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An investigation of polar substorms observed at Halley Bay, Antarctica Boteler, David H.


Ground observations of magnetic and ionospheric substorms are reviewed, and the processes involved are explained. Then magnetic and absorption results from an auroral zone station, Halley Bay, are examined. Positive H bays occur in the evening sector between 16.00 and 22.00 local time while negative H bays occur on the nightside between 22.00 and 06.00 local time. Clockwise and counterclockwise rotating Pi2 pulsations respectively have similar times of occurrence, as do westward and eastward moving radio aurora. Short-period absorption occurs coincident with magnetic bays while longer-period absorption occurs on the dayside (04.00 to 20.00 local time). This information is used to determine the disturbance pattern in local time seen at auroral zone stations. A simple model is presented to illustrate the processes responsible for the effects observed in the 3 different local-time zones. On the nightside there is direct injection of particles from the tail, into the ionosphere, accompanied by short-circuiting of the cross-tail current through the ionosphere to produce the westward electrojet. Protons are injected into the radiation belt on the evening side, and their westward drift constitutes a partial ring current. The plasmasphere bulge modifies the distribution of proton precipitation and influences the location of the ionospheric return current, the eastward electrojet. Trapped electrons drift into the morning and dayside sectors and precipitate steadily into the ionosphere producing periods of slowly-varying absorption, The diurnal and seasonal variations of this absorption at Halley Bay suggests that photodetachment of negative ions in the D region is a significant factor in the production of auroral absorption. It is shown that variations in fxI significantly affect the occurrence of blackout on the ionoscnde, making this an unreliable indicator of absorption. Anomalies in the magnetic bays observed at Halley Bay are shown to be due to the presence of induced currents in the sea flowing parallel to the continental shelf. An analysis of electrical power system disturbances identifies magnetic substorms as the primary cause, and discusses how knowledge about substorms can aid prediction of the power system disturbances.

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