Characteristics Of Decadal Variation In ENSO Persistence Barrier

Due to its intrinsic connection to predictability,persistence barrier(PB)has been known as a crucial property of some important phenomena like El Ni?o–Southern Oscillation(ENSO),typically depicted as a rapid decline of persistence of sea surface temperature(SST)anomalies occurring at specific season.In this study,a generalized PB intensity index is derived and the PB timing is newly defined as the target calendar month with the highest frequency of PB occurrence.Using the newly defined PB quantization index,the PB of global SST anomalies is quantified,and the PB characteristics of global SST anomalies are revealed.Based on the new quantization method,the decadal variation characteristics of ENSO PB intensity and timing are revealed.By statistical methods,the relationship between ENSO PB intensity and timing decadal variation and the factors related to the tropical Pacific background state is investigated,and the relationship between the decadal variation of ENSO PB time and the decadal signal in the North Pacific is explored.The results show that:(1)Obvious PB phenomenon exists in SSTA in most sea areas around the world.The strong PBs of the global SST anomaly is mainly distributed in the equatorial Pacific and the southeastern tropical Indian Ocean,and the PB phenomenon is also evident in some regions of the four oceans.PB timing varies greatly in different regions of the world.Particularly,ENSO PB timing shows the meridional evolution feature in the equatorial Pacific,and the PB intensity is very strong along the evolution path.(2)ENSO PB intensity and timing shows obvious decadal variation characteristics.Different Ni?o indices have obvious PB characteristics in different decades.Generally,bounded by two turns of 1940 s and 1980 s,1940s and 1980 s respectively experience the relative changes of PB timing in "late–early–late".In addition,it is found that the correlation between PB timing and PB intensity represented by different Ni?o indices in the decadal variation is negative in the eastern Tropical Pacific and significantly positive in the central and western Tropical Pacific.It shows that the PB intensity in the central and eastern tropical Pacific fluctuates and becomes stronger,which is basically reversed with the PB timing.The variation of PB intensity in the central and western tropical Pacific is "strong–weak–strong",which is basically the same phase with PB timing.(3)The decadal variation of ENSO PB intensity and timing is closely related to the background state related factors in the tropical Pacific.The decadal variation of ENSO PB timing is influenced by the input of decadal signal from the North Pacific.The decadal variation of PB intensity of ENSO(EP ENSO)is positively correlated with the decadal variation of SST amplitude,the seasonal variation of SST amplitude and the seasonal synchronization intensity of SST.However,compared with the amplitude of SST,the decadal variation of PB intensity of ENSO(EP ENSO)is more strongly correlated with the seasonal amplitude of SST and the seasonal synchronization intensity of SST with highly correlated.In the decadal variation,the stronger the seasonal amplitude of SST and the seasonal synchronization intensity of SST,the stronger the ENSO PB intensity.Notably,they do not affect the decadal variation of central and western ENSO PB intensity.In addition,the decadal variation of ENSO PB is closely related to the westward extension of SST activities,showing a significant negative correlation,indicating that the greater the westward extension of SST activities,the smaller the ENSO PB timing.In addition,in the decadal variation,there is a significant negative correlation between the tropical Pacific region and the North Pacific region and the ENSO PB timing,indicating that the factors affecting the ENSO PB timing decadal variation are related to the input of the decadal signal in the North Pacific region.