LEAKAGE IONS FROM THE LLBL TO MSBL - CONFIRMATION OF RECONNECTION EVENTS AT THE DAYSIDE MAGNETOPAUSE

This letter reports on leakage ions from the low latitude boundary lay er (LLBL) to the magnetosheath boundary layer (MSBL) as observed by Ge otail at the dayside magnetopause. A reconnection of the interplanetar y magnetic field (IMF) with magnetospheric field lines is shown to be responsible for the leakage. Based on analysis of a variation in lower cut-off levels occurring in the velocity distribution function of the leakage ions, we propose a ''velocity filter effect'' model with a fi nite source region to explain this variation. The location of the reco nnection region is subsequently calculated to be 2.2R(E) north of the geomagnetic equatorial plane under the proposed velocity filter effect model.