Collaborative Research: The role of microphysical processes and turbulence intermittency in droplet coalescence in warm cumulus clouds

合作研究：微物理过程和湍流间歇性在暖积云中液滴合并中的作用

基本信息

批准号：
1435953
负责人：
Donald Koch
金额：
$ 24.74万
依托单位：
Cornell University
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2014
资助国家：
美国
起止时间：
2014-09-01 至 2017-08-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1435953&HistoricalAwards=false
关键词：
Collaborative Research role microphysical processes

项目摘要

PI: Rani, Sarma L. /Koch, Donald L. Proposal Number: 1436100 / 1435953The goal of the proposed study is to explore the formation of droplets and the production of rain from a cumulus cloud. This is a topic relevant for the prediction of rainfall and of hazards such as tornados and flash flooding. Warm cumulus clouds exert significant influence on the climate system of the earth by processing atmospheric aerosols, interacting with electromagnetic radiation from the sun and earth, and redistributing earth's water and energy through the hydrologic cycle. This study addresses two central outstanding questions in the current understanding of warm rain production, namely, the mechanisms leading to the formation of fast-growing 'statistically fortunate' drops, and the growth of the cloud droplets, both of which hasten the 'colloidal instability' of the cloud, resulting in precipitation. To understand the effects of turbulence, it is essential to gain insights into the interactions between large-scale processes such as turbulent entrainment, mixing and intermittency, and microscale processes such as particle clustering, droplet relative velocities and collision efficiency. In terms of outreach and education, it is proposed to involve graduate and undergraduate students in interdisciplinary research at the confluence of turbulence, cloud and particle physics. The PIs plan to reach out to students at Alabama A&M University and Huntsville High School to encourage the students to pursue undergraduate and/or graduate degrees in STEM-related fields.The collaborating PIs will conduct a multiscale investigation, in which a Large Eddy Simulation (LES) will be used to model the whole cloud and to feed energy to a Direct Numerical Simulation (DNS) model, in order to explain how very small droplets appear and grow in size within a cloud. The hypothesis is that intermittency in turbulent shear and flow acceleration are driving the formation and the coalescence of the droplets. The proposed work is for high Reynolds number cloud turbulence at practical scales. Using the proposed energy transfer method, inertial-range LES turbulence intermittency information will be included in the DNS. The theoretical research will focus on developing stochastic models for both microscale and macroscale cloud physics including: 1) Detailed microscale models for the local flow field in the vicinity of bidisperse interacting drops with statistical properties characteristic of cloud Reynolds numbers; 2) Effects of particle inertia and differential sedimentation on the stochastic flow field ?seen? by the drops; 3) Effects of non-continuum, van der Waals and electrostatic interactions between drops on their collision efficiency; and 4) Macroscale model that accounts for the effects of turbulence intermittency and eddy mixing on the stochastic kinetics of droplet growth. The proposed research is expected to shed light on aerosol-cloud interactions that are important in generating precipitation and in affecting climate patterns.

PI：Rani，Sarma L. / Koch，Donald L.提案编号：1436100 /1435953拟议的研究的目标是探索液滴的形成和从积云云中产生雨水。这是一个与预测降雨和危害（例如龙卷风和山洪泛滥）有关的话题。温暖的积云云通过处理大气气溶胶，与来自太阳和地球的电磁辐射相互作用，对地球的气候系统产生重大影响，并通过水文循环重新分布地球的水和能量。这项研究解决了当前对温暖雨水生产的理解的两个核心问题，即导致形成快速增长的“统计上幸运”下降的机制，以及云滴的生长，这两者都加速了''胶体不稳定'云，导致降水。为了了解湍流的影响，必须深入了解大规模过程（例如湍流夹带，混合和间歇性）之间的相互作用，以及诸如粒子聚类，液滴相对速度和碰撞效率之类的显微镜过程。就宣传和教育而言，提议将研究生和本科生参与湍流，云和粒子物理学的融合。 PIS计划与阿拉巴马州A＆M大学和亨茨维尔高中的学生联系，以鼓励学生在与STEM相关的领域攻读本科和/或研究生学位。 LES）将用于对整个云进行建模并将能量馈送到直接的数值模拟（DNS）模型，以解释液滴在云中的出现和大小的大小。假设是湍流剪切和流动加速度的间歇性正在推动液滴的形成和聚结。拟议的工作是针对实际尺度上的高雷诺数云湍流。使用拟议的能量转移方法，DNS中将包括惯性范围LES湍流间歇性信息。理论研究将着重于为微观和宏观云物理学开发随机模型，包括：1）在bidisperse相互作用滴滴与云雷诺数的统计特性特征的局部流场相互作用的局部流场的详细微观模型； 2）粒子惯性和差分沉积对随机流场的影响吗？通过滴； 3）非义大星，范德华和滴之间的静电相互作用对它们的碰撞效率的影响； 4）宏观模型，该模型解释了湍流间歇性和涡流混合对液滴生长的随机动力学的影响。拟议的研究预计将阐明气溶胶云相互作用，这些相互作用对于产生降水和影响气候模式很重要。