中国科大地空学院“瀚海问天”日地空间物理前沿论坛讲座第42期-丁宇量

报告人简介：

Yuliang Ding was enrolled in the School of Earth and Space Sciences at the University of Science and Technology of China (USTC) in 2019 and graduated with a Bachelor's Degree in Geophysics in 2023, awarded the Guo Moruo Scholarship. Currently he is pursuing a Ph.D. in Space Physics at the University of California, Los Angeles (UCLA). His research focuses on: solar wind turbulence, solar wind evolution and acceleration, switchbacks and Spherically Polarized Alfvén Wave.

摘要：

Alfvén waves are thought to play critical roles in solar wind acceleration and plasma heating in the solar corona and inner heliosphere. Parker Solar Probe (PSP) has highlighted the role of large amplitude Spherically Polarized AlfvénWaves (SPAWs), where the locally constant magnetic field magnitude |B|together with outward propagation explains the observed one-sided radial velocity enhancement-the Gosling boost.Starting from the MHD equations, we derive the modified wave pressure and Poynting flux under the SPAW condition, and demonstrate both are governed solely by the transverse magnetic fluctuations. Using PSP data from Encounters 6--25, we define an unperturbed velocity baseline from the lower 10th-percentile running average and statistically characterize the radial evolution of Alfvénic fluctuations. The background solar wind velocity shows clear radial acceleration, while the velocity perturbation amplitude δv decreases with heliocentric distance. This decay is anisotropic between the radial and perpendicular directions, which is a direct consequence of the growing magnetic deflection angle related to the spherical polarization. Our results demonstrate that radial velocity enhancements in the young solar wind arise naturally from SPAWs rather than from localized velocity jets, and provide direct observational evidence for the anisotropic radial evolution of SPAWs in the inner heliosphere.