SIMULATION OF HIGH-FREQUENCY SOLAR-WIND POWER SPECTRA USING HALL MAGNETOHYDRODYNAMICS

Solar wind frequency spectra show a distinct steepening of the f(-5/3) power law inertial range spectrum at frequencies above the Doppler-sh ifted ion cyclotron frequency. This is commonly attributed to dissipat ion due to wave-particle interactions. We consider the extent to which this steepening can be described, using a magnetohydrodynamic formula tion that includes the Hall term. An important characteristic of Hall MHD is that although the ion cyclotron resonance is included, there is no wave-particle dissipation of energy. In this study we use a compre ssible Hall MHD code with a constant magnetic field and a polytropic e quation of state. Artificial dissipation in the form of a bi-laplacian operator is used to suppress numerical instabilities, allowing for a clear separation of the dissipative scales from the ion cyclotron scal es. A distinct steepening appears in the simulation power spectra near the cyclotron resonance for certain types of initial conditions. This steepening is associated with the appearance of right circularly pola rized fluctuations at frequencies above the ion cyclotron resonance. S imilar steepenings and polarization enhancements are observed in solar wind magnetic held data.