Boundary Layer, Urban Meteorology and Land-Surface Processes

The WRF-simulated effects of the Oklahoma City urban area on its environment on the dynamics of a simulated supercell thunderstorm

Larissa Reames
OU School of Meteorology

21 February 2014, 2:00 PM

National Weather Center, Room 5600
120 David L. Boren Blvd.
University of Oklahoma
Norman, OK

Severe storms are especially dangerous and costly when they encounter urban areas, causing significant damage and loss of life. These impacts will continue to grow in scope with increased urbanization throughout much of the world, hence understanding the effects that the urban environment can have on supercells is of paramount importance. Previous studies have shown that urban areas modify the structure of approaching thunderstorms and precipitation patterns due to land surface heterogeneity, but few have focused on supercells, and even fewer have evaluated separately the dynamic and thermodynamic effects of multiple urban environments. The goal of this study is to quantify the relative importance of changes in surface roughness and thermal characteristics associated with urban regions to thunderstorm dynamics. Towards this objective, the Advanced Research Weather Research and Forecasting (ARW-WRF) was used to simulate an isolated supercell storm that crossed just north of the Oklahoma City urban area (ORIG). Three more simulations (OKCM, OKCS1, and OKCS2) were run, with each representing a different location of OKC within the domain. An additional model run (CTRL) was performed wherein all model representations of urban areas were removed from the vicinity of the OKC metro area. This run was used as a control run as it represented how the modeled storm would have behaved in the absence of OKC. The results from these five simulations indicate that the presence of the city appears to have had a strengthening effect on the storm’s low- and mid-level dynamics, with the effect being greatest when the region of highest low-level storm rotation passed very near to downtown OKC (OKCM), although the source of this change remains uncertain. Future work will involve further storm analytics, moving the city to more locations within the domain, isolating dynamic versus thermodynamic effects of the urban area, and replacing OKC with different real and idealized cities.

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