Interrelation between physical processes during the main phases of geomagnetic storms related to the IMF B Z component according to a cluster analysis

Abstract

The main causes of the main phases of geomagnetospheric storms (Dstmin = −(37−226) nT) have been studied using a cluster analysis in the form of the nearest neighbor method. Weak, moderate, strong and severe storms (samples) related to the IMF BZ component have been distinguished based on the two-dimensional (with respect to the IMF BZ component and Dst index) scale cluster classification of storm main phases. The correlation clustering of 32 interrelated physical processes characterizing each main phase made it possible to determine that interrelated physical processes included the common part of the internal structure for all samples. The studied samples of storm main phases are characterized by different physical development levels, depending on the event scale. The presence of a common part indicates that magnetospheric activity mostly depends on the IMF BZ and BY components and the coupling functions between them, as well as on the total IMF B value during the main phases of storms of all Dst index scales. It has been established that the closest relationships are typical of Dst(V2BS) and Dst(VBS), where BS is the IMF southward component, and V is the solar wind velocity. Substorm activity (AE) generated by V2BS and VBS is only substantial during the main phases of weak and moderate storms, whereas grouping with respect to the velocity V only shows substantial activity during severe magnetic storms. The role of the Akasofu parameter (ɛ) proved to be less pronounced. It has been indicated that, in a first approximation, it is preferred to use the V2BS and VBS coupling functions in order to predict the Dst index and estimate the injection function Q during the main phases of geomagnetospheric storms.