Global seasonal forecasting

David Anderson
ECMWF, Shinfield Park, RG2 9AX Reading, United Kingdom.
Tel. : +44-118-949-9106, Fax: +44-118-986-9450,
E-mail: sta@ecmwf.int

At the European Centre for Medium-range Weather Forecast (ECMWF) a fully coupled atmosphere ocean model has been constructed and used to make seasonal forecasts. The model domain is global although sea-ice is not dynamically predicted. The atmospheric model has a resolution of ~1.875 degrees. The ocean resolution is comparable, but higher resolution is used in the equatorial ocean in order to represent equatorial Kelvin waves.

Each day an ocean analysis is performed, based on the ocean data received, mainly from the TAO array in the Pacific ocean. A two hundred day integration of the coupled model is also done daily using the ocean analysis and the meteorological analysis produced as part of the ECMWF weather forecasting procedure, as initial conditions. Over the period of a month typically thirty forecasts are made. From this ensemble the probability of climate variations as well as their amplitudes can be estimated.

The system was used to predict the evolution of the 1997/8 El Niño. The system will be described and results for the current event will be discussed.