Formation of Electron Butterfly Pitch Angle Distributions in Saturn's Magnetosphere Due To Scattering by Equatorial ECH Waves

Long, Minyi1; Cao, Xing1; Ni, Binbin1,2; Lou, Yuequn3; Yao, Zhonghua4; Roussos, Elias5; Qin, Tianshu6; Wu, Siyuan7

2023-10-16

10.1029/2023GL105318

GEOPHYSICAL RESEARCH LETTERS   Impact Factor & Quartile

0094-8276

1944-8007

["The features of electron pitch angle distributions (PADs) often imply different physical mechanisms in planetary magnetospheres. We report a simultaneous equatorial electrostatic electron cyclotron harmonic (ECH) wave event with butterfly PADs of electrons at L similar to 7.6-9 observed by the Cassini spacecraft. Via calculating the bounce-averaged electron diffusion rates, we found that Saturnian ECH waves can resonate with similar to 10 eV to several keV electrons at <60 degrees pitch angles at time scales from similar to 10 (-8) to 10(-4) s(-1). Simulations show that the formation of similar to 100 eV to similar to 1 keV electron butterfly PADs are mainly caused by the pitch angle scattering of electrons at low pitch angles (<30 degrees) and the momentum scattering at intermediate pitch angles of similar to 30 degrees-45 degrees, though previous studies suggested the adiabatic transport is the dominated mechanism. Additionally, our results successfully reproduce the variation of peak pitch angles (alpha(p)) and phase space density ratios between alpha(90 degrees) and alpha(p) with L-shell.","Plain Language Summary Charged particles present different pitch angle distributions (PADs) due to different physical mechanisms in Saturn's magnetosphere. Butterfly PADs have local minimum at similar to 90 degrees pitch angle, which are commonly observed in Saturn's magnetosphere for electrons over a wide energy range from similar to 100 eV to several MeV. Previous studies proposed that the adiabatic transport dominates the transformation from the electron field-aligned PADs of similar to 100 eV-several keV to the butterfly shapes in Saturn's magnetosphere. In our study, we report a simultaneous electrostatic electron cyclotron harmonic (ECH) wave event with the butterfly PADs of electrons at L similar to 7.6-9 observed by the Cassini spacecraft. Via calculating the bounce-averaged electron diffusion rates of ECH waves and simulating the evolution of electron phase space densities (PSDs), we find that the formation of similar to 100 eV to similar to 1 keV electron butterfly PADs is mainly caused by the scattering of electrons induced by ECH waves. Our simulation results successfully reproduce the variation of peak pitch angle (alpha(p)) and PSD ratios between alpha(90 degrees) and alpha(p) with L-shell. These results would improve the current understanding of the electron dynamics in Saturn's magnetosphere and shed light on understanding the plasma environment of the outer planets and exoplanets."]

Saturn's magnetosphere electron butterfly pitch angle distributions ECH waves wave-particle interactions

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This work was supported by the NSFC Grants 42188101, 42025404, and 42241143, the B-type Strategic Priority Program of the Chinese Academy of Sciences (Grant XDB41000000), the National Key Ramp;D Program of China (2022YFF0503700 and 2022YFF0503900), the Fu["42188101","42025404","42241143"] ; NSFC[XDB41000000] ; B-type Strategic Priority Program of the Chinese Academy of Sciences["2022YFF0503700","2022YFF0503900"] ; National Key Ramp;D Program of China[2042022kf1012]

Geology

Geosciences, Multidisciplinary

WOS:001074653600001

AMER GEOPHYSICAL UNION

GEOSCIENCES

Web of Science

1.Wuhan Univ, Sch Elect Informat, Dept Space Phys, Wuhan, Peoples R China
2.CAS Ctr Excellence Comparat Planetol, Hefei, Peoples R China
3.Harbin Inst Technol, Inst Space Sci & Appl Technol, Shenzhen, Peoples R China
4.Chinese Acad Sci, Inst Geol & Geophys, Key Lab Earth & Planetary Phys, Beijing, Peoples R China
5.Max Planck Inst Solar Syst Res, Gottingen, Germany
6.Univ Hong Kong, Dept Earth Sci, Hong Kong, Peoples R China
7.Southern Univ Sci & Technol, Dept Earth & Space Sci, Shenzhen, Peoples R China

Long, Minyi,Cao, Xing,Ni, Binbin,et al. Formation of Electron Butterfly Pitch Angle Distributions in Saturn's Magnetosphere Due To Scattering by Equatorial ECH Waves[J]. GEOPHYSICAL RESEARCH LETTERS,2023,50(19).

Long, Minyi.,Cao, Xing.,Ni, Binbin.,Lou, Yuequn.,Yao, Zhonghua.,...&Wu, Siyuan.(2023).Formation of Electron Butterfly Pitch Angle Distributions in Saturn's Magnetosphere Due To Scattering by Equatorial ECH Waves.GEOPHYSICAL RESEARCH LETTERS,50(19).

Long, Minyi,et al."Formation of Electron Butterfly Pitch Angle Distributions in Saturn's Magnetosphere Due To Scattering by Equatorial ECH Waves".GEOPHYSICAL RESEARCH LETTERS 50.19(2023).