Observation and modeling of magnetospheric cold electron heating by electromagnetic ion cyclotron waves

Abstract

A cold electron heating event associated with electromagnetic ion cyclotron (EMIC) waves is observed and modeled. The observational data of particles and waves are collected by the Time History of Events and Macroscale Interactions during Substorms spacecraft at magnetic local time 17.0–17.2. During this event, intense He+ band EMIC waves with the peak frequency 0.25 Hz are excited, corresponding to the observed phase space density (PSD) of distinct anisotropic ions. Meanwhile, substantial enhancements in energy flux of cold (1–10 eV) electrons are observed in the same period. The energy flux of electrons below 10 eV is increased by several to tens of times. We use a sum of kappa distribution components to fit the observed ion PSD and then calculate the wave growth rate driven by the anisotropic hot protons. The calculated result is in good agreement with the in situ observation. Then, we investigate whether the excited EMIC waves can transfer energy to cold electrons by Landau resonant absorption and yield electron heating. Using the typical Maxwellian distribution for cold electrons, we evaluate the wave damping rates resulted from the cold electrons in gyroresonance with EMIC waves. The simulating results show that the strong wave growth region in the He+ band induced by anisotropic ions corresponds to the strong wave damping region driven by cold electrons. Moreover, cold electrons can be heated efficiently at large wave normal angles. The current results provide a direct observational evidence for EMIC‐driven cold electron heating—a potential mechanism responsible for stable auroral red arc.