The EUROSIP multi-model seasonal forecasting system consists of a number of independent coupled seasonal forecasting systems integrated into a common framework. From September 2012, the systems include those from ECMWF, the Met Office, Météo-France and NCEP.
The reason for creating a multi-model forecasting system is that research has consistently shown that better and more reliable seasonal forecasts can be created by combining the output from several models, rather than taking just one model. In most cases, the multi-model combination is better than the best single model. The value of multi-model forecasting has in particular been explored in the DEMETER and ENSEMBLES projects.
The fundamental reason for the benefit of a multi-model approach is that all models have inaccuracies (generally referred to as errors) which are large enough to significantly degrade forecasts made on a seasonal timescale. Compared to medium-range forecasting, predicted seasonal signals are much smaller and the time over which model errors accumulate are longer, so the importance of model error is much, much higher. Although we are working hard to reduce model error, the requirements of seasonal forecasts are so exacting that we expect model error to be a critical problem for many years to come. Although all models have errors, these errors and the impact they have on a given forecast vary between models. By averaging across a number of models, a significant part of the model error can be reduced, resulting in better forecasts. Some of the remaining uncertainty can also be assessed by looking at the consistency of the forecasts. However, some errors tend to be common between models, so averaging is not a panacea nor a replacement for model development. Nonetheless, averaging across models is a very useful tool, and is likely to remain so for many years.
Data from all component models is archived at ECMWF, and can be accessed subject to the terms of the EUROSIP data policy.
ECMWF produces a number of multi-model products which are created from the integrated output of the component models. These multi-model products can be accessed just like any other ECMWF products. This user guide outlines what is available, how the products are created, and how they can be accessed.