BaltiX V 1.1 : A 3D Ocean Modelling Configuration for Baltic & North Sea Exchange Analysis

Type: Report
Series: RO 48
Author: R. Hordoir, B. W. An, J. Haapala, C. Dieterich, S. Schimanke, A. Höglund and H.E.M. Meier


There is a need for having a reliable numerical representation of the exchanges between the Baltic Sea and the North Sea from many points of view. First, the North Sea is the salt provider of the Baltic Sea, but also the oxygen provider of the lowermost layers of the Baltic Sea. This means that any numerical analysis which has for goal to study the long term changes in this exchange can not rely on a model of the Baltic Sea that has an open boundary condition at the entrance of the Baltic Sea (i.e.: the Kattegat area). In order to represent the long term changes in the exchanges between the North Sea and the Baltic Sea, one needs to consider the coupling between these two basins which have a very different dynamical behaviour which means one needs to consider them as a whole. This means that any regional model should have its open boundary condition further away from the entrance of the Baltic Sea, that is in a place that is remote enough to allow a buffer large enough in the North Sea, so that the SSH variability at the entrance of the Baltic Sea is well represented [7]. Second, the Baltic Sea outflow has a great influence on the Norwegian Coastal Current (NCC hereafter) which is also interesting to study, and which can only be well represented if the wind effect over the Baltic Sea is taken into account [9]. Many models were successfully applied to the Baltic Sea or/and to the North Sea/Baltic Sea area. On can cite the Rossby Centre Ocean model RCO [15], which successfully represents the thermo-haline as well as the ice structures and variability of the Baltic Sea. One can also cite HIROMB [6], which is a North & Baltic Seas numerical representation used in operational oceanography. However, all these modelling structures lack in at least one of the following points : - They include only the Baltic Sea area, which makes impossible the study of the exchanges with the North Sea. - They were mostly used for operational purpose, and do not have stability properties in terms of Baltic salt content which does not make them suitable for long term studies. - They do not follow anymore the framework of a community model, and therefore do not benefit of the recent scientific or technical developments implemented in most ocean modelling platform. - A Baltic & North Sea setup is also necessary for long term coupled simulations. There was therefore a need to build a new Baltic & North Sea configuration, based on a community modelling framework, and designed to follow this framework eventually. BaltiX is a Baltic & North Sea configuration based on the NEMO [14] ocean engine. Its development was started in 2011 at SMHI (Swedish Meteorological & Hydrological Institute, Norrköping, Sweden). It follows closely the development of the NEMO ocean engine, and BaltiX is updated each time an update is done in it. In the present report, Section 2 describes the configuration and explains the choices that have been made to build it. Based on a simulation done for the period 1961-2007, we then present several results. Section 3 presents a barotropic analysis of the results provided by the configuration, and Section 4 presents results in terms of salinity and temperature variability. Section 5 has been specifically written to present the sea-ice model coupled to BaltiX and its effects in terms of sea-ice variability. A last part provides a short conclusion to the present report.