An Assessment of Differences in ENSO Mechanisms in a Coupled GCM Simulation

2006 ◽  
Vol 19 (1) ◽  
pp. 69-87 ◽  
Author(s):  
Francisco Alvarez-Garcia ◽  
William Cabos Narvaez ◽  
Maria J. Ortiz Bevia
Keyword(s):  
Local Development ◽  
Southern Oscillation ◽  
Heat Content ◽  
Propagation Characteristic ◽  
Tropical Pacific ◽  
Wind Stress Curl ◽  
Coupled Gcm ◽  
Physical Mechanisms ◽  
Cold Events ◽  
The Tropical Pacific

Abstract This study investigates the physical mechanisms involved in the generation and decay of El Niño–Southern Oscillation episodes in a coupled GCM simulation. Warm and cold events found in a 100-yr-long record are separated into groups by means of a clustering technique that objectively discriminates common features in the evolution of the tropical Pacific heat content anomalies leading to the event’s peak. Through an analysis of the composites obtained from this classification, insight is gained as to the processes responsible for the presence of different behaviors. Three classes of warm events were identified. The first is characterized by the westward propagation of warm heat content anomalies north of the equator before the onset of the episode. This propagation characteristic of the delayed oscillator paradigm appears weakened in the decay of the episode. In the second class, local development of heat content anomalies in the northwest tropical Pacific, associated with overlying wind stress curl anomalies, dominates both the generation and the decay of the warm event. In addition, subsurface cold anomalies form in the equatorial western Pacific in association with the poleward flow considered by the recharge–discharge oscillator model. The third class is characterized by a relatively quick development of the warm episode. Attention is focused on the first two classes. The suitability of different conceptual models to explain them is addressed. Previous analyses of the simulation are reviewed throughout this work. Differences between the classes are related to a regime shift that occurs toward the middle of the record.

scholarly journals Improving statistical prediction and revealing nonlinearity of ENSO using observations of ocean heat content in the tropical Pacific

2021 ◽  
Author(s):  
Aleksei Seleznev ◽  
Dmitry Mukhin
Keyword(s):  
Southern Oscillation ◽  
Nonlinear Models ◽  
Heat Content ◽  
Optimization Method ◽  
Tropical Pacific ◽  
Ocean Heat Content ◽  
Bayesian Optimization ◽  
Statistical Prediction ◽  
Seasonal Predictability ◽  
The Tropical Pacific

Abstract It is well-known that the upper ocean heat content (OHC) variability in the tropical Pacific contains valuable information about dynamics of El Niño–Southern Oscillation (ENSO). Here we combine sea surface temperature (SST) and OHC indices derived from the gridded datasets to construct a phase space for data-driven ENSO models. Using a Bayesian optimization method, we construct linear as well as nonlinear models for these indices. We find that the joint SST-OHC optimal models yield significant benefits in predicting both the SST and OHC as compared with the separate SST or OHC models. It is shown that these models substantially reduces seasonal predictability barriers in each variable – the spring barrier in the SST index and the winter barrier in the OHC index. We also reveal the significant nonlinear relationships between the ENSO variables manifesting on interannual scales, which opens prospects for improving yearly ENSO forecasting.

scholarly journals A Pacific Centennial Oscillation Predicted by Coupled GCMs*

2012 ◽  
Vol 25 (17) ◽  
pp. 5943-5961 ◽  
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.

scholarly journals Impact of global warming on ENSO phase change

2006 ◽  
Vol 6 ◽  
pp. 103-110 ◽  
Author(s):  
W. Cabos Narvaez ◽  
F. Alvarez-Garcia ◽  
M. J. OrtizBeviá
Keyword(s):  
Global Warming ◽  
Phase Change ◽  
Heat Content ◽  
Tropical Pacific ◽  
Common Features ◽  
Clustering Technique ◽  
Physical Mechanisms ◽  
Enso Events ◽  
Ocean Atmosphere ◽  
The Tropical Pacific

Abstract. We compare the physical mechanisms involved in the generation and decay of ENSO events in a control (present day conditions) and Scenario (Is92a, IPCC 1996) simulations performed with the coupled ocean-atmosphere GCM ECHAM4-OPYC3. A clustering technique which objectively discriminates common features in the evolution of the Tropical Pacific Heat Content anomalies leading to the peak of ENSO events allows us to group into a few classes the ENSO events occurring in 240 years of data in the control and scenario runs. In both simulations, the composites of the groups show differences in the generation and development of ENSO. We present the changes in the statistics of the groups and explore the possible mechanisms involved.

