Observations of Cold Dense Plasma Sheet and Cusp Reconnection During Extended Periods of Northward IMF

During the October 22-25, 2003 interval strong solar activity resulted in several intervals of long duration strongly northward IMF. Using observations from Cluster, Geotail, DMSP, and FAST we investigate the state of the magnetosphere during these extreme solar wind conditions. We find that long duration strongly northward IMF results in global cooling (<1 keV) and densification ( ∼1 cm^-3) of the entire plasmasheet, at all local times, and at all latitudes, including the neutral sheet. The transition to cold and dense plasma sheet occurs gradually over 3-4 hours following the northward turning of the IMF and the cold dense plasma starts to disappear when the IMF becomes B_y dominated. During the cold dense plasma sheet intervals the FAST satellite observed inverse ion dispersion signatures in the cusp indicative of poleward-of-cusp reconnection, and nearly no polar cap. The observations show good quantitative agreement with global MHD simulations where the CDPS is formed by poleward-of-cusp reconnection capturing magnetosheath plasma which convects to the tail. The size of the lobes also shrank significantly in the simulation due to cusp reconnection.