Boundary Layer, Urban Meteorology and Land-Surface Processes

WRF model study of the Great Plains low-level jet: effects of grid spacing and boundary layer parameterization

Elizabeth Smith

School of Meteorology

11 December 2015, 2:00 PM

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

In association with the Plains Elevated Convection at Night (PECAN) field campaign, the ability of the Weather Research and Forecasting (WRF) model to accurately resolve the Great Plains low-level jet (LLJ) was investigated. WRF-modeled LLJs were compared to high-resolution observations collected during phase one of the Lower Atmospheric Boundary Layer Experiment (LABLE) at the Southern Great Plains Atmospheric Radiation Measurement site. Seeking the grid spacing that most accurately reproduces the observed LLJ at a reasonable computational expense, model runs were performed with various horizontal and vertical spacings. Data from WRF model runs with the default stretched vertical spacing on girds with 4-, 2-, and 1-kilometer horizontal spacing were evaluated in order to identify the optimal horizontal spacing for LLJ modeling. Using this optimal horizontal spacing, WRF-modeled LLJs were then compared using the default stretched vertical grid as well as 20- and 40-meter non-stretched vertical grids. Finally, three boundary layer parameterization schemes are compared. Results indicate that refinement of the horizontal spacing degrades the modelled wind speed. Furthermore, increasing the number of vertical levels on a non-stretched vertical grid provides additional information, but the benefit is limited by the increase in computational expense. Lastly, this work indicates that the Quasi-Normal Scale Elimination (QNSE) boundary layer scheme offers the best parameterization for resolving the LLJ compared to the Yonsei University (YSU) and the Mellor-Yamada Nakanishi Niino (MYNN) schemes.

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