Global cooling and densification of the plasma sheet during an extended period of purely northward IMF on October 22-24, 2003

The October 22-24, 2003 interplanetary magnetic cloud was characterized by an exceptionally long interval (~32 hours) of nearly purely northward interplanetary magnetic field (IMF). Following the northward IMF turning Cluster observed a gradual transition to a cold (<1 keV) and dense (~1-2 cm^-3) plasma sheet (CDPS). Cluster observed CDPS continuously for the following ~30 hours while passing through the neutral sheet from the northern to the southern hemisphere. DMSP observations mapped to the equatorial plasma sheet reveal that the CDPS extended to all nightside local times. The FAST satellite observed reversed ion dispersion signatures in the cusp indicative of poleward-of-cusp reconnection, and nearly no polar cap. The CDPS observations show good agreement with a global MHD simulation where the CDPS is formed by poleward-of-cusp reconnection capturing magnetosheath plasma and convecting it to the tail. The process shrinks the size of the lobes (and therefore the polar cap) significantly, as observed.