scholarly journals How Much Energy Is Transferred from the Winds to the Thermocline on ENSO Time Scales?

2010 ◽  
Vol 23 (6) ◽  
pp. 1563-1580 ◽  
Author(s):  
Jaclyn N. Brown ◽  
Alexey V. Fedorov
Keyword(s):  
Potential Energy ◽  
Wind Power ◽  
El Niño ◽  
General Circulation ◽  
El Nino ◽  
General Circulation Models ◽  
Tropical Ocean ◽  
Available Potential Energy ◽  
Enso Events ◽  
Damping Rate

Abstract The dynamics of El Niño–Southern Oscillation (ENSO) are studied in terms of the balance between energy input from the winds (via wind power) and changes in the storage of available potential energy in the tropical ocean. Presently, there are broad differences in the way global general circulation models simulate the dynamics, magnitude, and phase of ENSO events; hence, there is a need for simple, physically based metrics to allow for model evaluation. This energy description is a basinwide, integral, quantitative approach, ideal for intermodel comparison, that assesses model behavior in the subsurface ocean. Here it is applied to a range of ocean models and data assimilations within ENSO spatial and temporal scales. The onset of an El Niño is characterized by a decrease in wind power that leads to a decrease in available potential energy, and hence a flatter thermocline. In contrast, La Niña events are preceded by an increase in wind power that leads to an increase in the available potential energy and a steeper thermocline. The wind power alters the available potential energy via buoyancy power, associated with vertical mass fluxes that modify the slope of the isopycnals. Only a fraction of wind power is converted to buoyancy power. The efficiency of this conversion γ is estimated in this study at 50%–60%. Once the energy is delivered to the thermocline it is subject to small, but important, diffusive dissipation. It is estimated that this dissipation sets the e-folding damping rate α for the available potential energy on the order of 1 yr−1. The authors propose to use the efficiency γ and the damping rate α as two energy-based metrics for evaluating dissipative properties of the ocean component of general circulation models, providing a simple method for understanding subsurface ENSO dynamics and a diagnostic tool for exploring differences between the models.

scholarly journals 2015 Bernhard Haurwitz Memorial Lecture: Model Diagnosis of El Niño Teleconnections to the Global Atmosphere–Ocean System

2016 ◽  
Vol 97 (6) ◽  
pp. 981-988 ◽  
Author(s):  
Ngar-Cheung Lau
Keyword(s):  
El Niño ◽  
General Circulation ◽  
El Nino ◽  
Southern Oscillation ◽  
World Ocean ◽  
General Circulation Models ◽  
Memorial Lecture ◽  
Geophysical Fluid Dynamics Laboratory ◽  
Enso Events ◽  
The World

Abstract The El Niño–Southern Oscillation (ENSO) phenomenon is one of the most prominent modes of atmospheric and oceanic variability on interannual and interdecadal time scales. The essential ENSO signals originate from the tropical Pacific (TP). However, the impacts of ENSO are felt in many other parts of the world. Major ENSO events are accompanied by notable changes in the extratropical atmospheric circulation in both hemispheres, various monsoon systems located beyond the TP, global air temperature and precipitation patterns, and the sea surface temperature (SST) distribution throughout the World Ocean. During the past several decades, this author has participated in a sustained effort to study the processes contributing to these “teleconnections” between ENSO forcing in the TP and variations in the atmosphere–ocean system elsewhere. These investigations are based on a large suite of experiments with several generations of general circulation models (GCMs) at the Geophysical Fluid Dynamics Laboratory (GFDL). These experiments are specifically designed to reveal various facets of the teleconnections with ENSO. In this lecture, a summary is given of the principal findings of this series of model studies. An account is given of the train of thought underpinning the sequence of experiments described herein, so as to illustrate how certain experimental setups have been motivated by the problem or hypothesis at hand.

scholarly journals The relationship between intraseasonal tropical variability and ENSO and its modulation at seasonal to decadal timescales

2011 ◽  
Vol 3 (2) ◽  
Author(s):  
Daria Gushchina ◽  
Boris Dewitte
Keyword(s):  
El Niño ◽  
General Circulation ◽  
Rossby Waves ◽  
El Nino ◽  
General Circulation Models ◽  
Wave Radiation ◽  
Boreal Summer ◽  
Central Pacific ◽  
Tropical Variability ◽  
Intraseasonal Tropical Variability

