Magnetic Reconnection With a Fast Perpendicular Sheared Flow

<p> Magnetic reconnection at the Earth's low&hyphen;latitude magnetopause near the flank region is likely associated with a large sheared flow, being frequently quasi&hyphen;perpendicular to the antiparallel magnetic field components. The magnitude of a fast sheared flow can be super&hyphen;Alfv&eacute;nic and even overcome the local fast mode speed. A scaling analysis implies a contradiction between the Wal&eacute;n relation and the balance of the total pressure for magnetic reconnection with a supercritical perpendicular sheared flow. This study uses one&hyphen; and two&hyphen;dimensional magnetohydrodynamic (MHD) simulations to demonstrate that the traditional reconnection layer violates the Wal&eacute;n relation but still maintains the total pressure balance in such a configuration. The results show an expanded outflow region, consistent with the presence of divergent normal flow, and a significant decrease of the plasma density as well as the thermal pressure in the outflow region. In contrast, the magnitude of the magnetic field in the outflow region matches the value in the inflow region due to the total pressure balance, which is fundamentally different from the classical reconnection layer under sub&hyphen;Alfv&eacute;nic perpendicular sheared flow conditions. In three&hyphen;dimensional geometry, the fast sheared flow without being stabilized by the magnetic field is expected to be Kelvin&hyphen;Helmholtz unstable. However, the three&hyphen;dimensional MHD simulation suggests that such structure can be KH stable. Although, the presence of surface waves modulates some two&hyphen;dimensional features, the major characteristics of the expanded outflow region are likely to be observed by in situ satellites.</p>