WEDDEL · Wind-driven upwelling and eddy transports in the Southern Ocean - a model intercomparison in three dimensions

This project has the aim to study wind-driven upwelling (WDU) and eddy transports in the Southern Ocean in atmosphere-ocean global climate models (AOGCMs). This is done by conducting a model intercomparison study using the model data in the IPCC AR4/ CMIP3 database. Starting with classical diagnostics like streamfunctions and the strength of the Antarctic Circumpolar Current, the core of the project is to build a fully consistent three-dimensional picture of the overturning circulation in the Southern Ocean (SO), involving WDU, eddy transport, and meridional surface transports in both directions. For this purpose enhanced visualisation techniques will be used. The intercomparison will carry out data analysis on depth levels as wells as on isopycnal levels in order to study the Deacon cell. Comparison with eddy-permitting models will reveal the strengths and deficiencies of the common (bolus velocity) eddy transport parameterisation. The project might result in suggesting an improvement of this parameterization. Recent studies show the importance of the eddy-driven, highly localised southward currents, and we want to test how the models perform in representing these. The use of a reanalysis model that incorporates a comprehensive hydrographic data base serves to put the models' performance to test. Most of the models to be used here do not resolve eddies, but given the extensive use of AOGCMs for global climate change simulations it is of high societal relevance to understand the models behaviour. WDU is suggested as one driver of the Atlantic meridional overturning circulation that in turn is of strong climatic relevance as a potential trigger for abrupt climate change. While deep water formation processes in the North Atlantic and mixing processes in the interior ocean have been investigated in depth, the knowledge about Southern Ocean upwelling is much smaller, which calls for studies like the present one.