Research

Evaluating Mesoscale Simulations of the Coastal Flow Using Lidar Measurements

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Abstract

The atmospheric ﬂow in the coastal zone is investigated using lidar and mast measurements and model simulations. Novel dual-Doppler scanning lidars were used to investigate the ﬂow over a 7 km transect across the coast, and vertically proﬁling lidars were used to study the vertical wind proﬁle at oﬀshore and onshore positions. The Weather, Research and Forecasting model is set up in 12 diﬀerent conﬁgurations using 2 planetary boundary layer schemes, 3 horizontal grid spacings and varied sources of land use, and initial and lower boundary conditions. All model simulations describe the observed mean wind proﬁle well at diﬀerent onshore and oﬀshore locations from the surface up to 500 m. The simulated mean horizontal wind speed gradient across the shoreline is close to that observed, although all simulations show wind speeds that are slightly higher than those observed. Inland at the lowest observed height, the model has the largest deviations compared to the observations. Taylor diagrams show that using ERA-Interim data as boundary conditions improves the model skill scores. Simulations with 0.5 and 1 km horizontal grid spacing show poorer model performance compared to those with a 2 km spacing, partially because smaller resolved wave lengths degrade standard error metrics. Modeled and observed velocity spectra were compared and showed that simulations with the ﬁnest horizontal grid spacing resolved more high-frequency atmospheric motion.