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）是美国大平原和中西部夏季降水的主要来源，并产生大量的灾害，包括强风、冰雹、山洪和偶尔的龙卷风。因此，准确理解和预测这些系统对公共安全至关重要。特别是对一类发生在夜间的MCS的生长和进化过程了解甚少。该项目使用一组独特的数据来研究这种夜间风暴演变的机制，这些数据是由一架仪表飞机在2015年夜间平原高架对流（PECAN）现场实验期间在夜间雷暴产生的云中飞行并尾随在夜间雷暴之后获得的。特别是，该项目正在评估云中发生的小规模过程如何产生冷空气，冷空气反过来又产生迫使新空气团上升的特征，导致新雷暴的发展，随后产生更多的拖尾云和雨。该项目的第二个组成部分研究热带地区雷暴产生的云的特性。这一部分的动机是航空面临的一个问题，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，但会遇到雷达没有检测到的大量小冰晶;这种情况可能会对飞机发动机造成问题，过去30年的几次发动机事件证明了这一点。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年澳大利亚和法属圭亚那的达尔文海岸附近进行的高冰水含量（HIWC）项目期间，研究飞机配备了测量云特性的探针。该项目正在通过确定这些小晶体形成和生长的环境条件来研究导致大量小冰晶形成的过程。在这两个项目中，模型模拟也被用来评估特定过程在驱动和维持雷暴（PECAN）和生成小冰晶（HIWC）方面的作用。此外，这两个项目都获得了与飞机云观测相一致的下一代偏振雷达数据，以便可以验证从偏振雷达数据中检索到的云属性，这意味着将来来自偏振雷达的数据最终可以用于扩展现场实验测量的有限范围。在更技术层面上，PECAN数据正在被用来评估的假设，即微物理冷却过程中的发展和成熟的层状地区的MCS力下沉气流环流，创造中尺度重力波功能的稳定的夜间边界层（SNBL），反过来集中，组织和维持未来的对流活动。在多多普勒雷达分析和模拟研究的风暴运动学和动力学背景下，PECAN资料被用来（1）描述PECAN升高的夜间MCS形成、成熟和消散阶段的过渡区、凹口和后砧区的微物理和热力学结构;（2）量化和理解在MCSs的生命周期中，潜热冷却的水平和垂直分布如何在MCSs中演变，并对下沉气流和重力波特征做出贡献;（3）确定SNBL上的重力波特征是如何引起抬升，进而驱动对流，维持夜间MCS的组织和长寿命的。重冰警报数据正被用于：（1）确定重冰警报区域的微物理和热力学特性，并将其与在没有重冰警报区域的观测中获得的特性进行对比;（2）确定重冰警报区域的偏振雷达特征，并调查这些特征如何因小冰晶的相对普遍性而有所不同;（3）将高IWC区域的尺寸分布和质量-尺寸关系表示为适当系数相空间中的相等可实现解的体积或表面;（4）进行模拟，以确定海洋对流核心上方发现的大量小冰晶的形成过程，并与HIWC的观测结果进行比较。广泛的影响是：（1）提高认识，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）增加教育和培训机会（3）将PECAN和HAIC/HIWC的数据纳入公共机构的课程和出版的教科书;（4）对导致约150个功率损失的高IWC条件的先进科学理解和/或该奖项反映了NSF的法定使命，并通过使用基金会的学术价值和更广泛的影响审查标准。

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.