Effects of magnetic reconnection in the Kelvin-Helmholtz instability at the magnetospheric boundary

MHD simulation study is performed to investigate the evolution of the Kelvin-Helmholtz (KH) instability and the effects of magnetic reconnection at the magnetopause boundary. The long-term evolution is markedly different according to the initial configuration of the terrestrial and interplanetary magnetic fields. Highly distorted magnetic field lines due to the KH instability become reconnected and flattened so that they resume the straight field line structure when the terrestrial magnetic field and the interplanetary magnetic field are parallel to each other and the intensity of the involved magnetic field is weak. The detached magnetic islands are transported toward the magnetosheath region and suffer local reconnections. On the other hand, when the intensity of the magnetic field is increased but the Kelvin-Helmholtz instability condition is still satisfied, the wavy field lines due to the KH instability straighten without involving magnetic reconnection. When the terrestrial and interplanetary magnetic fields are anti-parallel to each other, magnetic reconnection occurs early but the strong plasma flow makes the magnetic islands flatter as time develops. No steady reconnection is observed in this case. Instead, neighboring magnetic islands merge together. Momentum transport is most effective in the parallel field case with magnetic reconnection among the three cases considered here. Reduction of the velocity shear is also most prominent in this case.