Analysis and Parameterization of Evolving Raindrop Size Distributions

降水是影响云动态的一个重要因素。例如，云底以下的雨滴蒸发会冷却周围的空气，并影响云的发展。由于水的蒸发速率取决于水滴的表面积，因此水滴的大小分布在云的演化中起着重要的作用。因此，为了模拟对流云的动力学，有必要包括雨滴大小分布的实际公式。这类模型必须考虑到小规模微物理过程(如水滴蒸发)和较大规模微物理过程(如空气运动)之间的相互作用。由于这两类过程在明显不同的时间和空间尺度上运行，从计算的角度来看，在模型中包括微物理方程的详细解是不可行的。相反，这样的模型必须依赖于使用简单的公式来近似雨滴分布的演变。Brown教授在这项研究中的目的有两个：通过对模式方程和观测数据的分析，更好地了解相关的微物理过程；以及根据这些知识，开发用于对流云模式的描述雨滴尺寸分布演变的简单参数化公式。分析和参数化将考虑液滴合并、破碎和蒸发的微物理过程。

Precipitation is an important factor in the dynamics of clouds. For example, evaporation of raindrops below cloud base cools the surrounding air and influences cloud development. Since the rate of water evaporation depends on the surface area of the drops, the drop size distribution plays an important role in the cloud evolution. In order to model the dynamics of convective clouds, it thus is necessary to include a realistic formulation of the raindrop size distribution. Such models must take account of the interaction between the small-scale microphysical process (such as water drop evaporation) and the larger-scale microphysical processes (such as air motion). Since the two types of processes operate on significantly different time and space scales, it is not feasible from a computational standpoint to include in the models detailed solution of the microphysical equations. Instead, such models must rely on the use of simple formulas to approximate the evolution of the raindrop distribution. Professor Brown's object in this research is twofold: to obtain a better knowledge of the relevant microphysical processes through analysis of model equations and observational data; and from this knowledge to develop simple parameterization formulas describing the evolving raindrop size distribution for use in convective cloud models. The analysis and parameterization are to take account of the microphysical processes of drop coalescence, breakup and evaporation.//