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

The influence of the interplanetary magnetic field (IMF) By component on the field-aligned currents (FACs) in 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 selected to do analysis. We present that the IMF By component plays a very important role in controlling the flow direction of the FACs in the PSBL in the magnetotail. In the northern hemisphere, the influence of the positive (negative) IMF By is an earthward (tailward) FACs. To the contrary, in the southern hemisphere, the effect of the positive (negative) IMF By is a tailward (earthward) FACs. There is a clear north-south asymmetry of the polarity of the FACs in the PSBL when IMF By is positive or negative, and this asymmetry of the polarity is more distinct when IMF By is positive. The FAC density is controlled by IMF By only when |IMF By| is large. When |IMF By| is more than 10 nT the absolute FAC density in the PSBL has an obvious positive correlation with the |IMF By|. When |IMF By| is less than 10 nT, there is no correlation between the absolute FAC density and |IMF By|. There is a clear dusk-dawn asymmetry in the current densities for the FACs in the PSBL, with the dawn currents appearing larger than the dusk currents. The FAC with the largest (smallest) density is located in the range of 0100≤MLT<0200 (2100≤MLT<2200).