The vortex gas scaling regime of baroclinic turbulence
The vortex gas scaling regime of baroclinic turbulence
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DOI：
10.1073/pnas.1916272117
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发表时间：
2020-03-03
影响因子：
11.1
通讯作者：
Ferrari, Raffaele
中科院分区：
文献类型：
--
作者：
Gallet, Basile;Ferrari, Raffaele
大气和海洋的平均状态是通过外部强迫（辐射、风、热量和淡水通量）和新兴湍流之间的平衡来设定的，新兴湍流将能量传递到耗散结构。这种强迫在大气中产生急流，在海洋中产生洋流，通过斜压不稳定性自发地形成湍流涡旋。气候理论发展的关键一步是适当地考虑涡流引起的热量、水分和碳等特性的湍流传输。在线性阶段，斜压不稳定性在罗斯贝变形半径处产生流动结构，其长度尺度在大气中为1000公里，在海洋中为100公里，分别小于行星尺度和海洋盆地的典型范围。因此，温度等性质的大尺度梯度与随机平流输送的较小涡流之间存在尺度分离，从而引起有效扩散。数值解表明，只要大气和海洋底部有足够的阻力，这种尺度分离仍然处于强非线性湍流状态。我们计算了控制与斜压湍流相关的涡流驱动传输的比例定律。首先，我们为先前研究中报告的经验缩放定律以及底部阻力定律的不同公式提供了理论基础。其次，这些标度定律被证明为准确的局部闭合提供了重要的第一步，以预测斜压湍流对设定大气和海洋大尺度温度剖面的影响。
The mean state of the atmosphere and ocean is set through a balance between external forcing (radiation, winds, heat and freshwater fluxes) and the emergent turbulence, which transfers energy to dissipative structures. The forcing gives rise to jets in the atmosphere and currents in the ocean, which spontaneously develop turbulent eddies through the baroclinic instability. A critical step in the development of a theory of climate is to properly include the eddy-induced turbulent transport of properties like heat, moisture, and carbon. In the linear stages, baroclinic instability generates flow structures at the Rossby deformation radius, a length scale of order 1,000 km in the atmosphere and 100 km in the ocean, smaller than the planetary scale and the typical extent of ocean basins, respectively. There is, therefore, a separation of scales between the large-scale gradient of properties like temperature and the smaller eddies that advect it randomly, inducing effective diffusion. Numerical solutions show that such scale separation remains in the strongly nonlinear turbulent regime, provided there is sufficient drag at the bottom of the atmosphere and ocean. We compute the scaling laws governing the eddy-driven transport associated with baroclinic turbulence. First, we provide a theoretical underpinning for empirical scaling laws reported in previous studies, for different formulations of the bottom drag law. Second, these scaling laws are shown to provide an important first step toward an accurate local closure to predict the impact of baroclinic turbulence in setting the large-scale temperature profiles in the atmosphere and ocean.