Latitudinal shift and tilt of the ring current during magnetic storms

The equatorial ring current (ERC) theory suggested that the distribution of global disturbed horizontal geomagnetic field only depends on the cosine of station’s latitude. However, we always observe a larger ΔH at higher latitude stations than lower ones, implying that the ERC could tilt or/and shift with respect to the equatorial plane during intense storms. In this paper, we analyze 11 intense magnetic storms from 2000 to 2004, and introduce two configurational factors to characterize the topology of storm time ring current. The results show that ERC has occasionally deviated off equatorial plane with both tilt angle δ _t ≈13°–25° and latitude shift δ _s ≈0°–21.8°. The ground disturbed field distribution should be improved as ΔH _k = ΔH _maxcos(ϕ _k –δ), which agree well with the geomagnetic observations. Supported by National Natural Science Foundation of China (Grant No. 40436016), KIP Pilot Project of the Chinese Academy of Sciences (Grant No. KZCX3-SW-144) and National Basic Research Program of China (Grant No. 2006CB806305)