Land Use Impacts on Surface Fluxes during Persistent Cold Air Pool Events

The surface energy balance influences interactions between the earth’s surface and atmosphere, where both play a role in atmospheric boundary layer development and vertical mixing. Understanding the land-atmosphere interactions is critical in numerical weather prediction and climate modeling to simulate the transport of heat, moisture, and momentum in the atmosphere. During persistent cold air pool (PCAP) events the boundary layer is typically stable with limited vertical mixing, therefore having lower turbulent fluxes at the surface. Numerical models are often unable to simulate the daytime, stable PCAP boundary layers and therefore do not capture the decrease in turbulence at the surface. This presentation will present results from both observations and numerical simulations during December 2010 to February 2011 in the Salt Lake Valley, Utah. The observations come from seven surface flux stations located over a mix of land use types in the valley. Results show that the surface turbulent fluxes have significant variability associated with different land use types and atmospheric stability. The bulk transfer coefficient for heat was also calculated to compare with numerical simulations, where the observed bulk transfer coefficient also has significant variability due to different land use types. A comparison of Weather Research and Forecasting (WRF) simulated fluxes with the observations will also be presented using four different planetary boundary layer schemes. Results show that the WRF simulated fluxes do not have as much variability across the different land use types as the observations, and the WRF model performance also depends on atmospheric stability. A discussion on the WRF calculated bulk transfer coefficients compared to the values calculated using observations will be given that describes potential limitations in this value for numerical models due to heterogeneous land surfaces.