Effect of By in three-dimensional reconnection at the dayside magnetopause

Asymmetric magnetic reconnection with a non-zero B-y component is studied using a three-dimensional magnetohydrodynamic simulation and the results are interpreted in terms of the dayside reconnection at the magnetopause. The B-y component is implemented by rotating the magnetosheath field. It is seen that a magnetic bulge is formed in the magnetosheath region but displaced in the y direction due to the tilted magnetic field line geometry of reconnection. The bulge moves away from the reconnection region along the magnetopause with a speed significantly slower than that of the symmetric case. In fact, the reconnection rate is seen much slower than the symmetric case. It is also seen that the reconnection rate decreases as the angle of rotation increases. The discontinuity associated with magnetic reconnection geometry is identified as a slow shock with Alfven waves attached to it on the magnetospheric side, while on the magnetosheath side an intermediate shock is seen, which evolves into a slow shock and a rotational discontinuity near the center of the bulge and near the y-directional edges of the current disruption region. A large B-y component is generated on the open field lines, exceeding the initial sheath B-y near the center of the bulge. The inflow mass flux into the reconnection region from the magnetosheath is seven times larger than that from the magnetosphere in the present study, while the outflow mass flux into the magnetosphere is five times larger than that into the magnetosheath, implying that a significant mass transfer occurs from the magnetosheath into the magnetosphere. The outflow plasmas move mostly along the magnetic field lines in the downstream and transported toward the polar region. (C) 2002 American Institute of Physics.