A UNIFIED MODEL OF THE MAGNETOTAIL CONVECTION IN GEOMAGNETICALLY QUIET AND ACTIVE TIMES

Geotail observations have shown that during geomagnetically quiet time s the northward magnetic field lines are convected tailward in the dis tant tail while they are convected earthward in the near-Earth magneto tail. These seemingly incompatible observations when the interplanetar y magnetic field (IMF) B-z is northward and \B-y\ greater than or equa l to B-z can be explained by the magnetic reconnection which occurs in the distant tail where the neutral sheet is twisted by tens of degree s. According to this interpretation, the tailward convection of the no rthward field lines occurs beyond the reconnection line because the re connected field lines that cross the neutral sheet from Its northern s ide to the southern side can have the northward polarity everywhere by virtue of the twisting of the neutral sheet. Hence the reconnection c an 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 \B-y\ greater than or equal to B-z) IMF conditions. Both Geotail and DE 2 observations suggest th at the closed field lines that are formed by the reconnection return t o the dayside by convecting through the inner magnetosphere in geomagn etically quiet times as well as in active times. This suggests that th e dayside reconnection with the northward IMF (with \B-y\ greater than or equal to B-z) on the magnetopause involves the closed field lines in addition to the open field lines as considered in the classical cus p reconnection model under the northward IMF.