Modulation Of ENSO Zonal Position On The Interdecadal Variations Of The ENSO-IOD Relationship

Using monthly sea surface temperature from Hadley Center(Had ISST),the atmospheric reanalysis dataset provided by the National Centers for Environmental Prediction/National Center for Atmospheric Research(NCEP/NCAR)and precipitation reconstruction(PREC)data provided by the US Oceanic and Atmospheric Administration(NOAA)from 1949 to 2017,this paper analyzes the interdecadal variation characteristics of the relationship between the relationship between El Ni(?)o and Southern Oscillation(ENSO)and Indian Ocean dipole(IOD).By studying the differences and possible mechanism of the relationship between different types of ENSO and IOD,the modulation effect of ENSO zonal position on the interdecadal variation of ENSO-IOD relationship is discussed.The major conclusions can be summarized as follows:(1)There is a significant positive correlation between ENSO and IOD on the interannual scale,that is,in the El Ni(?)o(La Ni(?)a)year,IOD is a significant positive(negative)phase,but the study found that there is an interdecadal change in the ENSO-IOD relationship.During 1949-1966 and 2004-2017,the linear relationship between ENSO-IOD is not significant(R=0.43),which can be considered as a weak coupling period between ENSO and IOD;the linear relationship between ENSO-IOD is significant during 1967-2003(R=0.75),which is a strong coupling period between ENSO and IOD.The interdecadal changes in the ENSO-IOD relationship are reflected in the cold and warm ENSO events: El Ni(?)o and La Ni(?)a show a decrease in correlation and a decrease in sign agreement rate,respectively.(2)Due to the asymmetry of the intensity of the cold and warm phases of ENSO and the variety of spatial patterns,the relationship between ENSO and IOD is also complicated.There is an asymmetry in the relationship between ENSO events at different phases and IOD,El Ni(?)o has a stronger effect on IOD than La Ni(?)a event.The non-linear response of convective precipitation causes the asymmetry of the atmospheric response of ENSO cold and warm phases,which in turn leads to the asymmetry of the IOD response,and this asymmetry of the influence of the cold and warm level on the IOD mainly occurs in the eastern ENSO years.In addition,the difference in the connection between different types of ENSO and IOD is mainly reflected in the El Ni(?)o event.The strength of the connection between the eastern El Ni(?)o and IOD is mainly related to its intensity,and the relationship between the central El Ni(?)o and IOD is mainly related to its east-west location.(3)The zonal position of ENSO modulates the interdecadal variation of ENSO-IOD relationship.During the weak coupling period of the ENSO-IOD relationship,the sea surface temperature and atmospheric response anomaly centers of ENSO events are westward and weaker,at this time,the correlation between ENSO and IOD is weak;during the period of strong coupling,the sea surface temperature and atmospheric response anomaly centers of ENSO events are eastward and strong,so the relationship between ENSO and IOD is significant.Further research found that the connection between ENSO and IOD is mainly due to the contribution of the EP El Ni(?)o year.In the period of strong coupling,the correlation coefficient of Ni(?)o 3.4 index and DMI index is significantly weakened except for the influence of strong EP El Ni(?)o.