TRAVERSAL OF THE NIGHTSIDE MAGNETOSPHERE AT 10 TO 15 RE DURING NORTHWARD IMF

The nightside magnetosphere under the northward IMF condition is not f lat at the distance of 10 to 15 Re but reveals a variety of interestin g features. The magnetospheric boundary layer consists of the tailward flowing outer layer and the earthward flowing inner layer. In the daw n as well as the dusk flank regions there are large amplitude oscillat ions with periods of 8 to 15 min which show the character of the slow mode or the mirror mode waves. Moreover, around the midnight meridian the ions and electrons are injected earthward at intervals of 1 to 2 h ours. The westward drift of the injected ions produces the energy-disp ersive ion signatures in the dusk region. The electric field Ey is pos itive on average at this distance while in the distant tail it has bee n found to be negative on average. These observations of Ey are compat ible with the magnetic reconnection in the magnetotail when the twisti ng of the neutral sheet is taken into account.