Observations of relativistic electron precipitation due to combined
scattering of whistler-mode and EMIC waves
Abstract
The two most important wave modes responsible for energetic electron
scattering to the Earth’s ionosphere are electromagnetic ion cyclotron
(EMIC) waves and whistler-mode waves. In this study, we report direct
observations of energetic electron (from 50 keV to 2.5 MeV) scattering
driven by the combined effect of whistler-mode and EMIC waves using
ELFIN measurements. We analyze several events exhibiting such
properties, and show that electron resonant interactions with
whistler-mode waves may enhance relativistic electron precipitation by
EMIC waves. During a prototypical event which benefits from conjugate
THEMIS measurements, we demonstrate that below the minimum resonance
energy (Emin) of EMIC waves, the whistler-mode wave may both scatter
electrons into the loss-cone and also accelerate them to higher energy
(1-3 MeV). These accelerated electrons above Emin resonate with EMIC
waves that, in turn, quickly scatter those electrons into the loss-cone.
This enhances relativistic electron precipitation beyond what EMIC waves
alone could achieve.