Solar wind magnetic field and pressure during magnetopause crossings at geosynchronous orbit

Solar wind dynamic pressure and the Bz component of the interplanetary magnetic field are analysed for time intervals from 1967-1993 when the magnetopause was observed at geosynchronous orbit (84 crossings), We conclude that: (1) when Bz>0 the pressure balance at the magnetopause corresponds to the gas dynamic theory and the shape of the magnetopause is well approximated by a parabolic model; (2) when -6<Bz<0 nT a new regime of magnetopause formation is found; furthermore the solar wind pressure was four to six times smaller in the case of Bz<-6 nT than in the case of Bz>0; (3) under both Bz>0 and Bz<0 considerable magnetopause asymmetry in the dawn-dusk direction was observed. (C) 1998 COSPAR. Published by Elsevier Science Ltd, All rights reserved.