Seasonal Prediction Assessment of the South Asian Summer Monsoon: ENSEMBLES versus DEMETER

The seasonal forecasting skill with respect to the South Asian summer monsoon (SASM) was compared between the European Commission FP7 project (ENSEMBLES) and the Development of a European Multimodel Ensemble System for Seasonal to Interannual Prediction project (DEMETER). The Webster-Yang index (WYI) was chosen to represent the intensity of the SASM. First, the authors compared the ability to forecast the zonal wind at 850 hPa (U850) and 200 hPa (U200) between ENSEMBLES and DEMETER models. The results indicated that the models from the European Centre for Medium-Range Weather Forecasts, International Organization (ECMWF) and UK Met Office (UKMO) in ENSEMBLES possess greater skill in seasonally forecasting the JJA (June, July, and August) U850, U200, and U850 minus U200 than in DEMETER. Compared to in DEMETER, the JJA U200 and U850 minus U200 forecasting skill was greater for the model from MeteoFrance (MF) in ENSEMBLES over most of the SASM region. The three coupled models (ECMWF, MF, and UKMO), especially the UKMO model in ENSEMBLES, all demonstrated improved skill in their seasonal forecasts compared to in DEMETER with respect to the interannual variability of the SASM. The three ENSEMBLES models also showed better ability in forecasting the sea surface temperature anomalies (SSTAs) over the eastern equatorial Pacific and North Indian Ocean, and more accurately reproduced the large-scale atmospheric circulation and precipitation over northern India, which are related to the SASM. It seems that the couple between the atmospheric system and external forcing of ENSMBLES over Indian Ocean and Pacific is better than that of DEMETER.