Simulation of interplanetary magnetic field B_y penetration into the magnetotail

Based on our global 3D magnetospheric MHD simulation model, we investigate the phenomena and physical mechanism of the B_y component of the interplanetary magnetic field (IMF) penetrating into the magnetotail. We find that the dayside reconnected magnetic field lines move to the magnetotail, get added to the lobe fields, and are dragged in the IMF direction. However, the B_y component in the plasma sheet mainly originates from the tilt and relative slippage of the south and north lobes caused by plasma convection, which results in the original B_z component in the plasma sheet rotating into a B_y component. Our research also shows that the penetration effect of plasma sheet B_y from the IMF B_y during periods of northward IMF is larger than that during periods of southward IMF.