Analyzing “grey zone” turbulent kinetic energy predictions in the boundary layer from three WRF PBL schemes over New York City and comparison to aircraft measurements

Abstract

We investigated the ability of three planetary boundary layer (PBL) schemes in the Weather Research and Forecasting (WRF) model to simulate boundary layer turbulence in the “grey zone” (i.e. resolutions from 100 m to 1 km). The three schemes chosen are the well-established MYNN PBL scheme and the two newest PBL schemes added to WRF: the SMS-3DTKE scheme and the EEPS scheme. The SMS-3DTKE scheme is designed to be scale-aware and avoid the double-counting of turbulent kinetic energy (TKE) in simulations within the grey zone. We evaluated their performance using aircraft measurements obtained during three research flights immediately downwind of Manhattan, New York City. The MYNN PBL scheme simulates TKE best, despite not being scale-aware and slightly underestimating TKE from observations, while the SMS-3DTKE scheme appears to be overly scale-aware for the three flights examined, in particular when combined with the MM5 surface layer scheme. The EEPS scheme significantly underestimates TKE, mostly in the elevated layers of the boundary layer. Additionally, we examined the impact of flow over tall buildings on observed TKE and found that only the windiest day showed a significant increase in TKE directly downwind of Manhattan. This impact was, however, not reproduced by any of the model configurations, regardless of the land use data selected, although the better resolved NLCD land use led to a slight improvement of the spatial distribution of TKE, implying that more explicit representation of the impact of tall buildings may be needed to fully capture their impact on boundary layer turbulence.