학술논문
On the evolution of the Anisotropic Scaling of Magnetohydrodynamic Turbulence in the Inner Heliosphere
Document Type
Working Paper
Author
Sioulas, Nikos; Velli, Marco; Huang, Zesen; Shi, Chen; Bowen, Trevor A.; Chandran, B. D. G.; Liodis, Ioannis; Davis, Nooshin; Bale, Stuart D.; Horbury, T. S.; de Wit, Thierry Dudok; Larson, Davin; Kasper, Justin; Owen, Christopher J.; Stevens, Michael L.; Case, Anthony; Pulupa, Marc; Malaspina, David M.; Bonnell, J. W.; Goetz, Keith; Harvey, Peter R.; MacDowall, Robert J.
Source
Subject
Language
Abstract
We analyze a merged Parker Solar Probe ($PSP$) and Solar Orbiter ($SO$) dataset covering heliocentric distances $13 \ R_{\odot} \lesssim R \lesssim 220$ $R_{\odot}$ to investigate the radial evolution of power and spectral-index anisotropy in the wavevector space of solar wind turbulence. Our results show that anisotropic signatures of turbulence display a distinct radial evolution when fast, $V_{sw} \geq ~ 400 ~km ~s^{-1}$, and slow, $V_{sw} \leq ~ 400 ~km ~s^{-1}$, wind streams are considered. The anisotropic properties of slow wind in Earth orbit are consistent with a ``critically balanced'' cascade, but both spectral-index anisotropy and power anisotropy diminish with decreasing heliographic distance. Fast streams are observed to roughly retain their near-Sun anisotropic properties, with the observed spectral index and power anisotropies being more consistent with a ``dynamically aligned'' type of cascade, though the lack of extended fast-wind intervals makes it difficult to accurately measure the anisotropic scaling. A high-resolution analysis during the first perihelion of PSP confirms the presence of two sub-ranges within the inertial range, which may be associated with the transition from weak to strong turbulence. The transition occurs at $\kappa d_{i} \approx 6 \times 10^{-2}$, and signifies a shift from -5/3 to -2 and -3/2 to -1.57 scaling in parallel and perpendicular spectra, respectively. Our results provide strong observational constraints for anisotropic theories of MHD turbulence in the solar wind.
Comment: Accepted to APJ
Comment: Accepted to APJ