Contribution Of The Tropical Atlantic Thermal Conditions To High Temperature In Summer Over The South China

The duration,intensity and frequency of extreme heat events(heatwaves)over the South China have increased with the global warming,and more serious consequences have been brought to human and natural system.Therefore understanding the factors and physical mechanisms associated with the occurrence of high temperature anomalies over the South China will be of great benefit.The persistent anomalies of Western Pacific Subtropical High(WPSH)and the South Asia High(SAH)is the direct cause for high temperature in summer over the South China.And these sustainabilities of these large scale circulation anomalies are usually affected by underlying surface anomalies.Obciously sea surface temperature(SST)anomaly is one of the most important external forcing factors.Therefore,based on the observation data and NCEP/NCAR reanalysis data and NOAA SST,we utlized wave-activity flux,partial correlation and composite analyses to examine the relationship between the tropical western Atlantic thermal conditions and summer temperature anomalies over the South China on interannual and seasonal scales.The main conclusions are as follows:(1)On interannual scales,the thermal anomalies of the tropical western Atlantic(10°N-30°N,60°W-35°W,0°-10°N 50°W-35°W)in the previous winter are highly correlated with the summer temperature over the South China.The influence can be explained by the following meachanisms.Firstly,coupled with SST,positive temperature anomalies in tropical Atlantic can persist from preceding winter to summer and cause a vertical circulation anomaly between the tropical Atlantic and the north Atlantic.Then by exciting a zonal wave train extending from the Atlantic to Eurasia,a deep and stable high pressure anomaly emerges in southern China.As a result,high temperature anomalies occur after a serious of surface heat flux feedback over this region.Secondly,the tropical Atlantic SST anomalies also exert an impact on summer high temperature anomalies over the South China by modulating the tropical Indian Ocean(TIO)SST variation.By adjusting the precipitation and condensation latent heat over Arabian sea and the Indian region,the tropical Indian SST variation changes downstream circulation including WPSH and SAH in eastern Asia,eventually affect summer temperature over the South China.(2)Both tropical western Atlantic(TWA)SST anomalies and tropical Indian Ocean SST variation contribute to summer temperature over the South China.Given the synergisticcontributions of them,we define a TWA–TIO thermal index.This TWA–TIO index effectively enhances the forecasting ability of summer high temperature anomalies over the South China relative to the individual TWAO or TIO thermal index.(3)The intraseasonal intensification of TWA positive SST anomalies can also excite a zonal wave train extending from the Atlantic to Eurasia causing the heat events over the South China.Because of the abnormal warming of TWA SST is usually manifested in the first one month before the heat events,so it can be used as a meaningful signal to predict the summer heat events over the South China.In addition to the contribution of tropical Atlantic ocean,along with El ni?o decaying and La Ni?a developing,northern Indian SST warming maintains,which also provides an important background conditions for persistent heat events occurring over the South China.