*Tatsuki Ogino[1]
Solar-Terrestrial Environment Laboratory, Nagoya University[1]
The magnetic field topology of the Earth's magnetosphere is critically
controlled by solar wind parameters and the interplanetary magnetic
field (IMF) via magnetic reconnection processes. Reconnection
site and reconnection rate are mainly determined by the following
two conditions: how well anti-parallel field condition is satisfied
between the IMF and the terrestrial magnetic field, and how small
the relative shear velocity is kept between the reconnection
field lines. Magnetic reconnection is an important mechanism
to energize and carry the plasma toward the earth as well as
toward the tail.
The magnetic field topology of the Earth's magnetosphere is critically controlled by solar wind parameters and the interplanetary magnetic field (IMF) via magnetic reconnection processes. Reconnection site and reconnection rate are mainly determined by the following two conditions: how well anti-parallel field condition is satisfied between the IMF and the terrestrial magnetic field, and how small the relative shear velocity is kept between the reconnection field lines. Magnetic reconnection is an important mechanism to energize and carry the plasma toward the earth as well as toward the tail. We have studied the magnetic field topology of magnetosphere and its dynamics by a 3-dimensional global MHD simulation of interaction between the solar wind and the magnetosphere. We found that magnetic reconnection favorably occurs in anti-parallel field region with a slower shear velocity in the magnetosheath. For pure northward IMF the terrestrial magnetic fields are almost closed because reconnection simultaneously occurs in northern and southern high latitude tail. When the IMF has a y-component as well as a z-component, open field region appears in the polar cap. It is to be emphasized that the field line configuration of the magnetosphere differs much from the superimposed model of terrestrial magnetic field and a uniform IMF. This is because the magnetic field configuration is also determined by magnetospheric plasma convection as a result of nonlinear processes: based on the the plasma frozen-in assumption the magnetospheric plasma convection is associated with the movement of the merging field lines and the removal of the merging field lines results in a decrease in the magnetic pressure. We have also studied dynamics of magnetic reconnection at the dayside magnetopause and in the magnetotail in detail when the solar wind velocity and magnitude of the IMF change over wide range of parameter by using a high resolution 3-dimensional global MHD simulation. Dayside reconnection rate and cross polar cap potential have a tendency of saturation for a larger electric field in the solar wind. When we look at spatial distributions of the plasma density, pressure, temperature and kinetic energy, and also the kinetic, internal and Poynting vector energy fluxes, it is noted that the kinetic energy quickly converts to internal plasma energy then Poynting flux. Therefore, it need not to find always the strong kinetic energy and kinetic flux on the earth side of NENL. The tail reconnection occurs in a patchy and intermittent manner to bring MHD fluctuations.