Collaborative Research: Topographic Influences on Extreme Warm-Season Precipitation

极端降雨影响全球数百万人，但我们对这种高影响天气现象的理解和预测能力有限。太平洋降雨极端活动预测（PRECIP，2020年5月至8月）现场活动旨在提高对台湾和北太平洋西部潮湿环境中产生极端降雨的多尺度过程的理解。PRECIP假设认为，极端降水是多尺度要素在水分丰富的环境中的最佳组合的结果，但不同的关键要素和过程会导致强垂直强迫和高降雨强度，强水平强迫和长持续时间，或强降水和持续降水的混合。该项目的重点是地形对极端降雨的影响，利用台湾中央山脉（CMR）两侧的雷达和无线电探空仪观测的独特组合，通过热力学，动力学、运动学和微观物理过程。总体假设是，地形通过增加产生暴雨所需成分的数量，增强了极端降雨的强度和持续时间。除了促进水分的上升和集中外，地形还通过微物理过程的变化改变降雨强度和持续时间。在台湾的副热带环境中，有效的暖雨过程可以产生高强度的对流性降水，而基于冰的过程变得越来越重要的持续时间长的事件为主的层状降水。此外，从TiMREX 2008年的结果表明，上坡倾斜的相对较浅的对流沿着台湾的CMR可以促进降水大小的冰的增长。 随后的冷池生成导致细胞的持续增长上游和降雨事件的持续时间沿着CMR。PRECIP提供了一个机会，以进一步探讨地形的作用，包括微物理过程的影响，在产生极端降雨的各种事件，无论是在西部斜坡和沿着台湾的数据稀疏的东海岸。为了验证上述假设，该研究将使用多频双极化多普勒雷达的PRECIP数据组合（S-PolKa，SEA-POL）、无线电探空仪和模式，以探索地形影响的日强迫对流过程、嵌入梅雨锋的中尺度对流系统和热带气旋。这项研究的一个重要的更广泛的目标是确定台湾极端降雨事件的关键成分和过程也是相关的在其他环境或地点的地形降水。三个早期职业女性科学家的团队带来了丰富的观测实地项目和地形影响的降水研究的知识，跨越各种全球制度，包括在马德雷山脉的温暖季节降雨，CMR，安第斯山脉，落基山脉，喜马拉雅山脉，典型的贸易风气流，热带气旋通过多米尼加，和冷季降雨在奥运会。PRECIP将提供一个机会，调查山脉迎风面和背风面的各种各样的降雨事件。该项目的研究结果将有可能通过在各种暴雨事件中收集的前所未有的数据建立一个基于成分的框架，从而提供对全球极端降雨的最新了解。该项目由刺激竞争研究的既定计划（EPSCoR）和PREEVENTS联合资助，极端事件的预测和复原力项目。该奖项反映了NSF的法定使命，并被认为值得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来支持。

Extreme rainfall affects millions of people globally, yet our understanding and forecast skill of this high-impact weather phenomenon is limited. The Prediction of Rainfall Extremes Campaign in the Pacific (PRECIP, May-August 2020) field campaign aims to improve understanding of the multi-scale processes important for generating extreme rainfall in the moisture-rich environment of Taiwan and the western North Pacific. The overarching PRECIP hypothesis is that extreme rainfall results from an optimal combination of multi-scale ingredients in a moisture-rich environment, but different key ingredients and processes lead to strong vertical forcing and high rainfall intensity, strong horizontal forcing and long duration, or a mixture of both intense and sustained precipitation.Intellectual Merit:This project focuses on orographic influences on extreme rainfall, using a unique combination of radar and radiosonde observations on both sides of Taiwan's Central Mountain Range (CMR) to determine the role of steep terrain in enhancing both intensity and duration of rainfall through a combination of thermodynamic, dynamic, kinematic, and microphysical processes. The overall hypothesis is that terrain enhances both intensity and duration of extreme rainfall through increasing the magnitude of ingredients needed to produce heavy rainfall. In addition to promoting lifting and concentrating moisture, terrain modifies rainfall intensity and duration through changes in microphysical processes. In the subtropical environment of Taiwan, efficient warm-rain processes can produce high intensity convective rainfall, while ice-based processes become increasingly important for long-duration events dominated by stratiform precipitation. Additionally, results from TiMREX 2008 suggest that upslope tilting of relatively shallow convection along Taiwan's CMR can promote growth of precipitation-sized ice. Subsequent cold-pool generation leads to continuous growth of cells upstream and prolongs the duration of rainfall events along the CMR. PRECIP offers the opportunity to further explore the role of terrain, including the influence on microphysical processes, in producing extreme rainfall for a wide variety of events, both on the western slopes and along the data-sparse east coast of Taiwan. To test the above hypotheses, the study will use a combination of PRECIP data from multi-frequency dual-polarization Doppler radars (S-PolKa, SEA-POL), radiosondes, and models to explore terrain-influenced processes for diurnally-forced convection, mesoscale convective systems embedded within the Meiyu front, and tropical cyclones.Broader Impacts:An important broader goal of this investigation is to determine which of the key ingredients and processes identified for Taiwan extreme rainfall events are also relevant to orographic precipitation in other environments or locations. The team of three early-career female scientists brings a wealth of knowledge of observational field projects and terrain-influenced precipitation studies spanning a variety of global regimes, including warm-season rainfall in the Sierra Madre Occidentals, CMR, Andes, Rockies, and Himalayas, typical trade-wind flow, a tropical cyclone passing over Dominica, and cold-season rainfall over the Olympics. PRECIP will give an opportunity to investigate a wide variety of rain-producing events, both the windward and leeward sides of the mountain range. The findings from this project will have the potential to provide an updated understanding of extreme rainfall globally by building off an ingredients-based framework through unprecedented data collected in a wide variety of heavy rain events.This project is jointly funded by the Established Program to Stimulate Competitive Research (EPSCoR) and PREEVENTS, Prediction of and Resilience against Extreme Events program.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.