Sondrestrom and EISCAT radar observations of poleward-moving auroral forms |
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| Institution: | 1. ITC Faculty, Twente University, P.O. Box 6, 7500 AA Enschede, the Netherlands;2. Department of Geography, Royal Holloway University of London, Egham, Surrey TW20 0EX, UK;3. Soil Geography Group, Wageningen University, P.O. Box 47, 6700 AA Wageningen, the Netherlands;4. Department of Geography, University of Newcastle, Newcastle upon Tyne, NE1 7RU, UK;5. Department of Geography, Harran University, 63300 Sanliurfa, Turkey;1. Department of Sciences, University of Basilicata, Campus di Macchia Romana, Viale dell''Ateneo Lucano 10, 85100 Potenza, Italy;2. Istituto Nazionale di Geofisica e Vulcanologia (INGV), Sezione di Palermo, Via Ugo La Malfa 153, 90146 Palermo, Italy;3. Department of Nature and Land Resources, University of Sassari, Via Piandanna 4, 07100 Sassari, Italy;4. Agenzia Regionale per la Protezione dell''Ambiente di Basilicata, Via della Fisica 18 C/D, 85100 Potenza, Italy;5. National Research Council, Institute of Methodologies for Environmental Analysis, C/da S. Loja, 85050 Tito Scalo (PZ), Italy;1. Institute of Physicochemical and Biological Problems in Soil Science, RAS, Institutskaya st., 2, Pushchino, Moscow Region 142290, Russia;2. Department of Soil Science of Temperate Ecosystems, Georg-August University of Göttingen, Büsgenweg 2, 37077 Göttingen, Germany |
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| Abstract: | During many magnetospheric substorms, the auroral oval near midnight is observed to expand poleward in association with strong negative perturbations measured by local ground magnetometers. We show Sondrestrom and EISCAT incoherent scatter radar measurements during three such events. In each of the events, enhanced ionization produced by the precipitation moved northward by several degrees of latitude within 10–20 min. The electric fields measured during the three events were significantly different. In one event the electric field was southward everywhere within the precipitation region. In the other two events a reversal in the meridional component of the field was observed. In one case the reversal occurred within the precipitation region, while in the other case the reversal was at the poleward boundary of the precipitation. The westward electrojet that produces the negative H-perturbation in the ground magnetic field has Hall and Pedersen components to varying degrees. In one case the Hall component was eastward and the Pedersen component was westward, but the net magnetic H-deflection on the ground was negative. Simultaneous EISCAT measurements made near the dawn meridian during one of the events show that the polar cap boundary moved northward at the same time as the aurora expanded northward at Sondrestrom. Most of the differences in the electrodynamic configuration in the three events can be accounted for in terms of the location at which the measurements were made relative to the center of the auroral bulge. |
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