A numerical model study of the effects of interannual timescale wave propagation on the predictability of the Atlantic meridional overturning circulation
A numerical model study of the effects of interannual timescale wave propagation on the predictability of the Atlantic meridional overturning circulation
We investigate processes leading to uncertainty in forecasts of the Atlantic meridional overturning circulation (AMOC). A climate model is used to supply initial conditions for ensemble simulations in which members initially have identical ocean states but perturbed atmosphere states. Baroclinic transports diverge on interannual timescales even though the ocean is not eddy-permitting. Interannual fluctuations of the model AMOC in the subtropical gyre are caused by westward propagating Rossby waves. Divergence of the predicted AMOC with time occurs because the waves develop different phases in different ensemble members predominantly due to differences in eastern boundary windstress curl. These windstress fluctuations communicate with interior ocean transports via modifications to the vertical velocity and the vortex stretching term dw/dz. Consequently, errors propagate westwards resulting in longer predictability times in the interior ocean compared with the eastern boundary. Another source of divergence is transport anomalies propagating along the Gulf Stream (and other boundary currents). The propagation mechanism seems to be predominantly advection by mean currents, and we show that the arrival of westward propagating waves can trigger development of these anomalies. The mean state of the AMOC has a small effect on interannual predictability in the subtropical gyre, most likely because eastern boundary windstress curl predictability is not strongly dependent on the state of the AMOC in the subtropics. Eastern boundary windstress curl was more predictable at 45{degree sign}N when the AMOC was in a strongly decreasing state, but, unlike at 30{degree sign}N, no mechanism was found linking windstress curl fluctuations with deep transports.
Atlantic meridional overturning circulation, predictability, Rossby waves
131-146
Sinha, Bablu
544b5a07-3d74-464b-9470-a68c69bd722e
Topliss, Brenda
a3d67169-6e34-4362-a878-43cb00148219
Blaker, Adam Tobias
94efe8b2-c744-4e90-87d7-db19ffa41200
Hirschi, Joel Jean-Marie
c8a45006-a6e3-4319-b5f5-648e8ef98906
January 2013
Sinha, Bablu
544b5a07-3d74-464b-9470-a68c69bd722e
Topliss, Brenda
a3d67169-6e34-4362-a878-43cb00148219
Blaker, Adam Tobias
94efe8b2-c744-4e90-87d7-db19ffa41200
Hirschi, Joel Jean-Marie
c8a45006-a6e3-4319-b5f5-648e8ef98906
Sinha, Bablu, Topliss, Brenda, Blaker, Adam Tobias and Hirschi, Joel Jean-Marie
(2013)
A numerical model study of the effects of interannual timescale wave propagation on the predictability of the Atlantic meridional overturning circulation.
Journal of Geophysical Research, 118 (1), .
(doi:10.1029/2012JC008334).
Abstract
We investigate processes leading to uncertainty in forecasts of the Atlantic meridional overturning circulation (AMOC). A climate model is used to supply initial conditions for ensemble simulations in which members initially have identical ocean states but perturbed atmosphere states. Baroclinic transports diverge on interannual timescales even though the ocean is not eddy-permitting. Interannual fluctuations of the model AMOC in the subtropical gyre are caused by westward propagating Rossby waves. Divergence of the predicted AMOC with time occurs because the waves develop different phases in different ensemble members predominantly due to differences in eastern boundary windstress curl. These windstress fluctuations communicate with interior ocean transports via modifications to the vertical velocity and the vortex stretching term dw/dz. Consequently, errors propagate westwards resulting in longer predictability times in the interior ocean compared with the eastern boundary. Another source of divergence is transport anomalies propagating along the Gulf Stream (and other boundary currents). The propagation mechanism seems to be predominantly advection by mean currents, and we show that the arrival of westward propagating waves can trigger development of these anomalies. The mean state of the AMOC has a small effect on interannual predictability in the subtropical gyre, most likely because eastern boundary windstress curl predictability is not strongly dependent on the state of the AMOC in the subtropics. Eastern boundary windstress curl was more predictable at 45{degree sign}N when the AMOC was in a strongly decreasing state, but, unlike at 30{degree sign}N, no mechanism was found linking windstress curl fluctuations with deep transports.
Text
jgrc20019_Sinha.pdf
- Version of Record
More information
Published date: January 2013
Keywords:
Atlantic meridional overturning circulation, predictability, Rossby waves
Organisations:
Marine Systems Modelling
Identifiers
Local EPrints ID: 346905
URI: http://eprints.soton.ac.uk/id/eprint/346905
ISSN: 0148-0227
PURE UUID: 33981f3d-b0d7-4003-a36a-289b4402eda1
Catalogue record
Date deposited: 11 Jan 2013 14:02
Last modified: 14 Mar 2024 12:43
Export record
Altmetrics
Contributors
Author:
Bablu Sinha
Author:
Brenda Topliss
Author:
Adam Tobias Blaker
Author:
Joel Jean-Marie Hirschi
Download statistics
Downloads from ePrints over the past year. Other digital versions may also be available to download e.g. from the publisher's website.
View more statistics