Integrated Laboratory and Modeling Studies of Early Cold-Cloud Development

在温度低于0摄氏度的大气云中发生的微物理过程链中，令人困惑的环节之一是来自蒸汽相的冰粒的生长。最近的实验室测量表明，对于小冰晶来说，质量容纳系数(衡量生长效率的指标)非常小。数值模拟研究表明，模拟的卷云中冰粒浓度和过饱和度以及混合相云的冰川速率都敏感地依赖于假定的质量调节系数。如果质量调节系数较低，则不断增长的冰粒不会像系数较高时那样有效地消耗水蒸气的过饱和。然后，过饱和度在上升的云团中达到更高的水平，由于更高的过饱和度，更多的冰粒在合适的气溶胶粒子上成核。较小增长的冰粒浓度的增加最终耗尽过饱和水蒸气，云达到成熟状态时，与质量调节系数较高的情况相比，云中较小粒子的浓度更高。这项综合的实验室-模拟研究集中在气相冰的早期生长，以减少过去测量和模拟中的不确定性，并检验关于气相沉积的分子机制的假设。近年来，实验室技术和数值模拟能力都已经非常成熟，现在可以取得重大的新进展。实验室方法利用电动悬浮将单个冰粒与系统壁隔离，并允许在精确控制的环境条件下无限期地跟踪冰粒的生长。作为大小和过饱和度函数的冰增长速度的新数据将有助于限制云模型中冰增长的数学表示。将结合实验室数据使用一套数值模型来指导实验室工作，从机理上解释实验结果，并提供一种将我们的实验室结果外推到云尺度系统的方法。这项实验室模拟研究提供的协同作用将使目前限制准确模拟冷云演变能力的冰过程获得新的曙光。这项研究对大气科学和社会具有潜在的广泛影响。更好地了解冷云的微物理演变将加强对云在天气和气候过程中所起作用的理解。这项研究将培养研究生，并让高级本科生在建模和实验方面接触到现代研究方法。过去向不同受众展示云过程的成功经验将继续与学院博物馆合作，帮助将这些过程与新一代K-12学生联系起来。此外，包裹微物理模型将利用大学资源开发成基于网络的大学课堂教学工具。

One of the confounding links in the chain of microphysical processes occurring in atmospheric clouds at temperatures below 0 degress C is the growth of ice particles from the vapor phase. Recent laboratory measurements suggest that the mass accommodation coefficient, a measure of growth efficiency, is very small for small ice crystals. Numerical modeling studies have shown that the simulated concentrations of ice particles and supersaturations in cirrus clouds, as well as the rates of glaciation of mixed-phase clouds, all depend sensitively on the assumed mass accommodation coefficient. If the mass accommodation coefficient is low, then growing ice particles do not deplete the supersaturation of water vapor as effectively as they would if the coefficient was higher. Then supersaturations reach higher levels in ascending cloud parcels, and more ice particles are nucleated on suitable aerosol particles due to the higher supersaturations. The increase in concentration of smaller growing ice particles eventually depletes the supersaturated vapor and the cloud reaches a mature state with higher concentrations of smaller particles than would be the case if the mass accommodation coefficient were higher.This integrated laboratory-modeling study is focused on the early growth of ice from the vapor phase in order to reduce uncertainties in past measurements and simulations, and to test hypotheses regarding the molecular mechanisms of vapor deposition. Both laboratory techniques and numerical modeling capabilities have matured greatly in recent years, now permitting significant new progress to be made. The laboratory methods make use of electrodynamic levitation to isolate individual ice particles from system walls and permit particle growth to be followed indefinitely under precisely controlled environmental conditions. New data on ice growth rates as functions of size and supersaturation will help constrain the mathematical representation of ice growth in cloud models. A suite of numerical models will be used in conjunction with the laboratory data to guide the laboratory work, interpret the experimental findings in terms of mechanisms, and provide a means for extrapolating our laboratory results to cloud-scale systems. The synergism afforded by this laboratory-modeling study will allow new light to be shed on ice processes that currently are limiting capability to simulate cold-cloud evolution accurately.This research has potentially broad impacts on the atmospheric sciences and society. Improved understanding of microphysical evolution of cold clouds will enhance understanding of the roles played by clouds in weather and climate processes. The research will train graduate students and give advanced undergraduate students exposure to modern research methods in modeling and experimentation. Past successes in demonstrating cloud processes to diverse audiences will be continued in collaboration with the College museum, helping to relate these processes to new generations of K-12 students. Moreover, parcel microphysical models will be developed into web-based college classroom teaching tools using College resources.