Decadal variability in an OGCM Southern Ocean: intrinsic modes, forced modes and metastable states

An ocean general circulation model (OGCM) is used to identify a Southern Ocean southeast Pacific intrinsicmode of low frequency variability. Using CORE data a comprehensive suite of experiments were carriedout to elucidate excitation and amplification responses of this intrinsic mode to low frequenc...

Full description

Bibliographic Details
Published in:Ocean Modelling
Main Authors: O'Kane, TJ, Matear, R, Chamberlain, MA, Risby, JS, Sloyan, BM, Horenko, I
Format: Article in Journal/Newspaper
Language:English
Published: Elsevier Sci Ltd 2013
Subjects:
Earth Sciences
Oceanography
Physical Oceanography
Antarctic
Southern Ocean
The Antarctic
Pacific
Antarc*
Sea ice
Online Access:https://doi.org/10.1016/j.ocemod.2013.04.009
http://ecite.utas.edu.au/119350
Description
Summary:An ocean general circulation model (OGCM) is used to identify a Southern Ocean southeast Pacific intrinsicmode of low frequency variability. Using CORE data a comprehensive suite of experiments were carriedout to elucidate excitation and amplification responses of this intrinsic mode to low frequencyforcing (ENSO,SAM) and stochastic forcing due to high frequency winds. Subsurface anomalies werefound to teleconnect the Pacific and Atlantic regions of the Antarctic Circumpolar Current (ACC) thermocline.The Pacific region of the ACC is characterised by intrinsic baroclinic disturbances that respond toboth SAM and ENSO, while the Atlantic sector of the ACC is sensitive to higher frequency winds thatact to amplify thermocline anomalies propagating downstream from the Pacific. Non-stationary clusteranalysis was used to identify the systems dynamical regimes and characterise meta-stability, persistenceand transitions between the respective states. This analysis reveals significant trends, indicating fundamentalchanges to the meta-stability of the ocean dynamics in response to changes in atmospheric forcing.Intrinsic variability in sea-ice concentration was found to be coupled to thermocline processes. Seaicevariability localised in the Atlantic was most closely associated with high frequency weather forcing.The SAM was associated with a circumpolar sea-ice response whereas ENSO was found to be a major driverof sea-ice variability only in the Pacific. This simulation study identifies plausible mechanisms thatdetermine the predictability of the Southern Ocean climate on multi-decadal timescales.

Similar Items