P73  Study of Nocturnal Surface Wind Bias by the WRF-ARW Model over Southeastern Texas

Ngan, Fong, Pius Lee, HyunCheol Kim, National Oceanic and Atmospheric Administration/ARL and Khalid Al-Wali, and Bright Dornblaser, TCEQ, TX

Accurate simulation of surface winds by a mesoscale model is critically important to guide atmospheric scientists to understand the role of different emission sources contributing to high air pollution events in a region. Simulated daytime wind is responsible for the accuracy of capturing the local maxima of concentrations in air quality modeling while nighttime wind prediction accuracy is important for simulating the transport of precursors that initiate the photochemistry for the following day. A 37-day simulation was done for a period of TexAQS-II, May 28 – July 3, 2006 using the WRF-ARW model. The model tends to increase the surface wind speed at the evening hours, especially in the coastal region such as the Houston-Galveston-Brazoria (HGB) area; whereas the observations show the opposite. The evening wind bias starts at around 19 CST when the sun goes down leading to the growth of nocturnal boundary layer. Through the comparison against surface monitors and wind profiler measurements, we intend to identify when and where the bias occurs and how it depends on synoptic weather patterns, thus to develop a localized conceptual model of the nocturnal boundary layer winds from such observations and modeling studies. Furthermore this study may serve as a priori to investigate the components of the momentum and thermodynamic equations that are primarily responsible for the evolution of the nocturnal boundary layer pointing to possible causes of the surface wind bias of the model under such circumstances.