Filamentation instability of MHD waves in solar wind plasma

The ISEE 1 and 2 spacecraft have detected both magnetosonic waves and Alfven waves propagating upstream in the high-speed solar wind. The magnetosonic wave is a hybrid and elliptically polarized mode that can propagate obliquely across the magnetic field. It becomes decoupled from the Alfven wave when the direction of its propagation is exactly perpendicular to the ambient magnetic field. The filamentation instability of the magnetosonic wave that propagates perpendicular to the magnetic field has been analyzed recently. The authors have extended this analysis to the general case of convective filamentation instabilities of obliquely propagating magnetosonic waves. The dispersion relation of the instability has been derived and solved numerically for the dependence of the threshold field and spatial growth rate on the wave number k of the nonoscillatory mode, the β of the plasma, and the frequency of the magnetosonic pump.