The Seasonal Cycle over the Tropical Pacific in Coupled Ocean–Atmosphere General Circulation Models

Abstract The multidecadal modulation of the El Niño–Southern Oscillation (ENSO) due to greenhouse warming has been analyzed herein by means of diagnostics of Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) coupled general circulation models (CGCMs) and the eigenanalysis of a simplified version of an intermediate ENSO model. The response of the global-mean troposphere temperature to increasing greenhouse gases is more likely linear, while the amplitude and period of ENSO fluctuates in a multidecadal time scale. The climate system model outputs suggest that the multidecadal modulation of ENSO is related to the delayed response of the subsurface temperature in the tropical Pacific compared to the response time of the sea surface temperature (SST), which would lead a modulation of the vertical temperature gradient. Furthermore, an eigenanalysis considering only two parameters, the changes in the zonal contrast of the mean background SST and the changes in the vertical contrast between the mean surface and subsurface temperatures in the tropical Pacific, exhibits a good agreement with the CGCM outputs in terms of the multidecadal modulations of the ENSO amplitude and period. In particular, the change in the vertical contrast, that is, change in difference between the subsurface temperature and SST, turns out to be more influential on the ENSO modulation than changes in the mean SST itself.

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Evaluating the performance of CMIP6 models in the tropical Atlantic: mean state, variability, and remote impacts

10.5194/egusphere-egu2020-12722 ◽

2020 ◽

Author(s):

Ingo Richter ◽

Hiroki Tokinaga

Keyword(s):

General Circulation ◽

General Circulation Models ◽

Tropical Pacific ◽

Boreal Summer ◽

Tropical Atlantic ◽

Westerly Wind ◽

Equatorial Atlantic ◽

Wide Range ◽

Mean State ◽

The Tropical Pacific

<p>General circulation models of the Coupled Model Intercomparison Project Phase 6 (CMIP6) are examined with respect to their ability to simulate the mean state and variability of the tropical Atlantic, as well as its linkage to the tropical Pacific. While, on average, mean state biases have improved little relative to the previous intercomparison (CMIP5), there are now a few models with very small biases. In particular the equatorial Atlantic warm SST and westerly wind biases are mostly eliminated in these models. Furthermore, interannual variability in the equatorial and subtropical Atlantic is quite realistic in a number of CMIP6 models, which suggests that they should be useful tools for understanding and predicting variability patterns. The evolution of equatorial Atlantic biases follows the same pattern as in previous model generations, with westerly wind biases during boreal spring preceding warm sea-surface temperature (SST) biases in the east during boreal summer. A substantial portion of the westerly wind bias exists already in atmosphere-only simulations forced with observed SST, suggesting an atmospheric origin. While variability is relatively realistic in many models, SSTs seem less responsive to wind forcing than observed, both on the equator and in the subtropics, possibly due to an excessively deep mixed layer originating in the oceanic component. Thus models with realistic SST amplitude tend to have excessive wind amplitude. The models with the smallest mean state biases all have relatively high resolution but there are also a few low-resolution models that perform similarly well, indicating that resolution is not the only way toward reducing tropical Atlantic biases. The results also show a relatively weak link between mean state biases and the quality of the simulated variability. The linkage to the tropical Pacific shows a wide range of behaviors across models, indicating the need for further model improvement.</p>

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ENSO dynamics and seasonal cycle in the tropical Pacific as simulated by the ECHAM4/OPYC3 coupled general circulation model

Climate Dynamics ◽

10.1007/s003820050232 ◽

1998 ◽

Vol 14 (6) ◽

pp. 431-450 ◽

Cited By ~ 45

Author(s):

A. Bacher ◽

J. M. Oberhuber ◽

E. Roeckner

Keyword(s):

General Circulation Model ◽

Seasonal Cycle ◽

General Circulation ◽

Circulation Model ◽

Tropical Pacific ◽

Coupled General Circulation Model ◽

Enso Dynamics ◽

The Tropical Pacific

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Evaluation of the eastern equatorial Pacific SST seasonal cycle in CMIP5 models

Ocean Science Discussions ◽

10.5194/osd-11-1129-2014 ◽

2014 ◽

Vol 11 (2) ◽

pp. 1129-1147

Author(s):

Z. Song ◽

H. Liu ◽

L. Zhang ◽

F. Qiao ◽

C. Wang

Keyword(s):

