Impact of the stratosphere on El Niño-Southern Oscillation

2020 ◽  
Author(s):  
Mario Rodrigo ◽  
Javier Garcia-Serrano ◽  
Ileana Bladé ◽  
Froila M. Palmeiro ◽  
Bianca Mezzina
Keyword(s):  
Radiative Forcing ◽  
Climate Models ◽  
Climate Model ◽  
Southern Oscillation ◽  
Active Role ◽  
Tropical Pacific ◽  
Boreal Summer ◽  
Enso Cycle ◽  
Vertical Resolution ◽  
The Tropical Pacific

<p>The European Consortium EC-EARTH climate model version 3.1 is used to assess the effects of a well-resolved stratosphere on the representation of El Niño-Southern Oscillation (ENSO). Three 100-year  long experiments with fixed radiative forcing representative of the present climate are compared: one with the top at 0.01hPa and 91 vertical levels (HIGH-TOP), another with the top at 5hPa and 62 vertical levels (LOW-TOP), and another high-top experiment with the stratosphere nudged to the climatology of HIGH-TOP from 10hPa upwards (NUDG). The differences in vertical resolution between HIGH-TOP and LOW-TOP start at around 100hPa. This study focuses on the canonical ENSO phenomenon, which is the most important source of variability and predictability on seasonal-to-interannual timescales.</p><p> </p><p>Preliminary results indicate that EC-EARTH realistically simulates the ENSO SST pattern in the tropical Pacific regardless of vertical resolution, although HIGH-TOP (LOW-TOP) overestimates (underestimates) the SST variability during boreal summer (winter). In both configurations, the SST tongue is narrower meridionally and slightly shifted towards the central-western Pacific compared to observations, a common bias of climate models. Resolving the stratosphere has a clear effect on the power spectrum of the Niño3.4 index: as compared to observations where there is a well-known frequency range of 2-7 years, HIGH-TOP and LOW-TOP have a prominent peak centered at 4-5 years but additionally both simulations display another peak, towards higher (~ 2yrs) and lower (~ 7yrs) frequencies, respectively. Another impact of including a well-resolved stratosphere is to systematically enhance the amplitude of the SST, wind and convective anomalies in the tropical Pacific throughout the entire ENSO cycle. Finally, similar differences are obtained when comparing HIGH-TOP and NUDG, suggesting an active role of the tropical stratospheric variability on ENSO.</p>

scholarly journals Seasonal Drought in the Greater Horn of Africa and Its Recent Increase during the March–May Long Rains

2014 ◽  
Vol 27 (21) ◽  
pp. 7953-7975 ◽  
Author(s):  
Bradfield Lyon
Keyword(s):  
Atmospheric Circulation ◽  
Climate Model ◽  
Southern Oscillation ◽  
Meteorological Drought ◽  
Tropical Pacific ◽  
Horn Of Africa ◽  
New Findings ◽  
Climate Model Simulations ◽  
Greater Horn Of Africa ◽  
The Tropical Pacific

Abstract This paper provides a review of atmospheric circulation and sea surface temperature (SST) conditions that are associated with meteorological drought on the seasonal time scale in the Greater Horn of Africa (the region 10°S–15°N, 30°–52°E). New findings regarding a post-1998 increase in drought frequency during the March–May (MAM) “long rains” are also reported. The period 1950–2010 is emphasized, although rainfall and SST data from 1901–2010 are used to place the recent long rains decline in a multidecadal context. For the latter case, climate model simulations and isolated basin SST experiments are also utilized. Climatologically, rainfall exhibits a unimodal June–August (JJA) maximum in west-central Ethiopia with a generally bimodal [MAM and October–December (OND) maxima] distribution in locations to the south and east. Emphasis will be on these three seasons. SST anomalies in the tropical Pacific and Indian Oceans show the strongest association with drought during OND in locations having a bimodal annual cycle, with weaker associations during MAM. The influence of the El Niño–Southern Oscillation (ENSO) phenomenon critically depends on its ability to affect SSTs outside the Pacific. Salient features of the anomalous atmospheric circulation during drought events in different locations and seasons are discussed. The post-1998 decline in the long rains is found to be driven strongly (although not necessarily exclusively) by natural multidecadal variability in the tropical Pacific rather than anthropogenic climate change. This conclusion is supported by observational analyses and climate model experiments, which are presented.

