Electromagnetic waves on ion gyro‐radii scales across the magnetopause

Abstract

This report presents the first study of the global distribution and properties of kinetic scale electromagnetic waves on the Earth's magnetopause. From a statistical study using THEMIS fields observations over a frequency range from 0.01–2 Hz, we find waves on scales of the order of ion gyro‐radii at all magnetic local times surveyed (4–20 MLT). The spectral energy densities (ε) within these waves across the magnetopause are larger on the dawn (4–12 MLT) than duskside (12–20 MLT) irrespective of the direction of the magnetosheath magnetic field BZ_sheath component. Furthermore, these observations reveal that ε is magnetic shear dependent with large enhancements for shear angle >60°. The similarity between dawn‐dusk asymmetry in ε we observe and reported distribution of magnetosheath ions in the magnetosphere suggest that gyro‐radii scale magnetic field structures/waves may facilitate a significant fraction of cross magnetopause plasma transport.