Danish Climate Centre Report 03 - 04 Downward propagation and statistical forecast of the near surface wind

We investigate the potential for utilising the downward propagation of anomalies from the stratosphere to the troposphere in extended range statistical forecasts of the near surface zonal mean zonal wind at 60 • N. It is found that the inclusion of stratospheric information increases the skill of the forecast on lead times larger than 5 days. Similar skill can not be obtained if the forecast model only includes tropospheric information. The largest skills are obtained for predictors in the lower stratosphere. Including more than one predictor-either in the stratosphere or in the troposphere-does not increase the skill. For lead times larger than 25 days daily mean values are predicted as well as values averaged over longer periods. The model that forecasts the wind averaged over 10 days with a lead time of 20 days explains about 14 % of the total variance of the wind. The skill can be improved by considering only strong anomalies.