That Can Make The Magnetic Layer Top Global Mhd Simulation Study

A three-dimensional adaptive magnetohydrodynamic (MHD) model is used to examinethe relation of the solar wind and the magnetopause size and shape as well as the energy flowfrom the solar wind to the magnetosphere. The magnetopause is identified with the plasmavelocity and density, the current density, and the solar wind streamlines. A three-dimensionalsurface function is constructed based on empirical model which allow description of theglobal magnetopause size and shape as well as the cusp geometry, and then study thevariation of the magnetopause changing with the solar wind. With the magnetopause wedirectly compute fluxes of mechanical and electromagnetic energy across the magnetopausesurface. The main interesting results in this thesis are as follows:1. The numerical results from a physics‐based global magnetohydrodynamic (MHD)model are used to examine the relationship between the shape and size of themagnetopause and the solar wind conditions. The magnetopause location isidentified by tracing three‐dimensional streamlines through the simulation domainand is fitted by simple analytical functions. The resulting model is applicable forapproximating magnetopause location for dipole tilt angle～0°and interplanetarymagnetic field (IMF) BXand BY=0nT at both low and high magnetosphericlatitudes. In both regions the results are compared with available empirical models.It is shown that IMF BZmainly affects the flaring angle (the magnetopause shape)and has smaller effects on the magnetopause size. In contrast, the solar wind PDmainly affects the magnetopause standoff distance (magnetopause size) and haslittle effect on the magnetopause shape. Both conclusions are consistent withempirical models.2. Numerical results from a physics-based global magnetohydrodynamic (MHD)model are used to examine the effect of the dipole tilt angle (ψ) on the location andshape of the magnetopause. Identification of the magnetopause location in thesimulation domain is automated using criteria based on the current density and theshape of the streamlines. These data are fitted with a three-dimensional surface controlled by10configuration parameters which allow description of the cuspgeometry as well as the asymmetry in the Z direction and the azimuthal asymmetryof the magnetopause. Effects of dipole tilt angle on the configuration parameters areanalyzed from a series of simulations for southward IMF and different dipole tiltangle values. It is found that dipole tilt angle has little impact on the equatorialmagnetopause but significantly affects the cusp locations and the degree ofasymmetry between the Northern and Southern hemispheres and theequatorial/meridional plane. The results are shown to be consistent with threefrequently used empirical models derived from satellite observations.3. Numerical results from a physics-based global magnetohydrodynamic (MHD)model are used to investigate the controlling effects of the interplanetary magneticfield (IMF) components, BYand BZ, on the location and shape of the magnetopause.The subsolar magnetopause is identified by using the plasma velocity and density,the cusp by using the current density, and the other area by streamlines and thecurrent density. These data are fitted with a three dimensional surface functionconstructed by Liu et al.[2012], which allows description of the cusp geometry aswell as the Z asymetry and azimuthal asymmetry of the magnetopause. A newparameter is introduced to describe the orientation of the elliptical cross-section ofthe magnetopause which depends on the IMF BY. Effects of IMF BYand BZon themagnetopause configuration parameters are analyzed and dependence of themagnetopause parameters in the IMF components are obtained. Magnetopausecross-section is found to be largely controlled by the IMF clock angle. Increasing BZor BYincreases the eccentricity of the magnetopause cross-section, and this effect islarger for southward IMF than for the northward IMF. Also, the stretching effect ofBYis smaller than that of BZ.4. For northward IMF most of the energy flux inflow occurs near the polar cusps onmagnetopause. Some plasma enters into plasma sheet, generating cooler and denserplasma near the flanks of plasma sheet. For southward IMF the largest electromagnetic energy input into the magnetosphere occurs at the tail lobe behindthe cusps, and largest mechanical energy input occurs at near-equatorial daysidemagnetopause. Under southward IMF conditions, mechanical energy transfer isenhanced at the flanks of magnetopause in response to increased IMF magnitude,while more electromagnetic energy input can be identified as increasing solar winddensity. Our results suggest that the mechanisms proposed to energy transfer aremainly due to reconnection and viscous interaction processes for northward IMF.For southward IMF reconnection is the dominant factor in energy transfer. If theelectromagnetic energy coupling between the solar wind and the magnetosphere canbe interpreted as a proxy for the reconnection efficiency, the average efficiencyduring northward IMF is about20%of that for southward IMF under the solar windconditions we considered.