Description: The wind driven and thermohaline circulation of the Baltic Sea and the exchange with the North Sea are investigated by using a coupled sea ice-ocean model of the Baltic Sea. Four consecutive years, namely 1992, 1993, 1994 and 1995 including the latest major Baltic inflow in January 1993 have been simulated. Atmospheric forcing and river runoff was prescribed from SMHI data bases. Data assimilation was utilized by merging hydrographic field measurements with model data. From 6 hourly analysis data 4-year averages of the 3-dimensional current and mass field have been calculated. Some aspects regarding the mean circulation, its stability and the thermohaline circulation especially where the turnover is happening are discussed from model results analysis.

Description: A coupled ice–ocean model is utilized to investigate the transports of heat, salt and water in the Baltic Sea for the years 1986, 1988, 1993 and 1994. The oceanic component of the coupled system is a three-dimensional baroclinic model of the Baltic Sea including the Belt Sea and the Skagerrak/Kattegat area. The model has a horizontal resolution of ∼5 km and 28 vertical levels specified. The ice model is based on the Hamburg Sea Ice model, with the same horizontal resolution. The coupled system is driven by atmospheric data provided by the Swedish Meteorological and Hydrological Institute (SMHI; Norrköping, Sweden) and river runoff taken from a monthly mean runoff database. The thermohaline variability of the Baltic Sea strongly depends on the fluctuations of the atmospheric forcing conditions. Therefore, high demands on the spatial and temporal resolution of the meteorological forcing are required. Besides heat and radiation fluxes, precipitation and evaporation rates have to be taken into account. From the coupled runs, the different components determining the energy and water cycle of the Baltic Sea are identified and estimates of the water, heat and salt transports are given for the different years. Furthermore, the thermohaline variability is investigated with respect to the relevant forcing mechanisms including atmospheric, as well as fresh water fluxes. Besides the heat and water fluxes of the Baltic Sea and the water mass exchange with the North Sea, internal fluxes of heat, salt and volume between the different subbasins of the Baltic Sea are presented. Sensitivity studies on the variation of the net fresh water flux indicate that uncertainties in precipitation and/or river runoff can have a strong impact on the inflow of highly saline water from the North Sea, thus, influencing the thermohaline circulation of the Baltic Sea.

Description: A three-dimensional fully coupled high resolution atmosphere-ocean model for the BALTEX (Baltic Sea Experiment) region has been developed from two independent models, the atmospheric regional model REMO and the Kiel Baltic Sea model. The coupled model was set up in the framework of the BALTEX program to contribute to one of its major objectives, the investigation and quantification of the energy and water cycle in the Baltic Sea and its catchment area. As a first step towards the fully coupled system, sensitivity studies with different forcings for its uncoupled components, the atmosphere and ocean models. were performed. These sensitivity studies demonstrated that both models are able to produce rea onable results which in turn can act as forcing for the respective other model. In the first simulation of the fu lly coupled system the modeled sea surface temperatures (SST) agree well with satellite observations. Thus they are at least as good as the previously used SSTs from operational analyses and in some cases even better. The detailed evaluation of the coupled model results reveals that often the coupling effects are superimposed by advective influences and that only under specific conditions the atmospheric variables show a remarkable response to different fluxes. The atmosphere-ocean model is coupled directly via the corresponding fluxes across the interface between atmosphere and ocean. For the here presented simulation no flux corrections were necessary. Thus a consistent model system has been developed which can be utilized for further studies of the energy and water cycle in the BALTEX area.