Radial evolution of Alfvén wave Parametric Decay Instability in the near-Sun solar wind: Effects of Temperature Anisotropy
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2026
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| _version_ | 1866917554651398144 |
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| author | Saguchi, Hayato Kawazura, Yohei Shoda, Munehito Katoh, Yuto |
| author_facet | Saguchi, Hayato Kawazura, Yohei Shoda, Munehito Katoh, Yuto |
| contents | Parametric decay instability (PDI) of Alfvén wave is thought to play an important role in the dissipation of the large-amplitude Alfvén waves and in the heating of magnetized plasmas. Temperature anisotropy is frequently observed by spacecraft, including Parker Solar Probe (PSP), in the near-Sun solar wind, yet its impact on PDI in the near-Sun solar wind has been understudied. We calculate the maximum growth rates of PDI, $γ_{\max}/ω_{0}$, where $ω_0$ is the frequency of the parent wave, by solving the linear dispersion relation of Chew-Goldberger-Low (CGL) equations under several expanding background models. To assess the effect of temperature anisotropy, the growth rate is compared with that derived from ideal magnetohydrodynamics (MHD). From $R_0$ ($ = 1.02R_\odot$) to $30R_0$, we consider three expansion cases: (i) spherically symmetric adiabatic expansion with constant wind speed, (ii) Multi-source observation- and model-constrained expansion, and (iii) a PSP-constrained profile of $(β_{\parallel},ξ)$, where $β_\parallel=8πp_{\parallel0}/B_0^2$ is the parallel plasma beta and $ξ=T_{\perp0} / T_{\parallel0}$ is the temperature anisotropy, that includes Parker-spiral effects. We find that temperature anisotropy increases $γ_{\max}/ω_{0}$ for $β\lesssim 0.1$ in the near-Sun solar wind: in the case of (iii), temperature anisotropy with $T_{\perp0} > T_{\parallel0}$ increases $γ_{\max}/ω_{0}$ by factors of $\sim 1.5$ over $R\simeq 1$--$10\,R_0$, whereas temperature anisotropy with $T_{\parallel0}>T_{\perp0}$ decreases $γ_{\max}/ω_{0}$ at larger $R$. Our results suggest that the temperature anisotropy plays an important role in the onset of PDI even in low-$β$ regimes, such as the near-Sun solar wind. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2604_22489 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Radial evolution of Alfvén wave Parametric Decay Instability in the near-Sun solar wind: Effects of Temperature Anisotropy Saguchi, Hayato Kawazura, Yohei Shoda, Munehito Katoh, Yuto Solar and Stellar Astrophysics Space Physics Parametric decay instability (PDI) of Alfvén wave is thought to play an important role in the dissipation of the large-amplitude Alfvén waves and in the heating of magnetized plasmas. Temperature anisotropy is frequently observed by spacecraft, including Parker Solar Probe (PSP), in the near-Sun solar wind, yet its impact on PDI in the near-Sun solar wind has been understudied. We calculate the maximum growth rates of PDI, $γ_{\max}/ω_{0}$, where $ω_0$ is the frequency of the parent wave, by solving the linear dispersion relation of Chew-Goldberger-Low (CGL) equations under several expanding background models. To assess the effect of temperature anisotropy, the growth rate is compared with that derived from ideal magnetohydrodynamics (MHD). From $R_0$ ($ = 1.02R_\odot$) to $30R_0$, we consider three expansion cases: (i) spherically symmetric adiabatic expansion with constant wind speed, (ii) Multi-source observation- and model-constrained expansion, and (iii) a PSP-constrained profile of $(β_{\parallel},ξ)$, where $β_\parallel=8πp_{\parallel0}/B_0^2$ is the parallel plasma beta and $ξ=T_{\perp0} / T_{\parallel0}$ is the temperature anisotropy, that includes Parker-spiral effects. We find that temperature anisotropy increases $γ_{\max}/ω_{0}$ for $β\lesssim 0.1$ in the near-Sun solar wind: in the case of (iii), temperature anisotropy with $T_{\perp0} > T_{\parallel0}$ increases $γ_{\max}/ω_{0}$ by factors of $\sim 1.5$ over $R\simeq 1$--$10\,R_0$, whereas temperature anisotropy with $T_{\parallel0}>T_{\perp0}$ decreases $γ_{\max}/ω_{0}$ at larger $R$. Our results suggest that the temperature anisotropy plays an important role in the onset of PDI even in low-$β$ regimes, such as the near-Sun solar wind. |
| title | Radial evolution of Alfvén wave Parametric Decay Instability in the near-Sun solar wind: Effects of Temperature Anisotropy |
| topic | Solar and Stellar Astrophysics Space Physics |
| url | https://arxiv.org/abs/2604.22489 |