Parallel-propagating Fluctuations at Proton-kinetic Scales in the Solar Wind Are Dominated By Kinetic Instabilities

Woodham, Lloyd D., Wicks, Robert, Verscharen, Daniel, Owen, Christopher J., Maruca, Bennett A. and Alterman, Benjamin L. (2019) Parallel-propagating Fluctuations at Proton-kinetic Scales in the Solar Wind Are Dominated By Kinetic Instabilities. The Astrophysical Journal Letters, 884 (2). L53. ISSN 2041-8205

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Official URL: https://doi.org/10.3847/2041-8213/ab4adc

Abstract

We use magnetic helicity to characterize solar wind fluctuations at proton-kinetic scales from Wind observations. For the first time, we separate the contributions to helicity from fluctuations propagating at angles quasi-parallel and oblique to the local mean magnetic field, ${{\boldsymbol{B}}}_{0}$. We find that the helicity of quasi-parallel fluctuations is consistent with Alfvén-ion cyclotron and fast magnetosonic-whistler modes driven by proton temperature anisotropy instabilities and the presence of a relative drift between α-particles and protons. We also find that the helicity of oblique fluctuations has little dependence on proton temperature anisotropy and is consistent with fluctuations from the anisotropic turbulent cascade. Our results show that parallel-propagating fluctuations at proton-kinetic scales in the solar wind are dominated by proton temperature anisotropy instabilities and not the turbulent cascade. We also provide evidence that the behavior of fluctuations at these scales is independent of the origin and macroscopic properties of the solar wind.

Item Type: Article
Uncontrolled Keywords: Space plasmas ; Plasma astrophysics ; Plasma physics ; Solar wind, Heliosphere, Interplanetary turbulence, Alfven waves, Slow solar wind, Fast solar wind
Subjects: F300 Physics
F500 Astronomy
Department: Faculties > Engineering and Environment > Mathematics, Physics and Electrical Engineering
Depositing User: John Coen
Date Deposited: 05 Aug 2020 11:33
Last Modified: 05 Aug 2020 12:52
URI: http://nrl.northumbria.ac.uk/id/eprint/44000

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