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Letters to Nature

Nature 392, 370-373 (26 March 1998) | doi:10.1038/32861; Received 21 August 1997; Accepted 25 February 1998

Open Innovation Challenges

Global seasonal rainfall forecasts using a coupled ocean–atmosphere model

T. N. Stockdale1, D. L. T. Anderson1, J. O. S. Alves1 & M. A. Balmaseda1

  1. European Centre for Medium-Range Weather Forecasts, Shinfield Park, Reading RG2 9AX, UK

Correspondence to: T. N. Stockdale1 Correspondence and requests for materials should be addressed to T.N.S. (e-mail: Email: t.stockdale@ecmwf.int). Further information and forecast plots can be found on the ECMWF Seasonal Forecast Project Web pages at http://www.ecmwf.int

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One conceptual model of weather is that of a series of events which are unconnected. That is, that the weather next week is essentially independent of the weather this week. However, although individual weather systems might be chaotic and unpredictable beyond a week or so, the statistics describing them may be perturbed in a deterministic and predictable way1, particularly by the ocean. In the past, seasonal forceasts of atmospheric variables have largely been based on empirical relationships, which are weak in most areas of the world2. More recently, atmosphere models forced by assumed or predicted ocean conditions have been used3,4. Here a fully coupled global ocean–atmosphere general circulation model is used to make seasonal forecasts of the climate system with a lead time of up to 6 months. Such a model should be able to simulate the predictable perturbations of seasonal climate, but to extract these from the chaotic weather requires an ensemble of model integrations, and hence considerable computer resources. Reliable verification of probabilistic forecasts is difficult, but the results obtained so far, when compared to observations, are encouraging for the prospects for seasonal forecasting. Rainfall predictions for 1997 and the first half of 1998 show a marked increase in the spatial extent of statistically significant anomalies during the present El Niño, and include strong signals over Europe.

  1. European Centre for Medium-Range Weather Forecasts, Shinfield Park, Reading RG2 9AX, UK

Correspondence to: T. N. Stockdale1 Correspondence and requests for materials should be addressed to T.N.S. (e-mail: Email: t.stockdale@ecmwf.int). Further information and forecast plots can be found on the ECMWF Seasonal Forecast Project Web pages at http://www.ecmwf.int