AN EMPIRICAL-MODEL OF THE SOLAR-WIND FLOW AROUND MARS

An empirical model that describes the proton velocity around Mars has been developed. The analytical axially symmetric model is based on Aut omatic Space Plasma Experiment with a Rotating Analyzer three-dimensio nal (3-D) proton velocity observations on the Phobos 2 spacecraft near Mars in early 1989. The model includes a bow shock, a magnetopause, a nd an impenetrable obstacle a few hundred kilometers above the surface of Mars. The flow model can be used to model both an open and a close d magnetosphere. The model velocity values are found to describe rathe r well the 3-D proton velocity observations in the Martian magnetoshea th and magnetosphere both on the dayside and on the nightside. Charact eristics of the velocity field are studied on the basis of an ideal MH D model, assuming that the magnetic field is frozen into the proton fl ow and that there are no proton sources or sinks. Under these assumpti ons the velocity field can be used to calculate the proton density and the magnetic field. When the proton density and the magnetic field ar e compared with the observations, quite good qualitative agreement bet ween the model and the data is found. Our model shows that a relative simple flow model can predict several observed plasma and field featur es near Mars.