Geophysical turbulence

大气是一种极其湍急的流体：天气系统、飓风、雷暴和沙尘暴都是大气湍动的表现。涉及的长度尺度范围很广，从10 000多公里的行星尺度到1毫米的粘性耗散尺度，是天气和气候预测提出的理论和计算挑战的核心。由于计算资源有限，大气的数值模型无法分辨出这种全范围的尺度，数十甚至数百公里量级的运动往往不能被显式捕捉到。然而，这些尺度上的湍流对整个大气来说是极其重要的：它混合了热量、水蒸气和污染物，耗散了能量，甚至可以激发大范围的运动。这些缺失的过程必须在大气模型中解释，在缺乏关于湍流的全面理论的情况下，这通常是以特殊的方式进行的。我的研究计划旨在增进我们对中尺度大气湍流的理解，中尺度大气湍流对应于长度尺度约为1至1000公里的运动范围。正是在中尺度上，天气和气候模式被截断，如果要在大气模式中更好地反映其影响，就有必要更好地理解这一区域的湍流。理想化数值模拟将被用来研究中尺度湍流的基本动力学过程。将讨论的具体未决问题包括：从大尺度到小尺度的中尺度能量级联的性质；云注入的中尺度能量；以及非均匀密度层结的影响，例如在行星边界层和对流层顶附近发现的影响。与此同时，将开发和使用新的计算工具来开发集群和大规模并行计算机，这些计算机正变得越来越容易获得。这项工作将有助于评估天气和气候模式准确再现中尺度湍流的能力，并将为改进战略提供依据。

The atmosphere is an extremely turbulent fluid: weather systems, hurricanes, thunderstorms, and dust devils are all manifestations of atmospheric turbulence. The enormous range of length scales involved, from the planetary scale of more than 10,000 km to the viscous dissipation scale of 1 mm, is at the heart of the theoretical and computational challenge presented by weather and climate prediction. Due to limited computational resources, numerical models of the atmosphere cannot resolve this full range of scales, and motions on the order of tens or even hundreds of kilometers are often not captured explicitly. However, turbulence on these scales is extremely important for the atmosphere as a whole: it mixes heat, water vapor, and pollutants, dissipates energy, and can even excite large-scale motion. These missing processes must be accounted for in atmospheric models, and in the absence of a comprehensive theory for turbulence, this is usually done in an ad hoc manner. My research program aims to advance our understanding of atmospheric turbulence in the mesoscale, which corresponds to the range of motions with length scales between around 1 and 1000 km. It is in the mesoscale where weather and climate models are truncated, and an improved understanding of turbulence in this regime is necessary if its effects are to be better represented in atmospheric models. Idealized numerical simulations will be employed to investigate the fundamental dynamical processes of mesoscale turbulence. Specific open questions that will be addressed include the nature of the mesoscale energy cascade from large to small scales; the injection of mesoscale energy by clouds; and the effect of non-uniform density stratification, such as that found near the planetary boundary layer and tropopause. At the same time, new computational tools will be developed and employed to exploit clusters and massively parallel computers, which are becoming increasingly accessible. This work will help to assess the ability of weather and climate models to accurately reproduce mesoscale turbulence and will inform strategies for improvements.