The Mean and the Time Variability of the Shallow Meridional Overturning Circulation in the Tropical South Pacific Ocean

2013 ◽  
Vol 26 (12) ◽  
pp. 4069-4087 ◽  
Author(s):  
N. V. Zilberman ◽  
D. H. Roemmich ◽  
S. T. Gille
Keyword(s):  
El Niño ◽  
El Nino ◽  
La Niña ◽  
Western Boundary ◽  
Meridional Transport ◽  
La Nina ◽  
The Pacific ◽  
Meridional Overturning ◽  
The Mean ◽  
Subtropical Cell

Abstract The meridional transport in the Pacific Ocean subtropical cell is studied for the period from 2004 to 2011 using gridded Argo temperature and salinity profiles and atmospheric reanalysis surface winds. The poleward Ekman and equatorward geostrophic branches of the subtropical cell exhibit an El Niño–Southern Oscillation signature with strong meridional transport occurring during La Niña and weak meridional transport during El Niño. At 7.5°S, mean basinwide geostrophic transport above 1000 dbar is 48.5 ± 2.5 Sv (Sv ≡ 106 m3 s−1) of which 30.3–38.4 Sv return to the subtropics in the surface Ekman layer, whereas 10.2–18.3 Sv flow northward, feeding the Indonesian Throughflow. Geostrophic transport within the subtropical cell is stronger in the ocean interior and weaker in the western boundary during La Niña, with changes in the interior dominating basinwide transport. Using atmospheric reanalyses, only half of the mean heat gain by the Pacific north of 7.5°S is compensated by oceanic heat transport out of the region. The National Oceanography Centre at Southampton air–sea flux climatology is more consistent for closing the oceanic heat budget. In summary, the use of Argo data for studying the Pacific subtropical cell provides an improved estimate of basinwide mean geostrophic transport, includes both interior and western boundary contributions, quantifies El Niño/La Niña transport variability, and illustrates how the meridional overturning cell dominates ocean heat transport at 7.5°S.

scholarly journals A 10–15-Yr Modulation Cycle of ENSO Intensity

2009 ◽  
Vol 22 (7) ◽  
pp. 1718-1735 ◽  
Author(s):  
Fengpeng Sun ◽  
Jin-Yi Yu
Keyword(s):  
El Niño ◽  
El Nino ◽  
Surface Wind ◽  
Tropical Pacific ◽  
La Niña ◽  
Central Pacific ◽  
La Nina ◽  
The Pacific ◽  
The Mean ◽  
Mean State

Abstract This study examines the slow modulation of El Niño–Southern Oscillation (ENSO) intensity and its underlying mechanism. A 10–15-yr ENSO intensity modulation cycle is identified from historical and paleoclimate data by calculating the envelope function of boreal winter Niño-3.4 and Niño-3 sea surface temperature (SST) indices. Composite analyses reveal interesting spatial asymmetries between El Niño and La Niña events within the modulation cycle. In the enhanced intensity periods of the cycle, El Niño is located in the eastern tropical Pacific and La Niña in the central tropical Pacific. The asymmetry is reversed in the weakened intensity periods: El Niño centers in the central Pacific and La Niña in the eastern Pacific. El Niño and La Niña centered in the eastern Pacific are accompanied with basin-scale surface wind and thermocline anomalies, whereas those centered in the central Pacific are accompanied with local wind and thermocline anomalies. The El Niño–La Niña asymmetries provide a possible mechanism for ENSO to exert a nonzero residual effect that could lead to slow changes in the Pacific mean state. The mean state changes are characterized by an SST dipole pattern between the eastern and central tropical Pacific, which appears as one leading EOF mode of tropical Pacific decadal variability. The Pacific Walker circulation migrates zonally in association with this decadal mode and also changes the mean surface wind and thermocline patterns along the equator. Although the causality has not been established, it is speculated that the mean state changes in turn favor the alternative spatial patterns of El Niño and La Niña that manifest as the reversed ENSO asymmetries. Using these findings, an ENSO–Pacific climate interaction mechanism is hypothesized to explain the decadal ENSO intensity modulation cycle.

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 Simulation of Asymmetric ENSO Transition in WCRP CMIP3 Multimodel Experiments

2010 ◽  
Vol 23 (22) ◽  
pp. 6051-6067 ◽  
Author(s):  
Masamichi Ohba ◽  
Daisuke Nohara ◽  
Hiroaki Ueda
Keyword(s):  
El Niño ◽  
El Nino ◽  
Transition Process ◽  
La Niña ◽  
Western Boundary ◽  
Central Pacific ◽  
Cold Event ◽  
Transition Processes ◽  
La Nina ◽  
Rapid Transition

