IMF By-controlled field-aligned currents in the magnetotail during northward IMF

The influences of the interplanetary magnetic field (IMF) By component on the field-aligned currents (FACs) at the plasma sheet boundary layer (PSBL) in the magnetotail during the northward IMF were investigated using the data from Cluster. There are 748 FACs cases were selected to do analysis. We present IMF By component plays a very important role in controlling the flow direction of the FACs at PSBL in the magnetotail. In the northern hemisphere the influence of the positive (negative) IMF By is an earthward (tailward) FACs on the dawnside and duskside. However, in the southern hemisphere the effect of the positive (negative) IMF By is a tailward (earthward) FACs on the dawnside and duskside. There is a clear north-south asymmetry of the polarity of the FACs at PSBL when IMF By is positive or negative, and this asymmetry of the polarity is more distinct when IMF By is positive. The FACs density is controlled by IMF By only when |IMF By| is large. When |IMF By| is more than 10nT the FACs density at PSBL has an obvious positive correlation with the |IMF By|. When |IMF By| is less than10nT, there is no correlation between the FACs density and |IMF By|. There is a clear dusk-dawn asymmetry for the FACs density at PSBL, with the dawn currents appearing larger than the dusk currents. The FACs with the largest (smallest) density is located in the range of 0100≤MLT<0200 (2000≤MLT<2100).