Stability of the magnetospheric boundary

The magnetospheric boundary which is the interface between solar wind and the magnetosphere is viewed as a surface of hydromagnetic Kelvin-Helmholtz discontinuity. The crucial effect of compressibility on its stability is discussed. It is shown that substantial portions of the dayside of the boundary are unstable under all conditions of solar wind. The spatial extent of the instability on the dayside is almost completely independent of the speed and density of solar wind. But it is critically dependent on the angle between the geomagnetic field and the compressed interplanetary field at the boundary. The stability of the nightside of the boundary is dependent on solar wind speed among other factors; the higher the speed, the more extensive is the stable region.