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The semi-enclosed Baltic Sea is located in Northern Europe and accommodates a complex marine ecosystem. It is impacted by changing climate. However, corresponding information provided by sparse long-term observations are limited and coarse resolution global models do not resolve local air-sea interactions. Hence, a coupled earth system model (IOW ESM) is currently under development to study regional past and future climate change in the Baltic Sea (Figure 1). It enables simulating time periods for which no observation data is available. The atmospheric boundary conditions that force the ocean model are dynamically downscaled from global model simulations. The coupling between the components then allows for feedback from the ocean to the atmosphere.

In the production phase, simulations will be performed for the recent past and evaluated with observations available at the IOW and other databases. They will provide information about the current state of the Baltic Sea. Further possible applications of the coupled model might be climate sensitivity analysis, reconstruction of ocean dynamics in the paleoclimate and process analysis of interactions between ocean and atmosphere.

In a first step, the atmospheric model COSMO-CLM (Rockel et al., 2008) is coupled to the ocean model MOM-5 (Griffies, 2012). The Model MOM-5 is already internally coupled to the sea-ice model SIS (Winton, 2000) and the ecosystem model ERGOM (Neumann, 2010). Technically, the main components are coupled via the OASIS3 coupler library (Valcke et al., 2015), but not directly. The atmosphere and the ocean models communicate their variables (temperature, pressure, velocity etc.) to a flux calculator executable. The flux calculator runs on an exchange grid and calculates fluxes (radiation, heat, mass, momentum). The fluxes are then back-communicated to the components (atmosphere, ocean). This procedure automatically ensures conservation of all exchanged quantities. Furthermore this approach simplifies adding and changing model components.

Current status:

Currently the IOW ESM is in the validation phase and is thus still under development. The project is developed on the IOW's git server and the main documentation can be found at github.


Griffies, S.M., (2012), Elements of the Modular Ocean Model (MOM). GFDL Ocean, Group Technical Resport No. 7, NOAA/Geophysical Fluid Dynamics Laboratory, 618pp.

Neumann, T., (2010), Climate-change effects on the Baltic Sea ecosystem, A model study, Journal of Marine Systems 81, 213-224, doi: 10.1016/j.jmarsys.2009.12.001.

Rockel, B., A. Will and A. Hense, (2008) The Regional Climate Model COSMO-CLM (CCLM), Meteorologische Zeitschrift Vol. 17 No. 4, p. 347 – 348, doi: 10.1127/0941-2948/2008/0309.

Valcke, S., T. Craig, and L. Coquart, (2015), OASIS3-MCT User Guide, OASIS3-MCT 3.0, Technical Report, TR/CMGC/15/38, CERFACS/CNRS SUC URA No 1875, Toulouse, France.

Winton, M., (2000), A reformulated three-layer sea ice model, Journal of Atmospheric and Ocean Technology, 17, 525-531, doi: 10.1175/1520-0426(2000)0172.0.CO;2.