Isopycnal analyses were performed on the Global Ocean Data Assimilation System （GODAS） to determine the oceanic processes leading to so-called second-year cooling of the La Nina event.In 2010-12,a horseshoe-like pat...Isopycnal analyses were performed on the Global Ocean Data Assimilation System （GODAS） to determine the oceanic processes leading to so-called second-year cooling of the La Nina event.In 2010-12,a horseshoe-like pattern was seen,connecting negative temperature anomalies off and on the Equator,with a dominant influence from the South Pacific.During the 2010 La Nina event,warm waters piled up at subsurface depths in the western tropical Pacific.Beginning in early 2011,these warm subsurface anomalies propagated along the Equator toward the eastern basin,acting to reverse the sign of sea surface temperature （SST） anomalies （SSTAs） there and initiate a warm SSTA.However,throughout early 2011,pronounced negative anomalies persisted off the Equator in the subsurface depths of the South Pacific.As isopycnal surfaces outcropped in the central equatorial Pacific,negative anomalies from the subsurface spread upward along with mean circulation pathways,naturally initializing a cold SSTA.In the summer,a cold SSTA reappeared in the central basin,which subsequently strengthened due to the off-equatorial effects mostly in the South Pacific.These SSTAs acted to initiate local coupled air-sea interactions,generating atmospheric-oceanic anomalies that developed and evolved with the second-year cooling in the fall of 2011.However,the cooling tendency in mid-2012 did not develop into another La Nina event,since the cold anomalies in the South Pacific were not strong enough.An analysis of the 2007-09 La Nina event revealed similar processes to the 2010-12 La Nina event.展开更多
After the strong 2015/16 El Nino event,cold conditions prevailed in the tropical Pacific with the second-year cooling of the 2017/18 La Ni?a event.Many coupled models failed to predict the cold SST anomalies(SSTAs)in ...After the strong 2015/16 El Nino event,cold conditions prevailed in the tropical Pacific with the second-year cooling of the 2017/18 La Ni?a event.Many coupled models failed to predict the cold SST anomalies(SSTAs)in 2017.By using the ERA5 and GODAS(Global Ocean Data Assimilation System)products,atmospheric and oceanic factors were examined that could have been responsible for the second-year cooling,including surface wind and the subsurface thermal state.A time sequence is described to demonstrate how the cold SSTAs were produced in the central-eastern equatorial Pacific in late 2017.Since July 2017,easterly anomalies strengthened in the central Pacific;in the meantime,wind stress divergence anomalies emerged in the far eastern region,which strengthened during the following months and propagated westward,contributing to the development of the second-year cooling in 2017.At the subsurface,weak negative temperature anomalies were accompanied by upwelling in the eastern equatorial Pacific,which provided the cold water source for the sea surface.Thereafter,both the cold anomalies and upwelling were enhanced and extended westward in the centraleastern equatorial Pacific.These changes were associated with the seasonally weakened EUC(the Equatorial Undercurrent)and strengthened SEC(the South Equatorial Current),which favored more cold waters being accumulated in the central-equatorial Pacific.Then,the subsurface cold waters stretched upward with the convergence of the horizontal currents and eventually outcropped to the surface.The subsurface-induced SSTAs acted to induce local coupled air–sea interactions,which generated atmospheric–oceanic anomalies developing and evolving into the second-year cooling in the fall of 2017.展开更多
After its maturity,El Niño usually decays rapidly in the following summer and evolves into a La Niña pattern.However,this was not the case for the 2018/19 El Niño event.Based on multiple reanalysis data...After its maturity,El Niño usually decays rapidly in the following summer and evolves into a La Niña pattern.However,this was not the case for the 2018/19 El Niño event.Based on multiple reanalysis data sets,the space-time evolution and triggering mechanism for the unusual second-year warming in late 2019,after the 2018/19 El Niño event,are investigated in the tropical Pacific.After a short decaying period associated with the 2018/19 El Niño condition,positive sea surface temperature anomalies(SSTAs)re-intensified in the eastern equatorial Pacific in late 2019.Compared with the composite pattern of El Niño in the following year,two key differences are evident in the evolution of SSTAs in 2019.First,is the persistence of the surface warming over the central equatorial Pacific in May,and second,is the re-intensification of the positive SSTAs over the eastern equatorial Pacific in September.Observational results suggest that the re-intensification of anomalous westerly winds over the western and central Pacific,induced remotely by an extreme Indian Ocean Dipole(IOD)event,acted as a triggering mechanism for the second-year warming in late 2019.That is,the IOD-related cold SSTAs in the eastern Indian Ocean established and sustained anomalous surface westerly winds over the western equatorial Pacific,which induced downwelling Kelvin waves propagating eastward along the equator.At the same time,the subsurface ocean provided plenty of warm water in the western and central equatorial Pacific.Mixed-layer heat budget analyses further confirm that positive zonal advection,induced by the anomalous westerly winds,and thermocline feedback played important roles in leading to the second-year warming in late 2019.This study provides new insights into the processes responsible for the diversity of El Niño evolution,which is important for improving the physical understanding and seasonal prediction of El Niño events.展开更多
基金supported by National Natural Science Foundation of China (Grant No. 40906014)the Ocean Public Welfare Scientific Research Project (Grant No. 201205018-2)+4 种基金the National Key Basic Research Program of China (Grant No. 2010CB950302)the China Scholarship Council (CSC)supported partly by the National Science Foundation (NSF) (Grant No. ATM0727668)NASA (Grant No. NNX08AI74G)the National Oceanic and Atmospheric Administration (NOAA) (Grant No. NA08OAR4310885)
文摘Isopycnal analyses were performed on the Global Ocean Data Assimilation System （GODAS） to determine the oceanic processes leading to so-called second-year cooling of the La Nina event.In 2010-12,a horseshoe-like pattern was seen,connecting negative temperature anomalies off and on the Equator,with a dominant influence from the South Pacific.During the 2010 La Nina event,warm waters piled up at subsurface depths in the western tropical Pacific.Beginning in early 2011,these warm subsurface anomalies propagated along the Equator toward the eastern basin,acting to reverse the sign of sea surface temperature （SST） anomalies （SSTAs） there and initiate a warm SSTA.However,throughout early 2011,pronounced negative anomalies persisted off the Equator in the subsurface depths of the South Pacific.As isopycnal surfaces outcropped in the central equatorial Pacific,negative anomalies from the subsurface spread upward along with mean circulation pathways,naturally initializing a cold SSTA.In the summer,a cold SSTA reappeared in the central basin,which subsequently strengthened due to the off-equatorial effects mostly in the South Pacific.These SSTAs acted to initiate local coupled air-sea interactions,generating atmospheric-oceanic anomalies that developed and evolved with the second-year cooling in the fall of 2011.However,the cooling tendency in mid-2012 did not develop into another La Nina event,since the cold anomalies in the South Pacific were not strong enough.An analysis of the 2007-09 La Nina event revealed similar processes to the 2010-12 La Nina event.
