Multi-Scale Modeling of Fine-Scale Structure and Droplet Spectral Evolution in Cumulus Clouds

这个项目将使用云模型来研究混合如何影响积云中云滴的大小分布。这是更广泛的“海洋积云中的雨”（RICO）实验的一部分，这是一个涉及超过15个机构的合作实验，计划在2004年12月和2005年1月观察信风积云的特性，然后对这些测量结果进行数年的分析。RICO的中心目标是了解导致热带积云降水的过程，其中一个需要解决的重要问题是云滴如何碰撞并成长为雨滴大小。一种可能的解释是，混合增加了云中液滴大小的范围，从而增加了不同大小的液滴之间的碰撞率。本项目将通过使用一种建模技术来研究这种可能性和其他可能性，该技术将精细尺度结构的一维表示嵌入到更大规模云结构的三维模型中。通过这种方式，研究人员获得了真实的轨迹和云场，同时也模拟了湍流产生的精细尺度结构。有了这个模型，研究人员将评估对液滴尺寸分布扩大的几个潜在贡献者的相对重要性。作为这项工作的一部分，他们还将评估和改进产生三维云场的大涡模拟（LES）模型。预计RICO和本项目的长期影响是，信风积云和暖云降雨的影响将在天气和气候模式中得到更准确的反映，从而改进对降雨的预测。这项研究还将对导致云滴大小分布扩大的各种过程的相对重要性进行评估，并将导致在积云模型中表示精细湍流场的新技术。该项目还将通过研究人员参与RICO研究生系列研讨会和在研究生参与研究时对他们进行培训，为研究生教育作出贡献。

This project will use models of clouds to study how mixing affects the size distribution of cloud droplets in cumulus clouds. It is part of the broader "Rain in Cumulus over the Ocean" (RICO) experiment, a collaborative experiment involving more than 15 institutions that plans to observe properties of trade-wind cumulus clouds in December 2004 and January 2005 and then analyze those measurements for several years. A central goal of RICO is to understand the processes leading to precipitation in tropical cumulus clouds, and an important question to be addressed is how cloud droplets collide and grow to raindrop size. One candidate explanation is that mixing increases the range of droplet sizes present in the cloud and so increases the rate of collisions among droplets of different size. This project will investigate that possibility and others through use of a modeling technique that embeds a one-dimensional representation of the fine-scale structure within a three-dimensional model of larger-scale cloud structure. In this way, the investigators obtain realistic trajectories and cloud fields while also simulating the fine-scale structure produced by turbulence. With this model, the investigators will evaluate the relative importance of several potential contributors to the broadening of droplet size distributions. As part of this work, they will also evaluate and improve the large-eddy simulation (LES) model that produces the three-dimensional cloud fields.The expected long-range impact of RICO and of this project is that the effects of trade-wind cumulus clouds and of rain from warm clouds will be represented more accurately in weather and climate models, leading to improved predictions of rainfall. The research will also result in an assessment of the relative importance of various processes that cause cloud droplet size distributions to broaden, and it will lead to new techniques for representing fine-scale turbulent fields in models of cumulus clouds. The project will also contribute to graduate education through participation by the investigators in the RICO Graduate Student Seminar Series and through training of graduate students as they participate in the research.