Extreme winds in Denmark

Wind-speed data from four sites in Denmark have been analyzed in order to o btain estimates of the basic wind velocity, defined as the 50 yr wind speed (10 min averages) under standard conditions, i.e., 10 m over a homogeneous terrain with the roughness length 0.05 m, The sites are Skjern (15 yr), Ke gnaes (7 yr), Sprogo (20 yr), and Tystofte (16 yr). The measured data are w ind speed, wind direction, temperature and pressure. The wind records are c leaned for terrain effects by means of WASP (Mortensew ct al., Technical Re port I-666 (EN), Riso National Laboratory, 1993. Vol. 2. User's Guide): ass uming geostrophic balance, all the wind-velocity data are transformed to fr iction velocity u(*) and direction at standard conditions by means of the g eostrophic drag law for neutral stratification. The basic wind velocity in 30 degrees sectors are obtained through ranking of the largest values of th e friction velocity pressure pu(*)(2)/2 taken once every two months. The ma in conclusion is that the basic wind velocity is significantly larger at th e 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 and Franck (Technical Report, Danish Technical press, 1970) and by Abild (Tech nical Report R-522 (EN), Riso National Laboratory, 1994). A short discussio n of the wind storm on the 3rd of December 1999 is included. It is demonstr ated how the data can be applied to non-standard situations where the rough ness length depends on the direction. (C) 2000 Elsevier Science Ltd. All ri ghts reserved.