scholarly journals An Equatorial Ocean Bottleneck in Global Climate Models

2012 ◽  
Vol 25 (1) ◽  
pp. 343-349 ◽  
Author(s):  
Kristopher B. Karnauskas ◽  
Gregory C. Johnson ◽  
Raghu Murtugudde
Keyword(s):  
Ocean Circulation ◽  
Radiative Forcing ◽  
Climate Models ◽  
Global Climate ◽  
Critical Role ◽  
Tropical Pacific ◽  
Global Climate Models ◽  
Momentum Balance ◽  
Equatorial Ocean ◽  
The Tropical Pacific

Abstract The Equatorial Undercurrent (EUC) is a major component of the tropical Pacific Ocean circulation. EUC velocity in most global climate models is sluggish relative to observations. Insufficient ocean resolution slows the EUC in the eastern Pacific where nonlinear terms should dominate the zonal momentum balance. A slow EUC in the east creates a bottleneck for the EUC to the west. However, this bottleneck does not impair other major components of the tropical circulation, including upwelling and poleward transport. In most models, upwelling velocity and poleward transport divergence fall within directly estimated uncertainties. Both of these transports play a critical role in a theory for how the tropical Pacific may change under increased radiative forcing, that is, the ocean dynamical thermostat mechanism. These findings suggest that, in the mean, global climate models may not underrepresent the role of equatorial ocean circulation, nor perhaps bias the balance between competing mechanisms for how the tropical Pacific might change in the future. Implications for model improvement under higher resolution are also discussed.

scholarly journals Impact of Equatorial Atlantic Variability on ENSO Predictive Skill

2021 ◽  
Author(s):  
Eleftheria Exarchou ◽  
Pablo Ortega ◽  
Maria Belén Rodrıguez de Fonseca ◽  
Teresa Losada Doval ◽  
Irene Polo Sanchez ◽  
...  
Keyword(s):  
Climate Models ◽  
Southern Oscillation ◽  
Sensitivity Study ◽  
Tropical Pacific ◽  
Climate Impacts ◽  
Equatorial Atlantic ◽  
Predictive Capacity ◽  
Predictive Skill ◽  
The Impact ◽  
The Tropical Pacific

<p>El Niño–Southern Oscillation (ENSO) is a key mode of climate variability with worldwide climate impacts. Recent studies have highlighted the impact of other tropical oceans on its variability. In particular, observations have demonstrated that summer Atlantic Niños (Niñas) favor the development of Pacific Niñas (Niños) the following winter, but it is unclear how well climate models capture this teleconnection and its role in defining the seasonal predictive skill of ENSO. Here we use an ensemble of seasonal forecast systems to demonstrate that a better representation of equatorial Atlantic variability in summer and its lagged teleconnection mechanism with the Pacific relates to enhanced predictive capacity of autumn/winter ENSO. An additional sensitivity study further shows that correcting SST variability in equatorial Atlantic improves different aspects of forecast skill in the Tropical Pacific, boosting ENSO skill. This study thus emphasizes that new efforts to improve the representation of equatorial Atlantic variability, a region with long standing systematic model biases, can foster predictive skill in the region, the Tropical Pacific and beyond, through the global impacts of ENSO.</p>

scholarly journals El Niño in a changing climate: a multi-model study

Ocean Science ◽  
2005 ◽  
Vol 1 (2) ◽  
pp. 81-95 ◽  
Author(s):  
G. J. van Oldenborgh ◽  
S. Y. Philip ◽  
M Collins
Keyword(s):  
Standard Deviation ◽  
Pacific Ocean ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Tropical Pacific ◽  
Enso Cycle ◽  
Tropical Pacific Ocean ◽  
Enso Variability ◽  
The Tropical Pacific

