The Structure, Origin, and Long-Term Trends of the West Coast Thermal Trough

西海岸热槽（WCTT）在温暖季节（大约5月至10月）对北美西部的天气和气候起着至关重要的作用，并在寒冷季节产生重大影响。WCTT表示为表面附近的压力槽和暖空气舌，从美国西南部的低压区延伸到太平洋西北部夏季热槽与热浪和空气质量差有关，并极大地影响可再生能源生产和野火增长。冬季热槽在许多北美西部沿海降雪事件中发挥作用。该项目开始时将完成一系列个案研究，利用高分辨率模型模拟和密集的区域观测，以确定北美西部热槽的详细结构演变，并确定其产生和维持的物理机制。将特别注意穿越区域地形障碍的热槽通道;这种通道往往与风和温度的急剧转变有关，可能导致野火爆发和风能的迅速变化。这项工作将使用高分辨率网格模型再分析数据集确定过去半个世纪热槽频率，强度和演变是否发生了变化，然后将评估自然变率（如太平洋十年振荡）或人为变暖是否可以解释这些变化。它还将评估人为全球变暖在下一个世纪改变美国西部热槽特征的潜力。为此，将利用区域气候模型，将各种温室气体情景下的全球气候模型动态缩小到高分辨率（12公里）。然后，这些场将被输入到客观算法中，该算法将确定热槽频率和强度的趋势。学术成就：在该奖项下完成的工作将全面描述北美西部夏季天气的主要特征，并在世界各地观察到类似的现象。这项工作不仅将描述这些特征的详细结构演化，而且还将描述它们的基本物理机制。这项研究将确定热槽发展的长期时间趋势，并评估这些趋势的起源。它将研究全球变暖是否会改变WCTTs的频率和强度，并将解释这些变化背后的机制。更广泛的影响：提高对这一现象的理解将带来巨大的社会效益。热槽对区域温度、野火发展和控制、可再生能源、空气质量和其他关键社会问题有很大影响。这一建议所产生的理解应该有助于提高我们预测热槽发展和演变的能力，提供与全球变暖相关的预期长期趋势的见解，并建议区域极端温度，可再生能源潜力和野火频率的预期变化。

The West Coast thermal trough (WCTT) plays a crucial role in western North American weather and climate during the warm season (approximately May through October) and has a substantial impact during the cold season. The WCTT is expressed as a pressure trough and tongue of warm air near the surface that extends into the Pacific Northwest from an area of low pressure over the southwestern U.S. Summer thermal troughs are associated with heat waves and poor air quality, and greatly impact renewable energy production and wildfire growth. Winter thermal troughs play a role in many western North America coastal snow events. The project will begin by completing a series of case studies, using both high-resolution model simulations and dense regional observations, to determine the detailed structural evolution of western North America thermal troughs, as well as to determine the physical mechanisms responsible for their generation and maintenance. Particular attention will be given to thermal trough passage across regional terrain barriers; such passages are often associated with sharp transitions in wind and temperature that can lead to wildfire blow-ups and rapid changes in wind energy. This work will determine whether thermal trough frequency, intensity, and evolution have changed over the past half-century using high-resolution gridded model reanalysis data sets, and then will evaluate whether natural variability (such as the Pacific Decadal Oscillation) or anthropogenic warming might explain such changes. It will also evaluate the potential of anthropogenic global warming for changing the characteristics of western U.S. thermal troughs over the next century. To do so, global climate models forced by a variety of greenhouse gas scenarios will be dynamically downscaled to high resolution (12 km) using a regional climate model. These fields will then be input into objective algorithms that will determine the trends in thermal trough frequency and intensity. Specific hypotheses regarding the effects of global warming on thermal trough intensity and frequency will be evaluated.Intellectual Merit :The work completed under this award will provide a comprehensive description of a feature that dominates the weather of western North America during the summer, with similar phenomena observed throughout the world. This work will not only describe the detailed structural evolution of such features, but their basic physical mechanisms as well. The research will determine the long-term temporal trends in thermal trough development and evaluate the origins of these trends. It will examine whether global warming will change the frequency and intensity of WCTTs, and will explain the mechanisms behind these changes.Broader Impacts :Improved understanding of this phenomenon will lead to substantial societal benefits. Thermal troughs have a large impact on regional temperatures, wildfire development and control, renewable energy, air quality, and other critical societal issues. The understanding generated by this proposal should help improve our ability to predict thermal trough development and evolution, provide insights into expected long-term trends associated with global warming, and suggest expected changes in regional temperature extremes, renewable energy potential, and wildfire frequency.