The standard deviation of the central Pacific sea surface temperature anomaly (SSTA) during the period from October to February shows that the central Pacific SSTA variation is primarily due to the occurrence of the...The standard deviation of the central Pacific sea surface temperature anomaly (SSTA) during the period from October to February shows that the central Pacific SSTA variation is primarily due to the occurrence of the Central Pacific E1 Nifio (CP-E1 Nifio) and has a connection with the subtropical air-sea interaction in the northeastern Pacific. After removing the influence of the Eastern Pacific E1 Nifio, an S-EOF analysis is conducted and the leading mode shows a clear seasonal SSTA evolving from the subtropical northeastern Pacific to the tropical central Pacific with a quasi-biennial period. The initial subtropical SSTA is generated by the wind speed decrease and surface heat flux increase due to a north Pacific anomalous cyclone. Such subtropical SSTA can further influence the establishment of the SSTA in the tropical central Pacific via the wind-evaporation-SST (WES) feedback. After established, the central equatorial Pacific SSTA can be strengthened by the zonal advective feedback and thermocline feedback, and develop into CP-E1 Nifio. However, as the thermocline feedback increases the SSTA cooling after the mature phase, the heat flux loss and the reversed zonal advective feedback can cause the phase transition of CP-EI Nifio. Along with the wind stress variability, the recharge (discharge) process occurs in the central (eastern) equatorial Pacific and such a process causes the phase consistency between the thermocline depth and SST anomalies, which presents a contrast to the original recharge/discharge theory.展开更多
El Nio events in the central equatorial Pacific (CP) are gaining increased attention,due to their increasing intensity within the global warming context.Various physical processes have been identified in the climate s...El Nio events in the central equatorial Pacific (CP) are gaining increased attention,due to their increasing intensity within the global warming context.Various physical processes have been identified in the climate system that can be responsible for the modulation of El Nio,especially the effects of interannual salinity variability.In this work,a comprehensive data analysis is performed to illustrate the effects of interannual salinity variability using surface and subsurface salinity fields from the Met Office ENSEMBLES (EN3) quality controlled ocean dataset.It is demonstrated that during the developing phase of an El Nio event,a negative sea surface salinity (SSS) anomaly in the western-central basin acts to freshen the mixed layer (ML),decrease oceanic density in the upper ocean,and stabilize the upper layers.These related oceanic processes tend to reduce the vertical mixing and entrainment of subsurface water at the base of the ML,which further enhances the warm sea surface temperature (SST) anomalies associated with the El Nio event.However,the effects of interannually variable salinity are much more significant during the CP-El Nio than during the eastern Pacific (EP) El Nio,indicating that the salinity effect might be an important contributor to the development of CP-El Nio events.展开更多
The relationships between the evolution of two types of El Ni?o events and the subsurface ocean temperature anomaly(SOTA) in the equatorial Pacific are compared in this study. The results show that both types of El Ni...The relationships between the evolution of two types of El Ni?o events and the subsurface ocean temperature anomaly(SOTA) in the equatorial Pacific are compared in this study. The results show that both types of El Ni?o are negatively correlated to the SOTA in the equatorial western Pacific, but relationships are different in different phases of El Ni?o. Furthermore, the occurrence of different types of El Ni?o is related to different features of the equatorial thermocline, e.g. its zonal gradient, significant variation area, amplitude and duration of thermocline oscillation. The propagation of SOTA in the equator plays an important role during the evolution of both types of El Ni?o, but shows dramatic differences in intensity, duration and phase reverse of warm SOTA. Moreover, the pathways of SOTA signal are different between these two types of El Ni?o. The dominant pathway in the life cycle of Eastern Pacific(EP)-El Ni?o lies on the equator and to its north, but there is no loop to the south of the equator. In contrast, the dominant pathway in Central Pacific(CP)-El Ni?o is located on the equator and to its south, and the propagation signal of SOTA to the north of the equator is very weak.The relationships between the zonal wind anomalies and the two types of El Ni?o are also preliminarily discussed. It is shown that EP-El Ni?o is more likely to respond to the westerly anomalies over the equatorial central and western Pacific, while CP-El Ni?o is more likely to respond to the westerly anomalies over the equatorial western Pacific and need the cooperation of easterly anomalies over the equatorial eastern Pacific to certain extent.展开更多
