Wind Atlas

The KNMI North Sea Wind (KNW) Atlas provides wind climatology for the North Sea and the Netherlands.

The climatology has an accuracy better than 0.3 m/s at wind turbine heights onshore and 0.2 m/s at wind turbine heights offshore, which is comparable to measurement accuracy. The atlas data (time series and fields) can be downloaded for free from the KNW-website (http://projects.knmi.nl/knw/). The website also provides  a user manual and all relevant scientific documentation and information tailored to the needs of the wind energy sector.

The atlas is based on the 35 year (1979-2013) ERA-Interim global re-analysis. A global re-analysis is a 3D summary of all relevant measurements in the world  (5 million every 12 hours) which is both the best possible fit of these measurements and consistent with the laws of physics. KNMI’s operational weather forecast model HARMONIE has been used to downscale the global re-analysis from 6 hourly to hourly and from 80 to 2.5 km grid-spacing.  With 225 quadrillion calculations 35 years of high-resolution wind information was produced up to 200m height. The downscaled re-analysis was then tuned to match high-quality wind speed measurements from the Cabauw mast (http://www.cesar-observatory.nl/) by applying a wind shear correction of 15% uniformly throughout the whole dataset. The shear-corrected data have been validated against wind mast and satellite measurements.

KNMI intends to:

  • Update the atlas regularly in order to enable comparison with more recent measurements for further validation or Measure Correlate Predict, which is a method used in the wind energy sector where short measurement campaigns are compared to climate records elsewhere to derive the wind climate at the measurement site.
  • Improve the atlas by using a method where HARMONIE is not only used as a downscaling tool, but in assimilation-mode, where measurements are “fed” directly into HARMONIE. For the KNW-atlas measurements were only “fed” into ERA-Interim. With HARMONIE in assimilation-mode, measurements can be used that are currently not in ERA-Interim, such as 10 years of commercial aircraft and satellite wind measurements. The quality of time series and the representation of the diurnal cycle of the wind are expected to improve.
  • Extend the atlas up to 600 m height, include climatology of e.g. gusts, turbulence, stability, available solar energy, icing and lightning (KNW only contains wind, pressure, temperature and humidity) and all information required for further downscaling with Large Eddy Simulation (LES) techniques.
Average wind speed 1979-2013 at 100 m height
Average wind speed 1979-2013 at 100 m height
Validation against MMIJ mast measurements (Meetmast IJmuiden, 75 km west of IJmuiden).
Validation against MMIJ mast measurements (Meetmast IJmuiden, 75 km west of IJmuiden): red = atlas values, blue = cup anemometer measurements, green = LiDAR measurements (for 2012 and 2013 when KNW-atlas and MMIJ measurements were both available).