5:15 PM - 7:15 PM
[PEM11-P07] The realistic radial evolution of decay instability of Alfvén waves considering temperature anisotropy in the solar wind
Keywords:solar wind, corona, parametric decay instability, temperature anisotropy, expansion
Magnetohydrodynamic waves known as Alfvén waves have attracted attention as a source of coronal heating and the solar wind acceleration. In fact, Alfvén waves are observed as turbulence in the solar wind (e.g., Zank et al., 2022; Zank et al., 2024). Shoda et al., (2019) conducted a numerical simulation of the solar wind acceleration driven by Alfvénic turbulence that included compressible waves and demonstrated that the parametric decay instability (PDI) of Alfvén waves is an essentially important physical process for the development of solar wind turbulence. Most previous studies on the PDI in the solar wind did not take temperature anisotropy into account except Tenerani et al., (2017), who first investigated the influence of temperature anisotropy on the PDI using the Chew-Goldberger-Low (CGL) model, an MHD model that incorporates temperature anisotropy. In their study, however, the variations of physical quantities in the radial direction were not considered, and thus the evolution of the PDI in the solar wind was not examined in detail.
In our study, we investigate how the PDI evolves in the solar wind by considering various possible variations of physical quantities in the radial direction using linear analysis. We use two models: an MHD model that does not consider temperature anisotropy and the CGL model that does. As a result, under the conditions of adiabatic expansion, where the magnetic field and density vary as R-2 and the amplitude of the parent wave evolves in a WKB-like manner, the PDI maximum growth rate in the CGL model was found to decrease more rapidly with increasing distance from the Sun compared to the MHD model. This indicates that considering temperature anisotropy in adiabatic expansion leads to significant differences in the radial development of the PDI. Furthermore, to better represent the realistic solar wind, we examined the radial evolution of the PDI by incorporating the radial profile of temperature anisotropy obtained by the 3D MHD model from Meng et al., (2015) and the Parker Solar Probe observation of the magnetic field and density variations from Huang et al., (2020). As a result, temperature anisotropy was found to enhance the PDI growth rate, and the decrease in its value with distance from the Sun was more gradual compared to the adiabatic expansion case. These findings demonstrate that temperature anisotropy significantly influences both the increase in the growth rate and the radial development of the PDI in the solar wind.
In our study, we investigate how the PDI evolves in the solar wind by considering various possible variations of physical quantities in the radial direction using linear analysis. We use two models: an MHD model that does not consider temperature anisotropy and the CGL model that does. As a result, under the conditions of adiabatic expansion, where the magnetic field and density vary as R-2 and the amplitude of the parent wave evolves in a WKB-like manner, the PDI maximum growth rate in the CGL model was found to decrease more rapidly with increasing distance from the Sun compared to the MHD model. This indicates that considering temperature anisotropy in adiabatic expansion leads to significant differences in the radial development of the PDI. Furthermore, to better represent the realistic solar wind, we examined the radial evolution of the PDI by incorporating the radial profile of temperature anisotropy obtained by the 3D MHD model from Meng et al., (2015) and the Parker Solar Probe observation of the magnetic field and density variations from Huang et al., (2020). As a result, temperature anisotropy was found to enhance the PDI growth rate, and the decrease in its value with distance from the Sun was more gradual compared to the adiabatic expansion case. These findings demonstrate that temperature anisotropy significantly influences both the increase in the growth rate and the radial development of the PDI in the solar wind.