东太平洋型与中太平洋型非超强El Niño触发多年La Niña事件的机制差异OA

Traditional theory attributes multi-year La Niña events primarily to oceanic recharge-discharge processes following super El Niño.However,recent studies have revealed that non-super El Niño can also trigger multi-year La Niña via the Pacific Meridional Mode(PMM)in the subtropics.Notably,Eastern Pacific(EP)and Central Pacific(CP)El Niño events exhibit substantial differences in spatial structure and evolution,yet the specific physical mechanisms through which they trigger multi-year La Niña remain unclear.Based on observational data from 1951-2024,this study classified events into two categories according to the spatial pattern of the preceding non-super El Niño:Eastern Pacific El Niño-Multi-year La Niña(EPE-ML)and Central Pacific El Niño-Multi-year La Niña(CPE-ML),and systematically compares their triggering mechanisms.Results demonstrate that EPE-ML events exhibit a stronger,longer-lasting first La Niña,but a substantially weakened and spatially confined second La Niña.In contrast,CPE-ML events feature a relatively weaker first La Niña that decays earlier,while the peak amplitude of the second La Niña is comparable to that of the first.The key to these divergent evolutions lies in the differential synergistic coupling between equatorial thermodynamic processes and subtropical PMM variability.For EPE-ML events,the first La Niña is jointly driven by strong thermocline uplift in the equatorial eastern Pacific during spring-summer and a pronounced negative phase of North Pacific Meridional Mode(NPMM),whereas the second La Niña relies on the sustained influence of subtropical PMM in both hemispheres for its maintenance.For CPE-ML events,the first La Niña is primarily promoted by the springtime equatorial Pacific Wind-Evaporation-SST(WES)feedback,summer thermocline uplift in the eastern Pacific,and synergistic interactions with the subtropical South Pacific Meridional Mode(SPMM).The redevelopment and maturation of the second La Niña is closely associated with the rapid development of the subtropical NPMM during spring-summer and strong thermocline uplift in the equatorial central-eastern Pacific during autumn.This study advances understanding of the formation mechanisms underlying multi-year La Niña events triggered by non-super El Niño,thereby providing a theoretical foundation for improving their seasonal-to-interannual predictability.