On Approaches to Improving the Description of North Sea Water Inflows in the General Circulation Models of the Baltic Sea

The paper considers the causes of underestimation of bottom salinity in the general circulation models of the Baltic Sea. The highly efficient Oceananigans model is used to calculate the propagation of the inflow of saline North Sea waters in the bottom layer of the Baltic Sea in the period January-April 1993. The results of these calculations are in better agreement with the V.T. Paka high-frequency scanning data of the vertical structure of the sea with a vertical resolution of 0.25 to 0.5 m and distances between stations of about 500 m than the results of a similar calculation (reanalysis) for the same situation performed using the NEMO-Nordic model. This was achieved by significantly reducing numerical diffusion by increasing the vertical resolution and using high-order advection schemes in the Oceananigans model without using the observational data assimilation procedure. The above improvements to the Oceananigans model reduced the calculation speed by only 30 %. The developed model configuration gives certain hope for obtaining, without the assimilation procedure, adequate estimates of the propagation of the bottom gravity density current in the Baltic Sea and its interaction with sediments, including oxygen exchange, which is important for modeling marine ecosystems.