Wave structure of magnetic substorms at high latitudes

Abstract

A new type of highlatitude magnetic bays is revealed at geomagnetic latitudes higher than 71°, called "polar substorms." It is shown that polar substorms differ from both classical substorms and highlat� itude geomagnetic disturbances of the type of polar boundary intensifications (PBIs). While classical sub� storms start at latitudes below 67° and then expand poleward, polar substorms start almost simultaneously in the evening-night polar region of the oval. In contrast to PBIs, accompanied by auroral streamers expanding southward, polar substorms are accompanied by auroral arcs quickly traveling northward. It is shown that polar substorms are observed before midnight (20-22 MLT) under weak geomagnetic activity (Kp ~ 2) during the late recovery phase of a magnetic storm. It is shown that a typical feature of polar substorms is the simul� taneous excitation of highly intensive Pi2 and Pi3 geomagnetic pulsations at high latitudes, which exceed the typical amplitude of these pulsations at auroral latitudes by more than an order of magnitude. The duration of pulsations is determined by the substorm duration, and their amplitude decreases sharply at geomagnetic latitudes below ~71°. It is suggested that pulsations reflect fluctuations in ionospheric currents connected with polar substorms.