The Sensitivity of a Persistent Cold-Air Pool to Changes in the Surface State in the Salt Lake Valley, UT

Persistent cold-air pools (CAPs) are observed frequently during the winter in Utah's Salt Lake Basin, and can result in prolonged periods of poor air quality. The land surface state plays an important role in the maintenance, evolution and intensity of CAPs. In this study, the sensitivity of Weather Research and Forecasting model simulations to variations in the surface state (i.e. land cover and snow cover) is examined for a persistent CAP that occurred in the Salt Lake Basin from 1 January 2011 to 8 January 2011.

The impacts of improvements in land cover and land use, as well as snow cover initialization fields on the urban CAP numerical simulation are studied. Simulations are compared using the 1993 United States Geological Survey land cover dataset and an updated version of the more recent 2011 National Land Cover Database that better prescribes the areal extent of the seasonally-varying Great Salt Lake. Snow cover provided by the North American Mesoscale Reanalysis was found to over predict snow depth in the Salt Lake Valley, so observations were used to derive an improved snow initialization dataset. The model simulations were found to be sensitive to land cover, land use, and snow cover initialization fields resulting in substantive changes in modeled boundary-layer temperature, wind, and moisture profiles.