The storm-time ring current: a statistical analysis at two widely separated low-latitude stations, Ann

Abstract. We conducted a statistical analysis of the geo-magnetic field variations during the storm main phase at two low-latitude stations, separated by several hours in magnetic local time, in order to investigate the asymmetry and lon-gitudinal extent of the storm-time ring current. The results show evidence for an asymmetric current which typically ex-tends from evening to noon and, during moderate solar wind electric field conditions, up to the early morning, confirming the important role of the magnetospheric convection in the ring current energization. We also analyzed a possible rela-tionship between the local current intensity during the storm main phase and the substorm activity observed at different time delays τ with respect to the storm onset. The results show a significant anticorrelation for τ=−1 h, indicating that if the substorm activity is high just before the storm, a weaker ring current develops. Key words. Magnetospheric physics (solar wind-magnetosphere interactions; storms and substorms; magne-tospheric configuration and dynamics)