Magnetic field structures on ion gyro-radius scale across the magnetopause

Magnetic field structures on gyro-radii scales across the magnetopause can facilitate the transport of magnetosheath plasmas into magnetosphere. From a statistical study using THEMIS observations we find these structures are observed at all magnetic local times surveyed (4-20 MLT). During periods of southward-directed magnetosheath magnetic field (Bsheath) spectral energy densities (ɛ) within these field structures across the magnetopause and boundary layer are larger on the dawn than duskside. A similar, albeit weaker asymmetry is observed during northward Bsheath along the magnetopause and extending out into the magnetosheath with enhanced ɛ from ∼8-13 MLT. Furthermore, these observations reveal that ɛ is magnetic shear dependent with large enhancements for shear angle >60°. The similarity between dawn-dusk asymmetry in ɛ we observe and reported distribution of magnetosheath ions in the magnetosphere suggest that gyro-radii scale magnetic field structures may facilitate a significant portion of cross magnetopause plasma transport.