Abstract
Prediction of wind resource in coastal zones is difficult due to the complexity of flow in the coastal atmospheric boundary layer (CABL). A three week campaign was conducted over Lake Erie in May 2013 to investigate wind characteristics and improve model parameterizations in the CABL. Vertical profiles of wind speed up to 200 m were measured onshore and offshore by lidar wind profilers, and horizontal gradients of wind speed by a 3-D scanning lidar. Turbulence data were collected from sonic anemometers deployed onshore and offshore. Numerical simulations were conducted with the Weather Research Forecasting (WRF) model with 2 nested domains down to a resolution of 1-km over the lake. Initial data analyses presented in this paper investigate complex flow patterns across the coast. Acceleration was observed up to 200 m above the surface for flow coming from the land to the water. However, by 7 km off the coast the wind field had not yet reached equilibrium with the new surface (water) conditions. The surface turbulence parameters over the water derived from the sonic data could not predict wind profiles observed by the ZephlR lidar located offshore. Horizontal wind speed gradients near the coast show the influence of atmospheric stability on flow dynamics. Wind profiles retrieved from the 3-D scanning lidar show evidence of nocturnal low level jets (LLJs). The WRF model was able to capture the occurrence of LLJ events, but its performance varied in predicting their intensity, duration, and the location of the jet core.
Highlights
The majority of offshore wind turbines are deployed within a few kilometers of the coastline and are located in the coastal zone [1], where the discontinuity in surface conditions induces non-stationarity, horizontal gradients of wind speeds and the development of internal boundary layers [2]
The results described focus on specific causes of flow modification and on evaluating the performance of Weather Research Forecasting (WRF) in simulating the flow relative to the observations
Low Level Jets The wind speed profiles retrieved from the Velocity Azimuth Display (VAD) scans of the Galion lidar deployed at the port frequently exhibited evidence of a low-level wind speed maximum, a phenomenon known as low level jet (LLJ)
Summary
The majority of offshore wind turbines are deployed within a few kilometers of the coastline and are located in the coastal zone [1], where the discontinuity in surface conditions induces non-stationarity, horizontal gradients of wind speeds and the development of internal boundary layers [2]. The objective of the research presented is to use detailed measurements in the CABL (from a measurement campaign in Lake Erie from May 8 to 25 in 2013) to diagnose causes of non-ideal profiles of wind and turbulence and to evaluate the performance of the Weather Research and Forecasting (WRF) model in simulating the observed conditions.
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