Annual Cycle ◽

Seasonal Cycle ◽

General Circulation ◽

General Circulation Models ◽

Tropical Pacific ◽

Equatorial Pacific ◽

Eastern Coast ◽

Cmip5 Models ◽

Eastern Equatorial Pacific ◽

Central Equatorial Pacific

Abstract. The annual cycle of sea surface temperature (SST) in the eastern equatorial Pacific (EEP) with the largest amplitude in the tropical oceans is poorly represented in the coupled general circulation models (CGCMs) of the Coupled Model Intercomparison Project phase 3 (CMIP3). In this study, 18 models from CMIP5 projects are evaluated in simulating the annual cycle in the EEP. Fourteen models are able to simulate the annual cycle, and four still show erroneous information in the simulation, which suggests that the performances of CGCMs have been improved. The results of multi-model ensemble (MME) mean show that CMIP5 CGCMs can capture the annual cycle signal in the EEP with correlation coefficients up to 0.9. For amplitude simulations, EEP region 1 (EP1) near the eastern coast shows weaker results than observations due to the large warm SST bias from the southeastern tropical Pacific in the boreal autumn. In EEP region 2 (EP2) near the central equatorial Pacific, the simulated amplitudes are nearly the same as the observations because of the presence of a quasi-constant cold bias associated with poor cold tongue climatology simulation in the CGCMs. To improve CGCMs in the simulation of a realistic SST seasonal cycle, local and remote climatology SST biases that exist in both CMIP3 and CMIP5 CGCMs must be resolved at least for the simulation in the central equatorial Pacific and the southeastern tropical Pacific.

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A Pacific Centennial Oscillation Predicted by Coupled GCMs*

Journal of Climate ◽

10.1175/jcli-d-11-00421.1 ◽

2012 ◽

Vol 25 (17) ◽

pp. 5943-5961 ◽

Cited By ~ 29

Author(s):

Kristopher B. Karnauskas ◽

Jason E. Smerdon ◽

Richard Seager ◽

Jesús Fidel González-Rouco

Keyword(s):

Time Scale ◽

General Circulation ◽

Southern Oscillation ◽

Heat Content ◽

General Circulation Models ◽

Wave Pattern ◽

Tropical Pacific ◽

Equatorial Pacific ◽

Centennial Time Scale ◽

The Tropical Pacific

Abstract Internal climate variability at the centennial time scale is investigated using long control integrations from three state-of-the-art global coupled general circulation models. In the absence of external forcing, all three models produce centennial variability in the mean zonal sea surface temperature (SST) and sea level pressure (SLP) gradients in the equatorial Pacific with counterparts in the extratropics. The centennial pattern in the tropical Pacific is dissimilar to that of the interannual El Niño–Southern Oscillation (ENSO), in that the most prominent expression in temperature is found beneath the surface of the western Pacific warm pool. Some global repercussions nevertheless are analogous, such as a hemispherically symmetric atmospheric wave pattern of alternating highs and lows. Centennial variability in western equatorial Pacific SST is a result of the strong asymmetry of interannual ocean heat content anomalies, while the eastern equatorial Pacific exhibits a lagged, Bjerknes-like response to temperature and convection in the west. The extratropical counterpart is shown to be a flux-driven response to the hemispherically symmetric circulation anomalies emanating from the tropical Pacific. Significant centennial-length trends in the zonal SST and SLP gradients rivaling those estimated from observations and model simulations forced with increasing CO2 appear to be inherent features of the internal climate dynamics simulated by all three models. Unforced variability and trends on the centennial time scale therefore need to be addressed in estimated uncertainties, beyond more traditional signal-to-noise estimates that do not account for natural variability on the centennial time scale.

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Correlative Evolutions of ENSO and the Seasonal Cycle in the Tropical Pacific Ocean

Journal of the Atmospheric Sciences ◽

10.1175/2008jas2573.1 ◽

2009 ◽

Vol 66 (4) ◽

pp. 1041-1049 ◽

Cited By ~ 5

Author(s):

Heng Xiao ◽

Carlos R. Mechoso

Keyword(s):

