Observation And Numerical Studies Of Suprathermal Electron Evolution In Earth's Plasmaspheric Plume

Suprathermal electrons are a major heat source of ionospheric plasma.The ionospheric plasma temperature variation can affect the escape of the Earth's atmospheric particles and decay of spacecraft's orbit.How these suprathermal electrons evolve during their bounces is a fundamental question for the magnetosphere-ionosphere coupling.During geomagnetically active times,the plasmaspheric suprathermal electrons are envisioned to conduct the heat flux from the ring current ions to the ionospheric thermal plasma.Two leading physical processes have been proposed for such energy transfer.One is the classical Coulomb collisional scattering of the plasmaspheric suprathermal electrons by the ring current ions.The other is the Landau heating of the plasmaspheric suprathermal electrons by the electromagnetic ion cyclotron waves growing from instabilities of the ring current ions.In contrast,little attention has been paid to the possible energy transfer between the ring current electrons and the plasmaspheric suprathermal electrons.Whistler mode hiss waves can be excited by the ring current electrons in the plasmasphere,and these waves are expected to subsequently transfer part of their energy to the plasmaspheric suprathermal electrons through the Landau resonance?In this paper,we present the detailed work of the suprathermal electron evolution in the plasmaspheric plume.On the basis of Van Allen Probes observations and quasi-linear simulations,we present here the first quantitative study on the evolution of suprathermal electrons under the competition between Landau heating by whistler mode hiss waves and Coulomb collisional cooling by background plasma inside a plasmaspheric plume.We show that the Landau heating can prevail over the collisional cooling for>50 eV electrons and cause the field-aligned suprathermal electron fluxes to increase by up to 1 order of magnitude within 1.5 hr.Our results imply that the plasmaspheric plume hiss waves could mediate energy from the ring current electrons to the ionospheric plasma.