Abstract
A technique is developed to identify the types of atmosphere-ocean interaction during El Niño-Southern Oscillation events using sea surface temperature, sea level pressure (SLP), and outgoing longwave radiation (OLR) data. Two pairs of indices are derived that separate the interactions into tropical and subtropical types and basin-wide and local types. The dominant interaction type for the observed El Niño events since 1980 is identified and shown to shift with time from the tropical to subtropical and from basin-wide to local. Thus, the 21st century El Niños have become dominated by subtropical and local interactions, in strong contrast to the 20th century El Niños that were dominated by the tropical and basin-wide interactions. These changes result in the 1997–98 and 2015–16 extreme El Niños being different in their evolutions and global impacts, despite having similar intensities. SLP is the key variable for separating the tropical and subtropical types of interactions, while OLR is the key variable for separating the basin-wide and local types of interactions.
Highlights
El Niño-Southern Oscillation (ENSO) is an important climate variation phenomenon that arises from interactions between the tropical Pacific Ocean and the overlying atmosphere (Bjerknes 1969, Rasmusson and Carpenter 1982, Philander 1990, Latif et al 1994)
We examine the characteristics of ENSO interaction associated with these two indices by regressing anomalies onto the indices
The regressed sea surface temperatures (SSTs) anomaly structures (figures 1(a) and (c)) indicate that the EIT1slp is characterized by SST anomalies centered in the tropical eastern Pacific that resemble those associated with the Eastern Pacific (EP) ENSO, whereas the EIT2slp is characterized by anomalies centered in the tropical central Pacific that resemble those associated with the Central Pacific (CP) ENSO
Summary
Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Keywords: El Niño, atmosphere-ocean coupling, ENSO complexity, tropical coupling, subtropical coupling, basin-wide coupling, local coupling
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