Effects of Turbulent Dissipation and Pressure Perturbations on Clouds

湍流耗散和非静水压力扰动对云场的结构和演化有着深刻的影响。例如，干燥的环境空气与积云的湍流混合可能会大大降低积云的浮力和水分含量。将这一过程视为夹带中的一个问题会引起争议，部分原因是夹带难以以精确和实际有用的方式定义。相反，它可能有助于把注意力集中在湍流标量耗散上，例如，总含水量，它有一个数学定义，并明确地出现在总含水量方差方程中。再举一个例子，逆温正下方的层积云的风场是高度各向异性的，上面的静稳定性抑制了垂直运动，而不是水平运动。智力优势：对这些现象的研究在一定程度上受到观测测量困难的阻碍。然而，最近出现了两个新的机会。首先，在模拟各种云情况的大涡模拟（LES）模型中，新的和有用的诊断方法正在变得可用。特别是，速度和标量方差的预算，以及耗散率的估计都变得可用。其次，高阶闭合参数化可以利用对湍流和压力影响的更好理解，现在已经在天气预报和气候模式中实施。这使得探索小规模湍流过程如何影响大规模涌现云特性成为可能。为了探索云场中的湍流和压力过程，将采取几个步骤。首先，将在LES模型中实施额外的预算和诊断。其次，为了更好地理解湍流和压力相关行为，将分析云案例的LES。第三，LES输出将用于评估现有的和新的湍流耗散和压力协方差的参数化。最后，将进行各种参数化的区域和全球模拟，以便更好地了解不同假设如何影响大尺度场。更广泛的影响：自2007年以来，该研究小组一直在为当地一所本科院校的软件工程专业学生提供实习机会。这些本科生亲眼目睹了使用大型软件的威力和缺陷。作为回报，学生们帮助项目改进软件开发。11名本科生完成了实习，都在软件行业找到了不错的工作。这个项目将继续这个学生的培训。此外，该项目将培养一名研究生，广泛传播研究成果，并改进可能用于天气预报和气候模型的建模技术。

Turbulent dissipation and non-hydrostatic pressure perturbations have profound effects on the structure and evolution of cloud fields. For example, turbulent mixing of dry environmental air into cumulus clouds may greatly reduce their buoyancy and moisture content. Viewing this process as a problem in entrainment has led to controversy in part because entrainment is difficult to define in a precise and practically useful way. Instead, it may help to focus attention on the turbulent scalar dissipation of, e.g., total water content, which has a mathematical definition and appears explicitly in the equation for the variance of total water. To cite another example, wind fields are highly anisotropic in stratocumulus layers just below the inversion, with the static stability above suppressing vertical motion but not horizontal motion. Intellectual Merit:Study of these phenomena has been impeded in part by the difficulty of making observational measurements. Recently, however, two new opportunities have arisen. First, new and useful diagnostics are becoming available in large-eddy simulation (LES) models that have simulated a variety of cloud cases. In particular, budgets of velocity and scalar variances are becoming available, along with estimates of dissipation rate. Second, higher-order closure parameterizations that can take advantage of improved understanding of turbulence and pressure effects have now been implemented in weather forecast and climate models. This enables the possibility of exploring how small-scale turbulent processes influence large-scale emergent cloud properties.To explore turbulent and pressure processes in cloud fields, several steps will be undertaken. First, additional budgets and diagnostics will be implemented in a LES model. Second, LES of cloud cases will be analyzed in order to better understand the turbulent and pressure-related behaviors. Third, the LES output will be used to evaluate existing and new parameterizations of turbulent dissipation and pressure covariances. Finally, regional and global simulations with various parameterizations will be performed in order to better understand how different assumptions influence large-scale fields.Broader Impacts:The research group has been offering internships since 2007 to software engineering students at a local undergraduate institution. Those undergraduates see firsthand both the power and pitfalls of working with large pieces of software. In return, the students help the project to improve software development. Eleven undergraduates have completed the internships, and all have obtained good jobs in software. This program will be continued this student training. In addition, the project will train a graduate student, disseminate research broadly, and improve modeling techniques that may be of use in weather forecast and climate models.