Seasonal-to-Interannual Prediction of the Asian Summer Monsoon in the NCEP Climate Forecast System Version 2

Abstract

he NCEP Climate Forecast System (CFS) is an important source of information for seasonal climate prediction in many Asian countries affected by monsoon climate. The authors provide a comprehensive analysis of the prediction of the Asian summer monsoon (ASM) by the new CFS version 2 (CFSv2) using the hindcast for 1983?2010, focusing on seasonal-to-interannual time scales. Many ASM features are well predicted by the CFSv2, including heavy monsoon rainfall centers, large-scale monsoon circulation patterns, and monsoon onset and retreat features. Several commonly used dynamical monsoon indices and their associated precipitation and circulation patterns can be predicted several months in advance. The CFSv2 has better skill in predicting the Southeast Asian monsoon than predicting the South Asian monsoon. Compared to CFS version 1 (CFSv1), the CFSv2 has increased skill in predicting large-scale monsoon circulation and precipitation features but decreased skill for the South Asian monsoon, although some biases in the CFSv1 still exist in the CFSv2, especially the weaker-than-observed western Pacific subtropical high and the exaggerated strong link of the ASM to ENSO.Comparison of CFSv2 hindcast with output from Atmospheric Model Intercomparison Project (AMIP) and Coupled Model Intercomparison Project (CMIP) simulations indicates that exclusion of ocean?atmosphere coupling leads to a weaker ASM. Compared to AMIP, both hindcast and CMIP show a more realistic annual cycle of precipitation, and the interannual variability of the ASM is better in hindcast. However, CMIP does not show any advantage in depicting the processes associated with the interannual variability of major dynamical monsoon indices compared to AMIP.