Home » Denton et al. 2019

Pitch Angle Scattering of Sub-MeV Relativistic Electrons by Electromagnetic Ion Cyclotron Waves

Denton R. E., L. Ofman, Y. Y. Shprits, J. Bortnik, R. M. Millan, C. J. Rodger, C. L. da Silva, B. N. Rogers, M. K. Hudson, K. Liu, K. Min, A. Glocer, C. Komar, (2019), Pitch Angle Scattering of Sub-MeV Relativistic Electrons by Electromagnetic Ion Cyclotron Waves, J. of Geophys. Res. [Space Physics], 124, 5610-5626, doi:10.1029/2018JA026384

Abstract

Abstract Electromagnetic ion cyclotron (EMIC) waves have long been considered to be a significant loss mechanism for relativistic electrons. This has most often been attributed to resonant interactions with the highest amplitude waves. But recent observations have suggested that the dominant energy of electrons precipitated to the atmosphere may often be relatively low, less than 1 MeV, whereas the minimum resonant energy of the highest amplitude waves is often greater than 2 MeV. Here we use relativistic electron test particle simulations in the wavefields of a hybrid code simulation of EMIC waves in dipole geometry in order to show that significant pitch angle scattering can occur due to interaction with low-amplitude short-wavelength EMIC waves. In the case we examined, these waves are in the H band (at frequencies above the He+ gyrofrequency), even though the highest amplitude waves were in the He band frequency range (below the He+ gyrofrequency). We also present wave power distributions for 29 EMIC simulations in straight magnetic field line geometry that show that the high wave number portion of the spectrum is in every case mostly due to the H band waves. Though He band waves are often associated with relativistic electron precipitation, it is possible that the He band waves do not directly scatter the sub-megaelectron volts (sub-MeV) electrons, but that the presence of He band waves is associated with high plasma density which lowers the minimum resonant energy so that these electrons can more easily resonate with the H band waves.

Authors (sorted by name)

Bortnik da Silva Denton Glocer Hudson Komar Liu Millan Min Ofman Rodger Rogers Shprits

Journal / Conference

Journal Of Geophysical Research (Space Physics)

Bibtex

@article{10.1029/2018JA026384,
author = {Denton, R. E. and Ofman, L. and Shprits, Y. Y. and Bortnik, J. and Millan, R. M. and Rodger, C. J. and da Silva, C. L. and Rogers, B. N. and Hudson, M. K. and Liu, K. and Min, K. and Glocer, A. and Komar, C.},
title = {Pitch Angle Scattering of Sub-MeV Relativistic Electrons by Electromagnetic Ion Cyclotron Waves},
journal = {Journal of Geophysical Research: Space Physics},
volume = {124},
number = {7},
pages = {5610-5626},
keywords = {electromagnetic ion cyclotron waves, EMIC, relativistic electron precipitation, pitch angle scattering, wave particle interaction, radiation belts},
doi = {https://doi.org/10.1029/2018JA026384},
url = {https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2018JA026384},
eprint = {https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2018JA026384},
abstract = {Abstract Electromagnetic ion cyclotron (EMIC) waves have long been considered to be a significant loss mechanism for relativistic electrons. This has most often been attributed to resonant interactions with the highest amplitude waves. But recent observations have suggested that the dominant energy of electrons precipitated to the atmosphere may often be relatively low, less than 1 MeV, whereas the minimum resonant energy of the highest amplitude waves is often greater than 2 MeV. Here we use relativistic electron test particle simulations in the wavefields of a hybrid code simulation of EMIC waves in dipole geometry in order to show that significant pitch angle scattering can occur due to interaction with low-amplitude short-wavelength EMIC waves. In the case we examined, these waves are in the H band (at frequencies above the He+ gyrofrequency), even though the highest amplitude waves were in the He band frequency range (below the He+ gyrofrequency). We also present wave power distributions for 29 EMIC simulations in straight magnetic field line geometry that show that the high wave number portion of the spectrum is in every case mostly due to the H band waves. Though He band waves are often associated with relativistic electron precipitation, it is possible that the He band waves do not directly scatter the sub-megaelectron volts (sub-MeV) electrons, but that the presence of He band waves is associated with high plasma density which lowers the minimum resonant energy so that these electrons can more easily resonate with the H band waves.},
year = {2019}
}