Upwelling in the Baltic Sea Studied by Combined SAR/infrared Satellite Data and Circulation Model
Gurova, Evgenia1; Lehmann, Andreas2; Ivanov, Andrei3
1Atlantic Branch of P.P. Shirshov Institute of Oceanology RAS, RUSSIAN FEDERATION; 2Helmholtz Centre for Ocean Research (GEOMAR), GERMANY; 3P.P. Shirshov Institute of Oceanology, Russian Academy of Sciences, RUSSIAN FEDERATION
Upwelling is considered to be a typical phenomenon of the Baltic Sea. Because the Baltic Sea is a semi-closed basin, winds from favorable directions blowing predominately parallel to the coast cause upwelling leading to vertical displacement of the water body and mixing. The appearance of upwelling signatures on synthetic aperture radar (SAR) and sea surface temperature (SST) images can have varied correlation because of many factors affecting the SAR imaging. In this study data and images of spaceborne SAR onboard the European Envisat satellite and MODIS spectroradiometers onboard the Terra and Aqua satellites, and the high resolution Sea Ice-Ocean Model of the Baltic Sea (BSIOM) have been used to investigate two upwelling events in the Southeastern Baltic Sea. The combined analysis was applied to upwelling occurred in July 2006 along the coasts of the Baltic States, and in June 2008 along the Polish coast and Hel Peninsula. Comparisons indicated a good agreement between SST and the sea roughness signatures detected in satellite SAR images and model results. However, SAR images are sensitive to changes in the background wind field. If a certain wind speed threshold which depends on the across-front temperature gradient is exceeded, the increase in sea surface roughness masks any structures of reduced back-scatter related to cold upwelling. It is shown that BSIOM is able to simulate upwelling events realistically. Upwelling structures and filaments are related to topographic features controlled by the vorticity dynamics of the coastal jet. Finally, it is concluded that utilization of modeled hydrodynamics and wind stress data together with SAR and SST information provides an extended analysis and deeper understanding of the upwelling processes taken place in the Baltic Sea.