The friction at the bottom is calculated using the quadratic relationship from the flow speed equation(3) CT99021 nmr Fbx=CD|u→|u,Fby=CD|u→|v, where CD   (= 2.5 × 10−3) is the bottom friction coefficient, and u→ is the current velocity. The bottom friction coefficient is taken to be constant, since reliable data on sea bottom irregularities are lacking. The wave-induced force per unit surface area is the gradient of radiation stresses. It reads: equation(4) Fwavex=1ρ0(−∂Sxx∂x−∂Sxy∂y),Fwavey=1ρ0(−∂Syx∂x−∂Syy∂y),

where ρ0 is the reference density and S is the radiation stress tensor as given by equation(5) Sxx=ρ0g∫ncos2θ+n12Edσdθ,Sxy=Syx=ρ0g∫nsinθcosθEdσdθ,Syy=ρ0g∫[nsin2θ+n−12]Edσdθ, where n is the ratio of the group velocity to the phase velocity. E(σ, θ) denotes the two-dimensional wave spectrum in frequency and directional space respectively. The terms of horizontal turbulence are calculated using the constant eddy viscosity coefficient AH: equation(6) Gx=AH(∂2u∂x2+∂2u∂y2),Gy=AH(∂2v∂x2+∂2v∂y2). The eddy viscosity coefficient for all grids is 50 m2 s−1. The kinematic wind stress components selleck chemicals llc are calculated as: equation(7) Fxw=τxwρ0=ρaρ0cduw|u→w|,Fyw=τywρ0=ρaρ0cdvw|u→w|, where u→w is the wind velocity vector, uw and vw are wind components, τwx and τwy are wind stress components, cd(= 1.3 × 10−3)

is the drag coefficient, and ρa is the air density. Thus, the numerical model takes into account bottom topography, the Earth’s rotation, friction at the sea bottom and horizontal eddy viscosity. Temperature and salinity fields are not calculated in the model. Consequently, the baroclinic component of currents is not taken into account; in the Väinameri region this is of minor importance compared to wind forcing and sea level changes (Otsmann et al. 2001). The model did not include the river runoff into the Gulf of Riga because of its minor role in the water exchange through the Suur Strait. According to previous modelling studies, the river inflow affects mainly the flows in the Irbe Strait because the Suur Strait has a smaller cross-section and Baricitinib a higher resistance (Otsmann et al., 1997, Otsmann et al., 2001 and Suursaar

et al., 2002: Figure 3f). A triple-nested circulation model was used for the simulation of currents and water exchange in the Suur Strait. The coarse grid model covered the whole Baltic Sea with a spatially constant grid size of 2×2 km. Digital topography was taken from Seifert et al. (2001). No open boundary conditions were implemented for this grid. The model for the Väinameri region had a grid size of 400×400 m (Figure 1b), whereas the boundary conditions for water transport were obtained from the whole Baltic Sea model. The high resolution model for the Suur Strait area had a grid step of 100×100 m (Figure 1c), and boundary conditions were obtained from the Väinameri model. One-way grid nesting was used for both model domains.