Abstract
The process of auroral bulge formation is modeled taking into account disruption of the near Earth tail current sheet and dipolarization of the magnetic field. The disruption of the near Earth tail current results in a considerable increase of magnetic flux tube volumes in that region. As a result, magnetic flux tube volume isolines in the equatorial plane move earthward. Their mapping to ionospheric altitudes leads to a configuration having a characteristic bulge near midnight. Thus, auroral bulge formation may be considered as the result of dipolarization of near midnight magnetic field. The increase in magnetic tube volume causes the decrease of particle pressure and formation of a pressure hole in the dipolarization region. On the east and west borders of such a region large plasma pressure gradients along magnetic flux tube volume isolines arise. Such gradients lead to the generation of powerful field-aligned currents of the Birkeland current wedge. The strength of such currents are estimated and compared with observations. Mechanisms of current disruption and field line dipolarization are discussed.
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