Pacific Ocean ◽

Seasonal Cycle ◽

General Circulation ◽

Tropical Pacific ◽

Tropical Pacific Ocean ◽

Mean Flow ◽

Data Set ◽

Enso Variability ◽

Equatorial Wave ◽

The Tropical Pacific

Abstract This study examines whether shifts between the correlative evolutions of ENSO and the seasonal cycle in the tropical Pacific Ocean can produce effects that are large enough to alter the evolution of the coupled atmosphere–ocean system. The approach is based on experiments with an ocean general circulation model (OGCM) of the Pacific basin, in which the seasonal and nonseasonal (interannually varying) components of the surface forcing are prescribed with different shifts in time. The shift would make no difference in terms of ENSO variability if the system were linear. The surface fluxes of heat and momentum used to force the ocean are taken from 1) simulations in which the OGCM coupled to an atmospheric GCM produces realistic ENSO variability and 2) NCEP reanalysis data corrected by Comprehensive Ocean–Atmosphere Data Set climatology for the 20-yr period 1980–99. It is found that the response to the shifts in terms of eastern basin heat content can be 20%–40% of the maximum interannual anomaly in the first experiment, whereas it is 10%–20% in the second experiment. In addition, the response to the shift is event dependent. A response of this magnitude can potentially generate coupled atmosphere–ocean interactions that alter subsequent event evolution. Analysis of a selected event shows that the major contribution to the response is provided by the anomalous zonal advection of seasonal mean temperature in the equatorial band. Additional OGCM experiments suggest that both directly forced and delayed signals provide comparable contributions to the response. An interpretation of the results based on the “delayed oscillator” paradigm and on equatorial wave–mean flow interaction is given. It is argued that the same oceanic ENSO anomalies in different times of the oceanic seasonal cycle can result in different ENSO evolutions because of nonlinear interactions between equatorially trapped waves at work during ENSO and the seasonally varying upper-ocean currents and thermocline structure.

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The Predictability of Tropical Pacific Decadal Variability: Insights from Attractor Reconstruction

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-18-0114.1 ◽

2019 ◽

Vol 76 (3) ◽

pp. 801-819 ◽

Cited By ~ 1

Author(s):

Nandini Ramesh ◽

Mark A. Cane

Keyword(s):

General Circulation ◽

Decadal Variability ◽

General Circulation Models ◽

Tropical Pacific ◽

The Other ◽

Intermediate Complexity ◽

Pacific Decadal Variability ◽

Attractor Reconstruction ◽

Climatic Impacts ◽

The Tropical Pacific

Abstract Tropical Pacific decadal variability (TPDV), though not the totality of Pacific decadal variability, has wide-ranging climatic impacts. It is currently unclear whether this phenomenon is predictable. In this study, we reconstruct the attractor of the tropical Pacific system in long, unforced simulations from an intermediate-complexity model, two general circulation models (GCMs), and the observations with the aim of assessing the predictability of TPDV in these systems. We find that in the intermediate-complexity model, positive (high variance, El Niño–like) and negative (low variance, La Niña–like) phases of TPDV emerge as a pair of regime-like states. The observed system bears resemblance to this behavior, as does one GCM, while the other GCM does not display this structure. However, these last three time series are too short to confidently characterize the full distribution of interdecadal variability. The intermediate-complexity model is shown to lie in highly predictable parts of its attractor 37% of the time, during which most transitions between TPDV regimes occur. The similarities between the observations and this system suggest that the tropical Pacific may be somewhat predictable on interdecadal time scales.

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The seasonal cycle in coupled ocean-atmosphere general circulation models

Climate Dynamics ◽

10.1007/s003820000081 ◽

2000 ◽

Vol 16 (10-11) ◽

pp. 775-787 ◽

Cited By ~ 37

Author(s):

C. Covey ◽

A. Abe-Ouchi ◽

G. J. Boer ◽

B. A. Boville ◽

U. Cubasch ◽

...

Keyword(s):

Seasonal Cycle ◽

General Circulation ◽

General Circulation Models ◽

Ocean Atmosphere

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The Tropical Pacific ENSO–Mean State Relationship in Climate Models over the Last Millennium

Journal of Climate ◽

10.1175/jcli-d-19-0673.1 ◽

2020 ◽

Vol 33 (17) ◽

pp. 7539-7551

Author(s):

D. Allie Wyman ◽

Jessica. L. Conroy ◽

Christina Karamperidou

Keyword(s):

General Circulation ◽

Climate Models ◽

Global Climate ◽

General Circulation Models ◽

Tropical Pacific ◽

Last Millennium ◽

Climate Simulations ◽

Intercomparison Project ◽

The Relationship ◽

The Tropical Pacific

AbstractENSO and the mean zonal sea surface temperature gradient (dSST) of the tropical Pacific are important drivers of global climate and vary on decadal to centennial time scales. However, the relationship between dSST and ENSO cannot be assessed with the short instrumental record, and is uncertain in proxy data, with intervals of both stronger and weaker ENSO postulated to occur with overall strong dSST in the past. Here we assess the ENSO–dSST relationship during the last millennium using general circulation models (GCMs) participating in phase 3 of the Paleoclimate Modeling Intercomparison Project. Last millennium GCM simulations show diversity in the strength and direction of the ENSO–dSST relationship. Yet, the models that best simulate modern tropical Pacific climate frequently have a more negative ENSO–dSST correlation. Thus, last millennium tropical Pacific climate simulations support the likelihood of enhanced ENSO during decadal to centennial periods of reduced tropical Pacific dSST. However, the alternating directional ENSO–dSST relationship in all model simulations suggests that this relationship is not constant through time and is likely controlled by multiple mechanisms.

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