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(MCSs)造成了美国大平原和中西部夏季降水的很大一部分，并产生了广泛的灾害，包括强风、冰雹、山洪暴发和偶尔发生的龙卷风。因此，准确了解和预测这些系统对公共安全非常重要。负责特定类别的MCS在夜间生长和进化的过程尤其鲜为人知。该项目利用2015年平原夜间高空对流(山核桃)现场实验期间在夜间雷暴产生的云中飞行的仪表化飞机获得的一组独特的数据，检查了这种夜间风暴的演变机制。特别是，该项目正在评估云中发生的小范围过程如何产生冷空气，冷空气又产生迫使新气团上升的特征，从而导致新雷暴的发展，从而产生更多的拖尾云和雨。该项目的第二部分研究热带地区雷暴产生的云的特性。这一构成部分的动机是航空面临的一个问题，即以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但雷达没有探测到大量小冰晶的情况；过去30年的几次发动机事件证明，这种情况可能会给飞机发动机带来问题。该项目使用了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外进行的高冰水含量(HIWC)项目期间，研究飞机配备了测量云层特性的探测器。该项目正在通过确定这些小冰晶形成和生长的环境条件来研究导致大量小冰晶生长的过程。在这两个项目中，模式模拟也被用来评估特定过程在驱动和维持雷暴(山核桃)和产生小冰晶(HIWC)方面的作用。此外，这两个项目都获得了与飞机云层观测一致的新一代极化雷达数据，以便能够验证从极化雷达数据中提取的云特性，这意味着未来来自极化雷达的数据最终可用于延长实地实验测量的有限射程。在更技术的层面上，山核桃数据正被用来评估一种假设，即MCSs发育和成熟层状区的微物理冷却过程迫使下沉气流环流，从而在稳定的夜间边界层(SNBL)上产生中尺度重力波特征，进而聚焦、组织和维持未来的对流活动。在多部多普勒雷达分析和模拟研究得出的风暴运动学和动力学背景下，山核桃数据将被用于：(1)描述夜间山核桃高耸MCSs形成、成熟和消散阶段过渡区、缺口和后砧区的微物理和热力学结构；(2)量化和了解潜热在整个MCSs生命周期内的水平和垂直分布如何演变，以及对下沉气流和重力波特征的贡献；(3)确定SNBL上的重力波特征如何引起抬升，进而驱动对流和维持夜间MCSs的组织和长寿命。HIWC数据将用于：(1)描述高IWC区的微观物理和热力学性质，并将其与对无高IWC区的观测所得的性质进行比较；(2)确定高IWC区的极化雷达特征，并调查这些特征随小冰晶的相对盛行情况有何不同；(3)将高IWC区的尺寸分布和质量-维度关系表示为在适当的系数相空间中同等可实现的解的体积或表面；(4)进行模拟，以确定海洋对流岩心上方发现的大量小冰晶的过程，并与HIWC的观测结果进行比较。广泛的影响是：(1)提高了对对流现象的认识，以便预报人员和预报员能够更好地预测对流现象的演变；(2)增加了教育和培训机会(一些研究生正在获得高级学位)；(3)将山核桃和HAIC/HIWC数据纳入PIS教授的课程和出版的教科书；(4)对过去几年导致商用飞机约150次电力损失和/或皮托管故障的IWC高位条件的先进科学理解。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.