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

Effect of AMOC collapse on ENSO in a high resolution general circulation model
Effect of AMOC collapse on ENSO in a high resolution general circulation model
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.
0930-7575
Williamson, Mark S.
167f1715-3df5-4523-b651-3b0eaeb2ce25
Collins, Mat
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Drijfhout, Sybren S.
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Kahana, Ron
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Mecking, Jennifer V.
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Lenton, Timothy M.
245a93ab-92e4-4719-a8b7-7ef66d65d048
Williamson, Mark S.
167f1715-3df5-4523-b651-3b0eaeb2ce25
Collins, Mat
a99a3e61-7340-4535-ad8d-59fccb60fd9c
Drijfhout, Sybren S.
a5c76079-179b-490c-93fe-fc0391aacf13
Kahana, Ron
88cc3be1-490b-448c-851d-cd5f173670f4
Mecking, Jennifer V.
9b090069-5061-4340-b736-9690894ce203
Lenton, Timothy M.
245a93ab-92e4-4719-a8b7-7ef66d65d048

Williamson, Mark S., Collins, Mat, Drijfhout, Sybren S., Kahana, Ron, Mecking, Jennifer V. and Lenton, Timothy M. (2017) Effect of AMOC collapse on ENSO in a high resolution general circulation model. Climate Dynamics. (doi:10.1007/s00382-017-3756-0).

Record type: Article

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.

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10.1007_s00382-017-3756-0 - Other
Available under License Creative Commons Attribution.
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Accepted/In Press date: 7 June 2017
e-pub ahead of print date: 17 June 2017

Identifiers

Local EPrints ID: 413333
URI: http://eprints.soton.ac.uk/id/eprint/413333
ISSN: 0930-7575
PURE UUID: b2b69a1f-0a3f-4100-8eda-523e4d1760e3

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Date deposited: 22 Aug 2017 16:31
Last modified: 06 Oct 2020 18:54

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Contributors

Author: Mark S. Williamson
Author: Mat Collins
Author: Ron Kahana
Author: Jennifer V. Mecking
Author: Timothy M. Lenton

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