Dayside magnetic topology at the Earth's magnetopause for northward IMF

Abstract

When the Interplanetary Magnetic Field is northward, magnetic reconnection occurs at the Earth's high latitude magnetopause in regions poleward of the Earth's magnetospheric cusps. Observations at the high latitude magnetopause appear to support reconnection poleward of both northern and southern hemisphere cusps, forming closed field lines in the magnetosheath. However, observations at the dayside low latitude magnetopause and in the low altitude cusp do not support this reconnection scenario. Using plasma and magnetic field data from the Cluster spacecraft, signatures of reconnection poleward of both cusps were investigated as a function of latitude. It was found that reconnection in at least one hemisphere occurs essentially all the time for northward IMF. This investigation also confirmed the apparent discrepancy between high and low latitude observations. A scenario for reconnection in both cusps whereby the field line reconnected poleward of one cusp convects away from the dayside magnetopause before reconnecting in the opposite hemisphere is consistent with observations at all latitudes.