Abstract. In many parts of the world, climate projections for the next century depend on potential changes in the properties of the El Niño - Southern Oscillation (ENSO). The current staus of these projections is assessed by examining a large set of climate model experiments prepared for the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Firstly, the patterns and time series of present-day ENSO-like model variability in the tropical Pacific Ocean are compared with that observed. Next, the strength of the coupled atmosphere-ocean feedback loops responsible for generating the ENSO cycle in the models are evaluated. Finally, we consider the projections of the models with, what we consider to be, the most realistic ENSO variability. Two of the models considered do not have interannual variability in the tropical Pacific Ocean. Three models show a very regular ENSO cycle due to a strong local wind feedback in the central Pacific and weak sea surface temperature (SST) damping. Six other models have a higher frequency ENSO cycle than observed due to a weak east Pacific upwelling feedback loop. One model has much stronger upwelling feedback than observed, and another one cannot be described simply by the analysis technique. The remaining six models have a reasonable balance of feedback mechanisms and in four of these the interannual mode also resembles the observed ENSO both spatially and temporally. Over the period 2051-2100 (under various scenarios) the most realistic six models show either no change in the mean state or a slight shift towards El Niño-like conditions with an amplitude at most a quarter of the present day interannual standard deviation. We see no statistically significant changes in amplitude of ENSO variability in the future, with changes in the standard deviation of a Southern Oscillation Index that are no larger than observed decadal variations. Uncertainties in the skewness of the variability are too large to make any statements about the future relative strength of El Niño and La Niña events. Based on this analysis of the multi-model ensemble, we expect very little influence of global warming on ENSO.

scholarly journals A CGCM Study on the Interaction between IOD and ENSO

2006 ◽  
Vol 19 (9) ◽  
pp. 1688-1705 ◽  
Author(s):  
Swadhin K. Behera ◽  
Jing Jia Luo ◽  
Sebastien Masson ◽  
Suryachandra A. Rao ◽  
Hirofumi Sakuma ◽  
...  
Keyword(s):  
Indian Ocean ◽  
General Circulation ◽  
Southern Oscillation ◽  
Walker Circulation ◽  
Tropical Pacific ◽  
Boreal Summer ◽  
Enso Variability ◽  
The Indian Ocean ◽  
Sst Anomalies ◽  
The Tropical Pacific

Abstract An atmosphere–ocean coupled general circulation model known as the Scale Interaction Experiment Frontier version 1 (SINTEX-F1) model is used to understand the intrinsic variability of the Indian Ocean dipole (IOD). In addition to a globally coupled control experiment, a Pacific decoupled noENSO experiment has been conducted. In the latter, the El Niño–Southern Oscillation (ENSO) variability is suppressed by decoupling the tropical Pacific Ocean from the atmosphere. The ocean–atmosphere conditions related to the IOD are realistically simulated by both experiments including the characteristic east–west dipole in SST anomalies. This demonstrates that the dipole mode in the Indian Ocean is mainly determined by intrinsic processes within the basin. In the EOF analysis of SST anomalies from the noENSO experiment, the IOD takes the dominant seat instead of the basinwide monopole mode. Even the coupled feedback among anomalies of upper-ocean heat content, SST, wind, and Walker circulation over the Indian Ocean is reproduced. As in the observation, IOD peaks in boreal fall for both model experiments. In the absence of ENSO variability the interannual IOD variability is dominantly biennial. The ENSO variability is found to affect the periodicity, strength, and formation processes of the IOD in years of co-occurrences. The amplitudes of SST anomalies in the western pole of co-occurring IODs are aided by dynamical and thermodynamical modifications related to the ENSO-induced wind variability. Anomalous latent heat flux and vertical heat convergence associated with the modified Walker circulation contribute to the alteration of western anomalies. It is found that 42% of IOD events affected by changes in the Walker circulation are related to the tropical Pacific variabilities including ENSO. The formation is delayed until boreal summer for those IODs, which otherwise form in boreal spring as in the noENSO experiment.

scholarly journals Impact of equatorial Atlantic variability on ENSO predictive skill

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Eleftheria Exarchou ◽  
Pablo Ortega ◽  
Belén Rodríguez-Fonseca ◽  
Teresa Losada ◽  
Irene Polo ◽  
...  
Keyword(s):  
Climate Models ◽  
Southern Oscillation ◽  
Sensitivity Study ◽  
Tropical Pacific ◽  
Climate Impacts ◽  
Equatorial Atlantic ◽  
Predictive Capacity ◽  
Predictive Skill ◽  
The Impact ◽  
The Tropical Pacific

