Collaborative Research: Impacts of Microphysical, Thermodynamic, and Dynamical Processes on Nocturnal and Oceanic Convective Systems via Analyses from PECAN and HAIC/HIWC

中尺度对流系统（mcs）是造成美国大平原和中西部大部分夏季降水的原因，并产生大范围的灾害，包括强风、冰雹、山洪暴发和偶尔的龙卷风。因此，准确了解和预测这些系统对公共安全至关重要。在夜间发生的一类特殊mcs的生长和进化过程，人们对其了解甚少。该项目利用2015年平原夜间高架对流（PECAN）野外实验期间在夜间雷暴产生和尾随的云层中飞行的仪器飞机获得的一组独特数据，研究了此类夜间风暴演变的机制。特别是，该项目正在评估云层中发生的小规模过程是如何产生冷空气的，冷空气反过来又产生一些特征，迫使新的气团上升，导致新的雷暴的发展，随后产生更多的尾随云和降雨。该项目的第二个组成部分考察了热带地区发生的雷暴所产生的云的特性。这一组成部分的动机是航空业面临的一个问题，即在商业飞行高度飞行的飞机可能会遇到雷达上没有明显回波的情况，但会遇到雷达未检测到的大量小冰晶；过去30年发生的几起发动机事故证明，这种情况可能会给飞机发动机带来问题。该项目使用在这种条件下飞行的研究飞机收集的数据。在2015年和2016年在澳大利亚达尔文和法属圭亚那海岸进行的高冰水含量（HIWC）项目中，研究飞机上安装了测量云特性的探测器。该项目通过确定这些小冰晶形成和生长的环境条件，研究导致大量小冰晶形成的过程。在这两个项目中，模型模拟也被用于评估驱动和维持雷暴（PECAN）和产生小冰晶（HIWC）的特定过程的作用。此外，这两个项目都获得了与飞机云观测相一致的下一代极化雷达数据，以便从极化雷达数据中检索到的云特性可以得到验证，这意味着未来极化雷达数据最终可以用于延长现场实验测量的有限范围持续时间。在更技术性的层面上，PECAN数据被用于评估mcs发展和成熟层状区域的微物理冷却过程迫使下行气流环流，从而在稳定的夜间边界层（SNBL）上产生中尺度重力波特征，进而集中、组织和维持未来的对流活动。根据多普勒雷达分析和建模研究得出的风暴运动学和动力学数据，PECAN数据被用于(1)表征PECAN夜间高架MCSs形成、成熟和消散阶段的过渡区、切口和后砧区微物理和热力学结构；(2)量化和理解MCSs生命周期中潜冷的水平和垂直分布演变及其对下沉气流和重力波特征的影响；(3)确定SNBL上的重力波特征如何引起抬升，进而驱动对流，维持夜间MCSs的组织和长寿命。HIWC数据被用于(1)表征高IWC区域的微物理和热力学性质，并将其与非高IWC区域的观测结果进行对比；(2)确定高IWC区域的极化雷达特征，并研究这些特征如何随小冰晶的相对流行率而变化；(3)将高IWC区域的尺寸分布和质量维度关系表示为适当系数相空间中同等可实现解的体积或表面；(4)进行模拟，确定海洋对流核上方大量小冰晶形成的过程，并与HIWC观测结果进行比较。广泛的影响是：(1)提高了人们的认识，使业务预报员和临近预报员能够更好地预测对流现象的演变；(2)增加了教育和培训的机会（一些研究生正在获得更高的学位）；(3)将PECAN和HAIC/HIWC数据纳入pi所教授的课程和出版的教科书中；(4)在过去几年中，高IWC条件导致商用飞机约150次功率损失和/或皮托管失效，对这些条件的科学认识有所提高。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Mesoscale convective systems (MCSs) are responsible for a large portion of summertime precipitation in the Great Plains and Midwest of the United States and produce a large range of hazards, including strong winds, hail, flash flooding and occasional tornadoes. Thus, accurate understanding and forecasting of these systems is important for public safety. Processes responsible for the growth and evolution of a particular class of MCSs, occurring at night, are especially poorly understood. This project examines mechanisms responsible for the evolution of such nocturnal storms using a unique set of data obtained by an instrumented aircraft flying in clouds generated by and trailing behind nocturnal thunderstorms during the 2015 Plains Elevated Convection at Night (PECAN) field experiment. In particular, the project is assessing how small-scale processes occurring in clouds generate cold air which in turn generates features that act to force new air masses to rise, leading to the development of new thunderstorms that subsequently generate more trailing clouds and rain. The second component of the project examines the properties of clouds generated by thunderstorms occurring in the Tropics. This component was motivated by a problem faced by aviation, namely that aircraft flying at commercial flight altitudes can encounter conditions where there is no noticeable echo on their radar yet encounter large amounts of small ice crystals not detected by the radar; such conditions can be problematic for aircraft engines as evidenced by several engine events over the last 30 years. This project uses data collected by research aircraft flying in such conditions. The research aircraft were instrumented with probes measuring cloud properties during the 2015 and 2016 High Ice Water Content (HIWC) projects conducted off the coast of Darwin, Australia and French Guiana. The project is examining processes that lead to the development of large numbers of small ice crystals by identifying the environmental conditions under which these small crystals form and grow. In both projects, model simulations are also being used to evaluate the role of specific processes in driving and maintaining thunderstorms (PECAN) and for generating small ice crystals (HIWC). Further, both projects acquired next generation polarimetric radar data coincident with the aircraft cloud observations so that cloud properties retrieved from polarimetric radar data can be validated, meaning that data from polarimetric radar in the future can ultimately be used to extend the limited range duration of the field experiment measurements. At a more technical level, the PECAN data are being used to evaluate the hypothesis that microphysical cooling processes in developing and mature stratiform regions of MCSs force downdraft circulations that create mesoscale gravity wave features on the stable nocturnal boundary layer (SNBL) that in turn focus, organize and maintain future convective activity. In context of storm kinematics and dynamics as derived from multiple Doppler radar analyses and modeling investigations, the PECAN data are being used to (1) characterize the microphysical and thermodynamic structure of the transition zone, notch and rear anvil regions in formative, mature and dissipative stages of the PECAN elevated nocturnal MCSs; (2) quantify and understand how the horizontal and vertical distribution of latent cooling evolves across MCSs during their lifecycles and contributes to downdrafts and gravity wave features; and (3), determine how gravity wave features on the SNBL give rise to lifting that then drives convection and maintains the organization and long lifetime of nocturnal MCSs. The HIWC data are being used to (1) characterize the microphysical and thermodynamic properties of high IWC regions and contrasting them against properties derived from observations obtained in regions without high IWCs; (2) determine polarimetric radar signatures of high IWC regions and investigate how these signatures differ depending upon the relative prevalence of small ice crystals; (3) develop representations of size distributions and mass-dimensional relationships for high IWC regions as a volume or surface of equally realizable solutions in the appropriate coefficient phase space; and (4) conduct simulations to identify processes responsible for the numerous small ice crystals found above oceanic convective cores, and compare against HIWC observations. The broad impacts are (1) improved understanding so that operational forecasters and nowcasters can better anticipate the evolution of convective phenomena; (2) enhanced education and training opportunities (several graduate students are earning advanced degrees); (3) incorporation of PECAN and HAIC/HIWC data into courses taught and textbooks published by the PIs; (4) advanced scientific understanding of high IWC conditions that have led to about 150 power loss and/or pitot tube failures in commercial aircraft over the last several years.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.