Derivation of polar cap AE indices

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We have derived on a test basis a geomagnetic index by using presently available data in the southern polar cap. Observatories used here are Scott Base, Dumont d'Urville, Vostok and Mirny. To derive disturbance fields a base value of each station for each month is first calculated using a moving average method, and this base value is subtracted from hourly data from the station in that month. Then after a coordinate transformation the largest and smallest values are selected from the four stations, respectively in the same way as the AU and AL indices are derived, and we call them the polar cap AU and AL indices. The difference between these values gives the polar cap AE index, and we derived these indices for the H and D components and T, the total force of the geomagnetic field for the years 1966 (near solar activity minimum) and 1980 (near solar activity maximum). The results of the variation of the disturbance fields from the four stations show a clear diurnal and seasonal variation depending on distribution of the stations and the ionospheric conductivities in the southern polar cap. We find the highest correlation between the polar cap AE indices and the AE, AU, and AL indices in the local winter, and the correlation decreases in the local summer due to the increase of the ionospheric conductivity in the polar cap caused by solar UV radiation. The relationship between the IMF B_y component and the polar cap AU index during local summer seems to be quadratic. The results indicate that both positive and negative B_y increase the value of the polar cap AU index due to enhancement of the B_y dependent currents in the polar cap.
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Derivation of polar cap AE indices

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