Traversal of the nightside magnetosphere at 10 to 15 Re during northward IMF

A. Nishida, T. Mukai, T. Yamamoto, Y. Saito, S. Kokubun, and R. P. Lepping

Institute of Space and Astronautical Science, Sagamihara, Japan


The nightside magnetosphere under the northward IMF condition is not flat at the distance of 10 to 15 Re but reveals a variety of interesting features. The magnetospheric boundary layer consists of the tailward flowing outer layer and the earthward flowing inner layer. In the dawn as well as the dusk flank regions there are large amplitude oscillations 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 hours. The westward drift of the injected ions produces the energy-dispersive ion signatures in the dusk region. The electric field Ey is positive on average at this distance while in the distant tail it has been found to be negative on average. These observations of Ey are compatible with the magnetic reconnection in the magnetotail when the twisting of the neutral sheet is taken into account.

Geophys. Res. Lett., 24, 939-942, 1997