THEMIS observations of penetration of the plasma sheet into the ring current region during a magnetic storm

Observations from the THEMIS spacecraft during a weak magnetic storm clearly show that the inner edge of the ion plasma sheet near dusk moved from r similar to 6 R-E during the pre-storm quiet time to r similar to 3.5 R-E during the main phase, and then moved outward during the recovery phase. The plasma sheet particles from the tail reached the inner magnetosphere during the main phase through open drift paths, which extended earthward with increasing convection, and were energized to ring current energies, resulting in an increase in ring current population. During the recovery phase, the plasma sheet region retreated to outside the inner magnetosphere as the region of open drift paths moved outward with decreasing convection, leaving the ring current particles within the expended closed drift path region. With no new particles from the plasma sheet, ring current population gradually decreased due to losses as the recovery phase proceeded.