AbstractThe intraseasonal tropical variability (ITV) patterns in the tropical troposphere are documented using double space-time Fourier analysis. Madden and Julian oscillations (MJO) as well as equatorial coupled waves (Kelvin and Rossby) are investigated based on the NCEP/NCAR Reanalysis data for the 1977–2006 period and the outputs of an intermediate ocean-atmosphere coupled model named LODCA-OTCM. A strong seasonal dependence of the ITV/ENSO relationship is evidenced. The leading relationship for equatorial Rossby waves (with the correlation of the same order than for the MJO) is documented; namely, it is shown that intensification of Rossby waves in the central Pacific during boreal summer precedes by half a year the peak of El Niño. The fact that MJO activity in spring-summer is associated to the strength of subsequent El Niño is confirmed. It is shown that LODCA-QTCM is capable of simulating the convectively coupled equatorial waves in outgoing long wave radiation and zonal wind at 850 hPa fields with skill comparable to other Coupled General Circulation Models. The ITV/ENSO relationship is modulated at low frequency. In particular the periods of low ENSO amplitude are associated with weaker MJO activity and a cancellation of MJO at the ENSO development phase. In opposition, during the decaying phase, MJO signal is strong. The periods of strong ENSO activity are associated with a marked coupling between MJO, Kelvin and equatorially Rossby waves and ENSO; the precursor signal of MJO (Rossby waves) in the western (central) Pacific is obvious. The results provide material for the observed change in ENSO characteristics in recent years and question whether the characteristics of the ITV/ENSO relationship may be sensitive to the observed warming in the central tropical Pacific.

scholarly journals Extended ENSO Predictions Using a Fully Coupled Ocean–Atmosphere Model

2008 ◽  
Vol 21 (1) ◽  
pp. 84-93 ◽  
Author(s):  
Jing-Jia Luo ◽  
Sebastien Masson ◽  
Swadhin K. Behera ◽  
Toshio Yamagata
Keyword(s):  
El Niño ◽  
General Circulation ◽  
El Nino ◽  
Southern Oscillation ◽  
Global Ocean ◽  
Enso Events ◽  
The Past ◽  
Ocean Atmosphere ◽  
First Time ◽  
Fully Coupled

Abstract Using a fully coupled global ocean–atmosphere general circulation model assimilating only sea surface temperature, the authors found for the first time that several El Niño–Southern Oscillation (ENSO) events over the past two decades can be predicted at lead times of up to 2 yr. The El Niño condition in the 1997/98 winter can be predicted to some extent up to about a 1½-yr lead but with a weak intensity and large phase delay in the prediction of the onset of this exceptionally strong event. This is attributed to the influence of active and intensive stochastic westerly wind bursts during late 1996 to mid-1997, which are generally unpredictable at seasonal time scales. The cold signals in the 1984/85 and 1999/2000 winters during the peak phases of the past two long-lasting La Niña events are predicted well up to a 2-yr lead. Amazingly, the mild El Niño–like event of 2002/03 is also predicted well up to a 2-yr lead, suggesting a link between the prolonged El Niño and the tropical Pacific decadal variability. Seasonal climate anomalies over vast parts of the globe during specific ENSO years are also realistically predicted up to a 2-yr lead for the first time.

Interannual oscillations in an ocean general circulation model coupled to a simple atmosphere model

1989 ◽  
Vol 329 (1604) ◽  
pp. 189-205 ◽  
Keyword(s):  
El Niño ◽  
General Circulation ◽  
El Nino ◽  
Southern Oscillation ◽  
Circulation Model ◽  
Coupled System ◽  
General Circulation Models ◽  
Atmospheric Model ◽  
Ocean General Circulation Model ◽  
Coupled Oscillations

A model is being developed for tropical air-sea interaction studies that is intermediate in complexity between the large coupled general circulation models (GCMS) that are coming into use, and the simple two-level models with which pioneering El Nino Southern Oscillation studies were done. The model consists of a stripped-down tropical Pacific Ocean GCM, coupled to an atmospheric model that is sufficiently simple that steady-state solutions may be found for low-level flow and surface stress, given oceanic boundary conditions. This permits examination of the nature of interannual coupled oscillations in the absence of atmospheric noise. In preliminary tests of the model the coupled system is found to undergo a Hopf bifurcation as certain parameters are varied, giving rise to sustained three to four year oscillations. For stronger coupling, a secondary bifurcation yields six month coupled oscillations during the warm phase of the El Nino-period oscillation. Such variability could potentially affect the predictability of the coupled system.

scholarly journals Understanding El Niño in Ocean–Atmosphere General Circulation Models: Progress and Challenges

2009 ◽  
Vol 90 (3) ◽  
pp. 325-340 ◽  
Author(s):  
Eric Guilyardi ◽  
Andrew Wittenberg ◽  
Alexey Fedorov ◽  
Mat Collins ◽  
Chunzai Wang ◽  
...  
Keyword(s):  
El Niño ◽  
General Circulation ◽  
El Nino ◽  
General Circulation Models ◽  
Ocean Atmosphere

scholarly journals Extratropical Influences on the El Niño–Southern Oscillation through the Late Quaternary

