SIMULATIONS OF THE CLIMATOLOGICAL WIND-FIELD IN THE BALTIC SEA AREA USING A MESOSCALE HIGHER-ORDER CLOSURE-MODEL

A three-dimensional mesoscale numerical model is utilized to investiga te the climatological wind field over the Baltic Sea. To cover all syn optic and boundary layer conditions, a large number of model runs have to be made. Since this type of model consumes a rather large amount o f computer time, the factors primarily affecting the wind field have b een identified to limit the number of model runs. To get accurate resu lts, it was necessary to make simulations representing the four season s, eight wind directions, and three values of the geostrophic wind spe ed. The model was run for these 96 conditions with the monthly mean da ily temperature variation at screen height over land to include the ef fects of the thermal stratification. The simulated wind fields were th en weighted together using climatological data of the geostrophic wind speed and direction. The model results have been compared with measur ements from two lighthouses outside the Swedish coast, as well as with an interpolation of ship measurements. The comparison shows good agre ement between the modeled wind field and measurements, with deviations of less than 0.5 m s(-1) in the main part of the Baltic Sea. Thus, th e small deviations between measurements and simulations suggest that t he main flow-forcing parameters, the climatological statistics, and as sumptions made are correct.