EMIC Wave Energy Dissipation as a Source of O⁺ Conics and Warm Plasma Cloak in the Earth's Inner Magnetosphere

This study focuses on a specific source of the O+ conics and warm plasma cloak in the Earth's inner magnetosphere due to electromagnetic ion cyclotron (EMIC) wave energy dissipation. We analyze the EMIC wave event observed by Van Allen Probe-A in the early afternoon off equatorial magnetosphere on 18 November 2015, where the two dominant EMIC wave bands, He+-band and H+-band, were observed for similar to 4 min. All the wave and plasma parameters, the DC magnetic field, and ion distributions needed for our analysis are taken from the Van Allen Probe-A observations during the event. The major results of our analysis are as follows. (a) The H+ and He+ heating by EMIC waves is negligible. (b) A strong heating of O+ by the wave energy dissipation around the third, fifth, and sixth harmonics of the O+ gyrofrequency is revealed, where the majority of energy dissipated goes into heating of O+ with the energies less than or similar to 100 eV and pitch angles similar to 20 degrees-90 degrees. The estimated energy deposition rate is similar to 0.1-3.4 eV/s per O+, totaling to the deposition of similar to 20-800 eV per O+ during the event. (c) EMIC waves substantially contribute to the formation of O+ conics and warm plasma cloak by heating the upgoing low-energy ionospheric O+ because waves heat ions with the energies and pitch angles that are characteristic of conics and warm plasma cloak, and the energy deposition per O+ is comparable to those characteristic energies.