Solar-wind control of the hot oxygen corona around Mars

摘要

The global behavior and escape rate of hot oxygen atoms around Mars and their response to different solar wind dynamic pressure (P SW) conditions are investigated using a multidimensional time-dependent magnetosheath-ionosphere-exosphere (Msh-I-E) coupling model. Recently we reported that an increase in P SW leads to a short-term increase in the escape rate of nonthermal oxygen using a one-dimensional (1-D) Msh-I-E model. The model used in the present paper is a multidimensional version of our previous 1-D model. For the exosphere model, we adopt a three-dimensional Monte Carlo approach above a 250-km altitude, while a time-dependent two-stream approach is employed below 250 km. The exosphere model is coupled with a two-dimensional resistive magnetohydrodynamic model of the magnetosheath-ionosphere interaction, assuming axial symmetry with respect to the Sun-Mars line. The results of the present model are consistent with the results of the 1-D model. The escape rate of hot oxygen for P SW = 0.36 nPa is roughly twice that for P SW = 1.43 nPa under steady state conditions. For nonstationary conditions, where P SW is suddenly increased from 0.36 to 1.43 nPa, the escape rate is temporarily enhanced by a factor of 2.3 to 4.5 compared with that of the steady state case. The hot oxygen density is found to be less dependent on P SW than is the escape rate.