Magnetohydrodynamic mode coupling at a large-density jump

Reflection and transmission of MHD waves when a fast wave is incident on an interface across which the density changes by a factor on the order of 100 is investigated. The gas pressure is assumed to be negligible in comparison with the pressure of a uniform magnetic field. Rather than lengthy computations of the exact reflection and transmission coefficients, the results can be approximated by the use of some simple physical concepts. That is, the transformation of the fast mode to the Alfven mode at the interface can be explained in terms of polarization matching. The transmitted wave (or reflected wave) whose electric and magnetic vectors best match the incident perturbations should carry a larger portion of the flux than the other secondary waves. Using only the continuity of the electric field, the efficiency of coupling is adequately gaged by considering how well wave's electric field matches the incident wave's electric field. This polarization matching of the electric fields is refined, and an intuitively appealing method for estimating reflection and transmission coefficients is developed. This method is accurate and much faster than an exact numerical code. 8 refs