RCA4-NEMO - a high resolution regional coupled model system

This model system is a regional coupled model system for the North Sea and the Baltic Sea area co-developed by the Rossby Centre and the Oceanographic research group at SMHI. It is used as a major tool for regional climate change studies.

In the integrated earth system, the air-sea coupling plays a critical role in explaining processes on time scales ranging from seasonal to decadal variability. It is fundamental to our understanding of the regional environment and climate. This model system will help to improve the understanding of key atmosphere-ocean interaction processes and to provide a better representation of air-sea fluxes in models. The high resolution will resolve more detailed local features, particularly along complex coastlines on land and in the sea.

Model description

This regional coupled model system for the North Sea and the Baltic Sea is composed of the regional setup of ocean model NEMO (Madec, 2011), the Rossby Center regional climate model RCA4 (Samuelsson et al., 2011; Kupiainen et al., 2014), the sea ice model LIM3 (Vancoppenolle et al., 2009) and the river routing model CaMa-Flood (Yamazaki et al., 2011).

RCA4-NEMO domains
RCA4 domain and topography (the red square is the domain of the river routing model CaMa-Flood) (left) NEMO domain and bathymetry (right) (unit: meter). (Wang et al., 2015)

Within the coupled system, the atmospheric component model RCA4, the oceanic component NEMO (sea ice model LIM3 is included) and the runoff model CaMa-Flood are run as three separate executables. To build up this coupled modelling system, the Ocean Atmosphere Sea Ice Soil Simulation Software (OASIS3) coupler (Valcke, 2013) integrates the sub-models simultaneously. The coupler works in a sequential fashion with synchronous coupling of the different model components with joint physical interfaces at different time intervals. A full description of this regional coupled model system can be found in Wang et al. (2015).

Model evaluation

The performance of this coupled model system is assessed using a simulation forced with ERA-Interim reanalysis data at the lateral boundaries. The coupled system can simulate observed conditions very well within reasonable limits of, e.g. seasonal mean temperature biases are largely within +/- 1 degree compared to observations). Our analyses show that this coupled model system is stable and suitable for different climate change studies.


Kupiainen, M., Jansson, C., Samuelsson, P., Jones, C., Willén, U., Hansson, U., Ullerstig, A., Wang, S., and Döscher, R. 2014: Rossby Centre regional atmospheric model, RCA4, Rossby Center News Letter, Rossby Centre regional atmospheric model, RCA4

Madec, G. 2011.NEMO ocean engine, User Manual 3.3  , IPSL, Paris, France.

Samuelsson, P., Jones, C., Willen, U., Ullerstig, A., and co-authors. 2011. The Rossby Centre Regional Climate model RCAS3:model description and performance, Tellus, 63A, 4-23.

Valcke, S.. 2013. The OASIS3 coupler: a European climate modelling community software. Geosci. Model Dev., 6, 373-388, doi:10.5194/gmd-6-373-2013

Vancoppenolle, M., Fichefet, T.,Goosse, H., Bouillon, S., Madec,G. and Maqueda, M.A.M. 2009. Simulating the mass balance and salinity of arctic and antarctic sea ice. Ocean Modelling, 27, 33–53.

Wang,S., Dieterich, C., Döscher, R., Höglund, A., Hordoir, R., Meier, H., Samuelsson, P., & Schimanke, S, Development and evaluation of a new regional  coupled atmosphere ocean model in the North Sea  and Baltic Sea, Tellus A67, 24284, dx.doi.org/10.3402/tellusa.v67.24284, 2015

Yamazaki, D., Kanae, S., Kim, H. and Oki, T. 2011. A physically-based description of floodplain inundation dynamics in a global river routing model. Water Resour. Res. 47,W04501, doi:10.1029/2010WR009726.