On the Energy Exchange between Tropical Ocean Basins Related to ENSO*

2014 ◽  
Vol 27 (17) ◽  
pp. 6393-6403 ◽  
Author(s):  
Michael Mayer ◽  
Leopold Haimberger ◽  
Magdalena A. Balmaseda
Keyword(s):  
El Niño ◽  
Energy Transport ◽  
El Nino ◽  
Southern Oscillation ◽  
Heat Content ◽  
Tropical Pacific ◽  
Surface Fluxes ◽  
Energy Budgets ◽  
Tropical Ocean ◽  
The Tropical Pacific

Abstract Vast amounts of energy are exchanged between the ocean, atmosphere, and space in association with El Niño–Southern Oscillation (ENSO). This study examines energy budgets of all tropical (30°S–30°N) ocean basins and the atmosphere separately using different, largely independent oceanic and atmospheric reanalyses to depict anomalous energy flows associated with ENSO in a consistent framework. It is found that variability of area-averaged ocean heat content (OHC) in the tropical Pacific to a large extent is modulated by energy flow through the ocean surface. While redistribution of OHC within the tropical Pacific is an integral part of ENSO dynamics, variability of ocean heat transport out of the tropical Pacific region is found to be mostly small. Noteworthy contributions arise from the Indonesian Throughflow (ITF), which is anticorrelated with ENSO at a few months lag, and from anomalous oceanic poleward heat export during the La Niña events in 1999 and 2008. Regression analysis reveals that atmospheric energy transport and radiation at the top of the atmosphere (RadTOA) almost perfectly balance the OHC changes and ITF variability associated with ENSO. Only a small fraction of El Niño–related heat lost by the Pacific Ocean through anomalous air–sea fluxes is radiated to space immediately, whereas the major part of the energy is transported away by the atmosphere. Ample changes in tropical atmospheric circulation lead to enhanced surface fluxes and, consequently, to an increase of OHC in the tropical Atlantic and Indian Ocean that almost fully compensates for tropical Pacific OHC loss. This signature of energy redistribution is robust across the employed datasets for all three tropical ocean basins and explains the small ENSO signal in global mean RadTOA.

scholarly journals What Controls the Duration of El Niño and La Niña Events?

2019 ◽  
Vol 32 (18) ◽  
pp. 5941-5965 ◽  
Author(s):  
Xian Wu ◽  
Yuko M. Okumura ◽  
Pedro N. DiNezio
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Surface Wind ◽  
Heat Content ◽  
Tropical Pacific ◽  
La Niña ◽  
Tropical Atlantic ◽  
La Nina ◽  
The Tropical Pacific

Abstract The temporal evolution of El Niño and La Niña varies greatly from event to event. To understand the dynamical processes controlling the duration of El Niño and La Niña events, a suite of observational data and a long control simulation of the Community Earth System Model, version 1, are analyzed. Both observational and model analyses show that the duration of El Niño is strongly affected by the timing of onset. El Niño events that develop early tend to terminate quickly after the mature phase because of the early arrival of delayed negative oceanic feedback and fast adjustments of the tropical Atlantic and Indian Oceans to the tropical Pacific Ocean warming. The duration of La Niña events is, on the other hand, strongly influenced by the amplitude of preceding warm events. La Niña events preceded by a strong warm event tend to persist into the second year because of large initial discharge of the equatorial oceanic heat content and delayed adjustments of the tropical Atlantic and Indian Oceans to the tropical Pacific cooling. For both El Niño and La Niña, the interbasin sea surface temperature (SST) adjustments reduce the anomalous SST gradient toward the tropical Pacific and weaken surface wind anomalies over the western equatorial Pacific, hastening the event termination. Other factors external to the dynamics of El Niño–Southern Oscillation, such as coupled variability in the tropical Atlantic and Indian Oceans and atmospheric variability over the North Pacific, also contribute to the diversity of event duration.

scholarly journals Integrating Ocean Subsurface Temperatures in Statistical ENSO Forecasts

2005 ◽  
Vol 18 (17) ◽  
pp. 3571-3586 ◽  
Author(s):  
Jose Eric Ruiz ◽  
Ian Cordery ◽  
Ashish Sharma
Keyword(s):  
Southern Oscillation ◽  
Heat Content ◽  
Enso Event ◽  
Empirical Orthogonal Functions ◽  
Boreal Winter ◽  
Orthogonal Functions ◽  
Subsurface Ocean ◽  
Prediction Scheme ◽  
Cold Events ◽  
The Tropical Pacific

Abstract Subsurface characteristics of oceans have recently become of interest to climate modelers. Here subsurface information has been linked to the evolution of the El Niño–Southern Oscillation (ENSO) in a simple statistical formulation. The hypothesis proposed is that the inclusion of subsurface ocean heat content in a persistence-based representation of ENSO results in an increase in prediction skill. The subsurface temperature field is represented by anomalies in the 20°C isotherm (Z20) in the Indian and Pacific Oceans. Using a cross-validation approach, the first two empirical orthogonal functions (EOFs) of the Z20 anomalies are derived, but only the second EOF is used as a predictor. The first EOF is found to be representative of the mature ENSO signal while the second EOF shows characteristics that are precursory to an ENSO event. When included in a persistence-based prediction scheme, the second EOF enhances the skill of ENSO hindcasts up to a lead time of 15 months. Results are compared with another model that uses the second EOF of the SST anomalies in the tropical Pacific Ocean and persistence as predictors. Cross-validated hindcasts from the isotherm-based scheme are generally more skillful than those obtained from the persistence and SST-based prediction schemes. Hindcasts of cold events are particularly close to the observed values even at long lags. Major improvements occur for predictions made during boreal winter and spring months when the addition of subsurface information resulted in predictions that are not greatly affected by the damping effect of the “spring barrier.”

