Walker Circulation controls ENSO Atmospheric Feedbacks in Uncoupled and Coupled Climate Model Simulations

Bayr, Tobias, Dommenget, Dietmar and Latif, Mojib (2020) Walker Circulation controls ENSO Atmospheric Feedbacks in Uncoupled and Coupled Climate Model Simulations Climate Dynamics, 54 . pp. 2831-2846. DOI 10.1007/s00382-020-05152-2.

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Abstract

Many climate models strongly underestimate the two most important atmospheric feedbacks operating in El Niño/Southern Oscillation (ENSO), the positive (amplifying) zonal surface wind feedback and negative (damping) surface-heat flux feedback (hereafter ENSO atmospheric feedbacks, EAF), hampering realistic representation of ENSO dynamics in these models. Here we show that the atmospheric components of climate models participating in the 5th phase of the Coupled Model Intercomparison Project (CMIP5) when forced by observed sea surface temperatures (SST), already underestimate EAF on average by 23%, but less than their coupled counterparts (on average by 54%). There is a pronounced tendency of atmosphere models to simulate stronger EAF, when they exhibit a stronger mean deep convection and enhanced cloud cover over the western equatorial Pacific (WEP), indicative of a stronger rising branch of the Pacific Walker Circulation (PWC). Further, differences in the mean deep convection over the WEP between the coupled and uncoupled models explain a large part of the differences in EAF, with the deep convection in the coupled models strongly depending on the equatorial Pacific SST bias. Experiments with a single atmosphere model support the relation between the equatorial Pacific atmospheric mean state, the SST bias and the EAF. An implemented cold SST bias in the observed SST forcing weakens deep convection and reduces cloud cover in the rising branch of the PWC, causing weaker EAF. A warm SST bias has the opposite effect. Our results elucidate how biases in the mean state of the PWC and equatorial SST hamper a realistic simulation of the EAF.

Document Type: Article
Keywords: El Niño/Southern Oscillation; ENSO; Walker Circulation; wind-SST feedback; net heat flux-SST feedback; ENSO atmospheric feedbacks; AMIP5; CMIP5
Research affiliation: OceanRep > GEOMAR > FB1 Ocean Circulation and Climate Dynamics > FB1-ME Maritime Meteorology
OceanRep > The Future Ocean - Cluster of Excellence
OceanRep > SFB 754
Refereed: Yes
DOI etc.: 10.1007/s00382-020-05152-2
ISSN: 0930-7575
Projects: Future Ocean, SFB754, InterDec, Beyond the linear dynamics of the El Nino Southern Oscillation, CMIP5, ECHAM5
Date Deposited: 12 Feb 2020 14:10
Last Modified: 13 Mar 2020 13:18
URI: http://eprints.uni-kiel.de/id/eprint/48948

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