Westward moving dynamic substorm features observed with the IMAGE magnetometer network and other ground-based instruments |
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| Authors: | H Lühr A Aylward S C Bucher A Pajunpää K Pajunpää T Holmboe S M Zalewski |
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| Institution: | (1) Institut für Geophysik und Meteorologie, Technische Universität Braunschweig, Mendelssohnstraße 3, Braunschweig, D-38106, Germany;(2) Atmospheric Physics Laboratory, University College London, 67 Riding House St., London, W1P 7PP, United Kingdom;(3) Finnish Meteorological Institute, Geophysical Research Division, 67 Riding House St., P. O. Box 503, Helsinki, FIN-00101, Finland;(4) Finnish Meteorological Institute, Nurmijärvi Geophysical Observatory, Röykkä, FIN-05100, Finland;(5) Auroral Observatory, University of Tromsø, Tromsø, N-9037, Norway;(6) Polish Academy of Sciences, Institute of Geophysics, Ks. Janusza 64, Warsaw, PL-01-452, Poland;(7) GeoForschungsZentrum Potsdam, Telegrafenberg, Ks. Janusza 64, Potsdam, D-14473, Germany;(8) Solar Terrestrial Environment Laboratory, Nagoya University, Honohara 3-13, Toyokawa 442, Japan |
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| Abstract: | We present the ground signatures of dynamic substorm features with particular emphasis on the event interpretation capabilities provided by the IMAGE magnetometer network. This array covers the high latitudes from the sub-auroral to the cusp/cleft region. An isolated substorm on 11 Oct. 1993 during the late evening hours exhibited many of well-known features such as the Harang discontinuity, westward travelling surge and poleward leap, but also discrete auroral forms, known as auroral streamers, appeared propagating westward along the centre of the electrojet. Besides the magnetic field measurements, there were auroral observations and plasma flow and conductivity measurements obtained by EISCAT. The data of all three sets of instruments are consistent with the notion of upward field-aligned currents associated with the moving auroral patches. A detailed analysis of the electro-dynamic parameters in the ionosphere, however, reveals that they do not agree with the expectations resulting from commonly used simplifying approximations. For example, the westward moving auroral streamers which are associated with field-aligned current filaments, are not collocated with the centres of equivalent current vortices. Furthermore, there is a clear discrepancy between the measured plasma flow direction and the obtained equivalent current direction. All this suggests that steep conductivity gradients are associated with the transient auroral forms. Also self-induction effects in the ionosphere may play a role for the orientation of the plasma flows. This study stresses the importance of multi-instrument observation for a reliable interpretation of dynamic auroral processes. |
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