Thermally driven wind modification in coastal areas and its influence on sound propagation with application to wind power

Abstract: The objective of the current study is to investigate the wind modifications in coastal areas and also to see the impact of atmospheric conditions on long-range sound propagation over sea. This is important when planning where to place wind turbines. Atmospheric measurements (wind, temperature, humidity) were performed in the Baltic Sea area, and a numerical meso-?-scale atmospheric model (the MIUU-model) was used. The study was performed in early summer when it is common for thermally driven flows e.g. sea breezes and low level jets to evolve, resulting in supergeostrophic winds. The most important parameters for these winds were found to be temperature and roughness differences between land and sea. Even though the wind climatologically increases over sea, a case where the wind decreases when advected out over a cold sea is investigated.This happens if the stable boundary layer (SBL) over sea is deep enough. Parameters that have a great positive influence on the increase in depth of the SBL are strong thermal winds in combination with large temperature differences between land and sea. With a shallower SBL the wind increases over sea. During one week, the sound level from a siren, placed on a lighthouse in the Baltic Sea, was measured 9.5 km away from the source. This was performed simultaneously with the atmospheric measurements. The influence of atmospheric changes on the sound propagation is studied in details. Higher sound levels are found when low level jets occur and the sound level also seems to be dependent on the height to the jet.