On an energy‐latitude dispersion pattern of ion precipitation potentially associated with magnetospheric EMIC waves

Abstract Ion precipitation mechanisms are usually energy dependent and contingent upon magnetospheric/ionospheric locations. Therefore, the pattern of energy‐latitude dependence of ion precipitation boundaries seen by low Earth orbit satellites can be implicative of the mechanism(s) underlying the precipitation. The pitch angle scattering of ions led by the field line curvature, a well‐recognized mechanism of ion precipitation in the central plasma sheet (CPS), leads to one common pattern of energy‐latitude dispersion, in that the ion precipitation flux diminishes at higher (lower) latitudes for protons with lower (higher) energies. In this study, we introduce one other systematically existing pattern of energy‐latitude dispersion of ion precipitation, in that the lower energy ion precipitation extends to lower latitude than the higher‐energy ion precipitation. Via investigating such a “reversed” energy‐latitude dispersion pattern, we explore possible mechanisms of ion precipitation other than the field line curvature scattering. We demonstrate via theories and simulations that the H‐band electromagnetic ion cyclotron (EMIC) wave is capable of preferentially scattering keV protons in the CPS and potentially leads to the reversed energy‐latitude dispersion of proton precipitation. We then present detailed event analyses and provide support to a linkage between the EMIC waves in the equatorial CPS and ion precipitation events with reversed energy‐latitude dispersion. We also discuss the role of ion acceleration in the topside ionosphere which, together with the CPS ion population, may result in a variety of energy‐latitude distributions of the overall ion precipitation. Key Points We investigate the reversed energy‐latitude dependence of ion precipitations The EMIC wave is found as one principal mechanism of the reversed‐type events Ion acceleration in topside ionosphere also contributes to reversed‐type events