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Forecasting of hydrological characteristics in the Gulf of Finland is made on the basis of the 3D non-stationary hydrodynamic model GOFM (Neelov, 2003) that has high resolution model structure including the blocks of circulation and sea ice. GOFM model is a modification of the Baltic Sea model SPBM (Saint-Petersburg Baltic Sea Model) (Neelov, 1996). The model of sea circulation is based on complete equations of hydrothermodynamics in the Boussinesq approximation and hydrostatics including the equation of sea water state in UNESCO form. Vertical turbulence is described basing on the original b-l turbulence model. Original iteration calculation scheme of free sea surface is used for numerical realization. The ice model is based on equations of the Hibler's viscous-plastic rheology model (1979) and describes in detail dynamics and thermodynamics of snow-ice cover. The model makes it possible to forecast current velocities, temperature, salinity and density of water, sea level changes, variability of ice drift velocity, its thickness and area, snow thickness on ice surface. The model is integrated on spherical grid for the entire Gulf of Finland with 1 nautical mile horizontal step and 1 m vertical resolution.

Weather forecast obtained by HIRLAM model (High Resolution Local Area Model) and forecast of hydrological characteristics at the entrance to the Gulf of Finland by operational model HIROMB (HIgh Resolution Operational Model for the Baltic Sea) are used as boundary conditions; monthly average climatic discharges of large rivers flowing to the Gulf of Finland are set as well (the Neva, the Luga, the Narva, the Kemijoki rivers).

The model uses results of the HIROMB model calculations as initial conditions when initializing operational calculation at the first time step (t0 time). When data of field observations is available a procedure of data assimilation is used to correct initial conditions.

HIRLAM atmospheric model and the 3D model of the Baltic Sea HIROMB

The version of the HIRLAM (http://www.dmi.dk/dmi/index/viden/dmi-hirlam.htm) atmospheric model provided to RSHU by the Danish Meteorological Institute has 11 km resolution and covers the area of the North Atlantic and the Northern Europe. Atmospheric model produces the short range weather forecast up to 48 hours.

Region of calculations of the 3D HIROMB (http://www.smhi.se/sgn0106/if/oceanografi/tool1.htm) model developed at SMHI (Swedish Institute of Meteorology and Hydrology) covers the North and the Baltic Seas. The model horizontal resolution in the Baltic Sea, in Skagerrak and Kattegat Straights is 1 nautical mile; number of layers is 24 with 4 m vertical resolution. The model is coupled with the HBV hydrological model producing daily discharges of the main rivers flowing into the Baltic Sea. The model forecasts sea level, salinity, temperature, thickness and compaction of ice and its drift up to 48 hours.