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A new paradigm for PBL modeling in meteorological and air quality models
Citation:
Alapaty, K., J. Bash, R. Gilliam, C. Hogrefe, B. Henderson, D. Kang, B. Cheng, C. Nolte, S. Arunachalam, AND A. Vette. A new paradigm for PBL modeling in meteorological and air quality models. 22nd Annual CMAS Conference, chapel hill, NC, October 16 - 18, 2023.
Impact/Purpose:
Pollutants are mostly trapped in the lower part of the atmosphere, known as boundary layer. A new paradigm for representing boundary layer processes in meteorology and air quality is being developed. The specialty of this new paradigm is that the physics used is independent of stability functions that are in use for the past 50+ years. Thus, for the first time a viable alternative formulation has been developed that can promise the reduction of differences in results among models contributed by the usage of different stability functions at regional and global scales.
Description:
For about half-a-century, similarity profile functions have been the only option to model planetary boundary layer (PBL) processes in meteorological and air quality models. These functions represent boundary layer stability conditions so that PBL processes are realistically modeled. However, differences in these functions across regional and global meteorological and air quality models can contribute to sizeable model-to-model differences in simulation results. To address this, we present the development, implementation, and testing of a new paradigm for PBL modeling that is independent of similarity functions in the WRF and CMAQ models. Previously, a 3-D turbulence velocity scale, e*, was proposed and validated with a decade of measurements from a 3-D sonic anemometer. Then, this turbulence velocity scale was successfully tested and validated in a box model to simulate aerosol deposition velocities where it replaced the default friction velocity and similarity functions. In this study, the e* was used to develop a new surface layer parameterization in the WRF model to estimate surface fluxes without the use of similarity functions. The e* was also used to develop new formulations in a boundary layer parameterization, again without using similarity functions. These formulations were also implemented in the CMAQ model to maintain consistency in representing boundary layer processes. Further, several resistances in the ozone dry deposition estimations were revised by the incorporation of e*. Thus, the new paradigm of PBL modeling was implemented in the WRF and CMAQ models. Numerical simulations for a hemispheric domain using WRF and CMAQ models were performed for the year 2016. We compare and evaluate model estimates of selected fields (e.g., simulated surface precipitation, 2 m air temperature(T2) and water vapor mixing ratios, 10 m winds, and surface HNO3 and ozone) from 2016 WRF and CMAQ simulations using the OLD (i.e., using similarity functions) and NEW (without using similarity functions) surface and mixed layer PBL schemes. Results for 2016 indicate that the new paradigm for PBL modeling works very well (e.g., T2 bias differences between NEW and OLD are well within measurements accuracy), providing the very first alternative to the 50-year old traditional method of PBL modeling.