Assessment of planetary boundary layer parameterizations and urban heat island comparison: Impacts and implications for tracer transport

Accurate simulation of planetary boundary layer height (PBLH) is key to greenhouse gas emission esti-mation, air quality prediction, and weather forecasting. This paper describes an extensive performance assessment of several Weather Research and Forecasting (WRF) Model configurations in which novel observations from ceilometers, surface stations, and a flux tower were used to study their ability to reproduce the PBLH and the impact that the urban heat island (UHI) has on the modeled PBLHs in the greater Washington, D.C., area. In addition, CO₂ measurements at two urban towers were compared with tracer transport simulations. The ensemble of models used four PBL parame-terizations, two sources of initial and boundary conditions, and one configuration including the building energy pa-rameterization urban canopy model. Results have shown low biases over the whole domain and period for wind speed, wind direction, and temperature, with no drastic differences between meteorological drivers. We find that PBLH errors are mostly positively correlated with sensible heat flux errors and that modeled positive UHI intensities are associated with deeper modeled PBLs over the urban areas. In addition, we find that modeled PBLHs are typically biased low during nighttime for most of the configurations with the exception of those using the MYNN parameterization, and these biases directly translate to tracer biases. Overall, the configurations using the MYNN scheme performed the best, reproducing the PBLH and CO₂ molar fractions reasonably well during all hours and thus opening the door to future nighttime inverse modeling.