Hydromagnetic stability of the magnetospheric boundary

The problem of the stability of the interface between the solar wind and the magnetosphere is investigated by means of hydromagnetic equations. An explicit criterion of instability is written for the special case in which both the solar plasma and the magnetospheric medium are supposed to be of the same density and carry a uniform magnetic field in the direction of streaming. It is concluded that the magnetospheric boundary is likely to be unstable toward the tail and under comparatively quiet solar conditions. It is suggested that the characteristic effects of instability should be observed toward the night side, preferably with space exploration vehicles.