Dynamical Processes Of 3D Magnetic Reconnection With External Shear Flow

Magnetic reconnection is an effective mechanism to convert magnetic energy to kinetic and thermal energies and also leads to exchange of mass, momentum, energy between the two sides of the central current sheet. Magnetic reconnection is often cited as an efficient mechanism for many eruptive physical phenomena such as flares in the solar corona, substorms in the Earth’s magnetosphere, and sawtooth oscillations in Tokamaks. In order to invoke magnetic reconnection to explain observational phenomena, the time scale of magnetic reconnection becomes a crucial issue, i.e., the reconnection time scale must be much faster than the diffusion time scale. Since plasma shear flow is ubiquitous in both space and laboratory plasmas, its impact in magnetic reconnection has been of much research interest.Based on the compressible resistive MHD and compressible Hall MHD models, we consider two initial magnetic field geometries, the slab and dipole geometries, to investigate the dynamics of 3D magnetic reconnection.First, we consider the slab magnetic field geometry with the varying thickness of current sheet in the y direction. It is found that the magnetic reconnection in 3D is reduced. The intensity of the associated shocks also decreases with the external shear flow. The structure of the current sheets (i.e., the magnetic reconnection process) is quiet different, but the location and intensity of the shock are almost the same, in the different y planes.Then, the Earth’s dipole magnetic field, is employed to investigate magnetic reconnection driven by the solar wind. Simulation results with the south or north interplanetary magnetic field are consistent with the existing observations. With the inclusion of the Hall effect, the quadrupolar field appears asymmetric. The strength of this Hall field becomes larger and the structure becomes broader as the ion inertial length increases. The z component of the solar wind velocity vswz will not affect the location of the X-point of the magnetic reconnection on the dayside magnetopause, but leads the central plasma sheet of the magnetotail to deviate away from equatorial plane. The reconnection rate and the deviation angle increase with increase of vswz.With inclusion of the y component interplanetary field in the 3D global MHD simulation, it is found that the magnetic field By is built up in the central plasma sheet of the Earth’ magnetotail. When θ= 30° (where BIMFy= BIMF sinθ), the magnetic field By in the plasma sheet is strongest and even larger than the initial imposed BIMFy. Also, BIMFy promotes the reconnection process of the dayside magnetopause. With further increase of θ, the reconnection rate of the dayside magnetopause and the magnetic field By become decrease, and the structure changes significantly.In summary,3D magnetic reconnection dynamics is investigated in detail, the results can be used to analyze observed data.