Interannual Variation Of The Western North Pacific Anomalous Anticyclone During El Ni(?)o Years And Its Impact

The interannual variation of the western North Pacific anomalous anticyclone(WNPAC)during El Nino years was investigated based on a variety of air-sea datasets,and its possible causes and impact on East Asian climate was also discussed.Results show that there are two main spatiotemporal modes for the WNPAC based on empirical orthogonal function(EOF)analysis,i.e.,the first mode as its intensity variation and the second mode as its position variation.During the El Nino mature phase in winter,the WNPAC intensity is highly correlated with sea surface temperature anomalies(SSTAs)over the equatorial central-eastern Pacific and the West Pacific(WP)teleconnection pattern at 500 hPa,while its position is highly related to SSTAs over the western North Pacific and Arctic Oscillation(AO).In the subsequent spring season after the El Nino mature phase,the intensity of WNPAC is also highly correlated with SSTAs over the equatorial Atlantic in addition to its high correlation with SSTAs over the equatorial central-eastern Pacific and WP teleconnection pattern in winter,while its position is greatly influenced by SSTAs over the western North Pacific and WP teleconnection pattern.In the subsequent early summer,the intensity of WNPAC is highly related to SSTAs over the northwestern and southwestern Indian Ocean and East Asia-Pacific(EAP)teleconnection pattern.Results further indicate that the interannual variations of both the WNPAC intensity and position have great impacts on precipitation over East Asia during El Nino mature winter and subsequent spring and early summer.Both the East Asian Winter Monsoon in the El Nino mature phase and the East Asian Early Summer Monsoon in the decaying year are significantly correlated with the WNPAC intensity in the same period.Additionally,the intensity of the WNPAC is also highly negatively correlated with the occurrence frequency of tropical cyclone over the western North Pacific during the early summer.Besides,it is also found that the WNPAC intensity has an impact on the ENSO transition,when the WNPAC is strong,it corresponds to a stronger coupling between the Indian ocean and Pacific,i.e.,the Indian Ocean Dipole(IOD)appear during the developing phase and the Indian Ocean basin-wide mode(IOBM)appear during the decaying phase,together with the stronger easterly wind anomaly in the equatorial western Pacific.What's more,the warm subsurface temperature anomalies decay rapidly in the eastern equatorial Pacific during the decaying phases,and then it is replaced by the eastward propagation of cold subsurface temperature anomalies in the western equatorial Pacific,resulting in the development of the La Nina event.On the contrary,when the WNPAC is weak,the inter-coupling between Indian ocean and Pacific and the easterly anomaly is both weak,besides,the cold subsurface temperature anomalies in the western equatorial Pacific decline and disappear with the recession of the warm subsurface temperature anomalies in the eastern equatorial Pacific,thus fail to develop to the La Nina event.