Abstract
The following hydromagnetic theory of geomagnetic storms is outlined: (a) A solar ion stream envelopes the geomagnetic cavity exerting radial pressure and tangential frictional drag. The former creates an O-type hydromagnetic wave, the latter E-type (twist) waves. The frictional effect may also scatter 104 eV electrons into the cavity and may carry field lines away to form a geomagnetic tail. (b) Hydromagnetic transmission to Earth leads, in general, to sea-level magnetic changes quite different from transmission through a vacuum. The O (pressure) wave envelopes the Earth to cause Dst (SC); it also creates an E wave as it travels and this is focused into the polar regions, contributing to DS(SC). The helical twist (E) wave also propagates to the polar regions to cause most of DS (main phase). (c) In the lower ionosphere the helical twist constitutes a “rotating field dynamo” driven from above by the ion stream and impeded by the Lorentz force of the Pedersen current. The dynamo also drives Hall current in loops above the auroral zone and space-charge field drives current in loops below this zone. (d) The sea-level magnetic effect of the Pedersen (radial) current system is nil. The Hall current system accounts for elementary polar disturbances, bays and the major features of DS (main phase); in effect the helical twist has been transformed into a pinch (morning) or expansion (evening) of the bundle of field lines. (e) Evidence is provided that the geomagnetic tail contributes to DS (main phase) and hence to Dst (main phase).
Published Version
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