ENSO空间形态变异对ENSO-IOD关系年代际减弱的可能作用

Possible role of ENSO spatial pattern variation in interdecadal weakening of ENSO-IOD relationship

基于1979-2017年哈得来中心的逐月海表温度资料(HadISST)和美国环境预报中心/美国大气研究中心(NCEP/NCAR)提供的大气环流再分析数据,研究了北半球秋季厄尔尼诺和南方涛动(ENSO)与印度洋偶极子(IOD)关系的年代际变化特征及其可能原因。结果显示,ENSO-IOD关系存在显著的年代际变化:21世纪初期前,二者呈显著正相关,厄尔尼诺(拉尼娜)年秋季常对应显著的印度洋偶极子正(负)异常;21世纪初期以后,ENSO-IOD关系显著减弱,统计上不显著。进一步研究表明,ENSO空间型态的变异对于该关系的年代际减弱起重要作用。在第二时段(2004-2017年),中部型厄尔尼诺事件和东部型拉尼娜事件频发,中部型厄尔尼诺事件与印度洋偶极子强度的关系与其纬向位置密切相关,与其强度的线性关系较弱;而东部型拉尼娜事件,由于海温距平位置偏东(位于赤道东太平洋冷舌区),在偏低的气候态海温作用下,其引起的大气局地响应很弱,对印度洋的遥强迫作用较弱,因而对印度洋偶极子强度的影响也较弱。在二者的共同作用下,ENSO-IOD的关系发生了年代际减弱。

Using monthly sea surface temperature from Hadley Center(HadISST)and the atmospheric reanalysis dataset provided by the National Centers for Environmental Prediction/National Center for Atmospheric Research(NCEP/NCAR)from 1979 to 2017,this study investigates the interdecadal variability characteristics of the relationship between El Ni?o Southern Oscillation(ENSO)and Indian Ocean Dipole(IOD)in boreal autumn and possible reasons behind.It is found that significant interdecadal variations exist in the ENSO-IOD relationship.Before the early 2000 s,there was a significant positive correlation between them,and El Ni?o(La Ni?a)often corresponded to significant positive(negative)IOD events in the autumn.However,since the early 2000 s,the ENSO-IOD relationship is significantly weakened and not statistically significant.Further studies indicate that the decadal change in ENSO spatial pattern plays an important role in the decadal change of their relationship.In the latter stage,the central Pacific El Ni?o events(CP El Ni?o)and eastern Pacific La Ni?a events(EP La Ni?a)occur more frequently,and the IOD intensity is more corelated with the longitudinal position than with the intensity of the CP El Ni?o.For the EP La Ni?a,the sea surface temperature anomaly(SSTA)is located more eastward than normal and over the cold tongue region of the equatorial Pacific.Under the effect of the cold climatic sea temperature,local atmospheric response is weak,and teleconnection effect over the Indian Ocean is weak,which results in a weak influence on the IOD intensity.Due to the combined effect of the CP El Ni?o and EP La Ni?a,the ENSO-IOD relationship is greatly weakened in the latter stage.