Global hybrid simulation of the dayside reconnection layer and associated field-aligned currents

Abstract

A two-dimensional global hybrid simulation is carried out to study the structure of the magnetopause boundary layer in the noon-midnight meridian plane associated with the dayside reconnection. In the simulation the bow shock, magnetosheath, and magnetopause are formed self-consistently by supersonic solar wind passing the geomagnetic field. The dayside reconnection is triggered by imposing a current-dependent resistivity at the subsolar magnetopause. A large-amplitude rotational discontinuity is formed in the quasi-steady reconnection layer in the northern and southern hemispheres. The rotational discontinuity possesses an electron sense, or right-hand polarization in the magnetic field as the discontinuity is formed from the X line, and the magnetic structures in the magnetopause northward and southward of the X line are asymmetric in the cases with a nonzero B-y component of the interplanetary magnetic field (IMF). However, later the rotational discontinuity tends to evolve to a structure with a smallest field rotational angle and thus may reverse its sense of the field rotation. The Walen relation is tested for electron and ion flows in the magnetopause rotational discontinuities with left-hand and right-hand polarizations. Field-aligned currents are generated in the magnetopause rotational discontinuity during the reconnection, and nearly 5% of the magnetopause currents propagate with Alfven waves along the field lines into the polar ionosphere. In addition, a weak secondary rotational discontinuity or Alfven wave pulse propagates from the reconnection site into the magnetosphere. The sense of the field-aligned currents is investigated for various values of the IMF B-y. The Hall effects on the structure of the magnetopause boundary layer and the field-aligned currents are discussed.