Radiative Cooling and Homogeneous Droplet Freezing in Laboratory Clouds

目前全球范围内传入的太阳辐射和传出的红外辐射之间的失衡继续使我们的星球变暖。变暖的大气中的水量也在继续增加。水的相变-蒸发、凝结和冻结-是驱动龙卷风、超级单体雷暴、飓风等灾害性天气的重要过程，但目前我们对这些相变过程及其与辐射的相互作用的了解还不够。为了加深我们对水的这些相变的了解，改进灾害性天气预报和长期气候变化预报，本研究将进行实验室和分析/理论研究。该项目将帮助培训一名在HBCU机构获得硕士学位的女性博士研究生。将为K-12年级的学生举办关于水性质、相变热传递和全球气候变化的本地工作坊。在这项研究中，辐射诱导的云滴生长、冷却和冻结将在实验室产生的云中进行实验研究，并通过分析和理论模型进行计算。将进行实验室实验，云滴将暴露在辐射冷却中，类似于在特热带、冷季气旋或其他风暴系统中的云顶发电单元中发生的情况。冷却将导致液滴的均匀冻结。将测量由于传质(主要是通过冷凝增长)造成的液滴尺寸变化以及温度变化。建立了辐射冷却和冷凝过程的分析模型。将对最近受到质疑的均匀(液滴非特定)过饱和度和液滴非特定辐射的常见建模假设进行研究和改进。实验室测量将用于开发和验证新的建模假设，方法是将测量结果与分析预测进行比较。对于液滴特有的、非均质过饱和的影响，将发展新的理论。还将获得有关具有溶质的均匀冻结液滴状态的新的基本科学信息。这些结果将影响云微物理中的一个基本问题：在复杂的、不断变化的流体力学、热力学和辐射大气环境中对云滴演化进行数值模拟的问题。这项研究的结果可能导致对基本工艺的新的和更深入的理解，这些基本工艺不仅有利于环境和气候，而且有利于工程和技术的其他领域，如相变换热器设计和电子冷却。这项研究的最终广泛影响是为理解云微物理以及进行天气预报和全球环流和气候建模提供了更好的科学基础。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The current global imbalance between incoming solar radiation and outgoing infrared radiation continues to warm our planet. The amount of water in the warming atmosphere also continues to increase. Phase changes of water—evaporation, condensation, and freezing—are the important processes that drive tornadoes, super-cell thunderstorms, hurricanes and other severe weather; but our understanding about these phase-change processes and their interactions with radiation is still insufficient at present. To increase our understanding of these phase changes of water and improve severe weather forecast and long-term climate change prediction, laboratory and analytical/theoretical study will be carried out in this study. This project will help to train a female PhD graduate student who received her master’s degree at an HBCU institution. Local workshops will be conducted for K-12 students on water properties, phase-change heat transfer, and global climate change.In this research, radiatively induced cloud-droplet growth, cooling, and freezing will be studied both experimentally in laboratory-produced clouds and computationally with analytical and theoretical modeling. Laboratory experiments will be conducted in which cloud droplets will be exposed to radiative cooling, similar to what can happen in cloud-top generating cells in extra-tropical, cold-season cyclones or other storm systems. Cooling will be such as to induce homogeneous freezing of droplets. Changes in droplet size due to mass transfer (primarily growth via condensation) will be measured as well as temperature changes. An analytical model of the radiative cooling and condensation process will be developed. The common modeling assumptions of homogeneous (droplet-non-specific) supersaturation and droplet-non-specific radiation, which have recently been questioned, will be investigated and improved upon. Laboratory measurements will be used to develop and validate new modeling assumptions by comparing the measurements with analytical predictions. New theory will be developed for the effect of droplet-specific, non-homogeneous supersaturation. New basic scientific information about the state of homogeneously frozen droplets with solute will also be obtained. These results will impact a fundamental problem in cloud microphysics: the problem of numerically modeling cloud droplet evolution in a complex, constantly changing fluid dynamic, thermodynamic, and radiative atmospheric environment. The results of this study could lead to a new and deeper understanding of basic processes that will not only benefit the environment and climate but other areas of engineering and technology such as phase-change heat exchanger design and electronics cooling. The ultimate broad impact of this study is a better scientific basis for understanding cloud microphysics and for conducting weather prediction and global circulation and climate modeling.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.