ULF wave absorption at Mercury

The field line resonance at Mercury is expected to occur when the ion-ion hybrid (IIH) and/or Alfven resonance conditions are satisfied. However, the relative efficiency of wave energy absorption at these resonances has not been studied in the context of Mercury's magnetosphere. To understand the efficiency of wave absorption, we evaluate absorption coefficients at the IIH and Alfven resonances for variable concentrations of sodium and azimuthal and field-aligned wave numbers in 1D multi-ion plasmas. The results show that wave absorption is much more efficient at the IIH resonance than at the Alfven resonance at Mercury. Our results suggest that the mode conversion efficiency is sensitive to the azimuthal and field aligned wave numbers as well as heavy ion concentration ratio. Therefore, the radial profile of field-line resonances at Mercury can exhibit complex, discontinuous structure. Citation: Kim, E.-H., J. R. Johnson, and K.-D. Lee (2011), ULF wave absorption at Mercury, Geophys. Res. Lett., 38, L16111, doi:10.1029/2011GL048621.