scholarly journals Is There Evidence of Changes in Tropical Atlantic Variability Modes under AMO Phases in the Observational Record?

2018 ◽  
Vol 31 (2) ◽  
pp. 515-536 ◽  
Author(s):  
Marta Martín-Rey ◽  
Irene Polo ◽  
Belén Rodríguez-Fonseca ◽  
Teresa Losada ◽  
Alban Lazar
Keyword(s):  
Southern Oscillation ◽  
Walker Circulation ◽  
Atlantic Multidecadal Oscillation ◽  
Boreal Summer ◽  
Tropical Atlantic ◽  
Equatorial Atlantic ◽  
The North ◽  
Sst Variability ◽  
Tropical Atlantic Variability ◽  
Atlantic Niño

The Atlantic multidecadal oscillation (AMO) is the leading mode of Atlantic sea surface temperature (SST) variability at multidecadal time scales. Previous studies have shown that the AMO could modulate El Niño–Southern Oscillation (ENSO) variance. However, the role played by the AMO in the tropical Atlantic variability (TAV) is still uncertain. Here, it is demonstrated that during negative AMO phases, associated with a shallower thermocline, the eastern equatorial Atlantic SST variability is enhanced by more than 150% in boreal summer. Consequently, the interannual TAV modes are modified. During negative AMO, the Atlantic Niño displays larger amplitude and a westward extension and it is preceded by a simultaneous weakening of both subtropical highs in winter and spring. In contrast, a meridional seesaw SLP pattern evolving into a zonal gradient leads the Atlantic Niño during positive AMO. The north tropical Atlantic (NTA) mode is related to a Scandinavian blocking pattern during winter and spring in negative AMO, while under positive AMO it is part of the SST tripole associated with the North Atlantic Oscillation. Interestingly, the emergence of an overlooked variability mode, here called the horseshoe (HS) pattern on account of its shape, is favored during negative AMO. This anomalous warm (cool) HS surrounding an eastern equatorial cooling (warming) is remotely forced by an ENSO phenomenon. During negative AMO, the tropical–extratropical teleconnections are enhanced and the Walker circulation is altered. This, together with the increased equatorial SST variability, could promote the ENSO impacts on TAV. The results herein give a step forward in the better understanding of TAV, which is essential to improving its modeling, impacts, and predictability.

scholarly journals Some Overlooked Features of Tropical Atlantic Climate Leading to a New Niño-Like Phenomenon*

2006 ◽  
Vol 19 (22) ◽  
pp. 5859-5874 ◽  
Author(s):  
Yuko Okumura ◽  
Shang-Ping Xie
Keyword(s):  
Southern Oscillation ◽  
Boreal Summer ◽  
Tropical Atlantic ◽  
Gulf Of Guinea ◽  
Equatorial Atlantic ◽  
Atlantic Sector ◽  
The Pacific ◽  
Interannual Rainfall Variability ◽  
Ocean Atmosphere ◽  
Atlantic Niño

Abstract The Atlantic Niño, an equatorial zonal mode akin to the Pacific El Niño–Southern Oscillation (ENSO), is phase-locked to boreal summer when the equatorial easterly winds intensify and the thermocline shoals in the Gulf of Guinea. A suite of satellite and in situ observations reveals a new mode of tropical Atlantic variability that displays many characteristics of the zonal mode but instead peaks in November–December (ND). This new mode is found to be statistically independent from both the Atlantic Niño in the preceding summer and the Pacific ENSO. The origin of this ND zonal mode lies in an overlooked aspect of the seasonal cycle in the equatorial Atlantic. In November the equatorial easterly winds intensify for the second time, increasing upwelling and lifting the thermocline in the Gulf of Guinea. An analysis of high-resolution climatological data shows that these dynamical changes induce a noticeable SST cooling in the central equatorial Atlantic. The shoaling thermocline and increased upwelling enhance the SST sensitivity to surface wind changes, reinvigorating equatorial ocean–atmosphere interaction. The resultant ocean–atmospheric anomalies are organized into patterns that give rise to positive mutual feedback as Bjerknes envisioned for the Pacific ENSO. This ND zonal mode significantly affects interannual rainfall variability in coastal Congo–Angola during its early rainy season. It tends to further evolve into a meridional mode in the following March–April, affecting precipitation in northeast Brazil. Thus it offers potential predictability for climate over the Atlantic sector in early boreal winter, a season for which local ocean–atmosphere variability was otherwise poorly understood.

