Discussion Of Relationship Between Tropical Pacific Sea Surface Temperature Anomaly And Winter Rainfall Over South China

Tropical Pacific is the mainly tropical sea area that influences our country climate. It decides the transportation of a large number of water vapor and energy from the Pacific and influences the climate in our country through the way of teleconnection. As global warming intensifies, the tropical Pacific sea surface temperature (SST) has taken place variation that is characterized by the continuous warming of the western Pacific warm pool and heating center of the tropic Eastern and Central Pacific El Nino westward shift, that is, the El Nino Modoki events occur frequently. Based on the observed station precipitation data over China in winter, the monthly Hadley Center Global Sea Ice and Sea Surface Temperature (HadISST) and reanalysis data provided by National Centers for Environmental Prediction-National Center for Atmospheric Research (NCEP/NCAR) from1951to2010, the different impacts of heating center of the Eastern and Central Pacific El Nino westward shift on winter rainfall over South China (SC) and its possible causes are analyzed. Further, the relationship of the warming of the western Pacific warm pool and winter rainfall over South China has been discussed. Main conclusions are as follows:(1) During the year of El Nino, it has more winter rainfall over SC While El Nino Modoki events result in reduced rainfall over SC. Therefore, the variation in tropic Eastern and Central Pacific, namely westward shift of heating center of El Nino may be not in favor of winter rain over SC.(2) During the winter of traditional El Nino, the western Pacific subtropical high moves southward and strengthens. SC is influenced by southwesterly anomalies and gets plenty of water vapor supply. In addition, the intensity of upper-layer pumping effect, ascending motion and convective activity in SC are reinforced, resulting in enhanced rainfall. While during the winter of El Nino Modoki, the western Pacific subtropical high is located more northward and SC is controlled by ridge. Upper-layer pumping action, ascending motion and convective activity become weaker in SC. And SC gets insufficient water vapor supply, resulting in reduced rainfall.(3) Continued warming of the tropical western Pacific warm pool makes its interannual relationship with winter precipitation over SC has obvious interdecadal transition in1972. Before1972, the negative correlation between them is weak and has not passed significance test. But the correlation between them has reached-0.5～-0.6and has passed significance test of95%after1972. And the interdecadal transition relationship between the western Pacific warm pool and winter precipitation over SC may have different influence mechanism with ENSO.(4) During the period of a weakly relationship between the western Pacific warm pool and winter rainfall over SC, before1972, the effect of the western Pacific warm pool on water vapor and dynamic conditions that affect winter rainfall over SC is not significant, so its relation with winter rainfall over SC is not obvious. During the period of significant relationship between the western Pacific warm pool and winter rainfall over SC, after1972, when the western Pacific warm pool SST is warmer, a cyclonic circulation has been aroused in the Philippine Sea area. The northerly wind of northwest of the cyclonic circulation is not favor of water vapor from the South China Sea transported to SC and water vapor divergence of SC increases. The convection and perturbation of the southern branch trough region has weakened significantly and the spread to the downstream region has suppressed, causing weakened perturbation over SC. In addition, warming of the western Pacific warm pool makes the remarkable increase of meridional circulation in the northern hemisphere and the sinking branch is located in the SC region. So the sinking movement over SC has strengthened, resulting in decreased winter rainfall over SC.