Two‐dimensional hybrid simulation of the dayside reconnection layer and associated ion transport

The structure of the reconnection layer at the dayside magnetopause is studied by using a two‐dimensional (2‐D) hybrid code. The simulation domain is a rectangle in the xz plane around an X line at the magnetopause. In our previous study the guide magnetic field B y was assumed to be zero. In the present simulation the effects of a finite B y on the reconnection layer are studied. In addition, the influence of shear flows on the magnetic reconnection is also investigated. In the cases with a shear flow speed Δ V = 0, as near the subsolar region, a large‐amplitude rotational discontinuity is present on the magnetosheath side of the reconnection layer, across which the magnetic field changes direction from the magnetosheath to the magnetosphere. A high‐speed accelerated flow is present on the magnetospheric side of the rotational discontinuity. For a higher‐latitude reconnection in the Northern Hemisphere, where a shear flow is present across the magnetopause, the structure of the reconnection layer northward of the X line is very different from that southward. Northward of the X line, the rotational discontinuity with a larger field rotational angle exists on the magnetospheric side if the shear flow speed Δ V > 0.33( V Am − V As ), where V Am and V As are the Alfvén speeds in the magnetosphere and the magnetosheath, respectively. Below the X line, a thin, strong rotational discontinuity is always present on the magnetosheath side. By tracing the orbits of individual ion particles, we have performed a detailed analysis of ion transmission and reflection at the magnetopause. The average transmission (reflection) rate of the magnetosheath ions is found to be ∼ 85% (15%). The reflection of the magnetosheath ions occurs mainly in the inner boundary layer.