Droplet Freezing in the Atmosphere

水滴在大气中结冰

• 批准号: 0211247
• 负责人: Marcia Baker
• 金额: $ 32.65万
• 依托单位: University of Washington
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-08-01 至 2006-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0211247&HistoricalAwards=false
• 关键词: Droplet; Freezing; Atmosphere

Atmospheric models used to predict precipitation and the effects of clouds on solar and terrestrial radiation are sensitive to variations in the types of ice crystals in clouds and their concentration, yet the processes by which drops freeze in clouds are not understood well enough to make reliable estimates of the ice content. This project is an investigation of the atmospheric relevance of several droplet freezing mechanisms that have been suggested on the basis of laboratory observations or theory. These include homogeneous freezing of solution drops and heterogeneous freezing as a result of evaporation that creates either organic surface films or solid phase inclusions within drops. Numerical modeling of these processes will be compared with existing data from several field programs to determine the extent to which the modeling results can be brought into accord with observations. One of the objectives is to study the conditions under which evaporation at the edges of clouds can promote freezing by heterogeneous nucleation. Another is to attempt to explain recent observations indicating that the homogeneous freezing temperature of solution drops depends only on the water activity, a measure of the reduction in equilibrium vapor pressure of the drop compared to pure water. Results of this research will contribute fundamentally to understanding ice formation in the atmosphere, and thus enable the improvement of weather and climate models in which the details of cloud composition are important.

用于预测降水和云对太阳和地面辐射影响的大气模型对云中冰晶类型及其浓度的变化很敏感，但对云中水滴冻结的过程还没有足够的了解，无法对冰含量做出可靠的估计。 该项目是一项关于几种根据实验室观测或理论提出的液滴冻结机制与大气相关性的调查。 这些包括溶液液滴的均匀冷冻和由于蒸发而产生的非均匀冷冻，所述非均匀冷冻在液滴内产生有机表面膜或固相内含物。 这些过程的数值模拟将与几个现场项目的现有数据进行比较，以确定模拟结果与观测结果的雅阁程度。 目的之一是研究在云的边缘蒸发可以促进冻结的非均质成核的条件。 另一个是试图解释最近的观察表明，均匀的冻结温度的溶液滴只取决于水的活动，减少的平衡蒸汽压的下降相比，纯水的措施。 这项研究的结果将从根本上有助于了解大气中的冰的形成，从而能够改进天气和气候模型，其中云组成的细节很重要。