Evidence for plasma transport via kinetic Alfven waves at the magnetopause: An event study of THEMIS observations

We investigated the plasma transport induced by kinetic Alfven waves (KAWs) as a candidate process of efficient plasma entry across the magnetopause during northward IMF periods. Due to the lack of observational evidence based on particle data, it remains unclear even whether KAWs really transport the plasma into the magnetosphere. First we show the physical process of the plasma transport via KAWs including the finite beta effect. A particle satisfying Cerenkov resonance condition experiences ExB drift via parallel electric field fluctuations and gradient-B drift via parallel magnetic field fluctuations, both resulting in cross-field transport. This process occurs selectively for particles in a specific velocity space. Then we report THEMIS observations of the dayside magnetopause at which kinetic Alfven turbulence exists. By comparing ion velocity distribution functions obtained in the magnetosheath and the low-latitude boundary layer, we found that cold ions in the low-latitude boundary layer result from the selective transport of the magnetosheath ions as expected from the theory of the KAW-induced transport. This is the first time to show by particle data that KAWs can indeed transport plasma across the magnetopause.