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Title: DIRECT NUMERICAL SIMULATIONS OF REFLECTION-DRIVEN, REDUCED MAGNETOHYDRODYNAMIC TURBULENCE FROM THE SUN TO THE ALFVÉN CRITICAL POINT

We present direct numerical simulations of inhomogeneous reduced magnetohydrodynamic (RMHD) turbulence between the Sun and the Alfvén critical point. These are the first such simulations that take into account the solar-wind outflow velocity and the radial inhomogeneity of the background solar wind without approximating the nonlinear terms in the governing equations. RMHD turbulence is driven by outward-propagating Alfvén waves (z {sup +} fluctuations) launched from the Sun, which undergo partial non-WKB reflection to produce sunward-propagating Alfvén waves (z {sup –} fluctuations). We present 10 simulations with different values of the correlation time τ{sub c{sub sun}{sup +}} and perpendicular correlation length L{sub ☉} of outward-propagating Alfvén waves at the coronal base. We find that between 15% and 33% of the z {sup +} energy launched into the corona dissipates between the coronal base and Alfvén critical point. Between 33% and 40% of this input energy goes into work on the solar-wind outflow, and between 22% and 36% escapes as z {sup +} fluctuations through the simulation boundary at r = r{sub A}. The z {sup ±} power spectra scale like k{sub perpendicular}{sup -α{sup ±}}, where k is the wavenumber in the plane perpendicular to B{sub 0}. In our simulation with themore » smallest value of τ{sub c{sub sun}{sup +}} (∼2 minutes) and largest value of L{sub ☉} (2 × 10{sup 4} km), we find that α{sup +} decreases approximately linearly with increasing ln (r), reaching a value of 1.3 at r = 11.1 R{sub ☉}. Our simulations with larger values of τ{sub c{sub sun}{sup +}} exhibit alignment between the contours of constant φ{sup +}, φ{sup –}, Ω{sub 0}{sup +}, and Ω{sub 0}{sup -}, where φ{sup ±} are the Elsässer potentials and Ω{sub 0}{sup ±} are the outer-scale parallel Elsässer vorticities.« less
Authors:
;  [1]
  1. Space Science Center, University of New Hampshire, Durham, NH 03824 (United States)
Publication Date:
OSTI Identifier:
22270808
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 776; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ALFVEN WAVES; APPROXIMATIONS; ASTRONOMY; ASTROPHYSICS; COMPUTERIZED SIMULATION; CORRELATIONS; FLUCTUATIONS; MAGNETOHYDRODYNAMICS; NONLINEAR PROBLEMS; REFLECTION; SOLAR CORONA; SOLAR WIND; SUN; TURBULENCE; WAVE PROPAGATION