scholarly journals Weakening Atlantic Niño–Pacific connection under greenhouse warming

2019 ◽  
Vol 5 (8) ◽  
pp. eaax4111 ◽  
Author(s):  
Fan Jia ◽  
Wenju Cai ◽  
Lixin Wu ◽  
Bolan Gan ◽  
Guojian Wang ◽  
...  
Keyword(s):  
Southern Oscillation ◽  
Walker Circulation ◽  
Boreal Summer ◽  
Boreal Winter ◽  
Greenhouse Warming ◽  
Equatorial Atlantic ◽  
Enso Predictability ◽  
The Pacific ◽  
Mean Climate ◽  
Atlantic Niño

Sea surface temperature variability in the equatorial eastern Atlantic, which is referred to as an Atlantic Niño (Niña) at its warm (cold) phase and peaks in boreal summer, dominates the interannual variability in the equatorial Atlantic. By strengthening of the Walker circulation, an Atlantic Niño favors a Pacific La Niña, which matures in boreal winter, providing a precursory memory for El Niño–Southern Oscillation (ENSO) predictability. How this Atlantic impact responds to greenhouse warming is unclear. Here, we show that greenhouse warming leads to a weakened influence from the Atlantic Niño/Niña on the Pacific ENSO. In response to anomalous equatorial Atlantic heating, ascending over the equatorial Atlantic is weaker due to an increased tropospheric stability in the mean climate, resulting in a weaker impact on the Pacific Ocean. Thus, as greenhouse warming continues, Pacific ENSO is projected to be less affected by the Atlantic Niño/Niña and more challenging to predict.

scholarly journals Spurious North Tropical Atlantic precursors to El Niño

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Wenjun Zhang ◽  
Feng Jiang ◽  
Malte F. Stuecker ◽  
Fei-Fei Jin ◽  
Axel Timmermann
Keyword(s):  
El Niño ◽  
Cross Correlation ◽  
El Nino ◽  
Southern Oscillation ◽  
Global Climate ◽  
Tropical Atlantic ◽  
The North ◽  
Sst Variability ◽  
Primary Driver ◽  
North Tropical Atlantic

AbstractThe El Niño-Southern Oscillation (ENSO), the primary driver of year-to-year global climate variability, is known to influence the North Tropical Atlantic (NTA) sea surface temperature (SST), especially during boreal spring season. Focusing on statistical lead-lag relationships, previous studies have proposed that interannual NTA SST variability can also feed back on ENSO in a predictable manner. However, these studies did not properly account for ENSO’s autocorrelation and the fact that the SST in the Atlantic and Pacific, as well as their interaction are seasonally modulated. This can lead to misinterpretations of causality and the spurious identification of Atlantic precursors for ENSO. Revisiting this issue under consideration of seasonality, time-varying ENSO frequency, and greenhouse warming, we demonstrate that the cross-correlation characteristics between NTA SST and ENSO, are consistent with a one-way Pacific to Atlantic forcing, even though the interpretation of lead-lag relationships may suggest otherwise.

