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Resonant scattering of plasma sheet electrons leading to diffuse auroral precipitation: 1. Evaluation for electrostatic electron cyclotron harmonic waves

Ni B., R. M. Thorne, R. B. Horne, N. P. Meredith, Y. Y. Shprits, L. Chen, W. Li, (2011), Resonant scattering of plasma sheet electrons leading to diffuse auroral precipitation: 1. Evaluation for electrostatic electron cyclotron harmonic waves, J. of Geophys. Res. [Space Physics], 116, doi:10.1029/2010JA016232

Abstract

Using statistical wave power spectral profiles obtained from CRRES and the latitudinal distributions of wave propagation modeled by the HOTRAY code, a quantitative analysis has been performed on the scattering of plasma sheet electrons into the diffuse auroral zone by multiband electrostatic electron cyclotron harmonic (ECH) emissions near L = 6 within the 0000–0600 MLT sector. The results show that ECH wave scattering of plasma sheet electrons varies from near the strong diffusion rate (timescale of an hour or less) during active times with peak wave amplitudes of an order of 1 mV/m to very weak scattering (on the timescale of 1 day) during quiet conditions with typical wave amplitudes of tenths of mV/m. However, for the low-energy (∼100 eV to below 2 keV) electron population mainly associated with the diffuse auroral emission, ECH waves are only responsible for rapid pitch angle diffusion (occasionally near the limit of strong diffusion) for a small portion of the electron population with pitch angles αeq 20°, dependent on electron energy and geomagnetic activity level. ECH scattering alone cannot account for the rapid loss of plasma sheet electrons during transport from the nightside to the dayside, nor can it explain the formation of the pancake electron distributions strongly peaked at αeq 70°. Computations of the bounce-averaged coefficients of momentum diffusion and (pitch angle, momentum) mixed diffusion indicate that both mixed diffusion and energy diffusion of plasma sheet electrons due to ECH waves are very small compared to pitch angle diffusion and that ECH waves have little effect on local electron acceleration. Consequently, the multiple harmonic ECH emissions cannot play a dominant role in the occurrence of diffuse auroral precipitation near L = 6, and other wave-particle interaction mechanisms, such as whistler mode chorus-driven resonant scattering, are required to explain the global distribution of diffuse auroral precipitation and the formation of the pancake distribution in the inner magnetosphere.

Authors (sorted by name)

Chen Horne Li Meredith Ni Shprits Thorne

Journal / Conference

Journal Of Geophysical Research (Space Physics)

Acknowledgments

This research was supported by NSF grant ATM‐0802843 and also by 09‐LR‐04116720‐SHPY. The authors thank the World Data Center for Geomagnetism, Kyoto, for providing the AE index.

Grants

09‐LR‐04116720 ATM‐0802843

Bibtex

@article{doi:10.1029/2010JA016232,
author = {Ni, Binbin and Thorne, Richard M. and Horne, Richard B. and Meredith, Nigel P. and Shprits, Yuri Y. and Chen, Lunjin and Li, Wen},
title = {Resonant scattering of plasma sheet electrons leading to diffuse auroral precipitation: 1. Evaluation for electrostatic electron cyclotron harmonic waves},
journal = {Journal of Geophysical Research: Space Physics},
volume = {116},
year = {2011},
number = {A4},
pages = {},
keywords = {diffuse auroral precipitation, resonant wave-particle interactions, electrostatic electron cyclotron harmonic waves, quasi-linear diffusion coefficients},
doi = {10.1029/2010JA016232},
url = {https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2010JA016232},
eprint = {https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2010JA016232},
abstract = {Using statistical wave power spectral profiles obtained from CRRES and the latitudinal distributions of wave propagation modeled by the HOTRAY code, a quantitative analysis has been performed on the scattering of plasma sheet electrons into the diffuse auroral zone by multiband electrostatic electron cyclotron harmonic (ECH) emissions near L = 6 within the 0000–0600 MLT sector. The results show that ECH wave scattering of plasma sheet electrons varies from near the strong diffusion rate (timescale of an hour or less) during active times with peak wave amplitudes of an order of 1 mV/m to very weak scattering (on the timescale of 1 day) during quiet conditions with typical wave amplitudes of tenths of mV/m. However, for the low-energy (∼100 eV to below 2 keV) electron population mainly associated with the diffuse auroral emission, ECH waves are only responsible for rapid pitch angle diffusion (occasionally near the limit of strong diffusion) for a small portion of the electron population with pitch angles αeq  20°, dependent on electron energy and geomagnetic activity level. ECH scattering alone cannot account for the rapid loss of plasma sheet electrons during transport from the nightside to the dayside, nor can it explain the formation of the pancake electron distributions strongly peaked at αeq  70°. Computations of the bounce-averaged coefficients of momentum diffusion and (pitch angle, momentum) mixed diffusion indicate that both mixed diffusion and energy diffusion of plasma sheet electrons due to ECH waves are very small compared to pitch angle diffusion and that ECH waves have little effect on local electron acceleration. Consequently, the multiple harmonic ECH emissions cannot play a dominant role in the occurrence of diffuse auroral precipitation near L = 6, and other wave-particle interaction mechanisms, such as whistler mode chorus-driven resonant scattering, are required to explain the global distribution of diffuse auroral precipitation and the formation of the pancake distribution in the inner magnetosphere.}
}