论文标题
通过直接模拟比较太阳风中的湍流级联反应与光谱各向异性
Comparing turbulent cascades and heating vs spectral anisotropy in solar wind via direct simulations
论文作者
论文摘要
In a previous work (MGV18), we showed numerically that the turbulent cascade generated by quasi-2D structures (with wave vectors mostly-perpendicular to the mean magnetic field) is able to generate a temperature profile close to the one observed in solar wind ($\simeq 1/R$) in the range 0.2 $\le R \le$ 1 au.理论，观察和数值模拟指出了另一个稳健的结构，即径向slab，沿着径向的主要波向量：我们在这里研究radial-slab cascade在构建$ 1/r $ $温度曲线中的效率。与MGV18一样，我们求解了三维MHD方程，包括扩展以模拟湍流演化。我们发现，在0.2 au时具有较大交叉螺旋性的波向量的各向同性分布以及较大的风膨胀速率，再次导致温度衰减速率接近$ 1/r $，但在1 au处具有radial-slab各向异性。令人惊讶的是，湍流的级联集中在横向径向方向的平面上，在此平面中显示了一维光谱，尺度接近$ k^{ - 5/3} $。这既支持太阳风的湍流加热的概念，也支持在加热的起源处存在两个不同的湍流级联A，准2D和径向板。 我们得出的结论是，在太阳风中采样径向光谱可能会提供有关当径向板是不可忽略的湍流部分时，关于真实级联体制和速率的信息很差。
In a previous work (MGV18), we showed numerically that the turbulent cascade generated by quasi-2D structures (with wave vectors mostly-perpendicular to the mean magnetic field) is able to generate a temperature profile close to the one observed in solar wind ($\simeq 1/R$) in the range 0.2 $\le R \le$ 1 au. Theory, observations and numerical simulations point to another robust structure, the radial-slab, with dominant wave vectors along the radial: we study here the efficiency of the radial-slab cascade in building the $1/R$ temperature profile. As in MGV18, we solve the three-dimensional MHD equations including expansion to simulate the turbulent evolution. We find that an isotropic distribution of wave vectors with large cross helicity at 0.2 au, along with a large wind expansion rate, lead again to a temperature decay rate close to $1/R$ but with a radial-slab anisotropy at 1 au. Surprisingly, the turbulent cascade concentrates in the plane transverse to the radial direction, displaying 1D spectra with scalings close to $k^{-5/3}$ in this plane. This supports both the idea of turbulent heating of the solar wind, and the existence of two different turbulent cascades, quasi-2D and radial slab, at the origin of the heating. We conclude that sampling the radial spectrum in the solar wind may give but a poor information on the real cascade regime and rate when the radial slab is a non-negligible part of turbulence.
