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Understanding the double peaked El Niño in coupled GCMs
journal contribution
posted on 2023-05-18, 21:32 authored by Felicity McCormack, Wittenberg, AT, Brown, JN, Marsland, SJ, Neil HolbrookNeil HolbrookCoupled general circulation models (CGCMs) simulate a diverse range of El Niño-Southern Oscillation behaviors. “Double peaked” El Niño events - where two separate centers of positive sea surface temperature (SST) anomalies evolve concurrently in the eastern and western equatorial Pacific - have been evidenced in Coupled Model Intercomparison Project version 5 CGCMs and are without precedent in observations. The characteristic CGCM double peaked El Niño may be mistaken for a central Pacific warming event in El Niño composites, shifted westwards due to the cold tongue bias. In results from the Australian Community Climate and Earth System Simulator coupled model, we find that the western Pacific warm peak of the double peaked El Niño event emerges due to an excessive westward extension of the climatological cold tongue, displacing the region of strong zonal SST gradients towards the west Pacific. A coincident westward shift in the zonal current anomalies reinforces the western peak in SST anomalies, leading to a zonal separation between the warming effect of zonal advection (in the west Pacific) and that of vertical advection (in the east Pacific). Meridional advection and net surface heat fluxes further drive growth of the western Pacific warm peak. Our results demonstrate that understanding historical CGCM El Niño behaviors is a necessary precursor to interpreting projections of future CGCM El Niño behaviors, such as changes in the frequency of eastern Pacific El Niño events, under global warming scenarios.
History
Publication title
Climate DynamicsVolume
48Issue
5Pagination
2045-2063ISSN
0930-7575Department/School
Institute for Marine and Antarctic StudiesPublisher
Springer-VerlagPlace of publication
175 Fifth Ave, New York, USA, Ny, 10010Rights statement
Copyright 2016 Springer-Verlag Berlin HeidelbergRepository Status
- Restricted