Influence of the IMF Azimuthal Component on Magnetospheric Substorm Dynamics

Abstract

The effect of the IMF azimuthal component on magnetospheric substorm dynamics has been studied on the basis of five-minute average values of the IMF B_y and B_z components and the AL index. The results obtained from case studies and from superposed epoch analysis show the dependence of substorm dynamics on the azimuthal component: the reversal of B_y from positive to negative increases the activity with minimum delay time, while the opposite reversal either does not change or only slightly changes the activity level. This effect is more evident in winter. The reversal of the IMF vertical component from south to north after an interval of sustained southward IMF statistically gives rise to magnetic activity, too, but this growth is less intense than that produced by the B_y negative turning.
The role of both vertical and azimuthal IMF components must be considered in future studies of substorm triggering mechanisms.