ENSO atmospheric feedbacks under global warming and their relation to mean-state changes.

Bayr, Tobias and Latif, Mojib (2022) ENSO atmospheric feedbacks under global warming and their relation to mean-state changes. Open Access Climate Dynamics . DOI 10.1007/s00382-022-06454-3.

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Abstract

Two atmospheric feedbacks play an important role in the dynamics of the El Nino/Southern Oscillation (ENSO), namely the amplifying zonal wind feedback and the damping heat flux feedback. Here we investigate how and why both feedbacks change under global warming in climate models participating in the 5th and 6th phase of the Coupled Model Intercomparison Project (CMIP5 and CMIP6) under the business-as-usual scenario (RCP8.5 and SSP5-8.5, respectively). The amplifying zonal wind feedback over the western equatorial Pacific (WEP) becomes significantly stronger in two third of the models, on average by 12 +/- 7% in these models. The heat flux damping feedback over the eastern and central equatorial Pacific (EEP and CEP, respectively) increases as well in nearly all models, with the damping effect increasing on average by 18 +/- 11%. The simultaneous strengthening of the two feedbacks can be explained by the stronger warming in the EEP relative to the WEP and the off-equatorial regions, which shifts the rising branch of the Pacific Walker Circulation to the east and increases the mean convection over the CEP. This in turn leads to a stronger vertical wind response during ENSO events over the CEP that strengthens both atmospheric feedbacks. We separate the climate models into sub-ensembles with STRONG and WEAK ENSO atmospheric feedbacks, as 2/3 of the models underestimate both feedbacks under present-day conditions by more than 40%, causing an error compensation in the ENSO dynamics. The biased mean state in WEAK in 20C constrains the ENSO atmospheric feedback projection in 21C, as the models of the WEAK sub-ensemble also have weaker ENSO atmospheric feedbacks in 21C. Further, due to the more realistic dynamics and teleconnections, we postulate that one should have more confidence in the ENSO predictions with models belonging to the STRONG sub-ensemble. Finally, we analyze the relation between ENSO amplitude change and ENSO atmospheric feedback change. We find that models simulating an eastward shift of the zonal wind feedback and increasing precipitation over the EEP during Eastern Pacific El Nino events tend to predict a larger ENSO amplitude in response to global warming.

Document Type: Article
Funder compliance: DFG: 429334714
Keywords: El Nino; Southern Oscillation; ENSO; ENSO atmospheric feedbacks; Global warming; ENSO amplitude change; CMIP5; CMIP6
Research affiliation: OceanRep > GEOMAR > FB1 Ocean Circulation and Climate Dynamics > FB1-ME Maritime Meteorology
Corresponding Author:
Corresponding Author Name
GEOMAR ID
Affiliation
Bayr, Tobias
Bayr, Tobias
FB1-ME Maritime Meteorology
Main POF Topic: PT2: Ocean and Cryosphere
Refereed: Yes
Open Access Journal?: No
Publisher: Springer
Related URLs:
Projects: Influence of Model Bias on ENSO Projections of the 21st Century
Date Deposited: 16 Sep 2022 09:00
Last Modified: 16 Sep 2022 09:05
URI: https://oceanrep.geomar.de/id/eprint/57036

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