Excitation of oblique Alfven waves by a parametric whistler instability in the near-earth plasma

A three-wave decay process with participation of two whistlers and an oblique Alfven wave is considered. It is shown that the contribution of Alfven-wave dispersion leads to a sharp increase in the interaction coefficients due to the component of the nonlinear current that is longitudinal with respect to the external magnetic field. The most efficient decay is the one in which a mirror-type whistler wave participates. The instability increment is estimated to be 1/sec for a whistler pump amplitude of 0.3 mV/m in the magnetosphere at L = 4.