Diagnose and Understand the Mechanisms behind Warm Season Extreme Weather over Central and Intermountain United States

极端天气，如持续干旱、热浪、火灾天气，是自然灾害的主要原因。近几十年来，它对生活、公共卫生、经济和环境的影响迅速升级。例如，2018年加利福尼亚州的野火是由强烈的火灾天气引起的，造成了超过1261亿至1929亿美元的经济损失。然而，我们并不完全了解其根本原因。例如，下列问题仍然困扰着科学界。为什么在类似的大气流动模式下，极端事件有时会发生，而在其他时候却不会发生？为什么暖季极端干旱和炎热天气有时会同时发生，而其他时候却不会？为什么自2000年以来，一些极端天气类型，如美国西部最大的野火期间的火灾天气，与20世纪80年代和90年代相比，似乎变得更难以用天气环流来解释？该项目将应用最先进的统计分析来捕捉导致极端事件的天气风模式的多样性和复杂性。更重要的是，云、降水和气溶胶相对于大气动力过程在极端天气加剧中的作用将被研究。此外，将采用综合方法系统地表征极端干湿期、炎热天气、火灾天气和洪水背后的大气物理和动力过程以及陆地表面反馈。多层面的综合方法将阐明大气动力学和物理过程在决定极端天气和多种极端天气类型的并发过程中的相对作用。这种方法可能导致范式转变，从基于事件和以天气环流为中心的方法，这些方法在该研究领域的文献中占主导地位，并显著提高我们对极端天气的理解，特别是对于那些不能用天气环流异常充分解释的极端天气。该项目将培养1名女博士研究生、1名本科生暑期研究实习生和1名博士后研究员，并将其研究成果纳入高年级本科生科学课程。这些活动将有助于国家科学基金会的教育使命和未来的物理和动态气象学的劳动力。通过媒体向公众宣传，将使PI能够将该项目有关极端天气的最新研究成果转化为对社会有意义甚至可操作的信息。该项目由美国国家科学基金会物理与动力气象与气候以及大尺度动力学项目共同资助。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。

Extreme weather, such as persistent dry spells, heatwaves, fire weather, is a major cause of natural disasters. Its impacts on lives, public health, economy, and environment have been escalating rapidly in recent decades. For example, the wildfires in 2018 over California, induced by intensive fire weather, have caused over $126.1-192.9 billion economic loss. Yet, we do not fully understand its underlying causes. For example, the following questions are still perplexing the scientific community. Why do extreme events occur sometimes, but not at other times under similar atmospheric flow patterns? Why do warm season extreme dry spells and hot days occur together sometimes, but not at other times? Why do some extreme weather types, such as fire weather during the largest wildfires in western United State, appear to become less explainable by the synoptic circulation since 2000 compared to those from the time in the 1980s’ and 90s’? This project will apply state-of-the-art statistical analyses to capture the variety and complexity of the synoptic wind patterns responsible for the extreme events. More importantly, the roles of clouds, precipitation, and aerosols relative to atmospheric dynamic process in intensifying extreme weather will be investigated. Furthermore, an integrated approach will be applied to systematically characterize the atmospheric physical and dynamic processes and land surface feedbacks behind extreme dry and wet spells, hot days, fire weather and floods. The multifaceted and integrated approach will clarify the relative roles of the atmospheric dynamics and physical processes in determining extreme weather and concurrence of multiple extreme weather types. Such an approach could lead to a paradigm shift from event-based and synoptic-circulation-focused approaches that have dominated the literature in this research area, and significantly advance our understanding of extreme weather, especially for that which cannot be sufficiently explained by synoptic circulation anomalies. The project will train a woman PhD student, undergraduate summer research interns, and a postdoctoral researcher, and incorporate its research results into a large upper-division undergraduate science course. These activities will contribute to the NSF educational mission and future workforce of physical and dynamic meteorology. The proposed public outreach through media will enable the PI to translate the latest research result about extreme weather from this project to meaningful or even actionable information for society. The project was co-funded by NSF Physical and Dynamic Meteorology and Climate and Large-scale Dynamics programs.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.