Simulations and measurements of mesoscale flow modifications in the Baltic Sea area

The wind climate over the Baltic Sea, with main focus over the island Gotland, has been studied. Tower and pilot balloon wind measurements have been performed on Gotland during May 2000 and the 3-D, higher order closure, MIUU model has been used to simulate the wind climate for 22-23 May. During these days thermally driven circulations were present, giving rise to e.g. low level jets and sea-breeze. Comparison between measurements and model simulations showed good agreement, which justified the use of the model output for further investigations. The evolution and cause of the wind field for May 22-23 were analysed in more detail from the model simulations. Also a sensitivity test of the influence of the surface properties of Gotland on the simulated wind field was performed with the model. The differences in surface temperatures between land and sea were found to be the most important factor in modifying the wind field. However, the wind field was also affected by the surface roughness.