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 previous theories based on the semi‐infinite uniform model with infinitesimally thin magnetopause showed that wave growth due to the Kelvin‐Helmholtz instability exhibits monotonic increase for shorter frequency. This finding implies that no monochromatic waves whose spatial scales 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 relation of the Kelvin‐Helmholtz unstable wave.