Initial Modeling of the August 2000 Houston-Galveston Ozone Episode

Abstract

This report describes MM5 modeling work to date at Texas A&M University, sponsored by the Texas Natural Resource Conservation Commission, with the goal of an accurate, fully validated meteorological simulation delivered by February 28, 2002. Specifically, this report describes the meteorological conditions during the August 25-September 1, 2000, Houston-Galveston ozone episode, describes the modeling philosophy being followed to develop high-quality meteorological fields, describes the MM5 modeling system itself, and describes the results of various experiments conducted over the past few months. Results so far indicate that, with suitable modification to land surface and/or radiative forcing, the MM5 is fully capable of simulating the temperatures and vertical extent of the daytime boundary layer. Low-level nighttime temperatures are too warm, which may lead to overly robust turbulent mixing at night. The present nesting scheme produces very good quality large-scale winds and realistic sea breeze evolution. Future work will focus on determining the accuracy of the model-simulated nighttime wind cycle, and, if necessary, investigating ways of improving the nighttime winds. Differences in behavior of various PBL schemes will be further investigated and evaluated. Wind profiler and Doppler lidar data will be assimilated on a coarse scale, and statistical measures of model accuracy will be used to provide objective measures of model performance. Of all model runs that have been conducted so far, the best performance has been exhibited by the dec6grid4 run, with the MRF planetary boundary layer scheme and an extra sigma layer near the ground.