Validation of three-dimensional hydrodynamic models of the Gulf of Finland

A model-intercomparison study was conducted, the first of its kind for the Baltic Sea, whose aim was to systematically simulate the basic three-dimensional hydrographic properties of a realistic, complex basin. Simulations of the hydrographic features of the Gulf of Finland for the summer–autumn of 1996 by six three-dimensional hydrodynamic models were compared. Validation was undertaken using more than 300 vertical hydrographic profiles of salinity and temperature. The analysis of model performance, including averaging of the ensemble results, was undertaken with a view to assessing the potential suitability of the models in reproducing the physics of the Baltic Sea accurately enough to serve as a basis for accurate simulations of biogeochemistry once ecosystem models are incorporated. The performance of the models was generally satisfactory. Nevertheless, all the models had some difficulties in correctly simulating vertical profiles of temperature and salinity, and hence mixed layer dynamics, particularly in the eastern Gulf of Finland. Results emphasized the need for high resolution in both vertical and horizontal directions in order to resolve the complex dynamics and bathymetry of the Baltic Sea. Future work needs to consider the choice of mixing and advection schemes, moving to higher resolution, high-frequency forcing, and the accurate representation of river discharges and boundary conditions

Building a human cortex: the evolutionary differentiation of Cajal-Retzius cells and the cortical hem

As apart of a research project, financially supported by the CDL, to study the thermal effects of waste heat discharged into natural water recipients, this report describes a numerical model for this purpose anda number of verifications against real data. The model is based on the conservation laws for mass momentum and energy. It is time-dependent, three-dimensional and has the possibility of using a varying horizontal resolution depending on the nature of the problem. A coordinate transformation in the vertical direction gives the model the same number of calculating points in the vertical all over the modelled area, which increases the confidence in the vertical description considerably. This is of great value, as most of the discharges and the pollution problems are in shallow areas, where other medels in general will have a poor resolution. Applications of the model to different types of recipients are presented and the effects of important mixing mechanisms are illustrated. The model results have been verified against field measurements, and important plume characteristics like area of heated surface water, vertical extent of the plume,and centerline temperature decay have all been successfully simulated. The verification study demonstrates in addition that recirculation of cooling water is well described by the model. The verification studies suggest enlarged use of this type of model studies both in the planning of new locations for power plants and in the monitoring of the environmental effects of the discharged heat. This model can be used both to predict thermal effects in the immediate neighbourhood of the power plant and to predict distribution and long term variations in wider surroundings. Of special interest is the use of the model when locations of the inlet and outlet are to be considered

Validation of three-dimensional hydrodynamic models in the Gulf of Finland based on a statistical analysis of a six-model ensemble

Six three-dimensional hydrodynamic models were compared in their simulations of the hydrographic features of the Gulf of Finland in the Baltic Sea in the summer-autumn period of 1996. Validation was undertaken using more than 300 vertical hydrographic profiles of salinity and temperature. The analysis of model performance, including ensemble averaging of the results, was undertaken with a view to assessing the potential utility of the models in reproducing the physics of the Baltic Sea accurately enough to serve as a basis for accurate simulations of biogeochemistry once ecosystem models are incorporated. The overall performance of the models was generally satisfactory. However, the comparison between observations and ensemble simulations indicated some drawbacks in the parameterization of vertical mixing. Also the choice of initial conditions, surface forcing and differences between real topography and that one used in the models influenced the differences between observations and model results. Looking from another perspective we can state that the accuracy of the present hydrodynamic models determines the upper limit for that of ecosystem models. In turn, the reliability of the hydrodynamic models depends on the physical forcing which is not always as accurate as one may expect. In the future further development of hydrodynamic models is needed in the following areas: the description of vertical mixing and advection should be improved, description of forcing functions including bathymetry, atmospheric forcing, river discharge and boundary conditions should be refined. Additionally more work should be focused on model inter comparisons to clarify the reasons behind the differences in between the models and between model and data Keywords: Baltic Sea, hydrodynamics, modeling, inter-comparison, statistical analysi