Abstract Based on the Coupled Model Intercomparison Project phase 3 (CMIP3) multimodel dataset, the relationships between the climatological states and transition processes of simulated ENSO are investigated. The air–sea coupled system of the observed ENSO can remain in the weak cold event for up to 2 yr, whereas those of the warm events tend to turn rapidly into a cold phase. Therefore, the authors separately investigate the simulated transition process of a warm-phase and a cold-phase ENSO in the CMIP3 models. Some of the models reproduce the features of the observed transition process of El Niño/La Niña, whereas most models fail to concurrently reproduce the process during both phases. In the CMIP3 models, four climate models simulate well the rapid transition from El Niño to La Niña. The intensity of a rapid transition of El Niño is mainly related to the intensity of the simulated climatological precipitation over the western–central Pacific (WCP). The models that have strong WCP precipitation can simulate the rapid termination of the equatorial zonal wind in the WCP, which tends to result in the termination of El Niño phase. This relationship is not applicable for the La Niña transition phase. The simulation of La Niña persistency is related to the reflection of off-equatorial Rossby waves at the western boundary of the Pacific and the seasonal evolution of the climatological precipitation in the WCP. Differences in the transition processes between El Niño and La Niña events are fundamentally due to the nonlinear atmospheric (convective) response to SST, which originates from the distribution of climatological SST and its seasonal changes. The results of the present study indicate that a realistic simulation of the climatological state and its seasonality in the WCP are important to be able to simulate the observed transition process of the ENSO.

scholarly journals PDO–ENSO Effects in the Climate of Mexico

2006 ◽  
Vol 19 (24) ◽  
pp. 6433-6438 ◽  
Author(s):  
Edgar G. Pavia ◽  
Federico Graef ◽  
Jorge Reyes
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
La Niña ◽  
Climate Anomalies ◽  
Enso Events ◽  
La Nina ◽  
Mean Temperature ◽  
The Pacific

Abstract The role of the Pacific decadal oscillation (PDO) in El Niño–Southern Oscillation (ENSO)-related Mexican climate anomalies during winter and summer is investigated. The precipitation and mean temperature data of approximately 1000 stations throughout Mexico are considered. After sorting ENSO events by warm phase (El Niño) and cold phase (La Niña) and prevailing PDO phase: warm or high (HiPDO) and cold or low (LoPDO), the authors found the following: 1) For precipitation, El Niño favors wet conditions during summers of LoPDO and during winters of HiPDO. 2) For mean temperature, cooler conditions are favored during La Niña summers and during El Niño winters, regardless of the PDO phase; however, warmer conditions are favored by the HiPDO during El Niño summers.

Asymmetric impacts of El Niño and La Niña on the Pacific–South America teleconnection pattern

2021 ◽  
pp. 1-50
Keyword(s):  
El Niño ◽  
El Nino ◽  
Wave Train ◽  
La Niña ◽  
Convective Precipitation ◽  
Eastern Region ◽  
Mean Flow ◽  
Amundsen Sea ◽  
La Nina ◽  
The Pacific

Abstract El Niño–Southern Oscillation (ENSO) has a huge influence on Antarctic climate variability via Rossby wave trains. In this study, the asymmetry of the ENSO teleconnection in the Southern Hemisphere, as along with the mechanisms involved, is systematically investigated. In four reanalysis datasets, the composite atmospheric circulation anomaly in austral winter over the Amundsen Sea during La Niña is situated more to the west than during El Niño. This asymmetric feature is reproduced by ECHAM5.3.2 forced with both composite and idealized symmetric sea surface temperature anomalies. Utilizing a linear baroclinic model, we find that ENSO-triggered circulation anomalies in the subtropics can readily extract kinetic energy from the climatological mean flow and develop efficiently at the exit of the subtropical jet stream (STJ). The discrepancy in the location of the STJ between El Niño and La Niña causes asymmetric circulation responses by affecting the energy conversion. During El Niño years, anomalous tropical convective precipitation increases the meridional temperature gradient, which in turn leads to the strengthening of the STJ and the eastward movement of the jet core and jet exit in the Pacific. With the movement of the STJ exit, the wave train tends to develop over the eastern region. The opposite is the case during La Niña when the westward shift of the jet exit favors the development of the wave train in the western region. Our findings expand the current understanding regarding ENSO teleconnection.

Impacts of El Niño and La Niña Cycles: Systems and Sectors

2008 ◽  
Author(s):  
Cynthia Rosenzweig ◽  
Daniel Hillel
Keyword(s):  
Pacific Ocean ◽  
El Niño ◽  
El Nino ◽  
Terrestrial Ecosystem ◽  
Terrestrial Ecosystems ◽  
La Niña ◽  
Enso Events ◽  
La Nina ◽  
The Pacific ◽  
The Pacific Ocean

