scholarly journals Revisiting the ENSO Teleconnection to the Tropical North Atlantic

2017 ◽  
Vol 30 (17) ◽  
pp. 6945-6957 ◽  
Author(s):  
Javier García-Serrano ◽  
Christophe Cassou ◽  
Hervé Douville ◽  
Alessandra Giannini ◽  
Francisco J. Doblas-Reyes
Keyword(s):  
Heat Flux ◽  
North Atlantic ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Mixed Layer Depth ◽  
Sensible Heat Flux ◽  
Atmospheric Forcing ◽  
Tropical North Atlantic ◽  
Sst Anomalies

One of the most robust remote impacts of El Niño–Southern Oscillation (ENSO) is the teleconnection to tropical North Atlantic (TNA) sea surface temperature (SST) in boreal spring. However, important questions still remain open. In particular, the timing of the ENSO–TNA relationship lacks understanding. The three previously proposed mechanisms rely on teleconnection dynamics involving a time lag of one season with respect to the ENSO mature phase in winter, but recent results have shown that the persistence of ENSO into spring is necessary for the development of the TNA SST anomalies. Likewise, the identification of the effective atmospheric forcing in the deep TNA to drive the regional air–sea interaction is also lacking. In this manuscript a new dynamical framework to understand the ENSO–TNA teleconnection is proposed, in which a continuous atmospheric forcing is present throughout the ENSO decaying phase. Observational datasets in the satellite era, which include reliable estimates over the ocean, are used to illustrate the mechanism at play. The dynamics rely on the remote Gill-type response to the ENSO zonally compensated heat source over the Amazon basin, associated with perturbations in the Walker circulation. For El Niño conditions, the anomalous diabatic heating in the tropical Pacific is compensated by anomalous diabatic cooling, in association with negative rainfall anomalies and descending motion over northern South America. A pair of anomalous cyclonic circulations is established at upper-tropospheric levels in the tropical Atlantic straddling the equator, displaying a characteristic baroclinic structure with height. In the TNA region, the mirrored anomalous anticyclonic circulation at lower-tropospheric levels weakens the northeasterly trade winds, leading to a reduction in evaporation and of the ocean mixed layer depth, hence to positive SST anomalies. Apart from the dominance of latent heat flux anomalies in the remote response, sensible heat flux and shortwave radiation anomalies also appear to contribute. The “lagged” relationship between mature ENSO in winter and peaking TNA SSTs in spring seems to be phase locked with the seasonal cycle in both the location of the mechanism’s centers of action and regional SST variance.

Non-linearity in the pathway of El Niño-Southern Oscillation to the tropical North Atlantic

2021 ◽  
pp. 1-54
Author(s):  
Jake W. Casselman ◽  
Andréa S. Taschetto ◽  
Daniela I.V. Domeisen
Keyword(s):  
North Atlantic ◽  
El Niño ◽  
Climate Model ◽  
El Nino ◽  
Southern Oscillation ◽  
Static Stability ◽  
Reanalysis Data ◽  
El Niño Southern Oscillation ◽  
El Nino Southern Oscillation ◽  
Tropical North Atlantic

AbstractEl Niño-Southern Oscillation can influence the Tropical North Atlantic (TNA), leading to anomalous sea surface temperatures (SST) at a lag of several months. Several mechanisms have been proposed to explain this teleconnection. These mechanisms include both tropical and extratropical pathways, contributing to anomalous trade winds and static stability over the TNA region. The TNA SST response to ENSO has been suggested to be nonlinear. Yet the overall linearity of the ENSO-TNA teleconnection via the two pathways remains unclear. Here we use reanalysis data to confirm that the SST anomaly (SSTA) in the TNA is nonlinear with respect to the strength of the SST forcing in the tropical Pacific, as further increases in El Niño magnitudes cease to create further increases of the TNA SSTA. We further show that the tropical pathway is more linear than the extratropical pathway by sub-dividing the inter-basin connection into extratropical and tropical pathways. This is confirmed by a climate model participating in the CMIP5. The extratropical pathway is modulated by the North Atlantic Oscillation (NAO) and the location of the SSTA in the Pacific, but this modulation insufficiently explains the nonlinearity in TNA SSTA. As neither extratropical nor tropical pathways can explain the nonlinearity, this suggests that external factors are at play. Further analysis shows that the TNA SSTA is highly influenced by the preconditioning of the tropical Atlantic SST. This preconditioning is found to be associated with the NAO through SST-tripole patterns.

scholarly journals Role of the Indo-Pacific Interbasin Coupling in Predicting Asymmetric ENSO Transition and Duration

