Statistical features of substorm indicators during geomagnetic storms

Abstract

This paper reports statistical features of two substorm indicators, magnetic dipolarization and energetic particle injection at the geosynchronous orbit, during the storm evolution period, which is divided into three phases: main, early recovery, and late recovery. Two separate sets of data for each of the indicators are used from two different sources: GOES and Los Alamos National Laboratory (LANL) spacecraft data for dipolarization and injection, respectively. We find that the statistical features of the two indicators are remarkably similar and well correlated to each other but clearly distinguish between three phases of storms in several aspects: (1) During the main phase, both substorm indicators are strong and most frequent in its occurrence. The occurrence probability of their onsets spreads out over wide local time sectors, ∼82% of onsets being scattered over 20–01 LT. (2) During the early recovery phase, the occurrence frequency of both indicators overall substantially reduces, but their intensity around the midnight is still significant as compared to the main phase. The onset probability now becomes concentrated to more limited sectors, ∼83% of them being concentrated over 21–24 LT with a distinct peak at 23–24 LT. (3) During the late recovery phase, both substorm indicators become much weaker than in the earlier two phases, least frequent in their occurrence, and over 92% of onsets are concentrated to 22–01 LT with a well prominent peak at 23–24 LT again. (4) The proton flux enhancement is greater at higher energy channels for most events of main and early recovery phases while it is prominent only at first two lowest energy channels for the late recovery phase events.