High-precision barometers have been deployed at six sites in Denmark, four west and two east of the Great Belt. The purpose is to establish long climatological records of the geostrophic wind as a supplement to the records of tens of years of duration ofsurface observations of wind, temperature, humidity etc., which have been obtained by Risø at many sites in Denmark. Three of these sites are in principle sufficient to determine an average of the magnitude and direction of the geostrophic wind inside thetriangle formed by the three sites. Ten, out of twenty possible, triangles have been selected as suitable for studying the geographical variations of the geostrophic wind. A tentative conclusion from about one year of data is that statistically thegeostrophic wind decrease in magnitude when going from west toward east. The data also showed that the largest mean values of the geostrophic mean wind speed are in a direction sector from 285 deg C to 315 deg C. The Weibull parameters were calculated forall ten triangles. The curvature of the isobars were determined by using simultaneous pressure measurements at all sic sites and the geostrophic and gradient winds were calculated and compared to the geostrophic wind based on three pressure measurementsin one particular triangle. Combining the geostrophic wind with the surface wind measured at Tystofte in southern Zealand, the two dimensionless constants ¤A¤ and ¤B¤ in the geostrophic drag law were determined as functions of the surface friction velocity.These data suggest that ¤A¤ = 0.5 and ¤B¤ = 3.5. The surface data at Tystofte and at Børglum in Vendsyssel in northern Jutland were used to predict the geostrophic wind by applying the geostrophic drag law with these constants and the predictions werecompared to the observed geostrophic wind.
Vindenergi og atmosfæriske processer; Risø-R-1145; Risø-R-1145(EN)