Effect of AMOC collapse on ENSO in a high resolution general circulation model

Mark S. Williamson*, Mat Collins, Sybren S. Drijfhout, Ron Kahana, Jennifer V. Mecking, Timothy M. Lenton

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

Abstract

We look at changes in the El Niño Southern Oscillation (ENSO) in a high-resolution eddy-permitting climate model experiment in which the Atlantic Meridional Circulation (AMOC) is switched off using freshwater hosing. The ENSO mode is shifted eastward and its period becomes longer and more regular when the AMOC is off. The eastward shift can be attributed to an anomalous eastern Ekman transport in the mean equatorial Pacific ocean state. Convergence of this transport deepens the thermocline in the eastern tropical Pacific and increases the temperature anomaly relaxation time, causing increased ENSO period. The anomalous Ekman transport is caused by a surface northerly wind anomaly in response to the meridional sea surface temperature dipole that results from switching the AMOC off. In contrast to a previous study with an earlier version of the model, which showed an increase in ENSO amplitude in an AMOC off experiment, here the amplitude remains the same as in the AMOC on control state. We attribute this difference to variations in the response of decreased stochastic forcing in the different models, which competes with the reduced damping of temperature anomalies. In the new high-resolution model, these effects approximately cancel resulting in no change in amplitude.

Original languageEnglish
Pages (from-to)2537-2552
Number of pages16
JournalClimate Dynamics
Volume50
Issue number7-8
DOIs
Publication statusPublished - 1 Apr 2018

Keywords

  • Abrupt climate change
  • AMOC
  • AMOC collapse
  • CGCM
  • ENSO
  • Hosing experiment

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