On the Offshore Advection of Boundary-Layer Structures and the Influence on Offshore Wind Conditions
Date
2015
Authors
Dörenkämper, Martin
Optis, Michael
Monahan, Adam H.
Steinfeld, Gerald
Journal Title
Journal ISSN
Volume Title
Publisher
Boundary-Layer Meteorology
Abstract
The coastal discontinuity imposes strong signals to the atmospheric conditions
over the sea that are important for wind-energy potential. Here, we provide a comprehensive
investigation of the influence of the land–sea transition on wind conditions in the Baltic Sea
using data from an offshore meteorological tower, data from a wind farm, and mesoscale
model simulations. Results show a strong induced stable stratification when warm inland air
flows over a colder sea. This stratification demonstrates a strong diurnal pattern and is most
pronounced in spring when the land–sea temperature difference is greatest. The strength of
the induced stratification is proportional to this parameter and inversely proportional to fetch.
Extended periods of stable stratification lead to increased influence of inertial oscillations and
increased frequency of low-level jets. Furthermore, heterogeneity in land-surface roughness
along the coastline is found to produce pronounced horizontal streaks of reduced wind speeds
that under stable stratification are advected several tens of kilometres over the sea. The
intensity and length of the streaks dampen as atmospheric stability decreases. Increasing sea
surface roughness leads to a deformation of these streaks with increasing fetch. Slight changes
in wind direction shift the path of these advective streaks, which when passing through an
offshore wind farm are found to produce large fluctuations in wind power. Implications of
these coastline effects on the accurate modelling and forecasting of offshore wind conditions,
as well as damage risk to the turbine, are discussed.
Description
Keywords
Coastal meteorology, Low-level jets, Offshore wind farms, Stable stratification, Wind energy
Citation
Dörenkämper, M., Opris, M., Monahan, A. H., & Steinfeld, G. (2015). On the Offshore Advection of Boundary-Layer Structures and the Influence on Offshore Wind Conditions. Boundary-Layer Meteorology, 155, 459-482. https://doi.org/10.1007/s10546-015-0008-x.