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Geoscientific Model Development An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/gmd-2019-100
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/gmd-2019-100
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: model evaluation paper 10 Jul 2019

Submitted as: model evaluation paper | 10 Jul 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Geoscientific Model Development (GMD).

Observed and simulated turbulent kinetic energy (WRF 3.8.1) overlarge offshore wind farms

Simon K. Siedersleben1, Andreas Platis2, Julie K. Lundquist3,4, Bughsin Djath5, Astrid Lampert6, Konrad Bärfuss6, Beatriz Canadillas7, Johannes Schultz-Stellenfleth5, Jens Bange2, Tom Neumann7, and Stefan Emeis1 Simon K. Siedersleben et al.
  • 1Institute for Meteorology and Climate Research (IMK-IFU), Garmisch-Partenkirchen, Germany
  • 2Environmental Physics, ZAG, University of Tübingen, Germany
  • 3University of Colorado, Department of Atmospheric and Oceanic Sciences, Boulder, Colorado, USA
  • 4National Renewable Energy Laboratory, Golden, Colorado, USA
  • 5Institute for Coastal Research, Helmholtz Zentrum Geesthacht, Germany
  • 6Institute of Flight Guidance, Technische Universität Braunschweig, Germany
  • 7UL-DEWI Gmbh

Abstract. Because wind farms affect local weather and microclimates, parameterizations of their effects have been developed for numerical weather prediction models. While most wind farm parameterizations (WFP) include drag effects of wind farms, models differ on whether or not an additional turbulent kinetic energy (TKE) source should be included in these parameterizations to simulate the impact of wind farms on the boundary layer. Therefore, we use aircraft measurements above large offshore wind farms in stable conditions to evaluate WFP choices. Of the three case studies we examine, we find the simulated ambient background flow to agree with observations of temperature stratification and winds. This agreement allowing us to explore the sensitivity of simulated wind farm effects with respect to modeling choices such as whether or not to include a TKE source, horizontal resolution, vertical resolution, and advection of TKE. For a stably stratified marine atmospheric boundary layer (MABL), a TKE source and a horizontal resolution in the order of 5 km or finer are necessary to represent the impact of offshore wind farms on the MABL. Additionally, TKE advection results in excessively reduced TKE over the wind farms, which in turn causes an underestimation of the wind speed above the wind farm. Furthermore, using fine vertical resolution increases the agreement of the simulated wind speed with satellite observations of surface wind speed.

Simon K. Siedersleben et al.
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Simon K. Siedersleben et al.
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In-situ airborne measurements of atmospheric and sea surface parameters related to offshore wind parks in the German Bight K. Bärfuss, R. Hankers, M. Bitter, T. Feuerle, H. Schulz, T. Rausch, A. Platis, J. Bange, and A. Lampert https://doi.org/10.1594/PANGAEA.902845

Simon K. Siedersleben et al.
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Latest update: 21 Sep 2019
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Short summary
Wind farms affect local weather and microclimates. These effects can be simulated in weather models, usually by removing momentum at the location of the wind farm. Some debate exists whether additional turbulence should be added to capture the enhanced mixing of wind farms. By comparing simulations to measurements from airborne campaigns near offshore wind farms, we show that additional turbulence is necessary. Without added turbulence, the mixing is underestimated during stable conditions.
Wind farms affect local weather and microclimates. These effects can be simulated in weather...
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