Effects of the interplanetary magnetic field on the location of the open-closed field line boundary

Using global magnetohydrodynamic(MHD) simulation, we investigate the effect of the interplanetary magnetic field (IMF) on the location of the open-closed field line boundary(OCB), in particular the duskside and dawnside OCB and their asymmetry. We first model the typical OCB-crossing events on 22 October 2001 and 24 October 2002 observed by DMSP. The MHD model presents a good estimate of OCB location under quasi-steady magnetospheric conditions. We then systemically study the location of the OCB under different IMF conditions. The model results show that the dawnside and duskside OCBs respond differently to IMF conditions when B-Y is present. An empirical expression describing the relationship between the OCB latitudes and IMF conditions has been obtained. It is found that the IMF conditions play an important role in determining the dawn-dusk OCB asymmetry, which is due to the magnetic reconnection at the dayside magnetopause. The differences between the dawn and dusk OCB latitudes from MHD predictions are in good agreement with the observations.