Electron Density Enhancements in the Polar Cap During Periods of Dayside Reconnection

Abstract:

Using field-aligned current data we monitor the location of the region 1 current oval which is related to the location of the polar cap boundary (PCB). We identify intervals when the current oval and hence the PCB moved equatorward for extended periods lasting at least 75 minutes and we term these intervals sustained dayside reconnection events (SDRE). We find 1059 SDREs between 2010 and 2012 and go on to study the dynamics of the total electron content (TEC) in the high-latitude region in a superposed epoch sense. Immediately after the beginning of a SDRE a plasma density increase forms at the poleward edge of the PCB and its edge moves from the location of the dayside PCB anti-sunward at speeds of about 500 m/s, consistent with ionospheric convection measurements. Our results show that the TEC inside the polar cap locally increases by up to 20\%. Averaged over the entire polar region poleward of 55 degrees magnetic latitude, however, we find no significant increase in the TEC, indicating that local increases and decreases are formed by transport and rearrangement of existing plasma rather than by impact ionization due to particle precipitation. We also observe a latitudinally narrow region between the TEC increases equatorward and poleward of the dayside PCB in which the TEC stagnates. This stagnation trough may be due to local flow channels associated with bursty dayside reconnection.