弱超临界行星大气宏观湍流的标度理论
A scaling theory for the macroturbulence of weakly supercritical planetary atmospheres
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中文总结 AI 辅助
针对弱超临界行星大气，提出基于纬向动量平衡和运动学效应的新标度理论，统一解释干大气环流模拟中的涡旋热通量，并成功预测全球温度分布。
中文摘要 AI 辅助
大气环流理论必须建立在宏观湍流理论的基础上。其核心组成部分之一是近地面涡旋热通量，它与环流地表分支的质量输运密切相关。现有的标度理论主要基于两层准地转框架，该框架假设超临界状态和动能逆级联——这些条件在行星大气（包括地球大气）中常常得不到满足。尽管如此，此类理论已显示出一定的经验成功，例如，即使在没有逆能量级联的情况下，Rhines尺度也与混合长度相关联。在此，我们分析了数百个理想化的干大气环流模型模拟，这些模拟涵盖了广泛的旋转速率、经向温度梯度、垂直层结和季节性变化。大多数模拟处于临界边缘状态，而强非线性标度理论在此状态下失效。我们提出了一种新理论，该理论能够捕捉所有模拟中的区域平均和局部涡旋热通量行为。该理论利用纬向动量平衡的标度论证，并考虑了涡旋混合的运动学效应。该标度依赖于一个无量纲的热力Rossby数，并隐含地考虑了跨急流的非线性涡旋动量通量的作用。我们展示了所提出的标度在简单能量平衡模型中解释广泛气候状态下全球近地表温度分布的能力。最后，讨论了对环流理论的意义以及将标度扩展到湿大气的可能性。
英文摘要
A theory for the general circulation of the atmosphere must be based on a theory of its macroturbulence. A central component is the near-surface eddy heat flux, which is closely tied to the mass transport of the surface branch of the circulation. Existing scaling theories are largely formulated within the two-layer quasi-geostrophic framework, which assumes supercritical states and an inverse cascade of kinetic energy---conditions that are frequently not satisfied in planetary atmospheres, including Earth's. Nevertheless, such theories have shown some empirical success, including that the Rhines scale is associated with the mixing length even in the absence of any inverse energy cascade. Here, we analyze hundreds of idealized, dry general circulation model simulations spanning wide ranges of rotation rates, meridional temperature gradients, vertical stratification, and seasonality. Most simulations reside in the marginally critical regime where strongly nonlinear scaling theories fail. We propose a new theory that captures both domain-averaged and local eddy heat flux behavior across all simulations. The theory uses scaling arguments for the zonal momentum balance and accounts for kinematic effects on eddy mixing. The scaling depends on a non-dimensional thermal Rossby number and implicitly accounts for the role of nonlinear eddy momentum fluxes across jets. We demonstrate the skill of the proposed scaling in explaining global near-surface temperature distributions across a wide range of climate states in a simple energy balance model. Implications for general circulation theory and extending the scalings to moist atmospheres are discussed.
发表机构
- California Institute of Technology（加州理工学院）
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