The dynamics and relationships of precipitation, temperature and convection boundaries in the dayside auroral ionosphere

A continuous band of high ion temperature, which persisted for about 8 h and zigzagged north-south across more than five degrees in latitude in the dayside (07:00-15:00 MLT) auroral ionosphere, was observed by the EISCAT VHF radar on 23 November 1999. Latitudinal gradients in the temperature of the F-region electron and ion gases (T, and T-i, respectively) have been compared with concurrent observations of particle precipitation and field-perpendicular convection by DMSP satellites, in order to reveal a physical explanation for the persistent band of high T-i, and to test the potential role of T-i and T-e gradients as possible markers for the open-closed field line boundary. The north/south movement of the equatorward T-i boundary was found to be consistent with the contraction/expansion of the polar cap due to an unbalanced dayside and nightside reconnection. Sporadic intensifications in T-i recurring on similar to10-min time scales, indicate that frictional heating was modulated by time-varying reconnection, and the band of high T-i was located on open flux. However, the equatorward T-i boundary was not found to be a close proxy of the open-closed boundary. The closest definable proxy of the open-closed boundary is the magnetosheath electron edge observed by DMSP. Although Te appears to be sensitive to magnetosheath electron fluxes, it is not found to be a suitable parameter for routine tracking of the open-closed boundary, as it involves case dependent analysis of the thermal balance. Finally, we have documented a region of newly-opened sunward convecting flux. This region is situated between the convection reversal boundary and the magnetosheath electron edge defining the open-closed boundary. This is consistent with a delay of several minutes between the arrival of the first (super-Alfvenic) magnetosheath electrons and the response in the ionospheric convection, conveyed to the ionosphere by the interior Alfven wave. It represents a candidate footprint of the low-latitude boundary mixing layer on sunward convecting open flux.