High-latitude substorm dependence on space weather conditions in solar cycle 23 and 24 (SC23 and SC24)

Abstract

The occurrence of the magnetic substorms at high geomagnetic latitudes (>70° CGC) has been visually analyzed using the ground-based IMAGE magnetometer chain and OMNI solar wind and Interplanetary Magnetic Field (IMF) data. We studied the time intervals closely to the minimum and maximum of the 23-th and 24-th solar cycles. The considered high-latitude substorms have been divided into two different types according to their occurrence relatively to the auroral oval dynamics. The first type - the substorms which expand from the auroral geomagnetic latitudes to the polar ones (named the “expanded” substorms, according to an expanded oval dynamics); the second type - the substorms which are observed only at the geomagnetic latitudes higher ∼ 70° CGC under the absence of simultaneous magnetic disturbances at lower latitudes (named the “polar” substorms, according to a polar latitude contracted oval dynamics). Both substorm types are identified at almost identical latitudes, however, with different latitude of their onset locations. It was found that the “polar” substorms show behavior opposite to the “expanded” ones. The “polar” substorms are observed under a low solar wind speed (V < 500 km/s) and the “expanded” substorms - under a high speed (V > 500 km/s). We found, that the PC-index of the polar cap activity, which could be used as a proxy of changes in solar wind electric field, was lower before the “polar” substorms than before the “expanded” ones. The summer maxima in the seasonal occurrence of the “polar” substorms correspond to the minima of the “expanded” substorm. We did not reveal any significant cycle differences in the distributions of the IMF and solar wind parameters before the both types of substorms observed near the maxima and minima of the 23-th and 24-th cycles of the solar activity.