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Resonant scattering of plasma sheet electrons leading to diffuse auroral precipitation: 2. Evaluation for whistler mode chorus waves

Ni B., R. M. Thorne, N. P. Meredith, R. B. Horne, Y. Y. Shprits, (2011), Resonant scattering of plasma sheet electrons leading to diffuse auroral precipitation: 2. Evaluation for whistler mode chorus waves, J. of Geophys. Res. [Space Physics], 116, doi:10.1029/2010JA016233

Abstract

Using the statistical wave power spectral profiles obtained from CRRES wave data within the 0000–0600 MLT sector under different levels of geomagnetic activity and a modeled latitudinal variation of wave normal angle distribution, we examine quantitatively the effects of lower band and upper band chorus on resonant diffusion of plasma sheet electrons for diffuse auroral precipitation in the inner magnetosphere. Whistler mode chorus-induced resonant scattering of plasma sheet electrons is geomagnetic activity dependent, varying from above the strong diffusion limit (timescale of an hour) during active times with peak wave amplitudes of 50 pT to weak scattering (timescale of a day) during quiet conditions with typical wave amplitudes of ≤10 pT. Chorus waves present at different magnetic latitudes make distinct contributions to the net diffusion rates of plasma sheet electrons, largely depending on the latitudinal variation of wave power. Upper band chorus is the controlling scattering process for electrons from ∼100 eV to ∼2 keV, and lower band chorus is most effective for precipitating the higher energy (∼2 keV) plasma sheet electrons in the inner magnetosphere. Efficient scattering by the combination of active time lower band and upper band chorus can cover a wide energy range from ∼100 eV to 100 keV and a broad interval of equatorial pitch angle, thereby accounting for the formation of observed electron pancake distribution. Decreased chorus scattering during less disturbed times can also modify the magnetic local time distribution of plasma sheet electrons. Compared to the effects of chorus waves, electron cyclotron harmonic wave-induced resonant diffusion coefficients are at least 1 order of magnitude smaller and are negligible under any geomagnetic condition, indicating that chorus waves act as the major contributor dominantly responsible for diffuse auroral precipitation in the inner magnetosphere. Chorus-driven momentum diffusion and mixed diffusion are also important. Lower band and upper band chorus can cause strong momentum diffusion of plasma sheet electrons in the energy ranges of ∼500 eV to ∼2 keV and ∼2 keV to ∼3 keV, respectively, which can significantly result in energization of the electrons and attenuation of the waves.

Authors (sorted by name)

Horne Meredith Ni Shprits Thorne

Journal / Conference

Journal Of Geophysical Research (Space Physics)

Acknowledgments

This research was supported in part by NSF grant ATM‐0802843, NASA GI 08‐H6I08‐0117 grant, and Lab Research Fee grant 09‐LR‐04116720‐SHPY.

Grants

08‐H6I08‐0117 09‐LR‐04116720 ATM‐0802843

Bibtex

@article{doi:10.1029/2010JA016233,
author = {Ni, Binbin and Thorne, Richard M. and Meredith, Nigel P. and Horne, Richard B. and Shprits, Yuri Y.},
title = {Resonant scattering of plasma sheet electrons leading to diffuse auroral precipitation: 2. Evaluation for whistler mode chorus waves},
year = {2011},
journal = {Journal of Geophysical Research: Space Physics},
volume = {116},
number = {A4},
pages = {},
keywords = {diffuse auroral precipitation, resonant wave-particle interactions, whistler mode chorus, quasi-linear diffusion coefficients, electron pancake distribution},
doi = {10.1029/2010JA016233},
url = {https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2010JA016233},
eprint = {https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2010JA016233},
abstract = {Using the statistical wave power spectral profiles obtained from CRRES wave data within the 0000–0600 MLT sector under different levels of geomagnetic activity and a modeled latitudinal variation of wave normal angle distribution, we examine quantitatively the effects of lower band and upper band chorus on resonant diffusion of plasma sheet electrons for diffuse auroral precipitation in the inner magnetosphere. Whistler mode chorus-induced resonant scattering of plasma sheet electrons is geomagnetic activity dependent, varying from above the strong diffusion limit (timescale of an hour) during active times with peak wave amplitudes of 50 pT to weak scattering (timescale of a day) during quiet conditions  with typical wave amplitudes of ≤10 pT. Chorus waves present at different magnetic latitudes make distinct contributions to the net diffusion rates of plasma sheet electrons, largely depending on the latitudinal variation of wave power. Upper band chorus is the controlling scattering process for electrons from ∼100 eV to ∼2 keV, and lower band chorus is most effective for precipitating the higher energy (∼2 keV) plasma sheet electrons in the inner magnetosphere. Efficient scattering by the combination of active time lower band and upper band chorus can cover a wide energy range from ∼100 eV to 100 keV and a broad interval of equatorial pitch angle, thereby accounting for the formation of observed electron pancake distribution. Decreased chorus scattering during less disturbed times can also modify the magnetic local time distribution of plasma sheet electrons. Compared to the effects of chorus waves, electron cyclotron harmonic wave-induced resonant diffusion coefficients are at least 1 order of magnitude smaller and are negligible under any geomagnetic condition, indicating that chorus waves act as the major contributor dominantly responsible for diffuse auroral precipitation in the inner magnetosphere. Chorus-driven momentum diffusion and mixed diffusion are also important. Lower band and upper band chorus can cause strong momentum diffusion of plasma sheet electrons in the energy ranges of ∼500 eV to ∼2 keV and ∼2 keV to ∼3 keV, respectively, which can significantly result in energization of the electrons and attenuation of the waves.}
}