The magnetic local time distribution of ring current during the geomagnetic storm

The magnetic local time distribution of the ring current during 879 geomagnetic storms (identified by SYMH < -30 nT) in the 23rd solar cycle (1996-2006) was investigated by using 23 mid-low latitude ground-based magnetometers. The storms are divided into eight different classes with a step of 20 nT for the statistical analysis. For each class, the dusk side events, for which the H component minimum located in the dusk sector is mostly corresponding to the UT of minimum SYMH index, are about 59.5% of the total events. Whereas the noon side events are about 20.0%, the night side events are about 18.7%, and the dawn side events are about 1.8%. The H component distributions with MLT indicate that the magnetic field disturbance during the magnetic storm events is not only related to the symmetrical ring current, but also to the other current, mainly the partial current. A further statistical study of the dusk side events shows that both the symmetric and partial ring currents enhance accompanied by the increase in the storm class during the main phase. And the partial ring current makes a greater contribution to the main phase of the storm. Referring to the interplanetary parameters, the distinction of the solar wind velocity V-x is more obvious than the interplanetary magnetic field B-z for the dusk side events in different classes. The comparisons between dusk side and other side events in the same class indicate that besides the solar wind velocity V-x, the interplanetary magnetic field B-y also affects on the disturbance of ring current on the ground in MLT. (C) 2013 Elsevier Ltd. All rights reserved.