Characterization of Turbulent Fluctuations in the Sub-Alfvenic Solar Wind
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arXiv
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| Autori principali: | , , , , , , , , , , |
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| Natura: | Preprint |
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2024
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| author | Zank, Gary P. Zhao, Lingling Adhikari, Laxman Telloni, Daniele Baruwal, Prashant Baruwal, Prashrit Zhu, Xingyu Nakanotani, Masaru Pitna, Alexander Kasper, Justin C. Bale, Stuart D. |
| author_facet | Zank, Gary P. Zhao, Lingling Adhikari, Laxman Telloni, Daniele Baruwal, Prashant Baruwal, Prashrit Zhu, Xingyu Nakanotani, Masaru Pitna, Alexander Kasper, Justin C. Bale, Stuart D. |
| contents | Parker Solar Probe (PSP) observed sub-Alfvenic solar wind intervals during encounters 8 - 14, and low-frequency magnetohydrodynamic turbulence in these regions may differ from that in super-Alfvenic wind. We apply a new mode-decomposition analysis (Zank et al 2023) to the sub-Alfvénic flow observed by PSP on 2021 April 28, identifying and characterizing entropy, magnetic islands, forward and backward Alfvén waves, including weakly/non-propagating Alfvén vortices, forward and backward fast and slow magnetosonic modes. Density fluctuations are primarily and almost equally entropy and backward propagating slow magnetosonic modes. The mode-decomposition provides phase information (frequency and wavenumber k) for each mode. Entropy-density fluctuations have a wavenumber anisotropy k_{||} >> k_{perp} whereas slow mode density fluctuations have k_{perp} > k_{||}. Magnetic field fluctuations are primarily magnetic island modes (delta B^i) with an O(1) smaller contribution from uni-directionally propagating Alfven waves (delta B^{A+}) giving a variance anisotropy of <{δB^i}^2> / <delta B^A}^2> = 4.1. Incompressible magnetic fluctuations dominate compressible contributions from fast and slow magnetosonic modes. The magnetic island spectrum is Kolmogorov-like k_{perp}^{-1.6} in perpendicular wavenumber and the uni-directional Alfven wave spectra are k_{||}^{-1.6} and k_{perp}^{-1.5}. Fast magnetosonic modes propagate at essentially the Alfvén speed with anti-correlated transverse velocity and magnetic field fluctuations and are almost exclusively magnetic due to beta_p<<1. Transverse velocity fluctuations are the dominant velocity component in fast magnetosonic modes and longitudinal fluctuations dominate in slow modes. Mode-decomposition is an effective tool in identifying the basic building blocks of MHD turbulence and provides detailed phase information about each of the modes. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2403_14861 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | Characterization of Turbulent Fluctuations in the Sub-Alfvenic Solar Wind Zank, Gary P. Zhao, Lingling Adhikari, Laxman Telloni, Daniele Baruwal, Prashant Baruwal, Prashrit Zhu, Xingyu Nakanotani, Masaru Pitna, Alexander Kasper, Justin C. Bale, Stuart D. Solar and Stellar Astrophysics Space Physics Parker Solar Probe (PSP) observed sub-Alfvenic solar wind intervals during encounters 8 - 14, and low-frequency magnetohydrodynamic turbulence in these regions may differ from that in super-Alfvenic wind. We apply a new mode-decomposition analysis (Zank et al 2023) to the sub-Alfvénic flow observed by PSP on 2021 April 28, identifying and characterizing entropy, magnetic islands, forward and backward Alfvén waves, including weakly/non-propagating Alfvén vortices, forward and backward fast and slow magnetosonic modes. Density fluctuations are primarily and almost equally entropy and backward propagating slow magnetosonic modes. The mode-decomposition provides phase information (frequency and wavenumber k) for each mode. Entropy-density fluctuations have a wavenumber anisotropy k_{||} >> k_{perp} whereas slow mode density fluctuations have k_{perp} > k_{||}. Magnetic field fluctuations are primarily magnetic island modes (delta B^i) with an O(1) smaller contribution from uni-directionally propagating Alfven waves (delta B^{A+}) giving a variance anisotropy of <{δB^i}^2> / <delta B^A}^2> = 4.1. Incompressible magnetic fluctuations dominate compressible contributions from fast and slow magnetosonic modes. The magnetic island spectrum is Kolmogorov-like k_{perp}^{-1.6} in perpendicular wavenumber and the uni-directional Alfven wave spectra are k_{||}^{-1.6} and k_{perp}^{-1.5}. Fast magnetosonic modes propagate at essentially the Alfvén speed with anti-correlated transverse velocity and magnetic field fluctuations and are almost exclusively magnetic due to beta_p<<1. Transverse velocity fluctuations are the dominant velocity component in fast magnetosonic modes and longitudinal fluctuations dominate in slow modes. Mode-decomposition is an effective tool in identifying the basic building blocks of MHD turbulence and provides detailed phase information about each of the modes. |
| title | Characterization of Turbulent Fluctuations in the Sub-Alfvenic Solar Wind |
| topic | Solar and Stellar Astrophysics Space Physics |
| url | https://arxiv.org/abs/2403.14861 |