Abstract
Three primary global modes of sea surface temperature (SST) variability during the period of 1871–2010 are identified through cyclostationary empirical orthogonal function analysis. The first mode exhibits a clear trend and represents global SST warming with an ‘El Niño-like’ SST pattern in the tropical Pacific. The second mode is characterized by considerable low-frequency variability in both the tropical Pacific and the North Pacific regions, indicating that there is a close connection between the two regions on interannual and decadal time scales. The third mode shows a seesaw pattern between El Niño and La Niña within a two-year period; this mode is derived by the oscillatory tendency of the tropical Pacific ocean–atmosphere coupled system. A SST reconstruction based on these three modes captures a significant portion of the SST variability in the raw data, which is primarily associated with El Niño-Southern Oscillation (ENSO) events in the tropical Pacific. Additionally, this study attempts to interpret the major ENSO events that have occurred since the 1970s in terms of the interplay originating from these three modes of variability. In particular, two key points are derived from this analysis: (1) the most extreme El Niño events occurred in 1982/1983 and 1997/1998 are attributed to the positive contributions of all three modes; and (2) the central Pacific (CP) El Niño events in the 1990s and 2000s have different physical mechanisms, that is, the CP El Niño events in the early 1990s originated mainly from the low-frequency mode, while those in the early 2000s derived mainly from the global warming mode.
Highlights
The El Nino-Southern Oscillation (ENSO) is an important phenomenon that involves variability in sea surface temperatures in the tropical Pacific Ocean, and it exerts a profound influence on the entire global climate system. Bjerknes (1969) was the first investigator who recognized that interactions between the ocean and the atmosphere in the tropical Pacific constitute ENSO, and he proposed that ENSO is a strongly coupled ocean–atmosphere phenomenon
A sea surface temperature (SST) reconstruction based on these three modes captures a significant portion of the SST variability in the raw data, which is primarily associated with El Nino-Southern Oscillation (ENSO) events in the tropical Pacific
In the second cyclostationary empirical orthogonal function (CSEOF) mode, positive SSTAs in the tropical Pacific are connected with SSTAs of the same sign in the western shore of North America along with negative SSTAs over the western to central North Pacific
Summary
The El Nino-Southern Oscillation (ENSO) is an important phenomenon that involves variability in sea surface temperatures in the tropical Pacific Ocean, and it exerts a profound influence on the entire global climate system. Bjerknes (1969) was the first investigator who recognized that interactions between the ocean and the atmosphere in the tropical Pacific constitute ENSO, and he proposed that ENSO is a strongly coupled ocean–atmosphere phenomenon. Much attention has been aimed at understanding these new types of El Nino events that display maximum warming in the tropical central Pacific (CP) (Larkin and Harrison 2005; Kao and Yu 2009; Ashok et al 2007; Kug et al 2009). Latif et al (1997) identified three modes for tropical Pacific SST variability through the use of a principal oscillation pattern (POP) analysis. Intrinsic modes of SST variability are extracted from a 140-year SST dataset covering 70°S– 70°N via CSEOF analysis for the purpose of delineating ENSO characteristics and recent changes in ENSO events. The primary goals of this study are to substantiate the physical mechanisms driving these three modes of behavior and to demonstrate how these modes jointly contribute to the unique characteristics of recently observed ENSO events. A summary of the results is given along with a physical interpretation of the present study and its main conclusions
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