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Title: Shear-driven Transition to Isotropically Turbulent Solar Wind Outside the Alfvén Critical Zone
Authors: D. Ruffolo
W. H. Matthaeus
R. Chhiber
A. V. Usmanov
Y. Yang
R. Bandyopadhyay
T. N. Parashar
M. L. Goldstein
C. E. Deforest
M. Wan
A. Chasapis
B. A. Maruca
M. Velli
J. C. Kasper
Southern University of Science and Technology
Space Science and Engineering Division
University of California, Los Angeles
University of Michigan, Ann Arbor
University of Maryland, Baltimore County
Mahidol University
Smithsonian Astrophysical Observatory
NASA Goddard Space Flight Center
Princeton University
Victoria University of Wellington
The Bartol Research Institute
University of Colorado Boulder
Keywords: Earth and Planetary Sciences
Issue Date: 20-Oct-2020
Citation: Astrophysical Journal. Vol.902, No.2 (2020)
Abstract: © 2020. The American Astronomical Society. All rights reserved. Motivated by prior remote observations of a transition from striated solar coronal structures to more isotropic "flocculated"fluctuations, we propose that the dynamics of the inner solar wind just outside the Alfvén critical zone, and in the vicinity of the first surface, is powered by the relative velocities of adjacent coronal magnetic flux tubes. We suggest that large-amplitude flow contrasts are magnetically constrained at lower altitude but shear-driven dynamics are triggered as such constraints are released above the Alfvén critical zone, as suggested by global magnetohydrodynamic (MHD) simulations that include self-consistent turbulence transport. We argue that this dynamical evolution accounts for features observed by Parker Solar Probe (PSP) near initial perihelia, including magnetic "switchbacks,"and large transverse velocities that are partially corotational and saturate near the local Alfvén speed. Large-scale magnetic increments are more longitudinal than latitudinal, a state unlikely to originate in or below the lower corona. We attribute this to preferentially longitudinal velocity shear from varying degrees of corotation. Supporting evidence includes comparison with a high Mach number three-dimensional compressible MHD simulation of nonlinear shear-driven turbulence, reproducing several observed diagnostics, including characteristic distributions of fluctuations that are qualitatively similar to PSP observations near the first perihelion. The concurrence of evidence from remote sensing observations, in situ measurements, and both global and local simulations supports the idea that the dynamics just above the Alfvén critical zone boost low-frequency plasma turbulence to the level routinely observed throughout the explored solar system.
ISSN: 15384357
Appears in Collections:Scopus 2020

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