Relationship of interplanetary magnetic field structure with development of substorm and storm main phase

Abstract

Development of a polar magnetic substorm and the main phase of a magnetic storm is compared with magnetic variation in interplanetary space. It is confirmed, using AE indices, that a polar substorm is well correlated with the southward component, B zs , of the interplanetary magnetic field. The hourly-value AE shows the highest correlation with B zs , of the preceding hour. It is also found in the ground magnetic data that the twin-vortex current system without enhancement of auroral zone current, called DP 2 or SP, develops with south ward changes in the interplanetary magnetic field before the expansion phase of magnetic substorm. In cases of magnetic storms following the ssc's, caused by interplanetary shock waves, developments of substorm and D st are found to be highly correlated with B zs . When B zs is small for about one day after the interplanetary shock no appreciable geomagnetic activity follows the ssc even in cases where the increase in kinetic energy flux of the solar wind is fairly large. In cases of large magnetic storms, large B zs changes are usually observed during several hours or more within a day after the ssc, accompanying the development of geomagnetic disturbances.