Kinetic scale field line resonances: A comparison of kinetic simulations and Van Allen probes observations.

Using Van Allen probes data, Chaston et al. (2014) established the existence of field line resonances in the inner magnetosphere on ion gyroradius scale lengths. One of the key features of the electron distributions associated with these resonances is a pronounced elongation in the direction of parallel velocity (e.g. Chaston et al., 2015). In this work, we use a hybrid gyrofluid-kinetic electron model in dipolar coordinates (Damiano et al., 2015), that has seen extensive use in the study of large-scale field line resonances in the outer magnetosphere (e.g. Damiano and Johnson, 2012), to consider the case of these kinetic scale resonances. The simulations are initialized using eigenmode solutions of the perpendicular electric field perturbation associated with both fundamental and higher order standing modes for plasma and wave parameters consistent with the observations. We illustrate that the electron distributions seen in the Van Allen probes data appear consistent with that resulting from electrons trapped in the potential associated with the standing wave. The evolution of the trapped electron populations within these waves is presented and their effects of on the wave evolution is discussed.