The modulation of ENSO variability in CCSM3 by extratropical Rossby waves

Shayne McGregor, Alexander Sen Gupta, Neil John Holbrook, Scott Brendan Power

Research output: Contribution to journalArticleResearchpeer-review

6 Citations (Scopus)

Abstract

Evidence suggests that the magnitude and frequency of the El Nino-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 off-equatorial 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. (c) 2009 American Meteorological Society.
Original languageEnglish
Pages (from-to)5839 - 5853
Number of pages15
JournalJournal of Climate
Volume22
Issue number22
DOIs
Publication statusPublished - 2009
Externally publishedYes

Cite this

McGregor, Shayne ; Sen Gupta, Alexander ; Holbrook, Neil John ; Power, Scott Brendan. / The modulation of ENSO variability in CCSM3 by extratropical Rossby waves. In: Journal of Climate. 2009 ; Vol. 22, No. 22. pp. 5839 - 5853.
@article{f5e4e1d8533b47cbb1710df548d0bb41,
title = "The modulation of ENSO variability in CCSM3 by extratropical Rossby waves",
abstract = "Evidence suggests that the magnitude and frequency of the El Nino-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 off-equatorial 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. (c) 2009 American Meteorological Society.",
author = "Shayne McGregor and {Sen Gupta}, Alexander and Holbrook, {Neil John} and Power, {Scott Brendan}",
year = "2009",
doi = "10.1175/2009JCLI2922.1",
language = "English",
volume = "22",
pages = "5839 -- 5853",
journal = "Journal of Climate",
issn = "0894-8755",
publisher = "American Meteorological Society",
number = "22",

}

The modulation of ENSO variability in CCSM3 by extratropical Rossby waves. / McGregor, Shayne; Sen Gupta, Alexander; Holbrook, Neil John; Power, Scott Brendan.

In: Journal of Climate, Vol. 22, No. 22, 2009, p. 5839 - 5853.

Research output: Contribution to journalArticleResearchpeer-review

TY - JOUR

T1 - The modulation of ENSO variability in CCSM3 by extratropical Rossby waves

AU - McGregor, Shayne

AU - Sen Gupta, Alexander

AU - Holbrook, Neil John

AU - Power, Scott Brendan

PY - 2009

Y1 - 2009

N2 - Evidence suggests that the magnitude and frequency of the El Nino-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 off-equatorial 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. (c) 2009 American Meteorological Society.

AB - Evidence suggests that the magnitude and frequency of the El Nino-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 off-equatorial 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. (c) 2009 American Meteorological Society.

UR - http://journals.ametsoc.org/doi/pdf/10.1175/2009JCLI2922.1

U2 - 10.1175/2009JCLI2922.1

DO - 10.1175/2009JCLI2922.1

M3 - Article

VL - 22

SP - 5839

EP - 5853

JO - Journal of Climate

JF - Journal of Climate

SN - 0894-8755

IS - 22

ER -