南太平洋副热带偶极子对中国气候影响的数值模拟

Numerical simulation of the influence of the South Pacific Ocean Dipole on climate in China

本文基于Hadley中心的海温数据集HadISST,利用EOF(Empirical Orthogonal Function)方法,分析了北半球冬季南太平洋副热带海温的特点,其第一模态呈现为马蹄型偶极子的空间分布(两个冷极中心和一个暖极中心),即为南太平洋副热带偶极模态(South Pacific Ocean Dipole,SPOD);其次采用通用地球系统模式(the Commuinty Earth System Model version1.0.4,简称CESM1.0.4)探讨了SPOD模态对中国冬夏气候的影响.数值试验结果表明,在北半球冬季,SPOD偶极模态可使中国华东和东北等地区的地表温度(Surface Temperature,TS)减小、海平面气压(Sea Level Pressure,SLP)升高,而在中国西南地区的TS、SLP分别增加和降低.与此同时,SPOD偶极模态通过海气相互作用可诱发低(高)层索马里越赤道气流(Somali Cross-Equatorial Flow,Somali CEF)和中国南海越赤道气流(South China Sea Cross-equatorial Flow)出现异常南(北)风、中国20°N—40°N附近的大气异常上升运动、水汽通量散度在中国华北和长江中下游地区异常辐合,从而引起该区域的降水增加.在北半球夏季,虽然SPOD偶极模态在衰退,但仍对中国区域的SLP、TS存在影响,且基本与冬季相反.此时SPOD偶极模态可使低(高)层索马里越赤道气流呈现北(南)风异常和中国南海越赤道气流呈现南(北)风异常、中国30°N、40°N附近大气的垂直运动分别呈现异常上升、下沉运动,从而水汽在华北附近区域为异常辐散、在华东至华南部分区域为异常辐合,这些可能是引起中国东部降水呈现北负南正的异常空间型的原因.

In this paper,based on the Hadley Center sea surface temperature(SST)dataset,the EOF(Empirical Orthogonal Function)method is used to analyze the characteristics of the South Pacific subtropical SST in the boreal winter,the result indicates that the first mode presents a spatial distribution of horseshoe-type dipoles(two cold pole and one warm pole),which is the South Pacific Ocean Dipole(SPOD).Then,the Community Earth System Model version1.0.4(CESM1.0.4)is adopted to discuss the influence of SPOD on winter and summer climate in China.The results of numerical simulation show that,in the boreal winter,the SPOD causes negative surface temperature(TS)anomalies and positive Sea Level Pressure(SLP)anomalies in eastern and northeastern China,whereas positive TS and negative SLP anomalies appear in southwestern China,respectively.Meanwhile,SPOD induce the low(high)Somali Cross-equatorial Flow(Somali CEF)and the South China Sea Cross-equatorial Flow(anomalous southerly(northerly)winds and anomalous atmospheric upward motion and water vapor flux dispersion 20°N—40°N in North China and the middle and lower reaches of the Yangtze River through sea-air interactions,thus causing increased precipitation in china.In boreal summer,although SPOD is declining,there is still a lagging effect on the SLP and TS in China,and it is basically opposite to the winter.Interestingly,SPOD trigger the north(south)wind anomaly in the low(high)Somalia trans-equatorial flow,and the South China Sea trans-equatorial flow show south(north)wind anomaly.At this time,the vertical motions of the atmosphere around 30°N、40°N in China show anomalous upward and downward motion,respectively,so that the water vapor is anomalously diffused in North China.These may be the reasons for the anomalous spatial pattern of North-negative south-positive rainfall in eastern and northern China.