A possible explanation for the divergent projection of ENSO amplitude change under global warming
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The El Niño-Southern Oscillation (ENSO) is the greatest climate variability on interannual time scale, yet what controls ENSO amplitude changes under global warming (GW) is uncertain. Here we show that the fundamental factor that controls the divergent projections of ENSO amplitude change within 20 coupled general circulation models that participated in the Coupled Model Intercomparison Project phase-5 is the change of climatologic mean Pacific subtropical cell (STC), whose strength determines the meridional structure of ENSO perturbations and thus the anomalous thermocline response to the wind forcing. The change of the thermocline response is a key factor regulating the strength of Bjerknes thermocline and zonal advective feedbacks, which ultimately lead to the divergent changes in ENSO amplitude. Furthermore, by forcing an ocean general circulation mode with the change of zonal mean zonal wind stress estimated by a simple theoretical model, a weakening of the STC in future is obtained. Such a change implies that ENSO variability might strengthen under GW, which could have a profound socio-economic consequence.
KeywordsENSO Global warming Ocean thermocline response to wind anomaly ENSO meridional structure Subtropical cell
We would like to thank Dr. Lu Wang and anonymous reviewers for insightful suggestions and comments. We acknowledge the PCMDI for providing the CMIP5 model data, which may be obtained from the website of http://pcmdi9.llnl.gov/esgf-web-fe/. This work was supported by NSFC project 41630423, National 973 project 2015CB453200, NSF AGS-1565653, NSFC 41475084, NRL grant N00173-161G906, Jiangsu NSF project BK20150062, Jiangsu Shuang-Chuang Team (R2014SCT001), NSFC Grant 41376002/41606011/41530426, CAS Strategic Priority Project XDA11010105, and by the IPRC that is sponsored by Japan Agency for Marine-Earth Science and Technology (JAMSTEC). This is SOEST contribution number 9938, IPRC contribution number 1237, and ESMC contribution 150.
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