Observations and Numerical Modeling of Persistent Cold Air Pools in Utah's Salt Lake Valley

A persistent cold air pool (PCAP), defined here as a topographic depression filled with cold air that lasts more than one day, is a common occurrence in the wintertime in basins worldwide. When PCAPs occur within urbanized basins the accumulation of emissions within the stagnant air can lead to hazardous air quality. Despite their societal impacts, PCAPs are not thoroughly understood and the mechanisms governing PCAP evolution are not well documented due to the limited observational resources available to previous researchers. Moreover, PCAPs are generally inadequately resolved in numerical weather prediction models, and even small model errors can have large impacts on temperature and air-quality forecasts. The Persistent Cold Air Pool field study was conducted in the Salt Lake Valley between 1 December 2010 - 7 February 2011 with the goal of improving scientific understanding of the detailed meteorological factors influencing poor air quality episodes in urban basins. In this study, observations from the PCAPS field campaign and real and idealized numerical modeling simulations are used to investigate the impacts of terrain, the Great Salt Lake, land use, synoptic and local background flows, and static stability on persistent cold air pool evolution and structure. The horizontal transport mechanisms (e.g., drainage flows, lake breezes, sloshing) within PCAPs are highly sensitive to variations in land surface characteristics and the near-surface stability and cloud cover, and may be dramatically altered by partial removal or displacement of the surface boundary-layer by synoptic weather systems.