2007 ◽  
Vol 20 (5) ◽  
pp. 788-800 ◽  
Author(s):  
Andrew B. G. Bush
Keyword(s):  
El Niño ◽  
General Circulation ◽  
El Nino ◽  
Southern Oscillation ◽  
Late Quaternary ◽  
Circulation Model ◽  
Linear Stability Theory ◽  
El Niño Southern Oscillation ◽  
El Nino Southern Oscillation ◽  
Enso Events

Abstract A sequence of numerical simulations with a coupled atmosphere–ocean general circulation model configured for particular times during the late Quaternary shows that simulated El Niño–Southern Oscillation (ENSO) events decrease in frequency from the Last Glacial Maximum (LGM) to today, in accord with linear stability theory, but increase in amplitude. Diagnostic analyses indicate that altered momentum fluxes from midlatitude eddy activity caused by changes in orbital forcing (in the Holocene) and topographic forcing (at the LGM) regulate the strength of climatological easterlies and therefore affect both the tropical mean state and the characteristics of interannual variability. The fact that climatic teleconnections associated with paleo-ENSO are fundamentally different during these times suggests a way in which to reconcile some of the existing discrepancies amongst interpretations of proxy records and numerical paleoclimate simulations.

scholarly journals Modulation of the Relationship between ENSO and Its Combination Mode by the Atlantic Multidecadal Oscillation

2020 ◽  
Vol 33 (11) ◽  
pp. 4679-4695 ◽  
Author(s):  
Xin Geng ◽  
Wenjun Zhang ◽  
Fei-Fei Jin ◽  
Malte F. Stuecker ◽  
Aaron F. Z. Levine
Keyword(s):  
El Niño ◽  
General Circulation ◽  
El Nino ◽  
Southern Oscillation ◽  
Circulation Model ◽  
Atlantic Multidecadal Oscillation ◽  
Climate Impacts ◽  
Enso Events ◽  
Combination Mode ◽  
The Relationship

AbstractRecent studies demonstrated the existence of a conspicuous atmospheric combination mode (C-mode) originating from nonlinear interactions between El Niño–Southern Oscillation (ENSO) and the Pacific warm pool annual cycle (AC). Here we find that the C-mode exhibits prominent decadal amplitude variations during the ENSO decaying boreal spring season. It is revealed that the Atlantic multidecadal oscillation (AMO) can largely explain this waxing and waning in amplitude. A robust positive correlation between ENSO and the C-mode is detected during a negative AMO phase but not during a positive phase. Similar results can also be found in the relationship of ENSO with 1) the western North Pacific (WNP) anticyclone and 2) spring precipitation over southern China, both of which are closely associated with the C-mode. We suggest that ENSO property changes due to an AMO modulation play a crucial role in determining these decadal shifts. During a positive AMO phase, ENSO events are distinctly weaker than those in an AMO negative phase. In addition, El Niño events concurrent with a positive AMO phase tend to exhibit a westward-shifted sea surface temperature (SST) anomaly pattern. These SST characteristics during the positive AMO phase are both not conducive to the development of the meridionally asymmetric C-mode atmospheric circulation pattern and thus reduce the ENSO/C-mode correlation on decadal time scales. These observations can be realistically reproduced by a coupled general circulation model (CGCM) experiment in which North Atlantic SSTs are nudged to reproduce a 50-yr sinusoidally varying AMO evolution. Our conclusion carries important implications for understanding seasonally modulated ENSO dynamics and multiscale climate impacts over East Asia.

scholarly journals Representing El Niño in Coupled Ocean–Atmosphere GCMs: The Dominant Role of the Atmospheric Component

2004 ◽  
Vol 17 (24) ◽  
pp. 4623-4629 ◽  
Author(s):  
E. Guilyardi ◽  
S. Gualdi ◽  
J. Slingo ◽  
A. Navarra ◽  
P. Delecluse ◽  
...  
Keyword(s):  
El Niño ◽  
General Circulation ◽  
State Of The Art ◽  
El Nino ◽  
Dominant Role ◽  
Power Spectra ◽  
General Circulation Models ◽  
Coupled Models ◽  
Model Improvement

Abstract A systematic modular approach to investigate the respective roles of the ocean and atmosphere in setting El Niño characteristics in coupled general circulation models is presented. Several state-of-the-art coupled models sharing either the same atmosphere or the same ocean are compared. Major results include 1) the dominant role of the atmosphere model in setting El Niño characteristics (periodicity and base amplitude) and errors (regularity) and 2) the considerable improvement of simulated El Niño power spectra—toward lower frequency—when the atmosphere resolution is significantly increased. Likely reasons for such behavior are briefly discussed. It is argued that this new modular strategy represents a generic approach to identifying the source of both coupled mechanisms and model error and will provide a methodology for guiding model improvement.

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