Model of enclosed and semi-enclosed sea hydrodynamics

We consider the numerical scheme of the three-dimensional model of enclosed and semienclosed sea hydrodynamics with variable sea surface topography described by a linear free-surface equation. We derive equations integrated over the upper sea layer and consider the formulation of the finite difference scheme of the model in the spherical coordinate system and the derivation of the sea free-surface equation which is approximated by an implicit time scheme. A peculiarity of the model is that it directly takes into account real water fluxes at the upper boundary in a mass balance equation, in this case we need not specify sources or artificial salt fluxes in a salt balance equation. We give an example of the model efficiency in the problem of modelling the seasonal variability of the Caspian Sea circulation and level.