Extreme Wind Shear Events in US Offshore Wind Energy Areas and the Role of Induced Stratification

Abstract. As the offshore wind industry emerges on the U.S. East Coast, a comprehensive understanding of the wind resource – particularly extreme events – is vital to the industry's success. Such understanding has been hindered by a lack of publicly available wind profile observations in offshore wind energy areas. However, the New York State Energy Research and Development Authority (NYSERDA) recently funded the deployment of two floating lidars within two current lease areas off the coast of New Jersey. These floating lidars provide publicly available wind speed data from 20 m to 200 m height with 20-m vertical resolution. In this study, we leverage a year of these lidar data to quantify and characterize the frequent occurrence of high wind shear and low-level jet events, both of which will have considerable impact on turbine operation. We find that almost 100 independent events occur throughout the year with mean wind speed at 100 m height and power-law exponent of 16 m/s and 0.28, respectively. The events have strong seasonal variability, with the highest number of events in summer and the lowest in winter. A detailed analysis reveals that these events are enabled by an induced stable stratification when when warmer air from the south flows over the colder mid-Atlantic waters, leading to a positive air–sea temperature difference.