Sea surface salinity-derived indexes for distinguishing two types of El Niño events in the tropical Pacific

2021 ◽  
Author(s):  
Hai Zhi ◽  
Pengfei Lin ◽  
Zhujun Fang ◽  
Hailong Liu ◽  
Rong-Hua Zhang ◽  
...  
Keyword(s):  
El Niño ◽  
El Nino ◽  
Tropical Pacific ◽  
Sea Surface ◽  
Sea Surface Salinity ◽  
Surface Salinity ◽  
El Niño Events ◽  
El Nino Events ◽  
The Tropical Pacific

The Contribution of Boreal Spring South Pacific Atmospheric Variability to El Niño Occurrence

2020 ◽  
Vol 33 (19) ◽  
pp. 8301-8313
Author(s):  
Qingye Min ◽  
Renhe Zhang
Keyword(s):  
El Niño ◽  
El Nino ◽  
South Pacific ◽  
Tropical Pacific ◽  
The South ◽  
Atmospheric Variability ◽  
Boreal Spring ◽  
El Niño Events ◽  
El Nino Events ◽  
The Tropical Pacific

AbstractDespite the fact that great efforts have been made to improve the prediction of El Niño events, it remains challenging because of limited understanding of El Niño and its precursors. This research focuses on the influence of South Pacific atmospheric variability on the development of the sea surface temperature anomaly (SSTA) in the tropical Pacific. It is found that as early as in the boreal spring of El Niño years, the sea level pressure anomaly (SLPA) shows a configuration characterized by two significant negative anomaly centers in the north and a positive anomaly center in the south between the subtropics and high latitudes in South Pacific. Such an anomalous SLPA pattern becomes stronger in the following late boreal spring and summer associated with the strengthening of westerly anomalies in the tropical Pacific, weakening the southeasterly trade winds and promoting the warming of tropical eastern Pacific, which is conducive to the development of El Niño events. It is demonstrated that the SLPA pattern in boreal spring revealed in this study is closely associated with boreal summer South Pacific Oscillation (SPO) and South Pacific meridional mode (SPMM). As a precursor in boreal spring, the prediction skill of the South Pacific SLPA in boreal spring for the SSTA in the eastern equatorial Pacific is better than that of the SPMM. This study is helpful to deepen our understanding of the contribution of South Pacific extratropical atmospheric variability to El Niño occurrence.

scholarly journals Tropical Pacific Climate Variability under Solar Geoengineering: Impacts on ENSO Extremes

2019 ◽  
Author(s):  
Abdul Malik ◽  
Peer J. Nowack ◽  
Joanna D. Haigh ◽  
Long Cao ◽  
Luqman Atique ◽  
...  
Keyword(s):  
El Niño ◽  
El Nino ◽  
Tropical Pacific ◽  
La Niña ◽  
La Nina ◽  
Solar Geoengineering ◽  
El Niño Events ◽  
Extreme El Niño ◽  
El Nino Events ◽  
The Tropical Pacific

Abstract. Many modelling studies suggest that the El Niño Southern Oscillation (ENSO), in interaction with the tropical Pacific background climate, will change under rising atmospheric greenhouse gas concentrations. Solar geoengineering (reducing the solar flux from outer space) has been proposed as a means to counteract anthropogenic greenhouse-induced changes in climate. Effectiveness of solar geoengineering is uncertain. Robust results are particularly difficult to obtain for ENSO because existing geoengineering simulations are too short (typically ~ 50 years) to detect statistically significant changes in the highly variable tropical Pacific background climate. We here present results from a 1000-year sunshade geoengineering simulation, G1, carried out with the coupled atmosphere-ocean general circulation model HadCM3L. In agreement with previous studies, reducing the shortwave solar flux more than compensates the warming in the tropical Pacific that develops in the 4×CO2 scenario: we observe an overcooling of 0.3 °C (5 %) and 0.23-mm day−1 (5 %) reduction in mean rainfall relative to preindustrial conditions in the G1 simulation. This is due to the different latitudinal distributions of the shortwave (solar) and longwave (CO2) forcings.The location of the Intertropical Convergence Zone (ITCZ) located north of equator in the tropical Pacific, which moved 7.5° southwards under 4×CO2, is also restored to its preindustrial location. However, other aspects of the tropical Pacific mean climate are not reset as effectively. Relative to preindustrial conditions, in G1 the zonal wind stress, zonal sea surface temperature (SST) gradient, and meridional SST gradient are reduced by 10 %, 11 %, and 9 %, respectively, and the Pacific Walker Circulation (PWC) is consistently weakened. The overall amplitude of ENSO strengthens by 5–8 %, but there is a 65 % reduction in the asymmetry between cold and warm events: cold events intensify more than warm events. Importantly, the frequency of extreme El Niño and La Niña events increases by 44 % and 32 %, respectively, while the total number of El Niño events increases by 12 %. Paradoxically, while the number of total and extreme events increase, the most extreme El Niño events also become weaker relative to preindustrial state while the La Niña events become stronger. That is, extreme El Niño events in G1 become less extreme than in preindustrial conditions, but extreme El Niño events become more frequent. In contrast, extreme La Niña events become stronger in G1. This is in agreement with the general overcooling of the tropical Pacific in G1 relative to preindustrial conditions, which depict a shift towards generally more La Niña-like conditions.

