Phase II of the Advanced Texas Air Quality Model (ATAQM) has been implemented to simulate the August 25-31, 1998 ozone-exceedance episode in the 8-county Houston-Galveston Non-Attainment Area. ATAQM is a new, state-of-science modeling system developed for the for the Texas Natural Resources Conservation Commission (TNRCC) that can significantly improve upon recognized deficiencies in current meteorological modeling systems used to drive air quality models in support of State Implementation Planning. ATAQM Phase II consists of the Fifth-Generation PSU/NCAR Mesoscale Model Version 3 (MM5v3); the TOPMODEL-based Land Atmosphere Transfer Scheme (TOPLATS) land surface hydrology model; and a Sea-Surface Atmosphere Transfer Scheme (SSATS). A high-performance OpenMP parallel version of the TOPLATS model is run on its own 90-meter grid and is driven with both in situ and remotely sensed estimates of key meteorological variables, including solar radiation and precipitation. The SSATS model may be driven with observed Sea Surface Temperature (SST) data from a combination of in situ (NOAA PORTS) and remotely sensed (CoastWatch AVHRR) sources.

Extensive evaluation against screen-level observations and GOES cloud imagery indicates that the ATAQM system performance is superior to that obtained from the original MM5 modeling system using the SLAB land surface model. ATAQM simulations without the GOES Surface Radation Budget (SRB) products indicate that the downward shortwave observations have the largest impact on the modeling system. Further, although the diurnal 2-m temperature cycle is clearly improved relative to the original modeling system, the 2-m humidity and 2-m wind results are strongly sensitive to lower limits imposed on wind speed and friction velocity within the HIRPBL scheme. Further, cloud development along the sea breeze convergence zone and the diurnal cycle of pbl development in the vicinity of the Houston heat island are better represented in the coupled modeling system.