Atlantic Zonal Mode-Monsoon Teleconnection in a Warming Scenario

2021 ◽  
Author(s):  
Sabeerali C. T ◽  
Ajaya Mohan Ravindran ◽  
Praveen V
Keyword(s):  
Indian Subcontinent ◽  
Coupled Model ◽  
Summer Monsoon Rainfall ◽  
Convincing Evidence ◽  
External Boundary ◽  
Boreal Summer ◽  
Tropical Atlantic ◽  
Equatorial Atlantic ◽  
Warming Scenario ◽  
Sst Variability

Abstract The dominant interannual SST variability in the eastern equatorial Atlantic referred to as the Atlantic Zonal Mode (AZM), which peaks in boreal summer impacts global weather patterns. The cold (warm) phase of this ocean-atmospheric coupled phenomenon enhances (weakens) the intensity of the Indian summer monsoon rainfall (ISMR). Observational studies show a strengthening relationship between AZM and ISMR in recent decades, providing a predictive signal for the ISMR. However, a suite of Coupled Model Intercomparison Project Phase 6 (CMIP6) model simulations in the highest emission scenario (SSP58.5) show a weakening relationship between ISMR and AZM in the future (2050-2099). The strengthening of atmospheric thermal stability over the tropical Atlantic in the warming scenario weakens the associated convection over the eastern equatorial Atlantic in response to the warm phase of AZM. This leads to weakening velocity potential response over the Indian subcontinent, resulting in a weak AZM-ISMR relationship. There is no convincing evidence to indicate that either the tropical Atlantic SST bias or the AZM-ISMR teleconnection bias plays a crucial role in the potential weakening of this relationship. These results imply that ISMR prediction will become more challenging in a warming scenario as one of the major external boundary forces that influence monsoon weakens.

scholarly journals ENSO Influence on the Atlantic Niño, Revisited: Multi-Year versus Single-Year ENSO Events

2019 ◽  
Vol 32 (14) ◽  
pp. 4585-4600 ◽  
Author(s):  
Hiroki Tokinaga ◽  
Ingo Richter ◽  
Yu Kosaka
Keyword(s):  
Southern Oscillation ◽  
Walker Circulation ◽  
Equatorial Atlantic ◽  
Bjerknes Feedback ◽  
Central Pacific ◽  
Boreal Spring ◽  
Enso Events ◽  
The Past ◽  
Convergence Zones ◽  
Atlantic Niño

Abstract The influence of El Niño–Southern Oscillation (ENSO) on the Atlantic Niño over the past 113 years is investigated by comparing multi-year and single-year ENSO events. Multi-year ENSO events sustain an anomalous zonal gradient of sea surface temperature (SST) in the equatorial western to central Pacific even during boreal spring and summer. This SST gradient is coupled with an anomalous Walker circulation and atmospheric deep convection through the Bjerknes feedback. During multi-year La Niñas, for example, a strengthened Pacific Walker circulation extends into the tropical Atlantic in boreal spring, a season when both the Pacific and Atlantic intertropical convergence zones become more symmetric about the equator. As a result, surface westerly wind anomalies appear over the equatorial Atlantic, triggering an Atlantic Niño. By contrast, such a teleconnection is not found in the spring following the peak of single-year ENSO events. A Pacific pacemaker model experiment reproduces the observed atmospheric response and its impact on the Atlantic Niño, further supporting the importance of prolonged ENSO forcing. The contrasting influence of multi-year and single-year events explains the fragile relationship between ENSO and the Atlantic Niño. An empirical orthogonal function (EOF) analysis shows that the leading EOF mode (EOF-1) for the spring tropical western to central Pacific SST anomalies captures the characteristics of multi-year ENSO events. EOF-1 is highly correlated with the summer Atlantic Niño over the past 113 years while the Niño-3 SST is not. These correlations indicate that ocean–atmosphere coupling in the equatorial western to central Pacific plays a major role in shaping ENSO teleconnections in boreal spring.

scholarly journals Relating model bias and prediction skill in the equatorial Atlantic

2021 ◽  
Author(s):  
François Counillon ◽  
Noel Keenlyside ◽  
Thomas Toniazzo ◽  
Shunya Koseki ◽  
Teferi Demissie ◽  
...  
Keyword(s):  
Surface Wind ◽  
Coupled System ◽  
Seasonal Prediction ◽  
Prediction Skill ◽  
Tropical Atlantic ◽  
Equatorial Atlantic ◽  
The North ◽  
Spring Predictability Barrier ◽  
The Impact ◽  
Atlantic Niño

