Efficient estimation of MHD parameters from magnetosheath observations

Abstract:

We present an approach to estimate the solar wind characteristics, the magnetic diffusivity as well as the planetary magnetic field parameters of an MHD model from magnetosheath spacecraft data. An approximation of the model is used to examine the dependence of observable magnetosheath properties on the model parameters. An analytical expression for the bow shock distance is derived which depends on the planetary magnetic field. A spacecraft, crossing the bow shock, measures the solar wind conditions postshock and the shock’s location. This data is used to estimate the planetary field parameters. The magnetic field and density distribution close to the magnetopause are used to estimate the local plasma resistivity which is essential to distinguish between Hall reconnection and reconnection due to anomalous resistivity. Our model is used to reconstruct the solar wind parameters from spacecraft data during a magnetosheath passage. To obtain a more precise estimate of the parameters, a complete magnetosheath MHD simulation can be used. We present the results for the dipole and quadrupole moments of the Earth, estimated from magnetosheath observations. The dipole and quadrupole parameters are varied until the simulation results match the observations. To perform the time-consuming minimization procedure, we use an adjoint approach.