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.