AbstractWe investigate the impact of large climatological biases in the tropical Atlantic on reanalysis and seasonal prediction performance using the Norwegian Climate Prediction Model (NorCPM) in a standard and an anomaly coupled configuration. Anomaly coupling corrects the climatological surface wind and sea surface temperature (SST) fields exchanged between oceanic and atmospheric models, and thereby significantly reduces the climatological model biases of precipitation and SST. NorCPM combines the Norwegian Earth system model with the ensemble Kalman filter and assimilates SST and hydrographic profiles. We perform a reanalysis for the period 1980–2010 and a set of seasonal predictions for the period 1985–2010 with both model configurations. Anomaly coupling improves the accuracy and the reliability of the reanalysis in the tropical Atlantic, because the corrected model enables a dynamical reconstruction that satisfies better the observations and their uncertainty. Anomaly coupling also enhances seasonal prediction skill in the equatorial Atlantic to the level of the best models of the North American multi-model ensemble, while the standard model is among the worst. However, anomaly coupling slightly damps the amplitude of Atlantic Niño and Niña events. The skill enhancements achieved by anomaly coupling are largest for forecast started from August and February. There is strong spring predictability barrier, with little skill in predicting conditions in June. The anomaly coupled system show some skill in predicting the secondary Atlantic Niño-II SST variability that peaks in November–December from August 1st.

scholarly journals Greenhouse warming intensifies north tropical Atlantic climate variability

2021 ◽  
Vol 7 (35) ◽  
pp. eabg9690
Author(s):  
Yun Yang ◽  
Lixin Wu ◽  
Ying Guo ◽  
Bolan Gan ◽  
Wenju Cai ◽  
...  
Keyword(s):  
Climate Variability ◽  
Southern Oscillation ◽  
Greenhouse Warming ◽  
Tropospheric Temperature ◽  
Tropical Atlantic ◽  
Moist Convection ◽  
Socioeconomic Impacts ◽  
The North ◽  
Sst Variability ◽  
North Tropical Atlantic

Variability of North Tropical Atlantic (NTA) sea surface temperature (SST), characterized by a near-uniform warming at its positive phase, is a consequential mode of climate variability. Modulated by El Niño–Southern Oscillation (ENSO) and the North Atlantic Oscillation, NTA warm anomalies tend to induce La Niña events, droughts in Northeast Brazil, increased frequency of extreme hurricanes, and phytoplankton blooms in the Guinea Dome. Future changes of NTA variability could have profound socioeconomic impacts yet remain unknown. Here, we reveal a robust intensification of NTA variability under greenhouse warming. This intensification mainly arises from strengthening of ENSO-forced Pacific-North American pattern and tropospheric temperature anomalies, as a consequence of an eastward shift of ENSO-induced equatorial Pacific convection and of increased ENSO variability, which enhances ENSO influence by reinforcing the associated wind and moist convection anomalies. The intensification of NTA SST variability suggests increased occurrences of extreme NTA events, with far-reaching ramifications.

scholarly journals Spurious North Tropical Atlantic pre-cursors to ENSO

2021 ◽  
Author(s):  
Wenjun Zhang ◽  
Feng Jiang ◽  
Malte Stuecker ◽  
Fei-Fei Jin ◽  
Axel Timmermann
Keyword(s):  
Cross Correlation ◽  
Southern Oscillation ◽  
Global Climate ◽  
Sea Surface ◽  
Time Varying ◽  
Tropical Atlantic ◽  
The North ◽  
Sst Variability ◽  
Primary Driver ◽  
North Tropical Atlantic

Abstract The El Niño-Southern Oscillation (ENSO), the primary driver of year-to-year global climate variability, is known to influence the North Tropical Atlantic (NTA) sea surface temperature (SST), especially during boreal spring season. Focusing on statistical lead-lag relationships, previous studies have proposed that interannual NTA SST variability can also feed back on ENSO in a predictable manner. However, these studies do not properly account for ENSO’s autocorrelation and the fact that the SST in the Atlantic and Pacific, as well as their atmospheric interaction are seasonally modulated. This can lead to misinterpretations of causality and the spurious identification of Atlantic precursors for ENSO. Revisiting this issue under consideration of seasonality, time-varying ENSO frequency, and greenhouse warming, we demonstrate that the cross-correlation characteristics between NTA SST and ENSO, are fully consistent with a one-way Pacific to Atlantic forcing, even though the interpretation of lead-lag relationships may suggest otherwise.

