Effects of the Sub-grid Scale Surface Undulations on the Forecasts in the Northern Hemisphere Winter

The performance of the enhanced PBL parameterization scheme proposed by Sumi (1985) have been examined by using an ensemble of 31 forecasts for 3 days conducted in January, 1984. The following results are obtained; (i) The warming bias in the lower troposphere in the polar region is much reduced. This is due to the suppression of overprediction of the mature cyclone in the polar region. (ii) The zonal wind field is slightly improved due to the improvement of the temperature fields in the troposphere. (iii) The improvement of the surface pressure field is slight. It is shown that the inclusion of the effects due to the sub-grid scale undulations represented in this scheme is effective in the improvement of the predicted fields. This suggests the effect of processes relating to the land (and the sub-grid scale undulations) should be included in our models. However, it has not yet been clarified how to formulate these processes. The details of parameterization of these processes should be further investigated.