Combined Laboratory and Modeling Studies of Ice Vapor Growth

低层大气中的任何地方都可能存在含冰的云层。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。低层云可能同时包含液体和冰，而中层云在大部分纬度包含一些液体。冰晶呈现出各种复杂的形状，仅靠水蒸气扩散就能长大。冰的存在使云微物理、动力学和辐射之间的联系变得复杂，使得精确的云模拟变得困难。事实证明，汽相中的冰生长是这一链中的关键但令人困惑的一环。以前的实验室测量表明，对于小冰晶来说，沉积系数(衡量生长效率的指标)非常小。此外，现在看来，纵横比预测对于模拟含冰云可能是关键的；然而，关于生长过程中晶面上的质量分布存在相互竞争的假设。模拟研究表明，卷云中模拟的冰浓度和过饱和度以及混合相云的冰化速率敏感地依赖于冰的生长速率。智力上的优点。这项综合研究将重点放在气相的冰生长上，目的是减少过去测量中的不确定性，并测试关于分子掺入和纵横比演变的假设。实验室方法利用电动悬浮将冰粒与系统壁隔离，并允许在精确控制的条件下跟踪冰粒的生长。作为尺寸、过饱和度、温度和纵横比的函数，将获得新的蒸汽增长速率测量结果。这些数据将被用来测试相互竞争的增长假设，并约束云模型中的参数化。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。这项实验室建模研究提供的协同效应将为目前限制我们准确预测云层演化能力的鲜为人知的冰川过程提供新的线索。这项研究对大气科学和社会具有潜在的广泛影响。在所有模拟尺度的含冰云的模拟中都存在很大的不确定性，这表明改进模式中的冰蒸汽增长参数的结果在科学上可能是深远的。这项研究将培养研究生，并让高级本科生接触到现代研究。该研究和实验室还可以向包括K-12学生在内的不同受众进行演示。

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. Previous laboratory measurements suggest that the deposition coefficient, a measure of growth efficiency, is very small for small ice crystals. In addition, it now appears that aspect ratio prediction may be critical for the simulation of ice-containing clouds; however competing hypotheses exist regarding mass distribution on the crystal faces during growth. Modeling studies show that simulated ice concentrations and supersaturation in cirrus clouds, as well as the rates of glaciation of mixed-phase clouds, depend sensitively on ice growth rates. Intellectual merit. This integrated study will focus on ice growth from the vapor phase with the intention to reduce uncertainties in past measurements and to test hypotheses regarding molecular incorporation and aspect ratio evolution. 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 aspect ratio. These data will be used to test competing growth hypotheses and constrain the parameterizations 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 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 research and laboratory can also be demonstrated to diverse audiences, including K-12 students.