SH029-0010
Shear-Driven Transition to Isotropically Turbulent Solar Wind Outside the Alfvén Critical Zone

Friday, 11 December 2020
Poster
David J Ruffolo1, William H Matthaeus2, Rohit Chhiber2,3, Arcadi V. Usmanov2,3, Yan Yang4, Riddhi Bandyopadhyay5, Tulasi Parashar2,6, Melvyn L Goldstein7, Craig DeForest8, Minping Wan4, Alexandros Chasapis9, Bennett Maruca2, Marco C M Velli10 and Justin Christophe Kasper11,12, (1)Mahidol University, Department of Physics, Faculty of Science, Bangkok, Thailand, (2)University of Delaware, Department of Physics and Astronomy, Newark, DE, United States, (3)NASA Goddard Space Flight Center, Greenbelt, DE, United States, (4)Southern University of Science and Technology, Shenzhen, China, (5)Princeton University, Department of Astrophysical Sciences, Princeton, NJ, United States, (6)Victoria University of Wellington, Wellington, New Zealand, (7)University of Maryland Baltimore County, Baltimore, MD, United States, (8)Southwest Research Institute, Boulder, CO, United States, (9)Laboratory for Atmospheric and Space Physics, Boulder, CO, United States, (10)University of California Los Angeles, Los Angeles, CA, United States, (11)University of Michigan, Climate and Space Sciences and Engineering, Ann Arbor, MI, United States, (12)Smithsonian Astrophysical Observatory, Cambridge, MA, United States
Abstract:
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 β=1 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. This research has been supported in part by grant RTA6280002 from Thailand Science Research and Innovation and the Parker Solar Probe mission under the ISOIS project (contract NNN06AA01C) and a subcontract to University of Delaware from Princeton University (SUB0000165). M.L.G. acknowledges support from the Parker Solar Probe FIELDS MAG team. Y.Y. is supported in part by NSFC grant 11902138. Additional support is acknowledged from the NASA LWS program (NNX17AB79G) and the HSR program (80NSSC18K1210 & 80NSSC18K1648).
<< Previous Abstract | Next Abstract >>