The Interannual Varibility And Diagnostic Analysis Of The South China Sea Summer Monsoon Intensity

Based on NCEP/NCAR reanalysis datasets, precipitation data from GPCP and160stations over China, sea surface temperature (SST) data from NOAA and HadiSST, Ishii monthly-mean Heat Content (HC) data, OAFlux monthly-mean heat flux data, this study mainly investigate the features of the general atmospheric circulation and precipitation in strong/weak South China Sea Summer Monsoon (SCSSM) years, the relationship between SCSSM intensity and SST and HC in the SCS. EOF, correlation and composite analysis and other statistical methods are utilized through the study. In addition, the meridional circulation of SCSSM is diagnosed using the local meridional circulation linear diagnostic equation. The major processes which affect the meridional circulation of SCSSM are discussed quantatively. The conclusions are as follow:(1) During anomoulous strong (weak) SCSSM years, the Western Pacific Subtropical High (WPSH) is weak (strong) and eastward (westward), the South Asian High (SAH) is weak (strong) and westward (eastward). Correspondingly, there is more preciptation in Yangtze River-Huaihe River valley (South China) and less perciptation in South China (southern Yangtze River). When SST is low (high) in the Middle East tropical Pacific in early winter, or we can say in the ENSO cold (warm) phase, the SCSSM is strong (weak) in the following year. When SCSSM is strong (weak), it is more likely to occur ENSO warm (cold) events in the fllowing fall and winter.(2) The dominant EOF mode of HC anomalies over SCS display uniform anomalies, the corresponding time coefficient (PC1) shows significant relationship with ENSO events. The second mode is north-south oriented which dispalys three pole anomalies, the second mode time coefficient (PC2) lags Nino322months.(3) The interannual variability of the HC anomaly over the SCS is closely related to the intensity of SCSSM. When the HC anomaly during the previous period (previous late summer to early spring) is high, the SCSSM is stronger, and vice ersa. Therefore the previous fall (sep-nov) HC anomaly over SCS could be a good predictor for SCSSM intensity. The HC anomaly over the SCS affects the intensity of SCSSM through the monsoon circulation and the Walker circulation, which further affect the WPSH. (4) The evaluation of monsoon meridional circulation shows that, the monsoon meridional circulation establishes in May, with a upward branch over SCS and a downward branch at South Heimisphere. Then the monsoon meridional circulation moves northward and reaches prevalence in summer. In September the monsoon meridional circulation begins to retreat and ends on November.(5) The quantative analysis shows that, the contributions to the anomalous meridional component of the meridional circulation in the lower level over SCS in anomalous strong SCSSM years are mainly from the forcing processes related to latent heating (68%), boundary effect (or the effect of cross-equatorial flow)(14%) and latent heat flux (12%). While in weak SCSSM years are mainly from the forcing processes related to latent heat (46%), boundary effect (38%) and vertical transport of heat (13%).