Combined Laboratory and Modeling Studies of Ice Vapor Growth at Low Temperatures

含冰云可以存在于低层大气中的任何地方。对流层上层的卷云就是一个常见的例子，它们全部或大部分由冰组成。低层云可能同时含有液体和冰，而中层云在大多数纬度都含有一些液体。冰晶呈现出各种复杂的形状，单靠蒸汽扩散就能变大。冰的存在使云微物理、动力学和辐射之间的联系变得复杂，使精确的云模拟变得困难。在这个过程中，由气相形成的冰被证明是一个关键但又令人困惑的环节。最近的实验室测量表明，对于小冰晶来说，沉积系数（一种生长效率的衡量标准）很小，而且它取决于过饱和度。模拟研究表明，卷云中模拟冰的浓度和过饱和度，以及混合相云的冰川速率，都敏感地依赖于冰的增长速率。这项工作旨在促进对冷大气云中冰蒸汽生长的理解。智力优势：这个综合研究将产生实验室和建模研究之间的协同作用。这项工作将集中在从气相生长的冰上，目的是减少过去沉积系数测量中的不确定性。实验室方法利用电动悬浮将冰粒从系统壁上分离出来，并允许在精确控制的条件下跟踪冰粒的生长。蒸汽生长速率的新测量将作为尺寸、过饱和、温度和压力的函数而得到。这些数据可以用来探索与冰晶在大气中经历的环境条件相似的沉积系数的依赖关系。此外，这些数据还可以用来评价新的和常用的蒸汽增长方法，并约束云模式中使用的参数化。冰晶生长理论和数值模型将为实验室工作提供指导，帮助解释实验结果，并为将实验室结果扩展到云系统提供框架。这项实验室模拟研究提供的协同作用将有助于揭示目前限制我们准确预测云演变能力的知之甚少的冰过程。更广泛的影响：本研究对大气科学和社会具有潜在的广泛影响。在所有模式尺度上对含冰云的模拟存在很大的不确定性，这表明在模式中改进冰蒸汽增长参数化的结果可能具有深远的科学意义。这项研究将培养研究生，并使高级本科生接触到现代研究。该作品还可以向包括K-12学生在内的不同观众展示。此外，计划利用学院资源，继续开发包裹微物理模型作为课堂教学工具。

Ice-containing clouds can exist anywhere within the lower atmosphere. Cirrus clouds in the upper troposphere are a common example, being composed entirely or mostly of ice. Low-level clouds may contain both liquid and ice while mid-level clouds contain some liquid at most latitudes. Ice crystals take on a variety of complex shapes and can grow large by vapor diffusion alone. The presence of ice complicates the links between cloud microphysics, dynamics, and radiation, making accurate cloud simulations difficult. Ice growth from the vapor phase proves to be a key but perplexing link in this chain. Recent laboratory measurements suggest that the deposition coefficient, a measure of growth efficiency, is small for small ice crystals and that it depends on the supersaturation. Modeling studies show that simulated ice concentrations and supersaturations in cirrus clouds, as well as the rates of glaciation of mixed-phase clouds, depend sensitively on ice growth rates. The work herein seeks to advance understanding of ice vapor growth in cold atmospheric clouds.Intellectual merit:This integrated study will produce a synergy between laboratory and modeling research. The work will focus on ice grown from the vapor phase with the intention being to reduce uncertainties in past measurements of the deposition coefficient. The laboratory methods make use of electrodynamic levitation to isolate ice particles from system walls and permit particle growth to be followed under precisely controlled conditions. New measurements of vapor growth rates will be obtained as functions of size, supersaturation, temperature, and pressure. These data can be used to explore the dependence of the deposition coefficient on environmental conditions similar to those ice crystals experience in the atmosphere. Moreover, these data can also be used to critique new and commonly used vapor growth methods, and constrain the parameterizations used in cloud models. Ice crystal growth theories and numerical models will provide guidance to the laboratory work, help interpret experimental findings, and provide a framework for extending lab results to cloud systems. The synergism afforded by this laboratory-modeling study will help shed new light on poorly understood ice processes that are currently limiting our ability to accurately predict cloud evolution.Broader impacts:This research has potentially broad impacts on the atmospheric sciences and society. Large uncertainties exist in simulations of ice-containing clouds at all modeling scales indicating that the consequences of improving ice vapor growth parameterizations in models could be scientifically far-reaching. The research will train graduate students and give advanced undergraduate students exposure to modern research. The work can also be demonstrated to diverse audiences including K-12 students. Moreover, continue development of parcel microphysical models as classroom teaching tools using College resources is planned.