Why were the 2015/2016 and 1997/1998 extreme El Niños different?

• Published in: Geophysical research letters Vol. 44; no. 4; pp. 1848 - 1856
• Main Authors: Paek, Houk, Yu, Jin‐Yi, Qian, Chengcheng
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 28.02.2017
• Subjects: 1997/1998 El Niño; 2015/2016 El Niño; Anomalies; Climate; Coastal environments; Convection; Decay; Dynamics; El Nino; El Nino phenomena; Evolution; extreme El Niño; La Nina; Marine; Meteorology; Ocean temperature; Rainfall; Sea surface; Sea surface temperature; Surface temperature; Temperature; Thermocline; Thermocline variations; Wave dynamics; Wave packets; United States > US; Pacific Ocean; I, Central Pacific; North America
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1002/2016GL071515

Subtle but important differences are identified between the 1997/1998 and 2015/2016 extreme El Niños that reflect fundamental differences in their underlying dynamics. The 1997/1998 event is found to evolve following the eastern Pacific El Niño dynamics that relies on basin‐wide thermocline variations, whereas the 2015/2016 event involves additionally the central Pacific (CP) El Niño dynamics that depends on subtropical forcing. The stronger CP dynamics during the 2015/2016 event resulted in its sea surface temperature (SST) anomalies lingering around the International Date Line during the decaying phase, which is in contrast to the retreat of the anomalies toward the South American Coast during the decaying phase of the 1997/1998 event. The different SST evolution excited different wave trains resulting in the western U.S. not receiving the same above‐normal rainfall during the 2015/2016 El Niño as it did during the 1997/1998 El Niño. Ensemble model experiments are conducted to confirm the different climate impacts of the two El Niños. Key Points The 1997/1998 event is the strongest EP El Niño, while the 2015/2016 event is the strongest mixed EP and CP El Niño ever recorded The two events exhibit subtle differences in their equatorial SST evolution that reflects fundamental differences in the underlying dynamics The SST differences led to large differences in tropical convection, resulting in different impacts on North American climate