Ice Nucleation in Maritime Cumuli: Considering Dynamical and Microphysical Interactions

云中冰晶成核的预测一直是大气科学中一个长期存在的问题。识别云中引发冰晶的冰核的困难可能是由于1)缺乏关于冰核的化学成分和激活谱的信息，2)可能发生成核的多种机制，以及3)过去的仪器在估计最小冰粒子数量方面的局限性。过去的观测经常显示出一种差异：观测到的冰核比冰晶少得多，尤其是在温度较高的海洋云中。实验室实验和对云的观测表明，在某些条件下可能会产生二次冰（通过激活单个冰核产生多个冰晶），有时可以解释冰晶数量的增加，但并非总是如此。这种知识的缺乏导致了混合相云中降水预测的不确定性，在混合相云中，液体和冰粒子以无数种方式相互作用形成降水。考虑到暖雨过程的影响是第一次结冰的主要解释，以及过去有时观测到的大量冰晶浓度，本研究的目的是获得关于海洋云中初级和次级冰晶成核的新知识。其他有待探索的候选假设包括：由夹带引起的蒸发区冰核增强，由沙漠尘埃侵入提供的额外冰核，以及通过研究飞机穿过云层人工增强冰晶。知识价值。在这项研究中，将收集一个前所未有的数据集，该数据集将详细记录冰核和海洋积云中第一批小冰颗粒的最早出现。然后对数据进行分析，同时考虑云的动力和微物理演化。还将进行高分辨率三维数值云模拟和拉格朗日微物理计算，这对于区分假设的冰核机制至关重要。云动力学控制了冰晶成核和生长的时间尺度、粒子在云中传输的时间尺度以及不同阶段水成物可以相互作用的区域。仅靠观测无法完整地捕捉云的运动和演变，因此数值模拟对于理解冰点以下和冰点以上的液体和冰粒子的演变和运输至关重要。整体（欧拉）微物理，包括10级冰方案，也将在模拟中运行，以测试不同微物理过程解释观测结果的能力。最后，将比较有和没有沙漠沙尘初始化的模拟，以阐明其对初级和次级冰核机制的影响。更广泛的影响。大气科学的许多领域将受益于对冰晶成核及其对对流降水的影响的理解，例如云的全球和区域气候模式预测，每日降水事件的数值天气预报，以及热带风暴和飓风的预测。研究生将受益于参与实地活动，获得观测分析和数值模拟的经验，并在科学研讨会和会议上展示他们的研究成果。在ICE-T期间为加勒比地区一个地方机构的大学生开展的一项外联计划也将使在大气科学领域代表性不足的群体受益。

The prediction of ice crystal nucleation in clouds has been a long-standing problem in atmospheric science. The difficulties in identifying ice nuclei that initiate ice crystals in a cloud may be due to 1) lack of information regarding chemical composition and activation spectrum of ice nuclei, 2) the multiple mechanisms by which the nucleation might occur, and 3) the limits of past instrumentation in estimating the number of the smallest ice particles. Past observations often exhibit a discrepancy: far fewer ice nuclei are observed than ice crystals, and especially so in maritime clouds at higher temperatures. Laboratory experiments and observations in clouds suggest that secondary ice production (where multiple ice crystals are produced by the activation of a single ice nucleus) may act under certain conditions, sometimes explaining the enhanced number of ice crystals, but not always. This deficiency of knowledge propagates into uncertainties in the prediction of precipitation in mixed phase clouds, where liquid and ice particles interact in a myriad of ways to form precipitation.The objective of this research is to acquire new knowledge regarding primary and secondary ice crystal nucleation in maritime clouds, considering the influence of the warm rain process as a leading explanation for the first ice, and the high number concentrations of ice crystals sometimes observed in the past. Other candidate hypotheses to be explored include enhanced ice nucleation in evaporation zonesresulting from entrainment, additional ice nuclei supplied by intrusions of desert dust, and artificial enhancement of ice crystals by passage of a research aircraft through the clouds.Intellectual merit. In this study, an unprecedented dataset will be collected that will have a detailed documentation of ice nuclei and the earliest appearance of the first small ice particles in maritime cumuli. Then the data will be analyzed considering both the dynamical and microphysical evolution of the clouds. High-resolution 3D numerical cloud simulations and Lagrangian microphysical calculations will also be conducted, critical for differentiating among the hypothesized ice nucleation mechanisms. The cloud dynamics control the temporal scales involved in ice crystal nucleation and growth, the transport of particles through the cloud, and the regions where different phases of hydrometeors can interact. The observations alone cannot capture the cloud motions and evolution in their entirety, making the numerical modeling essential to understand the evolution and transport of liquid and ice particles below and above the freezing level. Bulk (Eulerian) microphysics, including a 10-class ice scheme, will also be run in the simulations to test the ability of different microphysical processes to explain the observations. Finally, simulations initialized with and without desert dust will be compared to elucidate its effects on primary and secondary ice nucleation mechanisms.Broader impacts. Numerous areas in atmospheric science will benefit from the understanding of ice crystal nucleation and its effects on convective precipitation, such as global and regional climate model predictions of clouds, numerical weather prediction of daily precipitation events, and predictions of tropical storms and hurricanes. Graduate students will benefit from participating in a field campaign, gaining experience in both observational analysis and numerical modeling, and presenting their research findings at scientific workshops and conferences. An outreach program conducted during ICE-T for university students at a local institution in the Caribbean will also benefit under-represented groups in atmospheric science.