Shift of the magnetopause reconnection line to the winter hemisphere under southward IMF conditions: Geotail and MMS observations

Abstract : At 02:13 UT on 18 November 2015 when the geomagnetic dipole was tilted by -27°, the MMS spacecraft observed southward reconnection jets near the subsolar magnetopause under southward and dawnward interplanetary magnetic field conditions. Based on four-spacecraft estimations of the magnetic field direction near the separatrix and the motion and direction of the current sheet, the location of the reconnection line was estimated to be ~1.8 R_E or further northward of MMS. The Geotail spacecraft at GSM Z~1.4 R_E also observed southward reconnection jets at the dawnside magnetopause 30-40 min later. The estimated reconnection line location was northward of GSM Z~2 R_E. This crossing occurred when MMS observed purely southward magnetic fields in the magnetosheath. The simultaneous observations are thus consistent with the hypothesis that the dayside magnetopause reconnection line shifts from the subsolar point toward the northern (winter) hemisphere due to the effect of geomagnetic dipole tilt.