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تسجيل مستخدم جديدShear-Driven Transition to Isotropically Turbulent Solar Wind Outside the Alfven Critical Zone
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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 Alfven critical zone, and in the vicinity of the first $beta=1$ 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 Alfven 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 {it Parker Solar Probe} ({it PSP}) near initial perihelia, including magnetic ``switchbacks, and large transverse velocities that are partially corotational and saturate near the local Alfven 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 {it PSP} observations near the first perihelion. The concurrence of evidence from remote sensing observations, {it in situ} measurements, and both global and local simulations supports the idea that the dynamics just above the Alfven critical zone boost low-frequency plasma turbulence to the level routinely observed throughout the explored solar system.
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