Mechanisms of Intermountain Cold Front Evolution

也许世界上没有任何地方的冷锋的发展和演变比美国西部山脉之间的冷锋发展和演变更复杂。上游山脉，最著名的是内华达山脉，改变了落地冷锋，进而影响了下游山脉(如瓦萨奇山脉)的地形降水过程和降雨率。在其他事件中，强烈的冷锋在内华达山脉下游形成或加强，造成显著的气温下降、沙尘暴和大风，风力可超过40米S-1，并已造成超过1500万美元的财产损失。除了地形影响外，强烈的地表加热、深层对流边界层和湿对流升高也很重要，但这些过程对锋面演变和动力学的影响仍然难以捉摸，关于它们的综合影响仍有相当大的争议。首席调查员将利用山间西部作为一个天然实验室，进行一项全面的三年研究计划，以研究地面加热、边界层过程、高湿对流和地形对锋面演变的综合影响。要研究的关键问题是：(1)当陆地降落锋穿过像内华达山脉这样的主要山障时，它们在结构和动力学上是如何改变的；(2)大范围、地形、非绝热和边界层过程在大盆地上强冷锋的快速发展中起到了什么作用；(3)山间冷锋的演变与世界其他山区或干旱地区的冷锋相比如何？该项目将涉及观测分析和数值模拟。来自MesoWest合作网络和气象同化数据摄取系统(MADIS)的高密度地面观测、NEXRAD雷达网的雷达观测以及来自加利福尼亚州、内华达州、爱达荷州和犹他州的风廓线数据将用于描述所观测到的与内华达山脉锋面相互作用和大盆地上方快速锋生的案例的结构和演变。天气研究和预报(WRF)模式的真实数据模拟将用于为诊断分析提供高分辨率的动态一致的数据集，同时将进行理想化的模拟和敏感性研究，以隔离地形效应或边界层和非绝热过程对锋面演变的影响。这项研究将有助于全面了解锋面动力学和演变，特别是地形、非绝热和边界层过程的影响。这项研究对整个社会的好处包括改善对冷锋及其在西部山区和世界其他地区的相关危险天气的理解和预测。这些改善应该有助于降低内华达州、犹他州、亚利桑那州、爱达荷州和科罗拉多州这五个美国增长最快的州对恶劣天气的社会脆弱性。其他更广泛的影响包括将研究成果纳入犹他大学的本科生和研究生课程，指导两名研究生，并为教育学生、气象学家和其他对大气科学感兴趣的个人开发在线教学模块。

Perhaps nowhere in the world is the development and evolution of cold fronts more complex than over the Intermountain West of the United States. Upstream mountain ranges, most notably the Sierra Nevada, modify land-falling cold fronts, which in turn influence orographic precipitation processes and rates over downstream mountain ranges such as the Wasatch Mountains. In other events, intense cold fronts develop or intensify downstream of the Sierra Nevada, producing dramatic temperature falls, dust storms, and high winds that can exceed 40 m s-1 and have produced more than $15 mil in property damage. In addition to orographic effects, intense surface heating, deep convective boundary layers, and elevated moist convection are also important, yet knowledge of the influence of these processes on frontal evolution and dynamics remains elusive with considerable debate concerning their combined effects. Using the Intermountain West as a natural laboratory, the Principal Investigator will conduct a comprehensive three year research program to examine the combined effects of surface heating, boundary layer processes, elevated moist convection, and orography on frontal evolution. The key questions to be investigated are (1) how are land-falling fronts structurally and dynamically modified as they traverse a major mountain barrier like the Sierra Nevada, (2) what role do large-scale, orographic, diabatic, and boundary layer processes play in the rapid development of strong cold fronts over the Great Basin, and (3) how does the evolution of Intermountain cold fronts compare and contrast with that found in other mountainous or arid region of the world? The project will involve observational analysis and numerical modeling. High-density surface observations from the MesoWest cooperative networks and the Meteorological Assimilation Data Ingest System (MADIS), radar observations from the NEXRAD radar network, and wind profiler data from California, Nevada, Idaho, and Utah will be used to describe the observed structure and evolution of selected cases of frontal interaction with the Sierra Nevada and rapid frontogenesis over the Great Basin. Real-data simulations by the Weather Research and Forecast (WRF) model will be used to provide high-resolution dynamically consistent datasets for diagnostic analysis, while idealized simulations and sensitivity studies will be conducted to isolate orographic effects or the influence of boundary layer and diabatic processes on frontal evolution. The research will contribute to overall understanding of frontal dynamics and evolution, particularly the effect of orographic, diabatic, and boundary layer processes. Benefits of the research for society at large include improved understanding and prediction of cold fronts and their associated hazardous weather over the Intermountain West, as well as other regions of the world. These improvements should help reduce societal vulnerability to hazardous weather in Nevada, Utah, Arizona, Idaho, and Colorado, the five fastest growing states in the nation. Other broader impacts include the integration of research results into undergraduate and graduate courses at the University of Utah, the mentoring of two graduate students, and the development of on-line instructional modules for educating students, meteorologists, and other individuals interested in the atmospheric sciences.