Density fluctuation-Mach number scaling in compressible, high plasma beta turbulence: in-situ space observations and high-Reynolds number simulations
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| Format: | Preprint |
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2025
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| _version_ | 1866917920798408704 |
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| author | Bandyopadhyay, Riddhi Beattie, James R. Bhattacharjee, Amitava |
| author_facet | Bandyopadhyay, Riddhi Beattie, James R. Bhattacharjee, Amitava |
| contents | Understanding the nature of compressible fluctuations in a broad range of turbulent plasmas, from the intracluster medium to the solar wind, has been an active field of research in the past decades. Theoretical frameworks for weakly compressible MHD turbulence in an inhomogeneous background magnetic field predict a linear scaling of the normalized mass density fluctuation ($δρ/ ρ_0$), as a function of the turbulent Mach number ($\mathcal{M}_t$), $δρ/ ρ_0 \propto \mathcal{M}_t$. However, so far the scaling relation has been tested only using moderate to low plasma beta ($β\lesssim 1$) solar wind observational data where the compressibility is weak $δρ/ ρ_0 \sim 0.1$. Here, we combine NASA's Magnetospheric Multiscale Mission data in Earth's magnetosheath, where $β\sim 10$ is high, and $β\sim 1$ highly-compressible magnetohydrodynamic turbulence simulations at unprecedented resolutions. Both show that $δρ/ ρ_0 \propto \mathcal{M}_t$ holds across a broad range of $δρ/ ρ_0$, $\mathcal{M}_t$ and $β$, demonstrating that $δρ/ ρ_0 \propto \mathcal{M}_t$ is a robust compressible turbulence relation, going beyond the asymptotics of the weakly compressible theory. We discuss the findings in the context of understanding the nature of strongly compressible turbulent fluctuations and the driving parameter in astrophysical and space plasmas. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2502_08883 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Density fluctuation-Mach number scaling in compressible, high plasma beta turbulence: in-situ space observations and high-Reynolds number simulations Bandyopadhyay, Riddhi Beattie, James R. Bhattacharjee, Amitava Solar and Stellar Astrophysics Astrophysics of Galaxies Plasma Physics Space Physics Understanding the nature of compressible fluctuations in a broad range of turbulent plasmas, from the intracluster medium to the solar wind, has been an active field of research in the past decades. Theoretical frameworks for weakly compressible MHD turbulence in an inhomogeneous background magnetic field predict a linear scaling of the normalized mass density fluctuation ($δρ/ ρ_0$), as a function of the turbulent Mach number ($\mathcal{M}_t$), $δρ/ ρ_0 \propto \mathcal{M}_t$. However, so far the scaling relation has been tested only using moderate to low plasma beta ($β\lesssim 1$) solar wind observational data where the compressibility is weak $δρ/ ρ_0 \sim 0.1$. Here, we combine NASA's Magnetospheric Multiscale Mission data in Earth's magnetosheath, where $β\sim 10$ is high, and $β\sim 1$ highly-compressible magnetohydrodynamic turbulence simulations at unprecedented resolutions. Both show that $δρ/ ρ_0 \propto \mathcal{M}_t$ holds across a broad range of $δρ/ ρ_0$, $\mathcal{M}_t$ and $β$, demonstrating that $δρ/ ρ_0 \propto \mathcal{M}_t$ is a robust compressible turbulence relation, going beyond the asymptotics of the weakly compressible theory. We discuss the findings in the context of understanding the nature of strongly compressible turbulent fluctuations and the driving parameter in astrophysical and space plasmas. |
| title | Density fluctuation-Mach number scaling in compressible, high plasma beta turbulence: in-situ space observations and high-Reynolds number simulations |
| topic | Solar and Stellar Astrophysics Astrophysics of Galaxies Plasma Physics Space Physics |
| url | https://arxiv.org/abs/2502.08883 |