A unified model of the magnetotail convection in geomagnetically quiet and active times

Abstract

Geotail observations have shown that during geomagnetically quiet times the northward magnetic field lines are convected tailward in the distant tail while they are convected earthward in the near‐Earth magnetotail. These seemingly incompatible observations when the interplanetary magnetic field (IMF) Bz is northward and |By| ≥ Bz can be explained by the magnetic reconnection which occurs in the distant tail where the neutral sheet is twisted by tens of degrees. According to this interpretation, the tailward convection of the northward field lines occurs beyond the reconnection line because the reconnected field lines that cross the neutral sheet from its northern side to the southern side can have the northward polarity everywhere by virtue of the twisting of the neutral sheet. Hence the reconnection can be the generic mechanism of the plasma acceleration and heating in the magnetotail in both geomagnetically active and quiet times, namely, under both southward and northward (with |By| ≥ Bz) IMF conditions. Both Geotail and DE 2 observations suggest that the closed field lines that are formed by the reconnection return to the dayside by convecting through the inner magnetosphere in geomagnetically quiet times as well as in active times. This suggests that the dayside reconnection with the northward IMF (with |By| ≥ Bz) on the magnetopause involves the closed field lines in addition to the open field lines as considered in the classical cusp reconnection model under the northward IMF.