A mode filter for plasma waves in the Hall-MHD approximation

A filter method is presented which allows a qualitative and quantitative id entification of wave modes observed with plasma experiments on satellites. Hitherto existing mode filters are based on the MHD theory and thus they ar e restricted to low frequencies well below the ion cyclotron frequency. The present method is generalized to cover wave modes up to the characteristic ion frequencies. The spectral density matrix determined by the observation s is decomposed using the eigenvectors of the linearized Hall-MHD equations . As the wave modes are dispersive ill this formalism, a precise determinat ion of the k-vectors requires the use of multi-point measurements. Therefor e the method is particularly relevant to multi-satellite missions. The meth od is tested using simulated plasma data. The Hall-MHD filter is able to id entify the modes excited in the model plasma and to assign the correct ener getic contributions. By comparison with the former method it is shown that the simple MHD filter leads to large errors if the frequency is not well be low the ion cyclotron frequency. Further the range of validity of the linea r theory is examined rising the simulated wave amplitudes.