2012 ◽  
Vol 25 (9) ◽  
pp. 3321-3335 ◽  
Author(s):  
Masamichi Ohba ◽  
Masahiro Watanabe
Keyword(s):  
El Niño ◽  
General Circulation ◽  
El Nino ◽  
Southern Oscillation ◽  
La Niña ◽  
La Nina ◽  
The Pacific ◽  
Enso Asymmetry ◽  
Sst Anomalies

Warm and cold phases of El Niño–Southern Oscillation (ENSO) exhibit a significant asymmetry in their transition/duration such that El Niño tends to shift rapidly to La Niña after the mature phase, whereas La Niña tends to persist for up to 2 yr. The possible role of sea surface temperature (SST) anomalies in the Indian Ocean (IO) in this ENSO asymmetry is investigated using a coupled general circulation model (CGCM). Decoupled-IO experiments are conducted to assess asymmetric IO feedbacks to the ongoing ENSO evolution in the Pacific. Identical-twin forecast experiments show that a coupling of the IO extends the skillful prediction of the ENSO warm phase by about one year, which was about 8 months in the absence of the IO coupling, in which a significant drop of the prediction skill around the boreal spring (known as the spring prediction barrier) is found. The effect of IO coupling on the predictability of the Pacific SST is significantly weaker in the decay phase of La Niña. Warm IO SST anomalies associated with El Niño enhance surface easterlies over the equatorial western Pacific and hence facilitate the El Niño decay. However, this mechanism cannot be applied to cold IO SST anomalies during La Niña. The result of these CGCM experiments estimates that approximately one-half of the ENSO asymmetry arises from the phase-dependent nature of the Indo-Pacific interbasin coupling.

scholarly journals Indo-Western Pacific Climate Variability: ENSO Forcing and Internal Dynamics in a Tropical Pacific Pacemaker Simulation

2018 ◽  
Vol 31 (24) ◽  
pp. 10123-10139 ◽  
Author(s):  
Chuan-Yang Wang ◽  
Shang-Ping Xie ◽  
Yu Kosaka
Keyword(s):  
Indian Ocean ◽  
El Niño ◽  
General Circulation ◽  
El Nino ◽  
Southern Oscillation ◽  
Internal Variability ◽  
Tropical Pacific ◽  
Western Pacific ◽  
Ocean Atmosphere ◽  
Sst Anomalies

El Niño–Southern Oscillation (ENSO) peaks in boreal winter but its impact on Indo-western Pacific climate persists for another two seasons. Key ocean–atmosphere interaction processes for the ENSO effect are investigated using the Pacific Ocean–Global Atmosphere (POGA) experiment with a coupled general circulation model, where tropical Pacific sea surface temperature (SST) anomalies are restored to follow observations while the atmosphere and oceans are fully coupled elsewhere. The POGA shows skills in simulating the ENSO-forced warming of the tropical Indian Ocean and an anomalous anticyclonic circulation pattern over the northwestern tropical Pacific in the post–El Niño spring and summer. The 10-member POGA ensemble allows decomposing Indo-western Pacific variability into the ENSO forced and ENSO-unrelated (internal) components. Internal variability is comparable to the ENSO forcing in magnitude and independent of ENSO amplitude and phase. Random internal variability causes apparent decadal modulations of ENSO correlations over the Indo-western Pacific, which are high during epochs of high ENSO variance. This is broadly consistent with instrumental observations over the past 130 years as documented in recent studies. Internal variability features a sea level pressure pattern that extends into the north Indian Ocean and is associated with coherent SST anomalies from the Arabian Sea to the western Pacific, suggestive of ocean–atmosphere coupling.

scholarly journals Combined Impact of El Niño–Southern Oscillation and Pacific Decadal Oscillation on the Northern Winter Stratosphere

Atmosphere ◽  
2019 ◽  
Vol 10 (4) ◽  
pp. 211 ◽  
Author(s):  
Jian Rao ◽  
Rongcai Ren ◽  
Xin Xia ◽  
Chunhua Shi ◽  
Dong Guo
Keyword(s):  
El Niño ◽  
North Pacific ◽  
El Nino ◽  
Southern Oscillation ◽  
Polar Vortex ◽  
La Niña ◽  
Stratospheric Polar Vortex ◽  
The North ◽  
La Nina ◽  
Sst Anomalies

