The Defining Characteristics of ENSO Extremes and the Strong 2015/2016 El Niño

Abstract

The year 2015 was special for climate scientists, particularly for the El Niño Southern Oscillation (ENSO) research community, as a major El Niño finally materialized after a long pause since the 1997/1998 extreme El Niño. It was scientifically exciting since, due to the short observational record, our knowledge of an extreme El Niño has been based only on the 1982/1983 and 1997/1998 events. The 2015/2016 El Niño was marked by many environmental disasters that are consistent with what is expected for an extreme El Niño. Considering the dramatic impacts of extreme El Niño, and the risk of a potential increase in frequency of ENSO extremes under greenhouse warming, it is timely to evaluate how the recent event fits into our understanding of ENSO extremes. Here we provide a review of ENSO, its nature and dynamics, and through analysis of various observed key variables, we outline the processes that characterize its extremes. The 2015/2016 El Niño brings a useful perspective into the state of understanding of these events and highlights areas for future research. While the 2015/2016 El Niño is characteristically distinct from the 1982/1983 and 1997/1998 events, it still can be considered as the first extreme El Niño of the 21st century. Its extremity can be attributed in part to unusually warm condition in 2014 and to long‐term background warming. In effect, this study provides a list of physically meaningful indices that are straightforward to compute for identifying and tracking extreme ENSO events in observations and climate models.

Assessing the Pattern Differences between Satellite-Observed Upper Tropospheric Humidity and Total Column Water Vapor during Major El Niño Events

“…This is reflected in the smaller positive anomalies found in the 2015-16 central-eastern Pacific UTH. A study on the characteristics of extreme El Niño events showed that the 2015-16 El Niño was marked by a record-breaking warm anomaly in the central Pacific, but was weaker in many measures than the two previous extreme El Niño events [53]. In another study …”

“…huge forest fires that caused a haze crisis in neighboring countries [53]. The shorter TCWV time series has coverage for the 1997-98 El Niño, one of the three events discussed above, and the anomaly field for this event is displayed in Figure 5d.…”

“…This is reflected in the smaller positive anomalies found in the 2015-16 central-eastern Pacific UTH. A study on the characteristics of extreme El Niño events showed that the 2015-16 El Niño was marked by a record-breaking warm anomaly in the central Pacific, but was weaker in many measures than the two previous extreme El Niño events [53]. In another study [54] that compared the three El Niño events using reanalyses from the Modern-Era Retrospective Analysis for Research and Applications (MERRA) 2, it was found that the 2015-16 event had a shallower thermocline over the eastern Pacific with a weaker zonal contrast of subsurface water temperatures Remote Sens.…”

“…Figure 5c shows that though the positive anomalies over the equatorial central-eastern Pacific were not as large as those in the 1982-83 and 1997-98 events, the negative (dry) anomalies over Indonesia were nearly as significant. In the austral spring of 2015, Indonesia experienced huge forest fires that caused a haze crisis in neighboring countries [53].…”

What Does It Mean to Be El Niño Ready?

“…Speculating aloud, the relatively short history of scientific monitoring of El Niño [48] hints that very strong basin-wide events might recur on the order of every 10-20 years (i.e., suggested by differences in the number of years between onsets of major events during 1957-58, 1972-73, 1982-83, 1997-98 and 2015-16), and may suggest to policymakers that there is little need to direct resources to a problem that will likely not appear for many years after the last major event. Less intense El Niños can be handled in the normal scheme of coping with seasonal anomalies.…”