Amplitude Dependence of Nonlinear Precipitation Blocking of Relativistic Electrons by Large Amplitude EMIC Waves. Issue 12 (16th June 2022)

• Record Type: Journal Article
• Authors: Bortnik, Jacob; Albert, Jay M.; Artemyev, Anton; Li, Wen; Jun, Chae‐Woo; Grach, Veronika S.; Demekhov, Andrei G.
• Is Part Of: Geophysical research letters. Volume 49:Issue 12(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-06-16
• Subjects: EMIC -- nonlinear -- wave‐particle interactions -- radiation belts -- precipitation blocking -- force bunching; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2022GL098365
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: Recent work has shown that ElectroMagnetic Ion Cyclotron (EMIC) waves tend to occur in four distinct regions, each having their own characteristics and morphology. Here, we use nonlinear test‐particle simulations to examine the range of energetic electron scattering responses to two EMIC wave groups that occur at low L‐shells and overlap the outer radiation belt electrons. The first group consists of low‐density, H‐band region b waves, and the second group consists of high‐density, He‐band region c waves. Results show that while low‐density EMIC waves cannot precipitate electrons below ∼16 MeV, the high density EMIC waves drive a range of linear and nonlinear behaviors including phase bunching and trapping. In particular, a nonlinear force bunching effect can rapidly advect electrons at low pitch‐angles near the minimum resonant energy to larger pitch angles, effectively blocking precipitation and loss. This effect contradicts conventional expectations and may have profound implication for observational campaigns. Plain Language Summary: Based on a recent study that has shown how ElectroMagnetic Ion Cyclotron (EMIC) waves tend to occur in four distinct regions, we study two of those regions that occur at relatively low L‐shells, and overlap with the intense portion of the outer radiation belt energetic electrons. We use a nonlinear, test particle code to simulate the wave‐particle interaction of energetic electrons with two groups of waves: high‐density, He‐band EMIC waves and low‐density, H‐band EMIC waves. While the low‐density EMIC waves have resonant energies that are too high to affect the typical range of radiation belt electrons, the high‐density EMIC waves drive a range of linear and nonlinear responses in the electrons. In particular, as the EMIC waves get more intense, a nonlinear "force bunching" effect tends to reflect energetic electrons at low pitch angles out of the loss cone, and prevent them from precipitating, contrary to expectations based on quasilinear and (more conventional) nonlinear theory. The precipitation blocking could have profound effects on observational campaigns that attempt to simultaneously measure EMIC waves near the geomagnetic equator, and result in coincident precipitation along the same field line at low altitudes, in that the precipitation could be entirely absent. Key Points: The range of nonlinear responses of energetic electrons interacting with intense ElectroMagnetic Ion Cyclotron (EMIC) waves is studied using a test‐particle code Resonant energetic electrons at low pitch angles experience nonlinear force bunching which rapidly advects them to large pitch angles Increasing EMIC wave amplitudes enhances the force bunching positive advection relative to diffusion resulting in precipitation blocking