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

主要研究者：拉尼，Sarma L.作者：Koch，Donald L.提案编号：1436100 /1435953拟议研究的目标是探索积云中水滴的形成和降雨的产生。这是一个与预测降雨和龙卷风、山洪等灾害有关的主题。暖积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，并通过水文循环重新分配地球的水和能量，对地球的气候系统产生重要影响。这项研究解决了两个中心突出的问题，在目前的理解暖雨生产，即，机制导致形成快速增长的“统计上幸运”的下降，和云滴的增长，这两者都加速了“胶体不稳定”的云，导致降水。为了理解湍流的影响，必须深入了解大尺度过程（如湍流卷吸、混合和湍流）与微尺度过程（如颗粒聚集、液滴相对速度和碰撞效率）之间的相互作用。在外联和教育方面，建议让研究生和本科生参与湍流、云和粒子物理学交汇处的跨学科研究。研究所计划接触亚拉巴马农工大学和亨茨维尔高中的学生，鼓励他们攻读STEM相关领域的本科和/或研究生学位。合作的研究所将进行多尺度调查，其中大涡模拟（LES）将用于模拟整个云，并将能量输入直接数值模拟（DNS）模型，以解释非常小的液滴如何在云中出现和尺寸增长。假设是湍流剪切和流动加速中的不稳定性驱动液滴的形成和聚结。建议的工作是高雷诺数云湍流在实际尺度。使用所提出的能量传递方法，惯性范围LES湍流不稳定性信息将被包括在DNS中。理论研究将集中于发展微尺度和大尺度云物理的随机模型，包括：1）具有云雷诺数统计特性的双分散相互作用液滴附近局部流场的详细微尺度模型; 2）颗粒惯性和差异沉降对随机流场的影响？看见了吗？滴，3）液滴之间的非连续、货车德瓦耳斯和静电相互作用对它们的碰撞效率的影响;以及4）宏观尺度模型，该模型解释了湍流不稳定性和涡流混合对液滴生长的随机动力学的影响。拟议的研究有望阐明气溶胶-云的相互作用，这对产生降水和影响气候模式至关重要。

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.