|Title||Medium-range weather forecasting in the extratropics during wintertime with and without an interactive ocean.|
|Publication Type||Technical memorandum|
|Secondary Title||ECMWF Technical Memorandum|
|Authors||Jung, T, Vitart, F|
|Place Published||Shinfield Park, Reading|
The ECMWF monthly forecasting system is used to investigate the impact an interactive ocean has on medium-range weather predictions in the Northern Hemisphere extratropics during wintertime. On a hemispheric scale the predictive skill for mean sea level pressure (MSLP) with and without an interactive ocean is comparable. This can be explained by the relatively small impact that coupling has on MSLP forecasts. In fact, deterministic and ensemble integrations reveal that the magnitude of forecast error and the perturbation growth due to analysis uncertainties, respectively, by far outweigh MSLP differences between coupled and uncoupled integrations. Furthermore, no signi?cant difference of the ensemble spread between the uncoupled and coupled system is found. Our conclusions apply equally for a number of cases of rapidly intensifying extratropical cyclones in the North Atlantic region. Further experimentation with different atmospheric model cycles, different horizontal atmospheric resolutions and different ocean model formulation reveals the robustness of our ?ndings. Our results suggest that (for the cases, resolutions and model complexities considered in this study) the bene?t of using coupled atmosphere-ocean models to carry out medium-range MSLP forecasts is relatively small, at least in the Northern Hemisphere extratropics during wintertime.