A new insight on the cause of magnetic storms

A long outstanding problem in magnetospheric physics is the cause of magnet ic storms. Traditionally, the ring current buildup is attributed to the acc umulated effects of energetic magnetospheric particles injected by frequent occurrence of magnetospheric substorms. Recent studies, however, suggest e nhanced magnetospheric convection as the sole cause. We employ for the firs t time the relatively new remote-sensing technique based on global monitori ng of energetic neutral atom (ENA) emissions to address this controversy. T he ENA observations were combined with the ground-based magnetic indices fo r substorm activity and ring-current development as well as with the global monitor of magnetospheric convection in the ionosphere by the network of S uperDARN radars. The ring current is shown to intensify during enhanced con vection without substorm occurrence and during a substorm with a reduction in convection. Therefore, both substorms and enhanced convection contribute to the buildup of the storm-time ring current.