scholarly journals Disentangling the Impact of ENSO and Indian Ocean Variability on the Regional Climate of Bangladesh: Implications for Cholera Risk

2010 ◽  
Vol 23 (10) ◽  
pp. 2817-2831 ◽  
Author(s):  
Benjamin A. Cash ◽  
Xavier Rodó ◽  
James L. Kinter ◽  
Md Yunus
Keyword(s):  
Indian Ocean ◽  
El Niño ◽  
El Nino ◽  
Summer Precipitation ◽  
Tropical Pacific ◽  
Eastern Tropical Pacific ◽  
El Niño Events ◽  
Sst Anomalies ◽  
El Nino Events ◽  
The Tropical Pacific

Abstract Recent studies arising from both statistical analysis and dynamical disease models indicate that there is a link between the incidence of cholera, a paradigmatic waterborne bacterial illness endemic to Bangladesh, and the El Niño–Southern Oscillation (ENSO). Cholera incidence typically increases following boreal winter El Niño events for the period 1973–2001. Observational and model analyses find that Bangladesh summer rainfall is enhanced following winter El Niño events, providing a plausible physical link between El Niño and cholera incidence. However, rainfall and cholera incidence do not increase following every winter El Niño event. Substantial variations in Bangladesh precipitation also occur in simulations in which identical sea surface temperature (SST) anomalies are prescribed in the central and eastern tropical Pacific. Bangladesh summer precipitation is thus not uniquely determined by forcing from the tropical Pacific, with significant implications for predictions of cholera risk. Nonparametric statistical analysis is used to identify regions of SST anomalies associated with variations in Bangladesh rainfall in an ensemble of pacemaker simulations. The authors find that differences in the response of Bangladesh summer precipitation to winter El Niño events are strongly associated with the persistence of warm SST anomalies in the central Pacific. Also there are significant differences in the SST patterns associated with positive and negative Bangladesh rainfall anomalies, indicating that the response is not fully linear. SST anomalies in the Indian Ocean also modulate the influence of the tropical Pacific, with colder Indian Ocean SST tending to enhance Bangladesh precipitation relative to warm Indian Ocean SST for identical conditions in the central and eastern tropical Pacific. This influence is not fully linear. Forecasts of Bangladesh rainfall and cholera risk may thus be improved by considering the Niño-3 and Niño-4 indices separately, rather than the Niño-3.4 index alone. Additional skill may also be gained by incorporating information on the southeast Indian Ocean and by updating the forecast with information on the evolution of the SST anomalies into spring.

scholarly journals Tropical Pacific climate variability under solar geoengineering: impacts on ENSO extremes

2020 ◽  
Vol 20 (23) ◽  
pp. 15461-15485
Author(s):  
Abdul Malik ◽  
Peer J. Nowack ◽  
Joanna D. Haigh ◽  
Long Cao ◽  
Luqman Atique ◽  
...  
Keyword(s):  
El Niño ◽  
El Nino ◽  
Tropical Pacific ◽  
La Niña ◽  
La Nina ◽  
Solar Geoengineering ◽  
El Niño Events ◽  
Extreme El Niño ◽  
El Nino Events ◽  
The Tropical Pacific

