C.: Different Alfvén wave acceleration processes of electrons

Abstract. Recent statistical studies show the existence of an island of cavities and enhanced electric field structures at 4–5RE radial distance in the evening and midnight mag-netic local time (MLT) sectors in the auroral region during disturbed conditions, as well as ion beam occurrence fre-quency changes at the same altitude. We study the possi-bility that the mechanism involved is electron Landau reso-nance with incoming Alfvén waves and study the feasibility of the idea further with Polar electric field, magnetic field, spacecraft potential and electron data in an event where Po-lar maps to a substorm over the CANOPUS magnetometer array. Recently, a new type of auroral kilometric radiation (AKR) emission originating from ∼2–3RE radial distance, the so-called dot-AKR emission, has been reported to occur during substorm onsets and suggested to also be an effect of Alfvénic wave acceleration in a pre-existing auroral cavity. We improve the analysis of the dot-AKR, giving it a unified theoretical handling with the high-altitude Landau resonance phenomena. The purpose of the paper is to study the two types of Alfvénic electron acceleration, acknowledging that they have different physical mechanisms, altitudes and roles in substorm-related auroral processes. Key words. Magnetospheric physics (storms and sub-storms; auroral phenomena) – Space plasma physics (wave-particle interactions)