MHD WAVES GENERATED BY THE KELVIN-HELMHOLTZ INSTABILITY IN A NONUNIFORM MAGNETOSPHERE

A linear analysis of the Kelvin-Helmholtz instability is performed by assuming that one of the plasma regimes (magnetosphere) separated by a velocity shear layer of zero thickness is spatially nonuniform. The p revious theories based on the semi-infinite uniform model with infinit esimally thin magnetopause showed that wave growth due to the Kelvin-H elmholtz instability exhibits monotonic increase for shorter frequency . This finding implies that no monochromatic waves whose spatial scale s are as large as the magnetospheric size are generated by the Kelvin- Helmholtz instability. In contrast, the present analysis reveals that the Kelvin-Helmholtz instability generates global-scale monochromatic waves when the magnetosphere is nonuniform and the magnetosheath flow speed is quite fast. The wave number is given through the dispersion r elation of the Kelvin-Helmholtz unstable wave.