基金supported by the National Basic Research Program of China(973Program:2012CB955604)National Natural Science Foundation of China(Nos.40975038and40830106)+5 种基金the CMA Program(GYHY200906008)the financial support provided by the China Scholarship Counciljointly supported by the 973 Program of China(2010CB950404)DOE grant DE-SC0005110National Science Foundation(NSF)grants ATM1034798NOAA grand NA10OAR4310200
文摘The standard deviation of the central Pacific sea surface temperature anomaly (SSTA) during the period from October to February shows that the central Pacific SSTA variation is primarily due to the occurrence of the Central Pacific E1 Nifio (CP-E1 Nifio) and has a connection with the subtropical air-sea interaction in the northeastern Pacific. After removing the influence of the Eastern Pacific E1 Nifio, an S-EOF analysis is conducted and the leading mode shows a clear seasonal SSTA evolving from the subtropical northeastern Pacific to the tropical central Pacific with a quasi-biennial period. The initial subtropical SSTA is generated by the wind speed decrease and surface heat flux increase due to a north Pacific anomalous cyclone. Such subtropical SSTA can further influence the establishment of the SSTA in the tropical central Pacific via the wind-evaporation-SST (WES) feedback. After established, the central equatorial Pacific SSTA can be strengthened by the zonal advective feedback and thermocline feedback, and develop into CP-E1 Nifio. However, as the thermocline feedback increases the SSTA cooling after the mature phase, the heat flux loss and the reversed zonal advective feedback can cause the phase transition of CP-EI Nifio. Along with the wind stress variability, the recharge (discharge) process occurs in the central (eastern) equatorial Pacific and such a process causes the phase consistency between the thermocline depth and SST anomalies, which presents a contrast to the original recharge/discharge theory.
基金supported by the National Basic Research Program of China(Grant Nos.2012CB955202and2012CB41740)the National Natural Science Foundation of China(Grant Nos.41075064,41176014,and41006016)
文摘El Nio events in the central equatorial Pacific (CP) are gaining increased attention,due to their increasing intensity within the global warming context.Various physical processes have been identified in the climate system that can be responsible for the modulation of El Nio,especially the effects of interannual salinity variability.In this work,a comprehensive data analysis is performed to illustrate the effects of interannual salinity variability using surface and subsurface salinity fields from the Met Office ENSEMBLES (EN3) quality controlled ocean dataset.It is demonstrated that during the developing phase of an El Nio event,a negative sea surface salinity (SSS) anomaly in the western-central basin acts to freshen the mixed layer (ML),decrease oceanic density in the upper ocean,and stabilize the upper layers.These related oceanic processes tend to reduce the vertical mixing and entrainment of subsurface water at the base of the ML,which further enhances the warm sea surface temperature (SST) anomalies associated with the El Nio event.However,the effects of interannually variable salinity are much more significant during the CP-El Nio than during the eastern Pacific (EP) El Nio,indicating that the salinity effect might be an important contributor to the development of CP-El Nio events.
基金supported by the National Basic Research Program of China (2013CB956203)
文摘The relationships between the evolution of two types of El Ni?o events and the subsurface ocean temperature anomaly(SOTA) in the equatorial Pacific are compared in this study. The results show that both types of El Ni?o are negatively correlated to the SOTA in the equatorial western Pacific, but relationships are different in different phases of El Ni?o. Furthermore, the occurrence of different types of El Ni?o is related to different features of the equatorial thermocline, e.g. its zonal gradient, significant variation area, amplitude and duration of thermocline oscillation. The propagation of SOTA in the equator plays an important role during the evolution of both types of El Ni?o, but shows dramatic differences in intensity, duration and phase reverse of warm SOTA. Moreover, the pathways of SOTA signal are different between these two types of El Ni?o. The dominant pathway in the life cycle of Eastern Pacific(EP)-El Ni?o lies on the equator and to its north, but there is no loop to the south of the equator. In contrast, the dominant pathway in Central Pacific(CP)-El Ni?o is located on the equator and to its south, and the propagation signal of SOTA to the north of the equator is very weak.The relationships between the zonal wind anomalies and the two types of El Ni?o are also preliminarily discussed. It is shown that EP-El Ni?o is more likely to respond to the westerly anomalies over the equatorial central and western Pacific, while CP-El Ni?o is more likely to respond to the westerly anomalies over the equatorial western Pacific and need the cooperation of easterly anomalies over the equatorial eastern Pacific to certain extent.