MHD Simulation Of Energy Transfer Across The Magnetopause

A three-dimensional adaptive magnetohydrodynamic (MHD) model is used to examine the energy flow from the solar wind to the magnetosphere. Using the model we directly compute fluxes of mechanical and electromagnetic energy across the magnetopause surface quantificationally. The magnetopause is determined by finding approximately the inner edge of the void encompassed by the solar wind stream lines. The main interesting results in this thesis are as follows:(1) Under steady-state conditions:For northward IMF, most of the energy flux inflow occurs near the polar cusps on magnetopause. The viscous interaction leads the carrying energy plasma enter into high latitudes of the tail magnetopause and then divert to low-latitude regions tangentially, where the plasma gets cooler and denser near the flanks of plasma sheet. For southward IMF the largest electromagnetic energy input into the magnetosphere occurs at the tail lobe behind the cusps, and largest mechanical energy input occurs at near-equatorial dayside magnetopause. Under southward IMF conditions, mechanical energy transfer is enhanced at the flanks of magnetopause in response to increased IMF magnitude, while more electromagnetic energy input can be identified as increasing solar wind density. Our results suggest that the mechanisms proposed to energy transfer are mainly due to reconnection and viscous interaction processes for northward IMF. For southward IMF reconnection is the dominant factor in energy transfer. Under3nPa and5nT condition,1.7%of the solar wind energy impinging on magnetopause transfers into magnetosphere for northward IMF, while the magnetopause transfer rate increases to4.3%for southward IMF. If the electromagnetic energy coupling between the solar wind and the magnetosphere can be interpreted as a proxy for the reconnection efficiency, the average efficiency during northward IMF is about20% of that for southward IMF under the solar wind conditions we considered.(2) The energy flow from the solar wind to the magnetosphere in response to sudden turnings of the interplanetary magnetic field (IMF) on5June1998:During this dynamic period, the size of magnetospheric cavity was changing in response to solar wind dynamic pressure and the energy input was highly variable. Due to the significant dipole tilt angle during the event, the distribution of energy transfer between the two hemispheres of magnetopause was asymmetrical, with most energy transferred in the north hemisphere sunward of XGSE>0Re. The electromagnetic and mechanical energy inputs increase rapidly after the arrival of an interplanetary shock, while the electromagnetic energy rises much more slowly following a southward IMF turning. With a nearly invariable by component of IMF, under southward IMF the most electromagnetic energy is transferred near the plane anti-parallel to IMF clock angle. In contrast, for northward IMF it is mostly transferred near the plane perpendicular to IMF clock angle for northward IMF. The most significant mechanical energy input occurs in the polar cusp of north hemisphere for northward IMF and near equatorial plane of dayside magnetopause for southward IMF. Analyzing the distribution of the Poynting flux we infer that they are in terms of simultaneous occurrence of the two types of the high-latitude reconnections on the magnetopause under northward IMF with a large By component. It is also shown that the traditional energy transfer parameters from solar wind conditions do not include any of residual or hysteresis effects; therefore sometimes they do not reflect the right response to the solar wind variations.