AbstractEl Niño-Southern Oscillation (ENSO) is a key mode of climate variability with worldwide climate impacts. Recent studies have highlighted the impact of other tropical oceans on its variability. In particular, observations have demonstrated that summer Atlantic Niños (Niñas) favor the development of Pacific Niñas (Niños) the following winter, but it is unclear how well climate models capture this teleconnection and its role in defining the seasonal predictive skill of ENSO. Here we use an ensemble of seasonal forecast systems to demonstrate that a better representation of equatorial Atlantic variability in summer and its lagged teleconnection mechanism with the Pacific relates to enhanced predictive capacity of autumn/winter ENSO. An additional sensitivity study further shows that correcting SST variability in equatorial Atlantic improves different aspects of forecast skill in the Tropical Pacific, boosting ENSO skill. This study thus emphasizes that new efforts to improve the representation of equatorial Atlantic variability, a region with long standing systematic model biases, can foster predictive skill in the region, the Tropical Pacific and beyond, through the global impacts of ENSO.

scholarly journals Interactions between marine biota and ENSO: a conceptual model analysis

2011 ◽  
Vol 18 (1) ◽  
pp. 29-40 ◽  
Author(s):  
M. Heinemann ◽  
A. Timmermann ◽  
U. Feudel
Keyword(s):  
Southern Oscillation ◽  
Radiation Force ◽  
Ecosystem Model ◽  
Ocean Model ◽  
Tropical Pacific ◽  
Continuation Methods ◽  
Shortwave Radiation ◽  
Enso Cycle ◽  
Marine Biota ◽  
The Tropical Pacific

Abstract. We develop a conceptual coupled atmosphere-ocean-ecosystem model for the tropical Pacific to investigate the interaction between marine biota and the El Niño-Southern Oscillation (ENSO). Ocean and atmosphere are represented by a two-box model for the equatorial Pacific cold tongue and the warm pool, including a simplified mixed layer scheme. Marine biota are represented by a three-component (nutrient, phytoplankton, and zooplankton) ecosystem model. The atmosphere-ocean model exhibits an oscillatory state which qualitatively captures the main physics of ENSO. During an ENSO cycle, the variation of nutrient upwelling, and, to a small extent, the variation of photosynthetically available radiation force an ecosystem oscillation. The simplified ecosystem in turn, due to the effect of phytoplankton on the absorption of shortwave radiation in the water column, leads to (1) a warming of the tropical Pacific, (2) a reduction of the ENSO amplitude, and (3) a prolongation of the ENSO period. We qualitatively investigate these bio-physical coupling mechanisms using continuation methods. It is demonstrated that bio-physical coupling may play a considerable role in modulating ENSO variability.

scholarly journals Tropical Pacific Climate and Its Response to Global Warming in the Kiel Climate Model

2009 ◽  
Vol 22 (1) ◽  
pp. 71-92 ◽  
Author(s):  
W. Park ◽  
N. Keenlyside ◽  
M. Latif ◽  
A. Ströh ◽  
R. Redler ◽  
...  
Keyword(s):  
Global Warming ◽  
Climate Model ◽  
Southern Oscillation ◽  
Global Climate ◽  
Global Climate Model ◽  
Co2 Concentration ◽  
Tropical Pacific ◽  
Equatorial Pacific ◽  
Cold Bias ◽  
The Tropical Pacific

Abstract A new, non-flux-corrected, global climate model is introduced, the Kiel Climate Model (KCM), which will be used to study internal climate variability from interannual to millennial time scales and climate predictability of the first and second kind. The version described here is a coarse-resolution version that will be employed in extended-range integrations of several millennia. KCM’s performance in the tropical Pacific with respect to mean state, annual cycle, and El Niño–Southern Oscillation (ENSO) is described. Additionally, the tropical Pacific response to global warming is studied. Overall, climate drift in a multicentury control integration is small. However, KCM exhibits an equatorial cold bias at the surface of the order 1°C, while strong warm biases of several degrees are simulated in the eastern tropical Pacific on both sides off the equator, with maxima near the coasts. The annual and semiannual cycles are realistically simulated in the eastern and western equatorial Pacific, respectively. ENSO performance compares favorably to observations with respect to both amplitude and period. An ensemble of eight greenhouse warming simulations was performed, in which the CO2 concentration was increased by 1% yr−1 until doubling was reached, and stabilized thereafter. Warming of equatorial Pacific sea surface temperature (SST) is, to first order, zonally symmetric and leads to a sharpening of the thermocline. ENSO variability increases because of global warming: during the 30-yr period after CO2 doubling, the ensemble mean standard deviation of Niño-3 SST anomalies is increased by 26% relative to the control, and power in the ENSO band is almost doubled. The increased variability is due to both a strengthened (22%) thermocline feedback and an enhanced (52%) atmospheric sensitivity to SST; both are associated with changes in the basic state. Although variability increases in the mean, there is a large spread among ensemble members and hence a finite probability that in the “model world” no change in ENSO would be observed.

