Classification and properties of non-idealized coastal wind profiles – an observational study

Non-idealized wind profiles frequently occur over the Baltic Sea and are important to take into consideration for offshore wind power, as they affect not only the power production but also the loads on the structure and the behavior of the wake behind the turbine. In this observational study, we cla...

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Bibliographic Details
Published in:	Wind Energy Science Vol. 7; no. 3; pp. 1183 - 1207
Main Authors:	Hallgren, Christoffer, Arnqvist, Johan, Nilsson, Erik, Ivanell, Stefan, Shapkalijevski, Metodija, Thomasson, August, Pettersson, Heidi, Sahlée, Erik
Format:	Journal Article
Language:	English
Published:	Göttingen Copernicus GmbH 08-06-2022 Copernicus Publications
Subjects:	Atmospheric boundary layer Coasts Eddies Jets Lidar Observational studies Offshore Offshore operations Turbines Wind power Wind speed United States > US North Sea Baltic Sea
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Summary:	Non-idealized wind profiles frequently occur over the Baltic Sea and are important to take into consideration for offshore wind power, as they affect not only the power production but also the loads on the structure and the behavior of the wake behind the turbine. In this observational study, we classified non-idealized profiles as the following wind profiles having negative shear in at least one part of the lidar wind profile between 28 and 300 m: low-level jets (with a local wind maximum in the profile), profiles with a local minimum and negative profiles. Using observations spanning over 3 years, we show that these non-idealized profiles are common over the Baltic Sea in late spring and summer, with a peak of 40 % relative occurrence in May. Negative profiles (in the 28–300 m layer) mostly occurred during unstable conditions, in contrast to low-level jets that primarily occurred in stable stratification. There were indications that the strong shear zone of low-level jets could cause a relative suppression of the variance for large turbulent eddies compared to the peak of the velocity spectra, in the layer below the jet core. Swell conditions were found to be favorable for the occurrence of negative profiles and profiles with a local minimum, as the waves fed energy into the surface layer, resulting in an increase in the wind speed from below.
ISSN:	2366-7443 2366-7451 2366-7451
DOI:	10.5194/wes-7-1183-2022