Abstract. Many modelling studies suggest that the El Niño–Southern Oscillation (ENSO), in interaction with the tropical Pacific background climate, will change with rising atmospheric greenhouse gas concentrations. Solar geoengineering (reducing the solar flux from outer space) has been proposed as a means to counteract anthropogenic climate change. However, the effectiveness of solar geoengineering concerning a variety of aspects of Earth's climate is uncertain. Robust results are particularly challenging to obtain for ENSO because existing geoengineering simulations are too short (typically ∼ 50 years) to detect statistically significant changes in the highly variable tropical Pacific background climate. We here present results from a 1000-year-long solar-geoengineering simulation, G1, carried out with the coupled atmosphere–ocean general circulation model HadCM3L. In agreement with previous studies, reducing the solar irradiance (4 %) to offset global mean surface warming in the model more than compensates the warming in the tropical Pacific that develops in the 4 × CO2 scenario. We see an overcooling of 0.3 ∘C and a 0.23 mm d−1 (5 %) reduction in mean rainfall over the tropical Pacific relative to preindustrial conditions in the G1 simulation, owing to the different latitudinal distributions of the shortwave (solar) and longwave (CO2) forcings. The location of the Intertropical Convergence Zone (ITCZ) in the tropical Pacific, which moved 7.5∘ southwards under 4 × CO2, is restored to its preindustrial position. However, other aspects of the tropical Pacific mean climate are not reset as effectively. Relative to preindustrial conditions, in G1 the time-averaged zonal wind stress, zonal sea surface temperature (SST) gradient, and meridional SST gradient are each statistically significantly reduced by around 10 %, and the Pacific Walker Circulation (PWC) is consistently weakened, resulting in conditions conducive to increased frequency of El Niño events. The overall amplitude of ENSO strengthens by 9 %–10 % in G1, but there is a 65 % reduction in the asymmetry between cold and warm events: cold events intensify more than warm events. Notably, the frequency of extreme El Niño and La Niña events increases by ca. 60 % and 30 %, respectively, while the total number of El Niño events increases by around 10 %. All of these changes are statistically significant at either 95 or 99 % confidence level. Somewhat paradoxically, while the number of total and extreme events increases, the extreme El Niño events become weaker relative to the preindustrial state, while the extreme La Niña events become even stronger. That is, such extreme El Niño events in G1 become less intense than under preindustrial conditions but also more frequent. In contrast, extreme La Niña events become stronger in G1, which is in agreement with the general overcooling of the tropical Pacific in G1 relative to preindustrial conditions.

Isolation of sea surface salinity maps on various timescales in the tropical Pacific Ocean

2012 ◽  
Vol 68 (5) ◽  
pp. 687-701 ◽  
Author(s):  
Jian Chen ◽  
Ren Zhang ◽  
Huizan Wang ◽  
Yuzhu An ◽  
Peng Peng ◽  
...  
Keyword(s):  
Pacific Ocean ◽  
Tropical Pacific ◽  
Sea Surface ◽  
Sea Surface Salinity ◽  
Tropical Pacific Ocean ◽  
Surface Salinity ◽  
The Tropical Pacific

El Niño–Southern Oscillation, Pliocene climate and equifinality

2008 ◽  
Vol 367 (1886) ◽  
pp. 127-156 ◽  
Author(s):  
Sarah G Bonham ◽  
Alan M Haywood ◽  
Daniel J Lunt ◽  
Mathew Collins ◽  
Ulrich Salzmann
Keyword(s):  
Surface Temperature ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Tropical Pacific ◽  
El Nino Southern Oscillation ◽  
Climate Simulations ◽  
El Niño Events ◽  
East West ◽  
El Nino Events

It has been suggested that, during the Pliocene ( ca 5–1.8 Ma), an El Niño state existed as a permanent rather than an intermittent feature; that is, the tropical Pacific Ocean was characterized by a much weaker east–west gradient than today. One line of inquiry used to investigate this idea relates modern El Niño teleconnections to Pliocene proxy data by comparing regional differences in precipitation and surface temperature with climate patterns associated with present-day El Niño events, assuming that agreement between Pliocene data and observations of modern El Niño events supports this interpretation. Here, we examine this assumption by comparing outputs from a suite of Mid-Pliocene climate simulations carried out with the UK Met Office climate model. Regional patterns of climate change associated with changes in model boundary conditions are compared with observed El Niño–Southern Oscillation teleconnection patterns. Our results indicate that many of the proposed ‘permanent El Niño’ surface temperature and precipitation patterns are observable in Mid-Pliocene climate simulations even when they display variability in tropical Pacific sea surface temperatures (SSTs) or when forced with a modern east–west SST gradient. Our experiments highlight the possibility that the same outcome may be achieved through different initial conditions (equifinality); an important consideration for reconstructed patterns of regional Mid-Pliocene climate.

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