Using reanalysis and the sea surface temperature (SST) analysis, the combined impact of El Niño-Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) on the northern winter stratosphere is investigated. The warm and weak stratospheric polar vortex response to El Niño simply appears during positive PDO, whereas the cold and strong stratospheric polar vortex response to La Niña is preferable during negative PDO in the reanalysis. Two mechanisms may account for the enhanced stratospheric response when ENSO and PDO are in phase. First, the asymmetries of the intensity and frequency between El Niño and La Niña can be identified for the two PDO phases. Second, the extratropical SST anomalies in the North Pacific may also play a role in the varying extratropical response to ENSO. The North Pacific SST anomalies related to PDO superimpose ENSO SST anomalies when they are in phase but undermine them when they are out of phase. The superimposed North Pacific SST anomalies help to increase SST meridional gradient anomalies between tropical and extratropics, as well as to lock the local height response to ENSO. Therefore, the passages for the upward propagation of waves from the troposphere is more unimpeded when positive PDO is configured with El Niño, and vice versa when negative PDO is configured with La Niña.

scholarly journals A Nonstationary ENSO–NAO Relationship Due to AMO Modulation

2018 ◽  
Vol 32 (1) ◽  
pp. 33-43 ◽  
Author(s):  
Wenjun Zhang ◽  
Xuebin Mei ◽  
Xin Geng ◽  
Andrew G. Turner ◽  
Fei-Fei Jin
Keyword(s):  
North Atlantic ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Circulation Model ◽  
La Niña ◽  
Late Winter ◽  
The North ◽  
La Nina ◽  
The North Atlantic

Abstract Many previous studies have demonstrated a high uncertainty in the relationship between El Niño–Southern Oscillation (ENSO) and the North Atlantic Oscillation (NAO). In the present work, decadal modulation by the Atlantic multidecadal oscillation (AMO) is investigated as a possible cause of the nonstationary ENSO–NAO relationship based on observed and reanalysis data. It is found that the negative ENSO–NAO correlation in late winter is significant only when ENSO and the AMO are in phase (AMO+/El Niño and AMO−/La Niña). However, no significant ENSO-driven atmospheric anomalies can be observed over the North Atlantic when ENSO and the AMO are out of phase (AMO−/El Niño and AMO+/La Niña). Further analysis indicates that the sea surface temperature anomaly (SSTA) in the tropical North Atlantic (TNA) plays an essential role in this modulating effect. Because of broadly analogous TNA SSTA responses to both ENSO and the AMO during late winter, a warm SSTA in the TNA is evident when El Niño occurs during a positive AMO phase, resulting in a significantly weakened NAO, and vice versa when La Niña occurs during a negative AMO phase. In contrast, neither the TNA SSTA nor the NAO shows a prominent change under out-of-phase combinations of ENSO and AMO. The AMO modulation and the associated effect of the TNA SSTA are shown to be well reproduced by historical simulations of the HadCM3 coupled model and further verified by forced experiments using an atmospheric circulation model. These offer hope that similar models will be able to make predictions for the NAO when appropriately initialized.

scholarly journals An Asymmetry in the IOD and ENSO Teleconnection Pathway and Its Impact on Australian Climate

2012 ◽  
Vol 25 (18) ◽  
pp. 6318-6329 ◽  
Author(s):  
Wenju Cai ◽  
Peter van Rensch ◽  
Tim Cowan ◽  
Harry H. Hendon
Keyword(s):  
Indian Ocean ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Wave Train ◽  
Austral Spring ◽  
Southeast Australia ◽  
Unit Change ◽  
The Impact ◽  
Sst Anomalies

Abstract Recent research has shown that the climatic impact from El Niño–Southern Oscillation (ENSO) on middle latitudes west of the western Pacific (e.g., southeast Australia) during austral spring (September–November) is conducted via the tropical Indian Ocean (TIO). However, it is not clear whether this impact pathway is symmetric about the positive and negative phases of ENSO and the Indian Ocean dipole (IOD). It is shown that a strong asymmetry does exist. For ENSO, only the impact from El Niño is conducted through the TIO pathway; the impact from La Niña is delivered through the Pacific–South America pattern. For the IOD, a greater convection anomaly and wave train response occurs during positive IOD (pIOD) events than during negative IOD (nIOD) events. This “impact asymmetry” is consistent with the positive skewness of the IOD, principally due to a negative skewness of sea surface temperature (SST) anomalies in the east IOD (IODE) pole. In the IODE region, convection anomalies are more sensitive to a per unit change of cold SST anomalies than to the same unit change of warm SST anomalies. This study shows that the IOD skewness occurs despite the greater damping, rather than due to a breakdown of this damping as suggested by previous studies. This IOD impact asymmetry provides an explanation for much of the reduction in spring rainfall over southeast Australia during the 2000s. Key to this rainfall reduction is the increased occurrences of pIOD events, more so than the lack of nIOD events.

Sign in / Sign up

Export Citation Format

Share Document