The relation between the South China Sea summer monsoon onset and the heat content variations in the tropical western Pacific warm pool region

Multi-year JEDAC data of heat content in upper ocean and NCEP/NCAR reanalysis data were used to analyse the relationship between the heat content anomalies in the warm pool(WP) area of the western Pacific and onset of South China Sea summer monsoon(SCSM).The results show that the warm pool area is the place where heat content in the tropical upper layer changes with maximum range and which is most obviously influential on the SCSM.Compared with the central and eastern equatorial Pacific,the thermal state change in the WP aerea has more direct influence on Asian monsoon.Onset of the SCSM is very closely related to the heat content anomaly during the previous period(previous winter and spring) of the WP so that the heat content of March to April in the WP area is very good predictor for the onset of the SCSM.When the heat content of the WP area is positive convection center will be located in the South Chine Sea-West Pacific with strong convection,a positive anomaly of monsoon circulation and Walker circulation will take place and the subtropical high will be weaker and farther east.Positive anomalous monsoon circulation and Walker circulation will be favorable for westerly and southwesterly flow——the SCSM breaks off earlier than normal.Otherwise,the SCSM comes later than usual.Large-scale anomalous change of monsoon circulation and Walker circulation seems one of the important mechanisms to influence the SCSM.