Boundary Layer, Urban Meteorology and Land-Surface Processes

Evaluation of Planetary Boundary Layer Schemes within WRF for Wind Resource and Air Quality Assessments

Xiaoming Hu
Center for Analysis and Prediction of Storms (CAPS)

20 September 2013, 2:00 PM

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

Planetary-boundary layer (PBL) parameterization schemes are of vital importance for accurate simulations of wind, turbulence and air quality in the lower atmosphere and thus play an important role for a number of applications including wind resource and air quality assessments. While much progress has been made for PBL schemes in simulating the daytime convective boundary layer (CBL), progress with modeling of the nighttime boundary layer has been slower. Systematic over-estimations of near-surface winds during stable conditions have been noticed in simulations with several meteorological models; over-estimation of nighttime surface O3 is a common problem for many air quality models. In this study we will examine the impact of vertical mixing treatments with the WRF/Chem model on the prediction of nighttime boundary layer structure and O3 concentration over a domain focusing on the southern Great Plains. Six PBL schemes are examined, i.e., the Yonsei University (YSU), Mellor-Yamada-Janjić (MYJ), Nakanishi-Niino 2.5-order closure (MYNN2), Bougeault–Lacarrére (BouLac), Quasi-Normal Scale Elimination (QNSE), and University of Washington (UW) schemes. The main conclusions include: 1. The update of the YSU scheme in WRF3.4.1 improved predictions of the nighttime boundary layer and can thus provide better wind resource assessments; 2. Overestimation of nighttime O3 is related to overestimation of surface winds, both of which can be partially attributed to excessive vertical mixing. 3. The BouLac scheme gives the strongest vertical mixing in the nighttime boundary layer. It consequently overestimates near-surface wind and temperature and underestimates the wind shear exponent at night. Plans for future improvement of vertical mixing treatments will be also discussed.

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