Influence of May Atlantic Ocean initial conditions on the subsequent North Atlantic winter climate

Analyses of observational data have suggested a link between late spring/summer conditions in the North Atlantic Ocean and atmospheric conditions over the same region in the subsequent winter. This link, and its potential value for seasonal forecasting, is investigated using a coupled climate model, HadCM3. It is found that there is memory of ocean conditions from May through to the following winter, but that the model's sea-surface-temperature (SST) anomalies are too weak in the tropics in winter, partly because they are damped too strongly by comparison with observations and partly because of errors in the model SST anomalies in May, particularly in the east Atlantic where the mixed layer is found to be too deep. It is hypothesized that poor agreement between the winter atmospheric signals in the model and in observations is a consequence of the insufficient tropical SST anomalies. Nevertheless, it is demonstrated that, for suitable initial conditions, seasonal forecasts from 1 May could provide useful information about North Atlantic climate the following winter.