001 m. But unlike sea ice, water roughness varies strongly with the wind speed; therefore, the Charnock formula z0 = α0u2/g is used, where α0 = 0.0123, u is the

wind speed and g is the acceleration due to gravity. As in the surface albedo scheme, when COSMO-CLM is coupled to NEMO, the grid-cell roughness length is the weighted average of sea icecovered and water-covered areas. We used the NEMO ocean model version 3.3 adapted to the North and Baltic Sea region. This model setup is described by Hordoir et al. (2013) in a technical report in 2013. The horizontal resolution is 2 minutes (about 3 km), Stem Cell Compound Library supplier and the time step is 300 seconds. There are 56 depth levels of the ocean. The flux correction for the ocean surface was not applied in our experiments. The domain covers the Baltic Sea and a part of the North Sea with two open boundaries to the Atlantic Ocean; the western boundary lies in the English Channel and the northern boundary is the cross section between Scotland and Norway. BIBW2992 molecular weight The model domain of NEMO can be seen on Figure 6 (see p. 183). For the Baltic Sea, the fresh water inflow from the river basins plays a crucial role in the salinity budget. Meier & Kauker (2003) found that the accumulated fresh water inflow caused half of the decadal variability in the Baltic salinity. It is, therefore, very important to take the rivers into consideration when modelling Baltic Sea

salinity. In this paper, we use the daily time series from E-HYPE model outputs for the North and Baltic Seas (Lindström et al. 2010). The input for the E-HYPE model is the result from the atmospheric model RCA3 (Samuelsson et al. 2011) forced by ERA-Interim re-analysis data from the European Centre for Medium-Range Weather Forecasts (ECMWF) Niclosamide (Dee et al. 2011). The atmospheric and ocean models are coupled by the coupler OASIS3. The results from Meier & Kauker (2003) show that half the variability of salinity in the Baltic Sea is caused by fresh water inflow and the other half is related to the exchange of sea water between the North

and Baltic Seas through the Kattegat. This water exchange process is determined by the wind stress and the sea level pressure difference between the two seas. Therefore, when coupling the atmosphere to the ocean, we send the wind fluxes and the sea level pressure from COSMO-CLM to NEMO to get an appropriate inflow of water from the North Sea to the Baltic Sea. On the atmospheric side, the exchanged fields are the flux densities of water (Precipitation-Evaporation), momentum, solar radiation, non-solar energy and sea level pressure. On the ocean side, we send SST and the fraction of sea ice to COSMOCLM. This exchange process is done every 3 hours. The fields are gathered by OASIS3 and then interpolated to the other model’s grid. Apart from the coupled ocean area, COSMO-CLM takes the lower boundary from ERAInterim data for other sea surface areas.