Radial evolution of Alfv’en wave Parametric Decay Instability in the near-Sun solar wind: Effects of Temperature Anisotropy
Hayato Saguchi, Yohei Kawazura, Munehito Shoda, Yuto Katoh
arXiv:2604.22489v2 Announce Type: replace
Abstract: Parametric decay instability (PDI) of Alfv’en wave is thought to play an important role in the dissipation of the large-amplitude Alfv’en 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, $gamma_{max}/omega_{0}$, where $omega_0$ 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 $(beta_{parallel},xi)$, where $beta_parallel=8pi p_{parallel0}/B_0^2$ is the parallel plasma beta and $xi=T_{perp0} / T_{parallel0}$ is the temperature anisotropy, that includes Parker-spiral effects. We find that temperature anisotropy increases $gamma_{max}/omega_{0}$ for $betalesssim 0.1$ in the near-Sun solar wind: in the case of (iii), temperature anisotropy with $T_{perp0} > T_{parallel0}$ increases $gamma_{max}/omega_{0}$ by factors of $sim 1.5$ over $Rsimeq 1$–$10,R_0$, whereas temperature anisotropy with $T_{parallel0}>T_{perp0}$ decreases $gamma_{max}/omega_{0}$ at larger $R$. Our results suggest that the temperature anisotropy plays an important role in the onset of PDI even in low-$beta$ regimes, such as the near-Sun solar wind.arXiv:2604.22489v2 Announce Type: replace
Abstract: Parametric decay instability (PDI) of Alfv’en wave is thought to play an important role in the dissipation of the large-amplitude Alfv’en 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, $gamma_{max}/omega_{0}$, where $omega_0$ 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 $(beta_{parallel},xi)$, where $beta_parallel=8pi p_{parallel0}/B_0^2$ is the parallel plasma beta and $xi=T_{perp0} / T_{parallel0}$ is the temperature anisotropy, that includes Parker-spiral effects. We find that temperature anisotropy increases $gamma_{max}/omega_{0}$ for $betalesssim 0.1$ in the near-Sun solar wind: in the case of (iii), temperature anisotropy with $T_{perp0} > T_{parallel0}$ increases $gamma_{max}/omega_{0}$ by factors of $sim 1.5$ over $Rsimeq 1$–$10,R_0$, whereas temperature anisotropy with $T_{parallel0}>T_{perp0}$ decreases $gamma_{max}/omega_{0}$ at larger $R$. Our results suggest that the temperature anisotropy plays an important role in the onset of PDI even in low-$beta$ regimes, such as the near-Sun solar wind.

Comments are closed, but trackbacks and pingbacks are open.