Successive Modulation of ENSO to the Future Greenhouse Warming

2008 ◽  
Vol 21 (1) ◽  
pp. 3-21 ◽  
Author(s):  
Soon-Il An ◽  
Jong-Seong Kug ◽  
Yoo-Geun Ham ◽  
In-Sik Kang
Keyword(s):  
General Circulation ◽  
Southern Oscillation ◽  
General Circulation Models ◽  
Tropical Pacific ◽  
Greenhouse Warming ◽  
Delayed Response ◽  
Subsurface Temperature ◽  
Climate System Model ◽  
The Mean ◽  
The Tropical Pacific

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.

scholarly journals Indian Ocean impact on ENSO evolution 2014–2016 in a set of seasonal forecasting experiments

2021 ◽  
Author(s):  
Michael Mayer ◽  
Magdalena Alonso Balmaseda
Keyword(s):  
Pacific Ocean ◽  
Indian Ocean ◽  
El Niño ◽  
Initial Conditions ◽  
El Nino ◽  
Southern Oscillation ◽  
Heat Content ◽  
Tropical Pacific ◽  
Decadal Variations ◽  
The Indian Ocean

AbstractThis study investigates the influence of the anomalously warm Indian Ocean state on the unprecedentedly weak Indonesian Throughflow (ITF) and the unexpected evolution of El Niño-Southern Oscillation (ENSO) during 2014–2016. It uses 25-month-long coupled twin forecast experiments with modified Indian Ocean initial conditions sampling observed decadal variations. An unperturbed experiment initialized in Feb 2014 forecasts moderately warm ENSO conditions in year 1 and year 2 and an anomalously weak ITF throughout, which acts to keep tropical Pacific ocean heat content (OHC) anomalously high. Changing only the Indian Ocean to cooler 1997 conditions substantially alters the 2-year forecast of Tropical Pacific conditions. Differences include (i) increased probability of strong El Niño in 2014 and La Niña in 2015, (ii) significantly increased ITF transports and (iii), as a consequence, stronger Pacific ocean heat divergence and thus a reduction of Pacific OHC over the two years. The Indian Ocean’s impact in year 1 is via the atmospheric bridge arising from altered Indian Ocean Dipole conditions. Effects of altered ITF and associated ocean heat divergence (oceanic tunnel) become apparent by year 2, including modified ENSO probabilities and Tropical Pacific OHC. A mirrored twin experiment starting from unperturbed 1997 conditions and several sensitivity experiments corroborate these findings. This work demonstrates the importance of the Indian Ocean’s decadal variations on ENSO and highlights the previously underappreciated role of the oceanic tunnel. Results also indicate that, given the physical links between year-to-year ENSO variations, 2-year-long forecasts can provide additional guidance for interpretation of forecasted year-1 ENSO probabilities.

scholarly journals Skillful prediction of tropical Pacific fisheries provided by Atlantic Niños

2021 ◽  
Author(s):  
Iñigo Gómara ◽  
Belén Rodríguez-Fonseca ◽  
Elsa Mohino ◽  
Teresa Losada ◽  
Irene Polo ◽  
...  
Keyword(s):  
Large Scale ◽  
Southern Oscillation ◽  
Marine Ecosystem ◽  
Ecosystem Model ◽  
Tropical Pacific ◽  
Equatorial Atlantic ◽  
Climate Conditions ◽  
Marine Food Web ◽  
Marine Ecosystem Model ◽  
The Tropical Pacific

AbstractTropical Pacific upwelling-dependent ecosystems are the most productive and variable worldwide, mainly due to the influence of El Niño Southern Oscillation (ENSO). ENSO can be forecasted seasons ahead thanks to assorted climate precursors (local-Pacific processes, pantropical interactions). However, owing to observational data scarcity and bias-related issues in earth system models, little is known about the importance of these precursors for marine ecosystem prediction. With recently released reanalysis-nudged global marine ecosystem simulations, these constraints can be sidestepped, allowing full examination of tropical Pacific ecosystem predictability. By complementing historical fishing records with marine ecosystem model data, we show herein that equatorial Atlantic Sea Surface Temperatures (SSTs) constitute a superlative predictability source for tropical Pacific marine yields, which can be forecasted over large-scale areas up to 2 years in advance. A detailed physical-biological mechanism is proposed whereby Atlantic SSTs modulate upwelling of nutrient-rich waters in the tropical Pacific, leading to a bottom-up propagation of the climate-related signal across the marine food web. Our results represent historical and near-future climate conditions and provide a useful springboard for implementing a marine ecosystem prediction system in the tropical Pacific.

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