The 2015/16 El Niño Event in Context of the MERRA-2 Reanalysis: A Comparison of the Tropical Pacific with 1982/83 and 1997/98

Abstract

AbstractThe 2015/16 El Niño is analyzed using atmospheric and oceanic analysis produced using the Goddard Earth Observing System (GEOS) data assimilation systems. As well as describing the structure of the event, a theme of this work is to compare and contrast it with two other strong El Niños, in 1982/83 and 1997/98. These three El Niño events are included in the Modern-Era Retrospective Analysis for Research and Applications (MERRA) and in the more recent MERRA-2 reanalyses. MERRA-2 allows a comparison of fields derived from the underlying GEOS model, facilitating a more detailed comparison of physical forcing mechanisms in the El Niño events. Various atmospheric and oceanic structures indicate that the 2015/16 El Niño maximized in the Niño-3.4 region, with a large region of warming over most of the Pacific and Indian Oceans. The eastern tropical Indian Ocean, Maritime Continent, and western tropical Pacific are found to be less dry in boreal winter, compared to the earlier two strong events. Whereas the 2015/16 El Niño had an earlier occurrence of the equatorial Pacific warming and was the strongest event on record in the central Pacific, the 1997/98 event exhibited a more rapid growth due to stronger westerly wind bursts and the Madden?Julian oscillation during spring, making it the strongest El Niño in the eastern Pacific. Compared to 1982/83 and 1997/98, the 2015/16 event had a shallower thermocline over the eastern Pacific with a weaker zonal contrast of subsurface water temperatures along the equatorial Pacific. While the three major ENSO events have similarities, each is unique when looking at the atmosphere and ocean surface and subsurface.