DIRECT NUMERICAL SIMULATIONS OF REFLECTION-DRIVEN, REDUCED MAGNETOHYDRODYNAMIC TURBULENCE FROM THE SUN TO THE ALFVÉN CRITICAL POINT
DIRECT NUMERICAL SIMULATIONS OF REFLECTION-DRIVEN, REDUCED MAGNETOHYDRODYNAMIC TURBULENCE FROM THE SUN TO THE ALFVÉN CRITICAL POINT
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从太阳到阿尔文临界点的反射驱动的简化磁流体动力湍流的直接数值模拟
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发表时间：
2013
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通讯作者：
B. Chandran
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作者：
J. C. Perez;B. Chandran
我们提出了直接数值模拟的非均匀约化磁流体动力学（RMHD）之间的太阳和阿尔文临界点的湍流。这是第一次考虑太阳风外流速度和背景太阳风的径向不均匀性而不近似控制方程中的非线性项的模拟。RMHD湍流是由从太阳发射的向外传播的阿尔文波（z+波动）驱动的，它经历部分非WKB反射，产生向日传播的阿尔文波（z−波动）。我们提出了10个模拟与不同的值的相关时间和垂直的相关长度L的向外传播的阿尔文波在日冕底部。我们发现发射到日冕的z+能量的15%到33%在日冕底部和阿尔文临界点之间消散。输入能量的33%到40%用于太阳风外流，22%到36%作为z+波动通过r = rA的模拟边界逃逸。z±功率谱的尺度类似，其中k ±是垂直于B0的平面中的波数。在我们的模拟中，最小值为（102分钟），最大值为（2 × 104 km），我们发现α+随着ln（r）的增加而近似线性下降，在r = 11.1 R时达到1.3。我们的模拟与较大的值显示出恒定的ε +，ε −，和之间的轮廓对齐，其中ε ±是Elsässer势，是外尺度平行Elsässer涡度。
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+ fluctuations) launched from the Sun, which undergo partial non-WKB reflection to produce sunward-propagating Alfvén waves (z− fluctuations). We present 10 simulations with different values of the correlation time and perpendicular correlation length L⊥☉ of outward-propagating Alfvén waves at the coronal base. We find that between 15% and 33% of the z+ 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+ fluctuations through the simulation boundary at r = rA. The z± power spectra scale like , where k⊥ is the wavenumber in the plane perpendicular to B0. In our simulation with the smallest value of (∼2 minutes) and largest value of L⊥☉ (2 × 104 km), we find that α+ decreases approximately linearly with increasing ln (r), reaching a value of 1.3 at r = 11.1 R☉. Our simulations with larger values of exhibit alignment between the contours of constant ϕ+, ϕ−, , and , where ϕ± are the Elsässer potentials and are the outer-scale parallel Elsässer vorticities.