Magnetic activity in the polar cap—A new index

A magnetic activity index PC measuring DP2 magnetic perturbations in the central polar cap is derived, and its relationship to various solar wind parameters is investigated through a linear correlation analysis. The PC index is based on data from a single nearpole station, and the index values derived from a station near the south pole, Vostok, are compared with simultaneous index values derived from a station near the north pole, Thule. It is concluded that the index shows a good correlation with the southward component of the interplanetary magnetic field IMF or, even better, the solar wind parameters vB z orvB t sin 2 θ 2 . In the derivation of the index the following items are taken into account: (1) seasonal changes, (2) inhomogeneity in magnitude and direction of the magnetic perturbation in the nearpole region and (3) a time delay between variations in the solar wind parameters and the subsequent response in the polar cap.