Microphysics of Clouds and Precipitation

云与降水的微观物理学

• 批准号: 0314049
• 负责人: Ramesh Srivastava
• 金额: $ 33.23万
• 依托单位: University of Chicago
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2003
• 资助国家: 美国
• 起止时间: 2003-07-01 至 2007-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0314049&HistoricalAwards=false
• 关键词: Microphysics; Clouds; Precipitation

AbstractATM-0314049Srivastava, Ramesh C.University of ChicagoTitle: Microphysics of Clouds and PrecipitationThis project is a continuation of theoretical and observational investigations of certain aspects of cloud and precipitation physics. It comprises the following three topics:1. Growth of cloud drops by condensation. A long-standing puzzle in cloud physics is the discrepancy between observed drop-size distributions in clouds and the distributions predicted from classical condensation-diffusion theory. The observed distributions are broader than those predicted, with important implications for the development of rain by the collision-coalescence process, because broad distributions favor collisions and a more rapid production of large drops. Many mechanisms have been suggested in the past for explaining the discrepancy, though none is generally accepted. This project focuses on two effects: the slow broadening of the distribution caused by the greater equilibrium vapor pressure over the smaller drops, and the broadening caused by fine-scale fluctuations of humidity in the vicinity of drops.2. Growth of drops by the simultaneous action of condensation and coalescence. The rate of growth of drops by the collision-coalescence process increases in a rapid and nonlinear way with increasing drop size. The usual approach is to calculate growth by condensation until the drops become large enough for collisions to occur, and to calculate growth by collision-coalescence from there on, because it quickly becomes much more important than condensation. However, even a small increase in drop size by condensation causes a substantial increase in the collision efficiency, so the two processes acting simultaneously produce more rapid growth than obtained by treating them separately and adding the results. The project will develop new computational methods of treating condensation and coalescence simultaneously.3. Evaporation of rain from stratiform clouds. Rain falling through subsaturated air below cloud base evaporates and cools the air. The effect should be taken into account in large-scale models that include parameterizations for the effects of clouds and precipitation. The approach here is to compute the dependence of sub-cloud evaporation on the drop-size distribution and the vertical profiles of temperature, humidity, and vertical air velocity. An objective is to develop ways of estimating the evaporation from the vertical profile of radar reflectivity below the cloud.These studies contribute to the fundamental understanding of precipitation development and to applications such as the remote measurement of precipitation by radar.

云和降水的微观物理学这个项目是云和降水物理学某些方面的理论和观测研究的继续。 它包括以下三个主题：1。凝结作用下云滴的增长。 云物理学中一个长期存在的难题是观测到的云中水滴尺寸分布与经典凝聚扩散理论预测的分布之间的差异。 观察到的分布比预测的更广泛，与发展的雨的碰撞合并过程的重要影响，因为广泛的分布有利于碰撞和更快地生产大滴。 过去曾提出过许多解释这种差异的机制，但没有一种被普遍接受。 该项目侧重于两个效果：由较小的液滴上的较大平衡蒸汽压引起的分布的缓慢加宽，以及由液滴附近的湿度的精细尺度波动引起的加宽。2.由于凝结和聚结的同时作用而产生的液滴增长。 通过碰撞-聚结过程的液滴增长速率随着液滴尺寸的增加而以快速和非线性的方式增加。 通常的方法是通过冷凝来计算增长，直到液滴变得足够大，足以发生碰撞，然后从那里开始计算碰撞合并的增长，因为它很快变得比冷凝更重要。 然而，即使是小的增加液滴大小的冷凝导致碰撞效率的大幅增加，所以这两个过程同时作用产生更快的增长比通过单独处理它们并将结果相加获得。 该项目将开发新的计算方法来处理凝结和聚结的错误.雨水从层状云中蒸发。 雨通过云底以下的不饱和空气降落，蒸发并冷却空气。 在包括云和降水影响参数化的大尺度模型中应考虑到这种影响。 这里的方法是计算云下蒸发的水滴大小分布和垂直廓线的温度，湿度和垂直空气速度的依赖性。 目的之一是发展从云层下雷达反射率的垂直廓线估算蒸发量的方法，这些研究有助于对降水发展的基本了解，并有助于诸如用雷达遥测降水量等应用。