The features of auroral bulge expansion |
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| Authors: | VA Sergeev AG Yahnin |
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| Institution: | aPhysical Institute, University of Leningrad, Leningrad 198 904, U.S.S.R. |
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| Abstract: | The development of the auroral bulge during substorms is studied using all-sky data from the dense net of stations and also riometer data. A few features seem to be essential for the interpretation of the expansive phase mechanism. The first is the existence of low energy electron precipitation (auroral arcs with the lower border height near 140 km) polewards of the expanding bulge, suggesting that the bulge often arises and develops on closed field lines. Secondly only the localized bulges (with dimensions  2° and 40°Λ) are generated by the continuous deformation of the auroral arc. The greater expansions develop mainly at the expense of the new bright arc formations at the front of the expanding auroral bulge. During each new arc formation impulsive acceleration and precipitation of energetic electrons takes place and brief changes of plasma sheet geometry are sometimes observed at 18 RE in the magnetotail. This apparently shows a re-distribution of plasma sheet current during the substorm expansive phase. |
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