Links between tropical SST anomalies and precursory signals associated with the interannual variability of Asian summer monsoon

The interannual variability of broad-scale Asian summer monsoon was studied using a general circulation model (GCM) and NCEP (National Center for Envi ronmental Prediction) data set during 1979-95. In the GCM experiment, the m ain emphasis was given to isolate the individual role of surface boundary c onditions on the existence of winter-spring time circulation anomalies asso ciated with the interannual variability of Asian summer monsoon. In order to understand the role of sea-surface temperatures (SSTs) alone on the existence of precursory signals, we have conducted 17 years numerical integration with a GCM forced with the real-time monthly averaged SSTs of 1 979 to 1995. In this experiment, among the many surface boundary conditions only SSTs are varying interannually. The composite circulation anomalies s imulated by the GCM have good resemblance with the NCEP circulation anomali es over subtropical Asia. This suggests that the root cause of the existenc e of winter-spring time circulation anomalies associated with the interannu al variability of Asian summer monsoon is the interannual variability of SS T. Empirical Orthogonal Functions (EOFs) of 200-mb winds and OLR were construc ted to study the dynamic coupling between SST anomalies and winter-spring t ime circulation anomalies. It is found that the convective heating anomalie s associated with SST anomalies and stationary eddies undergo systematic an d coherent interannual variations prior to summer season, We have identifie d Matsuno-Gill type mode in the velocity potential and stream function fiel ds. This suggests the existence of dynamic links between the SST anomalies and the precursory signals of Asian summer monsoon.