Adv. Sci. Res., 20, 109-128, 2023 
https://doi.org/10.5194/asr-20-109-2023 
© Author(s) 2023. This work is distributed under 
the Creative Commons Attribution 4.0 License. 
Advances in 
Science & Research 
Open Access Proceerdinas 
intercomparing the quality of recent reanalyses 
for offshore wind farm planning in Germany’s 
exclusive economic zone of the North Sea 
Thomas Spangehl!, Michael Borsche!, Deborah Niermann', Frank Kaspar”, Semjon Schimanke* 
Susanne Brienen“‘, Thomas Möller”, and Maren Brast® 
“National Climate Monitoring, Deutscher Wetterdienst, Offenbach, Germany 
?Hydrometeorology, Deutscher Wetterdienst, Offenbach, Germany 
Swedish Meteorological and Hydrological Institute, Norrköping, Sweden 
4Central Climate Office, Deutscher Wetterdienst, Offenbach, Germany 
Marine Climate Monitoring, Deutscher Wetterdienst, Hamburg, Germany 
©Site Investigation, Bundesamt für Seeschifffahrt und Hydrographie, Hamburg, Germany 
Correspondence: Thomas Spangehl (thomas.spangehl@dwd.de) 
Received: 25 February 2023 — Revised: 25 September 2023 — Accepted: 4 October 2023 — Published: 17 November 2023 
Abstract. In order to facilitate offshore wind farm tenders, Deutscher Wetterdienst (DWD, Germany’s national 
meteorological service) provides reanalysis data and quality assessments to Bundesamt für Seeschifffahrt und 
Hydrographie (BSH, Federal Maritime and Hydrographic Agency). The regional reanalysis COSMO-REAG6 is 
Jsed besides the global reanalysis ERAS. New reanalyses and derived products getting available are (i) the re- 
gional reanalysis CERRA (C35$), (ii) COSMO-R6G2, a successor of COSMO-REAG6 which is currently produced 
»y DWD and (ii) HoKliSim-De, a convection-permitting climate simulation for Germany with COSMO-CLM 
as a regional downscaling of ERAS. In the present study, the quality of the different data sets for offshore wind 
energy application is compared using in-situ measurements of the wind speed and wind direction from the top 
anemometer and vane of the FINO1 research platform and satellite-based data of the near-surface wind speed 
from the Copernicus Marine Environment Monitoring Service (CMEMS) and the EUMETSAT Satellite Appli- 
cation Facility on Climate Monitoring (CM SAP). 
Evaluation at FINO1 focuses on the time period prior to the installation of nearby wind farms to avoid wake 
effects. COSMO-REA6, CERRA and HoKliSim-De show only small biases and resemble the observed distri- 
ution of the wind speed at FINO1 whereas ERAS5 shows slightly lower values of the wind speed at 100m. All 
model-based products tend to slightly underestimate the occurrence of south-westerly wind directions and over- 
estimate wind directions from West to Northwest. Smallest directional biases are analysed for COSMO-REA6. 
Analysis of the windstorm CHRISTIAN suggests that ensemble information is required for the representation of 
individual extreme events. 
Evaluation of the near-surface wind speed using satellite-based data is performed for an area around the 
German Exclusive Economic Zone (EEZ) of the North Sea. The median bias of ERA5 and COSMO-REA6 
is close to zero. CERRA shows a systematic overestimation of the near-surface wind speed compared to the 
satellite-based reference datasets. By contrast, a slight underestimation is analysed for HoKliSim-De. The bias 
distribution analysed for a first simulation stream of COSMO-R6CG2 is similar to COSMO-REAG6 which provides 
initial indication for the applicability of the new product. 
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7ublished by Copernicus Publications.