Calculating the development of the thermal vertical stratification in the North Sea with a three-dimensional baroclinic circulation model

The vertical thermal stratification in the North Sea has been investigated with the help of a three-dimensional baroclinic circulation model. The main intention of the current investigation is to reproduce the actual conditions in the North Sea as realistically as possible. In order to obtain an appropriate representation of all the thermal parameters in space and time it is essential to use a model that treats temperature as a prognostic quantity. In particular, processes connected with the existence of the summer thermocline require attention. This is guaranteed by choosing adequate time- and space-dependent vertical eddy viscosity Av and diffusivity coefficients, respectively. y, the month-to-month changes of the summer vertical stratification in the North Sea are discussed by presenting climatological monthly mean conditions (average over the period 1983–1992) of the following parameters: thermocline extension, depth, occurrence probability. These parameters are related to shear and buoyancy production of turbulent kinetic energy. It turned out that, in mid-summer, the location of the frontal zone is mainly controlled by tidal stirring and not by meteorological forcing. ly, in order to illustrate the pronounced inter-annual variability of these thermal parameters, actual daily mean situations are analyzed for the coldest and warmest summer, during this ten-year period. From these results, it is possible to conclude that compared with a warm summer, in a cold one a significantly higher shear production is responsible for the destruction or deepening of the thermocline, which in turn results in higher negative values of the buoyancy production term.