer campaign

M. Pinnock1, A. S. Rodger1, K. B. Baker2, G. Lu3, and M. Hairston4 M. Pinnock et al.
  • 1British Antarctic Survey, Natural Environment Research Council, Cambridge, UK
  • 2The Johns Hopkins University, Applied Physics Laboratory, Laurel, Maryland, USA
  • 3High Altitude Observatory, National Center for Atmospheric Research, Boulder, Colorado, USA
  • 4Center for Space Sciences, Univ. of Texas at Dallas, Richardson, Texas, USA
  • Correspondence to: M. Pinnock E-mail: M. Pinnock@bas.ac.uk

Abstract. Data from HF-radars are used to make the first simultaneous conjugate measurements of the day-side reconnection electric field. A period of 4 h around local magnetic noon are studied during a geospace environment modeling (GEM) boundary layer campaign. The interplanetary magnetic field (IMF) was southward whilst the eastward component (By) was variable. The flow patterns derived from the radar data show the expected conjugate asymmetries associated with 
IMF |By| > 0. High-time resolution data (50 and 100 s) enable the flow of plasma across the open/closed field line boundary (the separatrix) to be studied in greater detail than in previous work. The latitude of the separatrix follows the same general trend in both hemispheres but shows a hemispherical difference of 4°, with the summer cusp at higher latitude, as expected from dipole tilt considerations. However, the short-time scale motion of the separatrix cannot be satisfactorily resolved within the best resolution (300 m s-1) of the experiment. The orientation of the separatrix with respect to magnetic latitude is found to follow the same trend in both hemispheres and qualitatively fits that predicted by a model auroral oval. It shows no correlation with IMF By. However, the degree of tilt in the Northern (summer) Hemisphere is found to be significantly greater than that given by the model oval. The convection pattern data show that the meridian at which throat flow occurs is different in the two hemispheres and is controlled by IMF By, in agreement with empirically derived convection patterns and theoretical models. The day-side reconnection electric field values are largest when the radar's meridian is in the throat flow or early afternoon flow regions. In the morning or afternoon convection cells, the reconnection electric field tends to zero away from the throat flow region. The reconnection electric field observed in the throat flow region is bursty in nature.

Key words. Ionosphere (plasma convection; polar ionosphere) · Magnetospheric physics (magnetosphere-ionosphere interactions)

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