Climate model teleconnection patterns govern the Niño 3.4 response to early 19th century volcanism in coral-based data assimilation reconstructions

2020 ◽  
pp. 1-51
Author(s):  
Sara C. Sanchez ◽  
Gregory J. Hakim ◽  
Casey P. Saenger
Keyword(s):  
Data Assimilation ◽  
Radiative Forcing ◽  
Climate Model ◽  
Southern Oscillation ◽  
Low Frequency ◽  
Volcanic Eruptions ◽  
Tropical Pacific ◽  
Model Bias ◽  
Early 19Th Century ◽  
Paleoclimate Data

AbstractScientific understanding of low-frequency tropical Pacific variability, especially responses to perturbations in radiative forcing, suffers from short observational records, sparse proxy networks, and bias in model simulations. Here, we combine the strengths of proxies and models through coral-based paleoclimate data assimilation. We combine coral archives (δ18O, Sr/Ca) with the dynamics, spatial teleconnections, and intervariable relationships of the CMIP5/PMIP3 Past1000 experiments using the Last Millennium Reanalysis data assimilation framework. This analysis creates skillful reconstructions of tropical Pacific temperatures over the observational era. However, during the period of intense volcanism in the early 19th century, southwestern Pacific corals produce El Niño Southern Oscillation (ENSO) reconstructions that are of opposite sign from those from eastern Pacific corals and tree ring records. We systematically evaluate the source of this discrepancy using 1) single-proxy experiments, 2) varied proxy system models (PSMs), and 3) diverse covariance patterns from the Past1000 simulations. We find that individual proxy records and coral PSMs do not significantly contribute to the discrepancy. However, following major eruptions, the southwestern Pacific corals locally record more persistent cold anomalies than found in the Past1000 experiments and canonical ENSO teleconnections to the southwest Pacific strongly control the reconstruction response. Furthermore, using covariance patterns independent of ENSO yield reconstructions consistent with coral archives across the Pacific. These results show that model bias can strongly affect how proxy information is processed in paleoclimate data assimilation. As we illustrate here, model bias influences the magnitude and persistence of the response of the tropical Pacific to volcanic eruptions.

scholarly journals Exceptionally strong easterly wind burst stalling El Niño of 2014

2016 ◽  
Vol 113 (8) ◽  
pp. 2005-2010 ◽  
Author(s):  
Shineng Hu ◽  
Alexey V. Fedorov
Keyword(s):  
El Niño ◽  
Climate Models ◽  
Climate Model ◽  
Extreme Event ◽  
El Nino ◽  
Tropical Pacific ◽  
Bjerknes Feedback ◽  
Easterly Wind ◽  
Wind Bursts ◽  
The Tropical Pacific

Intraseasonal wind bursts in the tropical Pacific are believed to affect the evolution and diversity of El Niño events. In particular, the occurrence of two strong westerly wind bursts (WWBs) in early 2014 apparently pushed the ocean–atmosphere system toward a moderate to strong El Niño—potentially an extreme event according to some climate models. However, the event’s progression quickly stalled, and the warming remained very weak throughout the year. Here, we find that the occurrence of an unusually strong basin-wide easterly wind burst (EWB) in June was a key factor that impeded the El Niño development. It was shortly after this EWB that all major Niño indices fell rapidly to near-normal values; a modest growth resumed only later in the year. The easterly burst and the weakness of subsequent WWBs resulted in the persistence of two separate warming centers in the central and eastern equatorial Pacific, suppressing the positive Bjerknes feedback critical for El Niño. Experiments with a climate model with superimposed wind bursts support these conclusions, pointing to inherent limits in El Niño predictability. Furthermore, we show that the spatial structure of the easterly burst matches that of the observed decadal trend in wind stress in the tropical Pacific, suggesting potential links between intraseasonal wind bursts and decadal climate variations.

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