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Theory of polar substorms Atkinson, Gerald

Abstract

The magneto-sphere may be considered as consisting of two regions the tail and region of closed lines of force. The interchange of field lines between these two region is important in magnetospheric processes. Transport of magnetic field lines from the closed region into the tail may occur by Dungey's mechanism or by viscous interaction of the magnetosphere with the solar wind. Transport from the tail to the closed region occurs by recombination through the neutral sheet. Convective flow within the closed region is controlled by the “foot dragging” effect which arises from the discharging action of the ionosphere on flux tubes. The model of polar substorms presented is a flow or time sequence as follows: (1) Field lines are dragged from the closed region into the tail by the solar wind with a resulting storage of potential energy in the tail. (2) The polar substorm begins when the field lines recombine in an implosive fashion at the neutral sheet, releasing the stored potential energy. (3) The recombined flux tubes are added to the nightside of the closed region as a giant bulge. (4) The bulge drives are turn flow of flux tubes towards the dayside in the closed region. It is likely that recombination is initiated by the formation of a neutral point at about 13 or 14 earth radii in the antisolar direction and occurs across a width of tail of about 6 or 7 earth radii and that 10⁸ webers are annihilated in a time of about 1/2 hour. The recombination iis probably stopped by the build-up of a giant bulge on the nightside and the closed region which maps to the earth’s surface along fieldlines as the auroral break-up bulge and which, as i t spreads out over the nightside of the region of closed fieldlines causes the observed auroral effects. The Pedersen current is not expected to produce significant magnetic effects at the surface of the earth except at anomalies in ionospheric conductivity. Such an anomaly along the auroral arcs can explain the westward electrojet. However, it seems probable that the remainder of the polar cap current system is the result of Hall currents.

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