![]() 2015), although this classification is somewhat arbitrary (Takahashi et al. 1998), recent research is focused on understanding the diversity among the individual events, for which a popular procedure is to classify these based on whether the maximum SST anomalies are predominantly found in the central or eastern Pacific (see review by Capotondi et al. In practice, the definition of “El Niño” is therefore more a matter of convenience of its users than a strict scientific result (Trenberth 1997).Īlthough the essential physics of ENSO have been largely identified (e.g. However, the relation between EN and the SO is not always strong (Deser and Wallace 1987), while the SO has been shown to exist even without the ocean dynamics generally associated with EN (Clement et al. Nowadays, the term “El Niño” (EN) is used as shorthand for referring to the warm phase of the large-scale El Niño–Southern Oscillation (ENSO) coupled ocean–atmosphere phenemenon, characterized by anomalously high SST in the central–eastern equatorial Pacific (El Niño) and the reduction of the zonal gradient in sea level pressure across the basin (Southern Oscillation SO). The warm southward ocean flow was named “Corriente del Niño” (Child’s current) in reference to the weaker climatological version of this current that is normally present after Christmas time (Carrillo 1893). “El Niño” was first introduced to the scientific community in reference to the anomalous climatic event that took place in 1891 along the coast of Peru, described as an abnormal intrusion of warm oceanic water from the north, replacing the normally cold coastal-upwelled water and favoring the occurrence of strong rainfall and flooding in the otherwise arid northern coast of Peru (Carranza 1891). In summary, there are two types of EN events with very strong impacts in the FEP, both apparently associated with nonlinear convective feedbacks but with very different dynamics: the very strong warm ENSO events like 1982–19–1998, and the very strong “coastal” EN events like 1925. This is indicated by the nonlinear relation between the Piura river record at 5°S and the SST difference between the FEP and the western-central equatorial Pacific, a stability proxy. We propose that the cold conditions in the western-central equatorial Pacific, through its teleconnection effects on the FEP, helped destabilize the ITCZ and enhanced the meridional ocean–atmosphere feedback, as well as helping produce the very strong coastal rainfall. Observations indicate lack of external atmospheric forcing by the Panama gap jet and the south Pacific anticyclone and suggest that the coupled ocean–atmosphere feedback dynamics associated with the ITCZs, northerly winds, and the north–south SST asymmetry in the FEP lead to the enhancement of the seasonal cycle that produced this EN event. Instead, ship data indicate an abrupt onset of strong northerly winds across the equator and the strengthening/weakening of the intertropical convergence zones (ITCZ) south/north of the equator. Hydrographic and tide-gauge data indicate that downwelling equatorial Kelvin waves had little role in its initiation. ![]() In contrast to the extreme 1982–19–1998 events, this very strong “coastal El Niño” in early 1925 was characterised by warm conditions in the FEP, but cool conditions elsewhere in the central Pacific. In this study we gathered and synthesised a large diversity of in situ observations to provide a new assessment of this event from a modern perspective. The 1925 El Niño (EN) event was the third strongest in the twentieth century according to its impacts in the far-eastern Pacific (FEP) associated with severe rainfall and flooding in coastal northern Peru and Ecuador in February–April 1925. ![]()
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