On nonlinear decay of kinetic Alfven waves and application to some processes in space plasmas

This paper considers the nonlinear decay of the kinetic Alfven waves (KAW) in the space plasmas. By using a two-fluid model, we obtain a nonlinear equation to investigate the resonant interaction among three kinetic Alfven waves. It is shown that the parametric instability of the kinetic Alfven wave becomes important when its perpendicular wavelength is the order of the ion acoustic gyroradius or the electron inertial length. We give a detailed discussion for the KAW decay in the plasma inertial range and show that (1) the reverse decay of the kinetic Alfven wave is stronger than its parallel decay for the arbitrary wavelength range; (2) the reverse decay is lager than the parallel decay for small angles of two perpendicular wave vectors of the decay waves, and these two decays are zero for large angles; (3) both growth rates depend on the choice of the wave number range of the decay waves; and (4) there exists two forbidden regions for the KAW decay. In this paper, we also discuss the nonlinear decay of the kinetic Alfven waves in the auroral zone and show that the parametric instability can occur there and may play an important role in forming two reverse electron streaming fluxes in the electron acceleration region.