Relating model bias and prediction skill in the equatorial Atlantic

2021 ◽  
Author(s):  
Francois Counillon ◽  
Noel Keenlyside ◽  
Thomas Toniazzo ◽  
Shunya Koseki ◽  
Teferi Demissie ◽  
...  
Keyword(s):  
Surface Wind ◽  
Coupled System ◽  
Seasonal Prediction ◽  
Prediction Skill ◽  
Tropical Atlantic ◽  
Equatorial Atlantic ◽  
The North ◽  
Spring Predictability Barrier ◽  
Sst Variability ◽  
The Impact

<p>We investigate the impact of large climatological biases in the tropical Atlantic on reanalysis and seasonal prediction performance using the Norwegian Climate Prediction Model (NorCPM) in a standard and an anomaly coupled configuration. Anomaly coupling corrects the climatological surface wind and sea surface temperature (SST) fields exchanged between oceanic and atmospheric models, and thereby significantly reduces the climatological model biases of precipitation and SST. NorCPM combines the Norwegian Earth system model (NorESM) with the Ensemble Kalman Filter and assimilates SST and hydrographic profiles. We perform a reanalysis for the period 1980-2010 and a set of seasonal predictions for the period 1985-2010 with both model configurations. Anomaly coupling improves the accuracy and the reliability of the reanalysis in the tropical Atlantic, because the corrected model enables a dynamical reconstruction that satisfies better the observations and their uncertainty.<span>  </span>Anomaly coupling also enhances seasonal prediction skill in the equatorial Atlantic to the level of the best models of the North American multi-model ensemble, while the standard model is among the worst. However, anomaly coupling slightly damps the amplitude of Atlantic Niño and Niña events. The skill enhancements achieved by anomaly coupling are largest for forecast started from August and February. There is strong spring predictability barrier, with little skill in predicting conditions in June. The anomaly coupled system show some skill in predicting the secondary Atlantic Niño-II SST variability that peaks in November-December from August 1st.</p>

scholarly journals Diabatic heating governs the seasonality of the Atlantic Niño

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Hyacinth C. Nnamchi ◽  
Mojib Latif ◽  
Noel S. Keenlyside ◽  
Joakim Kjellsson ◽  
Ingo Richter
Keyword(s):  
Feedback Loop ◽  
Diabatic Heating ◽  
Seasonal Migration ◽  
Equatorial Atlantic ◽  
Bjerknes Feedback ◽  
Atlantic Sector ◽  
Inter Tropical Convergence Zone ◽  
Sst Variability ◽  
Leading Mode ◽  
Atlantic Niño

AbstractThe Atlantic Niño is the leading mode of interannual sea-surface temperature (SST) variability in the equatorial Atlantic and assumed to be largely governed by coupled ocean-atmosphere dynamics described by the Bjerknes-feedback loop. However, the role of the atmospheric diabatic heating, which can be either an indicator of the atmosphere’s response to, or its influence on the SST, is poorly understood. Here, using satellite-era observations from 1982–2015, we show that diabatic heating variability associated with the seasonal migration of the Inter-Tropical Convergence Zone controls the seasonality of the Atlantic Niño. The variability in precipitation, a measure of vertically integrated diabatic heating, leads that in SST, whereas the atmospheric response to SST variability is relatively weak. Our findings imply that the oceanic impact on the atmosphere is smaller than previously thought, questioning the relevance of the classical Bjerknes-feedback loop for the Atlantic Niño and limiting climate predictability over the equatorial Atlantic sector.

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