Agus Santoso etal. published a paper in BAMS

 Enso Extremes and Diversity: Dynamics, Teleconnections, and Impacts

Agus Santoso, Wenju Cai, Mat Collins, Mike McPhaden, Fei-Fei Jin, Eric Guilyardi, Gabriel Vecchi, Dietmar Dommenget, Guojian Wang

Underlying a predictive capability of the El Niño– Southern Oscillation (ENSO) is a grounded understanding of its dynamics. The 1982/83 and 1997/98 “super–El Niño” events pose a challenge to this understanding. The 1997/98 event was dubbed “the climate event of the twentieth century” for its extraordinary magnitude and global-scale destruc¬tive effects. Modeling studies over the last 2 years have led to further insights into extreme El Niños and have found that their frequency is projected to increase significantly under greenhouse warming.
In boreal spring of 2014, the tropical Pacific was primed for an El Niño, when most forecast agen¬cies such as the National Oceanic and Atmospheric Administration (NOAA) and the Australian Bureau of Meteorology elevated their El Niño probability to more than 60%. A remarkable increase in warm water volume with a series of westerly wind bursts in boreal spring alerted ENSO experts to the possibility of a strong event, one which some thought could be the first extreme El Niño since 1997, generating news headlines worldwide. However, while the equatorial Pacific remained anomalously warm, the expected super–El Niño did not materialize. That failed expec-tation may, in part, be a reflection of our incomplete knowledge of extreme El Niño and its predictability or perhaps the very nature of the ENSO system itself.
Against this backdrop of progress, uncertainties, and ensuing greenhouse warming, it is timely to ask— what is the current state of understanding of ENSO diversity, extremes, impacts, and teleconnections? It is for this reason that ENSO researchers gathered in Sydney, Australia, earlier this year for a 3-day workshop at the University of New South Wales. The 60 participants consisted of leading ENSO experts,including 20 postdoctorates and graduate students, who delivered 39 oral and 24 poster presentations, highlighting recent advances and ongoing research to facilitate the discussions of ENSO extremes and diversity. The science presented covered the use of modeling, observations, theories, and paleorecon¬structions.
The workshop was opened by a stimulating pre¬sentation called “Who Killed the Big 2014 El Niño,” which outlined the possible factors that may hold the key to understanding this elusive event. The general perception is that the atmospheric feedback failed to occur, despite the significant ocean subsurface warming, and this appears to be due to various factors such as the cold phase of the interdecadal Pacific oscillation (IPO) or the Pacific decadal oscillation (PDO), an anomalously warm Indian Ocean, and muted westerly wind bursts, among other possibili¬ties. All of these factors reflect the main complexities of ENSO dynamics, which remain today an active topic of investigation. These are outlined below as discussed by several presenters.

Published by BAMS NOVEMBER 2015