基金jointly supported by grants from the National Natural Science Foundation of China[Grant Nos.41576029 and 41690122(41690120)]the National Program on Global Change and Air–Sea Interaction(Grant No.GASIIPOVAI-03)+1 种基金the National Key Research and Development Program(Grant No.2018YFC1505802)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant Nos.XDA19060102 and XDB 40000000)。
文摘After the strong 2015/16 El Nino event,cold conditions prevailed in the tropical Pacific with the second-year cooling of the 2017/18 La Ni?a event.Many coupled models failed to predict the cold SST anomalies(SSTAs)in 2017.By using the ERA5 and GODAS(Global Ocean Data Assimilation System)products,atmospheric and oceanic factors were examined that could have been responsible for the second-year cooling,including surface wind and the subsurface thermal state.A time sequence is described to demonstrate how the cold SSTAs were produced in the central-eastern equatorial Pacific in late 2017.Since July 2017,easterly anomalies strengthened in the central Pacific;in the meantime,wind stress divergence anomalies emerged in the far eastern region,which strengthened during the following months and propagated westward,contributing to the development of the second-year cooling in 2017.At the subsurface,weak negative temperature anomalies were accompanied by upwelling in the eastern equatorial Pacific,which provided the cold water source for the sea surface.Thereafter,both the cold anomalies and upwelling were enhanced and extended westward in the centraleastern equatorial Pacific.These changes were associated with the seasonally weakened EUC(the Equatorial Undercurrent)and strengthened SEC(the South Equatorial Current),which favored more cold waters being accumulated in the central-equatorial Pacific.Then,the subsurface cold waters stretched upward with the convergence of the horizontal currents and eventually outcropped to the surface.The subsurface-induced SSTAs acted to induce local coupled air–sea interactions,which generated atmospheric–oceanic anomalies developing and evolving into the second-year cooling in the fall of 2017.
基金This work is jointly supported by grants from the National Key Research and Development Program(Grant No.2018YFC1505802)the National Natural Science Foundation of China(Grant Nos.41576029,42030410,41690122(41690120),41420104002)the Strategic Priority Research Program of Chinese Academy of Sciences(Grant Nos.XDA19060102,XDB 40000000 and XDB 42000000).
文摘After its maturity,El Niño usually decays rapidly in the following summer and evolves into a La Niña pattern.However,this was not the case for the 2018/19 El Niño event.Based on multiple reanalysis data sets,the space-time evolution and triggering mechanism for the unusual second-year warming in late 2019,after the 2018/19 El Niño event,are investigated in the tropical Pacific.After a short decaying period associated with the 2018/19 El Niño condition,positive sea surface temperature anomalies(SSTAs)re-intensified in the eastern equatorial Pacific in late 2019.Compared with the composite pattern of El Niño in the following year,two key differences are evident in the evolution of SSTAs in 2019.First,is the persistence of the surface warming over the central equatorial Pacific in May,and second,is the re-intensification of the positive SSTAs over the eastern equatorial Pacific in September.Observational results suggest that the re-intensification of anomalous westerly winds over the western and central Pacific,induced remotely by an extreme Indian Ocean Dipole(IOD)event,acted as a triggering mechanism for the second-year warming in late 2019.That is,the IOD-related cold SSTAs in the eastern Indian Ocean established and sustained anomalous surface westerly winds over the western equatorial Pacific,which induced downwelling Kelvin waves propagating eastward along the equator.At the same time,the subsurface ocean provided plenty of warm water in the western and central equatorial Pacific.Mixed-layer heat budget analyses further confirm that positive zonal advection,induced by the anomalous westerly winds,and thermocline feedback played important roles in leading to the second-year warming in late 2019.This study provides new insights into the processes responsible for the diversity of El Niño evolution,which is important for improving the physical understanding and seasonal prediction of El Niño events.
