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的一个难题。 识别在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活化谱的信息，2）成核可能发生的多种机制，以及3）过去的仪器在估计最小冰粒的数量方面的限制。 过去的观测结果常常表现出差异：观察到的冰核比冰晶少得多，尤其是在温度较高的海洋云中。 实验室实验和对云中的观测表明，二次冰的产生（其中多个冰晶是由单个冰核的激活产生的）可能在某些条件下起作用，有时解释了冰晶数量的增加，但并不总是如此。 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，液体和冰粒以无数方式相互作用形成降水。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，考虑暖雨过程的影响作为第一次冰的主要解释，以及过去有时观察到的冰晶的高浓度。 其他有待探讨的候选假设包括：由于卷吸作用而使蒸发区的冰成核作用增强，由于沙漠尘埃的侵入而使冰核增加，以及由于研究飞机穿过云层而使冰晶人为增强。 在这项研究中，将收集一个前所未有的数据集，其中将详细记录冰核和海洋积云中最早出现的第一个小冰粒。 然后，将考虑云的动力学和微物理演变的数据进行分析。 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成核机制至关重要。 云动力学控制着冰晶成核和生长的时间尺度，粒子通过云的传输，以及不同相的水凝物可以相互作用的区域。 单靠观测无法完整地捕捉云的运动和演变，这使得数值模拟对于理解冻结层以下和以上的液体和冰粒子的演变和运输至关重要。 大量（欧拉）微观物理，包括10级冰计划，也将在模拟中运行，以测试不同的微观物理过程解释观测的能力。 最后，模拟初始化和没有沙漠尘埃将进行比较，以阐明其对初级和次级冰成核机制的影响。 在大气科学的许多领域将受益于冰晶成核及其对流降水的影响，如全球和区域气候模式预测云，数值天气预报的日常降水事件，热带风暴和飓风的预测的理解。 研究生将受益于参与实地活动，获得观测分析和数值建模的经验，并在科学研讨会和会议上展示他们的研究成果。 在ICE-T期间为加勒比当地机构的大学生开展的一项外联方案也将使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.