Abstract
The diversity of El Niño is a critical field of the climate research. The eastern Pacific (EP) and central Pacific (CP) types of El Niño have been identified in the previous studies. However, the extreme El Niño event that occurred in 2015–2016 is quite different from both the EP and CP El Niño events. The sea surface temperatures anomalies (SSTA) for this event widely spread in both the central and eastern Pacific and have a small zonal gradient in the central-eastern Pacific. Many researchers regarded this event as a mixed type of El Niño. Using the regression-EOF method, the Mix El Niño pattern is extracted from the tropical Pacific SSTA field during the period from 1900 to 2019. Here, we reveal that the Mix El Niño is a very usual rather than a new type of El Niño, it is just that the EP and CP El Niño events are more frequent since the 1980s, while the Mix El Niño events frequently appear before the 1980s. The time-spatial features of the Mix El Niño are further investigated. The results demonstrate a unique westward propagation of the maximum SSTA for the Mix El Niño from the far eastern Pacific to the central Pacific. In contrast, the SSTA center is locked in the far eastern Pacific region for the EP El Niño and the central Pacific region for the CP El Niño. The evolutions of subsurface ocean temperature anomalies and sea surface height anomalies are also examined to support this. The ocean–atmosphere interaction plays an important role in the evolution of the Mix El Niño. The anomalous atmospheric Walker circulation for the Mix El Niño is mainly in the western and central Pacific as well as very weak in the eastern Pacific. In contrast, there are significant westerlies/easterlies in the eastern Pacific for the EP/CP El Niño. The small gradient of SSTA in the central-eastern Pacific for the Mix El Niño leads to weak zonal wind anomalies, which further weaken the zonal gradient of SSTA. All this suggests that the Mix El Niño is not unusual and fundamentally different from the EP and CP El Niño with important implications for global climate effects.
Highlights
El Niño is the strongest signal in annual time-scale for the climate change with anomalous warming sea surface temperature anomalies (SSTA) in tropical central and easternPacific region [1]
The small gradient of SSTA in the central-eastern Pacific for the Mix El Niño leads to weak zonal wind anomalies, which further weaken the zonal gradient of SSTA
All this suggests that the Mix El Niño is not unusual and fundamentally different from the eastern Pacific (EP) and central Pacific (CP) El Niño with important implications for global climate effects
Summary
El Niño is the strongest signal in annual time-scale for the climate change with anomalous warming sea surface temperature anomalies (SSTA) in tropical central and eastern. As the SSTA during these two events are mainly in the eastern Pacific region, this type of El Niño is called as EP El Niño [9]. Many El Niño events that with the warming center in the central Pacific occurred since 1980s [12] This type of El Niño is generally called as CP El Niño [9] The cluster 1 and 2 are EP and CP types of El Niño and the cluster 3 has a widely spread of SSTA in both central and eastern Pacific which could be regarded as the Mix El Niño. We investigated the unique time-spatial features, evolutions, ocean–atmosphere coupled interaction of the mixed type of El Niño.
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