High-latitude geomagnetic variations and substorms

Abstract

The present review concerns high-latitude geomagnetic variations, and in particular those caused by fluctuations of the interplanetary magnetic field. It is shown that IMFB z,B x,B y and |B y| produce four kinds of geomagnetic effects, which qualitatively agree with the expected consequences of the reconnection hypothesis. At quiet time the cleft into the Earth's magnetosphere has a quasi-circular shape at Φ ≈ 78° that also fits qualitatively the reconnection model by Stern (1973) but does not agree with the conception ofdayside cusps. From the analysis of the geomagnetic effects of IMFB z it was found also that the contribution of magnetospheric dynamo to the electric field of the dayside plasmasphere (middle and low latitudes) does not exceed 15–20%. Characteristics of this contribution are given (i.e.DP-2 fields). The magnetic substorm models are reviewed as well. Geomagnetic data confirm the existence of the substorm growth phase both atB z < 0 and atB z > 0. The expansion phase of most substorms evidently involves the processes of reconnection and neutral line formation near the inner edge of the plasma sheet (LT ≈ 23h), resulting from instability of field-aligned currents of the westward electrojet ath ~ 1000 km. Such a mechanism accounts for a number of signatures for local development of substorms, including coastal effect, jumplike development of the electrojet, etc. The second kind of substorms, not involving the magnetic disturbances, is probably caused by the development of ion tearing instability in the plasma sheet. The original results are presented against a general review background, which includes a method for mathematical description of global fields of magnetic variations and substorms.