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


Previous studies have shown that the Weather Research and Forecasting (WRF) model often under-predicts the strength of the Great Plains nocturnal low-level jet (NLLJ), which has implications for weather, climate, aviation, air quality, and wind energy in the region. During the Lower Atmospheric Boundary Layer Experiment (LABLE) conducted in 2012, NLLJs were frequently observed at high temporal resolution allowing for detailed documentation of their development and evolution throughout the night. Ten LABLE cases with observed NLLJs were chosen to systematically evaluate the WRF model’s ability to reproduce the observed NLLJs. Model runs were performed with 4-, 2-, and 1-km horizontal spacing, and with the default stretched grid and a non-stretched 40-m vertically spaced grid to investigate which grid configurations are optimal for NLLJ modeling. These tests were conducted using three common boundary layer parameterization schemes: the Mellor-Yamada Nakanishi Niino (MYNN), the Yonsei University (YSU), and the Quasi-Normal Scale Elimination (QNSE) schemes. It was found that refining horizontal spacing does not necessarily improve the modeled NLLJ wind. Increasing the number of vertical levels on a non-stretched grid provides more information about the structure of the NLLJ with some schemes, but the benefit is limited by computational expense and model stability. Simulations of the NLLJ were found to be less sensitive to boundary layer parameterization than grid configuration. The QNSE scheme was chosen for future NLLJ simulation studies.

Journal of Applied Meteorology and Climatology