The Modulation of ENSO Variability in CCSM3 by Extratropical Rossby Waves

McGregor, Shayne and Gupta, Alex Sen and Holbrook, Neil J. and Power, Scott B. (2009) The Modulation of ENSO Variability in CCSM3 by Extratropical Rossby Waves. Journal of Climate, 22 (22). pp. 5839-5853. ISSN 0894-8755


Abstract

Evidence suggests that the magnitude and frequency of the El Niño-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. © 2009 American Meteorological Society.


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Item Type: Article (Commonwealth Reporting Category C)
Refereed: Yes
Item Status: Live Archive
Faculty/School / Institute/Centre: No Faculty
Faculty/School / Institute/Centre: No Faculty
Date Deposited: 05 Jan 2022 23:07
Last Modified: 07 Feb 2022 04:45
Uncontrolled Keywords: Organic Compounds; Chemical Reactions; Telephone and Other Line Communications; Electro-Optical Communication; Electronic Equipment, Radar, Radio and Television; Inorganic Compounds; Fluid Flow, General; Atmospheric Properties; Strength of Building Materials; Mechanical Properties; Waterways; Buildings and Towers; Seawater, Tides and Waves; Air-sea interaction; Air-sea interaction; MIXING AND SEPARATION; COASTAL AND OCEAN ENGINEERING; Coupled general circulation models; ENSO events; Equatorial Pacific; Extra-tropical Rossby waves; Extratropical; Extratropics; Inter-decadal variability; Interannual; Interdecadal; Oceanic waves; Pacific ocean; Predictive capabilities; Primitive equations; Probabilistic prediction; Rossby wave; Rossby wave mechanisms; Shallow-water models; Southern Oscillation; Thermocline depth; Time-scales; Tropical Pacific ocean; Western boundary;
Fields of Research (2008): 04 Earth Sciences > 0401 Atmospheric Sciences > 040105 Climatology (excl.Climate Change Processes)
Fields of Research (2020): 37 EARTH SCIENCES > 3702 Climate change science > 370202 Climatology
Socio-Economic Objectives (2008): D Environment > 96 Environment > 9603 Climate and Climate Change > 960304 Climate Variability (excl. Social Impacts)
Socio-Economic Objectives (2020): 19 ENVIRONMENTAL POLICY, CLIMATE CHANGE AND NATURAL HAZARDS > 1905 Understanding climate change > 190502 Climate variability (excl. social impacts)
Identification Number or DOI: https://doi.org/10.1175/2009JCLI2922.1
URI: http://eprints.usq.edu.au/id/eprint/42450

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