Magnetohydrodynamic waveguide/resonator for Pc3 ULF pulsations at cusp latitudes

We present a possible theoretical model for the generation of travelling Al fven waves by external compressional disturbances in a two-dimensional inho mogeneous plasma. The transformation of a compressional wave mode into Alfv en waves guided by the magnetic field is considered in a region with decrea sed Alfven velocity. This region represents, on the one hand, a waveguide f or compressional oscillations, and on the other hand, a resonator with opaq ue boundaries for Alfven waves. The wave transformation is most effective i n a resonant case, when the frequency of a compressional mode approaches th e local Alfven frequency of a resonator. This model is applied to the inter pretation of Pc3 observations in the cusp region. The mechanism can ensure the selective amplification of magnetosheath turbulence in the Pc3 band in the high-latitude cusp.