Rogier Ralph Floors

The Wind Profile in the Coastal Boundary Layer: Wind Lidar Measurements and Numerical Modelling

Traditionally it has been difficult to verify mesoscale model wind predictions against observations in the planetary boundary layer (PBL). Here we used measurements from a wind lidar to study the PBL up to 800 m above the surface at a flat coastal site in Denmark during a one month period in autumn. We ran the Weather Research and Forecasting numerical model with two different roughness descriptions over land, two different synoptic forcings and two different PBL schemes at two vertical resolutions and evaluated the wind profile against observations from the wind lidar. The simulated wind profile did not have enough vertical shear in the lower part of the PBL and also had a negative bias higher up in the boundary layer. Near the surface the internal boundary layer and the surface roughness influenced the wind speed, while higher up it was only influenced by the choice of PBL scheme and the synoptic forcing. By replacing the roughness value for the land-use category in the model with a more representative mesoscale roughness, the observed bias in friction velocity was reduced. A higher-order PBL scheme simulated the wind profile from the west with a lower wind-speed bias at the top of the PBL. For easterly winds low-level jets contributed to a negative wind-speed bias around 300 m and were better simulated by the first-order scheme. In all simulations, the wind-profile shape, wind speed and turbulent fluxes were not improved when a higher vertical resolution or different synoptic forcing were used.

The RUNE Experiment—A Database of Remote-Sensing Observations of Near-Shore Winds

We present a comprehensive database of near-shore wind observations that were carried out during the experimental campaign of the RUNE project. RUNE aims at reducing the uncertainty of the near-shore wind resource estimates from model outputs by using lidar, ocean, and satellite observations. Here, we concentrate on describing the lidar measurements. The campaign was conducted from November 2015 to February 2016 on the west coast of Denmark and comprises measurements from eight lidars, an ocean buoy and three types of satellites. The wind speed was estimated based on measurements from a scanning lidar performing PPIs, two scanning lidars performing dual synchronized scans, and five vertical profiling lidars, of which one was operating offshore on a floating platform. The availability of measurements is highest for the profiling lidars, followed by the lidar performing PPIs, those performing the dual setup, and the lidar buoy. Analysis of the lidar measurements reveals good agreement between the estimated 10-min wind speeds, although the instruments used different scanning strategies and measured different volumes in the atmosphere. The campaign is characterized by strong westerlies with occasional storms.

A Study on the Effect of Nudging on Long-Term Boundary Layer Profiles of Wind and Weibull Distribution Parameters in a Rural Coastal Area

AbstractBy use of 1 yr of measurements performed with a wind lidar up to 600-m height, in combination with a tall meteorological tower, the impact of nudging on the simulated wind profile at a flat coastal site (Hovsore) in western Denmark using the Advanced Research version of the Weather Research and Forecasting model (WRF) is studied. It was found that the mean wind speed, the wind direction change with height, and the wind power density profiles are underestimated with the configuration of WRF used and that the impact of nudging on the simulated mean values was minor. Nudging was found to reduce the scatter between the simulated and measured wind speeds, expressed by the root-mean-square error, by about 20% between altitudes of 100 and 500 m. The root-mean-square error was nearly constant with height for the nudged case (~2.2 m s−1) and slightly increased with height for the nonnudged one, reaching 2.8 m s−1 at 300 and 500 m. In studying the long-term wind speed variability with the Weibull distributi...

Evaluating Mesoscale Simulations of the Coastal Flow Using Lidar Measurements

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. Plain Language Summary There is strong interest in accurate estimation of the wind resource for wind farms that are located in the coastal zone. These areas have high wind speeds for onshore flow conditions and grid connectivity is relatively easy. The atmospheric flow in the coastal zone is investigated using weather model simulations and a relatively new device (a scanning wind lidar) that can measure the wind speed using a laser beam. The weather model is set up in 12 different configurations, with varying parametrization schemes and boundary conditions. All model simulations describe the observed mean wind profile well at different onshore and offshore locations. 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. Simulations with the finest horizontal grid show poorer model performance, whereas using boundary conditions from the European Centre gives a better model performance. Although having a negative impact on standard performance metrics, simulations with the finest horizontal grid spacing resolved more atmospheric motion.

Measurements and Modeling of the Wind Profile Up to 600 meters at a Flat Coastal Site

This study shows long-term ABL wind profile features by comparing long-range wind lidar measurements and the output from a mesoscale model. The study is based on 1-year pulsed lidar (Wind Cube 70) measurements of wind speed and direction from 100 to 600 m with vertical resolution of 50 m and time resolution of 10 min at a coastal site on the West coast of Denmark and WRF ARW (NCAR) simulations for the same period. The model evaluation is performed based on wind speed, wind direction, as well as statistical parameters of the Weibull distribution of the wind speed time series as function of height. It is found that (1) WRF is generally under predicting both the profiles of the measured wind speed, direction and power density, (2) the scatter of observations to model results of the wind speed does not change significantly with height between 100 and 600 m, and (3) the scale (A) and shape (k) parameters of the Weibull distribution above 100 m. The latter signifies that the model suggests a wider distribution in the wind speed compared to measurements.