A Theory of Baroclinic Turbulence
A Theory of Baroclinic Turbulence
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斜压湍流理论
DOI：
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发表时间：
2009
期刊：
影响因子：
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通讯作者：
P. Ioannou
中科院分区：
文献类型：
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作者：
B. Farrell;P. Ioannou
理解维持流体湍流的物理机制仍然是一个基本的理论问题。两层模型是一个分析和计算简单的系统，可以方便地研究湍流的动力学；在本工作中，建立了该系统中统计定常湍流状态的最大简化模型，以分离和识别湍流的基本机制。在这个最小复杂的湍流模型中，非线性的影响被用时空白色的能量相容随机过程来参数化，湍流通量用随机湍流模型(STM)得到，统计定常的湍流状态用随机结构稳定性理论(SSST)识别。这些湍流态是非线性SSST系统的不动点平衡点。对于中纬度大气的典型参数值，这些平衡预测了边缘稳定的涡旋驱动斜压急流的出现。与这些急流相关的涡方差和涡通量以及涡方差和涡通量的幂律尺度与斜压湍流的观测和模拟是一致的。这个最简单的模式隔离了斜压湍流的基本物理：通过瞬变扰动增长来维持方差，通过非线性能量守恒的涡旋散射来补充瞬变增长的子空间，通过非线性涡流诱导的平均喷流修正和涡散的组合平衡到边缘稳定的统计稳定状态。这些统计平衡态为斜压湍流行星大气的一般环流提供了理论依据。
Understanding the physical mechanism maintaining fluid turbulence remains a fundamental theoretical problem. The two-layer model is an analytically and computationally simple system in which the dynamics of turbulence can be conveniently studied; in this work, a maximally simplified model of the statistically steady turbulent state in this system is constructed to isolate and identify the essential mechanism of turbulence. In this minimally complex turbulence model the effects of nonlinearity are parameterized using an energetically consistent stochastic process that is white in both space and time, turbulent fluxes are obtained using a stochastic turbulence model (STM), and statistically steady turbulent states are identified using stochastic structural stability theory (SSST). These turbulent states are the fixed-point equilibria of the nonlinear SSST system. For parameter values typical of the midlatitude atmosphere, these equilibria predict the emergence of marginally stable eddy-driven baroclinic jets. The eddy variances and fluxes associated with these jets and the power-law scaling of eddy variances and fluxes are consistent with observations and simulations of baroclinic turbulence. This optimally simple model isolates the essential physics of baroclinic turbulence: maintenance of variance by transient perturbation growth, replenishment of the transiently growing subspace by nonlinear energetically conservative eddy‐eddy scattering, and equilibration to a statistically steady state of marginal stability by a combination of nonlinear eddy-induced mean jet modification and eddy dissipation. These statistical equilibrium states provide a theory for the general circulation of baroclinically turbulent planetary atmospheres.