The ion cyclotron anisotropy instability and the inverse correlation between proton anisotropy and proton beta

Magnetosheath observations have shown an inverse correlation between the proton temperature anisotropy and the parallel proton β. Computer simulations have produced similar correlations and have demonstrated that they are due to wave‐particle scattering by ion cyclotron anisotropy instabilities. Three derivations of this correlation in an electron/proton plasma yield physical insight into this relationship.