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

University Of Washington, Seattle WA

Investigators

Abstract

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.