Wednesday, 17 January 2007: 11:30 AM
An Examination of WRF/Chem: Physical Schemes, Nesting Options, and Grid Resolutions
212A (Henry B. Gonzalez Convention Center)
The Weather Research and Forecast/Chemistry Model (WRF/Chem) offers several options for planetary boundary layer (PBL) schemes (the MRF, YSU and MYJ schemes), land-surface models (LSM) (the slab, NOAH, and RUC schemes), and shortwave radiation schemes (Goddard, Dudhia, andGFDL). In a previous study, WRF/Chem V2.03 was applied for the 28 August – 2 September 2000 Texas Air Quality Study (TexAQS-2000) episode over the Houston-Galveston area, Texas to examine the effects of various meteorological parameterizations on simulating meteorological parameters and chemical species. Three physical pairs (NOAH/YSU, slab/YSU, and NOAH/MYJ) were studied and measurements acquired from the TexAQS-2000 were used for model evaluation. It was found that the slab/YSU combination performs the best for meteorological variables overall, though the NOAH/YSU simulation gives the most accurate surface temperatures. For O[sub]3[/sub] and CO predictions, the NOAH/MYJ coupling performs the best due to a better representation of the nocturnal PBL by the MYJ scheme. In this paper, we continue to examine the sensitivity of WRF/Chem predictions to various PBL schemes, LSMs, and radiation schemes using the latest version of WRF/Chem (V2.1.1 released in December 2005). Several additional simulations at a 12-km grid spacing with different combinations of LSM, PBL, and radiation schemes (e.g., RUC/YSU/Goddard, NOAH/MRF/Goddard, and NOAH/YSU/GFDL) will be conducted and compared with those from the baseline simulation with NOAH/YSU/Goddard. In addition, one-way and two-way nested simulations with 12-, 4-, and 1.33-km grid spacings will also be conducted with the base physics configurations. A comprehensive intercomparison of meteorological and chemical predictions using the two nested grids and various parameterizations is presented. While two-way nesting involves transferring information back and forth from coarse and fine resolutions, one-way nesting only involves communication from coarse to fine. The CPU cost to benefit ratio will be compared for the two nesting options. These simulations and analyses may provide an in-depth understanding regarding WRF/Chem's sensitivity to various physical schemes and capability of capturing variability of meteorological variables and chemical species at various grid resolutions.