Extreme winds in Denmark

Wind-speed data from four sites in Denmark have been analyzed in order to obtain estimates of the basic wind velocity, defined as the 50-year wind speed (ten minute averages) under standard conditions, i.e. 10 meter over a homogeneous terrain with the roughness length 0.05 m. The sites are Skjern (15 years),. Kegnaes (7 years), Sprogo (20 years), and Tystofte (16 years). The measured data are wind speed, wind direction, temperature and pressure. The wind records are cleaned for terrain effects by means of WASP (Mortensen et al. 1993): assuming geostrophic balance, all the wind-velocity data are transformed to friction velocity u* and direction at standard conditions by means of the geostrophic drag law for neutral stratification. The basic wind velocity in 30 degrees sectors are obtained through ranking of the largest values of the friction velocity pressure 1/2 rho u(2) taken once every two months. The main conclusion is that the basic wind velocity is significantly larger at the west coast of Jutland (25 +/- 1 m/s) than at any of the other sites (22 +/- 1 m/s). These results are in agreement with those obtained by Jensen & Franck (1970) and Abild (1994). It is demonstrated how the data can be applied to non-standard situations where the roughness length depends on the direction. The entire analysis is part of the larger project WA(S)P-Engineering.