Turbulent characteristics in complex coastal areas assessed using BSWO observations and WRF-LES simulation results

Abstract

Studies exploring the turbulent structure of the planetary boundary layer (PBL) over complex topographies are very limited, especially at night, because of the lack of available observations and difficulty of highly resolved simulation. In this study, micro-meteorological and turbulent characteristics over complex coastal areas were investigated based on high spatial-temporal resolution by using the Weather Research and Forecasting–Large Eddy Simulation (WRF-LES) model. Then, the simulations were compared to comprehensive observations obtained at the Boseong Standard Weather Observatory (BSWO), which is equipped with various observation facilities, such as a meteorological observation tower with a height of 307 m, and aiding ground-based remote sensing measurements used for PBL research. The comparison between the WRF-LES model results and the measurements by the wind lidar system at the BSWO showed that the LES approach in this study reproduced the spatial/vertical wind field structure and land-sea wind circulation distinctly better than the conventional PBL schemes. High turbulent kinetic energy (TKE) was observed near the surface level at night due to the increased nocturnal shear production following the evolution of land and mountain breezes. The calculated TKE from WRF-LES model was applied to identify the mixing intensity based on the mixing length and eddy diffusion coefficient within the boundary layer, and then those were evaluated with the observed extinction coefficient from the aerosol Micro-Pulse Lidar system (MPL). In addition, the planetary boundary layer height (PBLH) at night was explored by using the TKE threshold method combined with the bulk Richardson number threshold method for the daytime PBLH. Compared with the observed value from a ceilometer at the BSWO, we found that the TKE threshold method proposed in this study could yield highly accurate PBLH values, especially at night. It is also expected that the enhanced application of WRF-LES like to this study can lead to understanding and prediction with the high confidence for much detail and accurate spatiotemporal turbulent structure over complex coastal areas, which will contribute to more comprehensive air quality modeling studies.