Simulation of mode conversion at the magnetopause

Two-dimensional (2-D) and three-dimensional (3-D) hybrid simulations are carried out for mode conversion from fast mode compressional wave to kinetic Alfven waves (KAWs) at the inhomogeneous magnetopause boundary. For cases in which the incident fast wave propagates in the xz plane, with the magnetopause normal along x and the background magnetic field pointing along z, the 2-D (xz) simulation shows that KAWs with large wave number k(x)rho(i) similar to 1 are generated near the Alfven resonance surface, where rho(i) is the ion Larmor radius. Several nonlinear wave properties are manifest in the mode conversion process. Harmonics of the driver frequency are generated. As a result of nonlinear wave interaction, the mode conversion region and its spectral width are broadened. In the 3-D simulation, after this first stage of the mode conversion to KAWs with large k(x), a subsequent generation of KAW modes of finite k(y) is observed in the later stage, through a nonlinear parametric decay process. Since the nonlinear cascade to k(y) can lead to massive transport at the magnetopause, the simulation results provide an effective transport mechanism at the plasma boundaries in space as well as laboratory plasmas.