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The modulation of ENSO variability in CCSM3 by extratropical Rossby waves
Citation
McGregor, S and Gupta, AS and Holbrook, NJ and Power, SB, The modulation of ENSO variability in CCSM3 by extratropical Rossby waves, Journal of Climate, 22, (22) pp. 5839-5853. ISSN 0894-8755 (2009) [Refereed Article]
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Copyright Statement
Copyright © 2009 American Meteorological Society
Official URL: http://ams.allenpress.com
DOI: doi:10.1175/2009JCLI2922.1
Abstract
Evidence suggests that the magnitude and frequency of the El Nin˜ o–Southern Oscillation (ENSO) changes
on interdecadal time scales. This is manifest in a distinct shift in ENSO behavior during the late 1970s. This
study investigates mechanisms that may force this interdecadal variability and, in particular, on modulations
driven by extratropical Rossby waves. Results from oceanic shallow-water models show that the Rossby wave
theory can explain small near-zonal changes in equatorial thermocline depth that can alter the amplitude of
simulated ENSO events. However, questions remain over whether the same mechanism operates in more
complex coupled general circulation models (CGCMs) and what the magnitude of the resulting change would
be. Experiments carried out in a state-of-the-art z-coordinate primitive equation model confirm that the
Rossby wave mechanism does indeed operate. The effects of these interactions are further investigated using
a partial coupling (PC) technique. This allows for the isolation of the role of wind stress–forced oceanic exchanges
between the extratropics and the tropics and the subsequent modulation of ENSO variability. It is
found that changes in the background state of the equatorial Pacific thermocline depth, induced by a fixed offequatorial
wind stress anomaly, can significantly affect the probability of ENSO events occurring. This
confirms the results obtained from simpler models and further validates theories that rely on oceanic wave
dynamics to generate Pacific Ocean interdecadal variability. This indicates that an improved predictive capability
for seasonal-to-interannual ENSO variability could be achieved through a better understanding of
extratropical-to-tropical Pacific Ocean transfers and western boundary processes. Furthermore, such an
understanding would provide a physical basis to enhance multiyear probabilistic predictions of ENSO indices.
Item Details
Item Type: | Refereed Article |
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Keywords: | ENSO variability, Rossby waves, extratropical, equatorial Pacific thermocline |
Research Division: | Earth Sciences |
Research Group: | Oceanography |
Research Field: | Physical oceanography |
Objective Division: | Environmental Management |
Objective Group: | Marine systems and management |
Objective Field: | Measurement and assessment of marine water quality and condition |
UTAS Author: | Holbrook, NJ (Professor Neil Holbrook) |
ID Code: | 60595 |
Year Published: | 2009 |
Web of Science® Times Cited: | 8 |
Deposited By: | Geography and Environmental Studies |
Deposited On: | 2010-02-12 |
Last Modified: | 2014-12-08 |
Downloads: | 0 |
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