Perturbations of the climate system caused by El Niño and La Niña events affect natural and managed systems in vast areas of the Pacific Ocean and far beyond it. (Other oscillations affect systems and sectors in wide swaths of the world as well.)1 El Niño–Southern Oscillation (ENSO) events have been associated with ecosystem disruptions and forest fires, crop failures and famines, disease epidemics, and even market fluctuations in various regions. The forms and degrees of impact depend not only on the strength and duration of an El Niño or La Niña event and its associated teleconnections, but also on the state, sensitivity, and vulnerability of the affected system and its biotic community, as well as its human population. The underlying characteristics of ecosystems and human societies in each region are important factors in their susceptibility to ENSO-related damages. Variation may be enhanced as ENSO effects ripple through natural and managed ecosystems. The underlying health of the affected biota, interrelationships among different biotic associations, and pressure by humans all affect marine as well as terrestrial ecosystem responses to ENSO events. Impacts on human systems can be both direct and indirect. Some ENSO phenomena, such as severe storms, affect human lives and infrastructures directly. Other impacts occur through alterations in the marine and terrestrial ecosystems and water supplies upon which human populations ultimately depend. In this chapter we consider some of the impacts that ENSO and other oscillations (described with their teleconnections in chapter 1) have on marine and terrestrial ecosystems and on human-managed systems apart from agriculture. The significant and geographically widespread changes that El Niño events induce in the Pacific Ocean alter conditions for various marine communities. These alterations include dramatic changes in the abundance and distribution of organisms, associated collapses of commercial fisheries, and ensuing consequences affecting human livelihood (Glantz, 2004; Lehodey et al., 2006). Some of the effects are well documented. Reductions in primary production of up to 95% were measured in the eastern equatorial Pacific in 1982–83 (Barber and Chavez, 1983.) Large changes in ecosystem structure and productivity have also been recorded in other parts of the Pacific Ocean, including the western Pacific and in the North Pacific subtropical gyre (north of the Hawaiian Islands) (Karl et al., 1995).

scholarly journals Influência do el niño e la niña no número de dias de precipitação pluviométrica do estado do Mato Grosso do Sul

2016 ◽  
Vol 10 (1) ◽  
pp. 73
Author(s):  
Nayhara De Lima Oliveira ◽  
Francisco Fernando Noronha Marcuzzo
Keyword(s):  
El Niño ◽  
Direct Relationship ◽  
El Nino ◽  
La Niña ◽  
Mato Grosso ◽  
La Nina ◽  
The Pacific ◽  
The Pacific Ocean ◽  
Mato Grosso Do Sul ◽  
Key Words Temperature

ResumoUm melhor detalhamento do comportamento da precipitação pluvial pode ser obtido com o estudo do NDC (Número de Dias de Chuva) e a sua correlação com fenômenos climáticos. O presente trabalho teve como objetivo correlacionar a variação do NDC no Estado do Mato Grosso do Sul com a intensidade do Índice Oceânico Niño(a) (ION). Utilizaram-se dados de 37 estações pluviométricas com 30 anos de dados e 55 estações com dados variando de 20 a 29 anos, sendo que toda série histórica está entre os anos de 1977 a 2006. No período de 1977 a 2006 o ION mensal médio variou entre -1,1°C e 1,3°C, variações consideradas moderadas, com algumas variações consideradas fortes nos anos de 1982 (2,3°C), 1983 (2,3°C). 1988 (-1,9°C), 1991 (1,6°C), 1992 (1,8°C), 1997 (2,5°C), 1998 (2,3°C), 1999/2000 (-1,6°C) e 2002 (1,5°C). Observa-se que o NDC de cada ano do período não tem uma relação direta com os fenômenos El Niño e La Niña, já que a linha de tendência polinomial de segunda ordem pouco variou.Palavras-chave: Temperatura do Oceano Pacífico, ENOS, Número de Dias de Chuva, Climatologia. AbstractA more detailed behavior of rainfall can be obtained from the study of Number of Days Rain (NDC) and its correlation with weather phenomena. This study aimed to correlate the variation of the NDC in the state of Mato Grosso do Sul with the intensity Niño Index (a). We used data from 37 rainfall stations with 30 years of data and 55 stations with data ranging from 20 to 29 years, and throughout this series between the years 1977 to 2006. In the period 1977 to 2006 the average monthly Niño índex ranged between -1,1°C and 1,3°C, variations considered moderate, with some variations considered strong in the years 1982 (2.3°C), 1983 (2.3°C), 1988(-1.9°C), 1991 (1.6°C), 1992 (1,8°C), 1997 (2.5°C), 1998 (2.3°C), 1999/2000 (-1.6°C) and 2002 (1.5°C). It is observed that in general the NDC for each year of the period has a direct relationship with El Niño and La Niña, since the polynomial trendline second order changed little. Key-words: Temperature of the Pacific Ocean, ENSO, Number of Days of Rain, Climatology ResumenUn comportamiento más detallado de la precipitación se pueden obtener a partir del estudio de Número de días de lluvia (NDL) y su correlación con los fenómenos meteorológicos. Este estudio tuvo como objetivo relacionar la variación de lo NDL en el estado de Mato Grosso do Sul, con la intensidad de El Niño Index (a). Se utilizaron los datos de 37 estaciones pluviométricas con 30 años de datos y 55 estaciones con datos de entre 20 y 29 años (1977 y 2006). En el período de 1977 a 2006, el índice de El Niño (a) promedio mensual osciló entre -1,1°C y 1,3° C, las variaciones considera moderado, con algunas variaciones consideradas fuerte en 1982 (2,3°C), 1983 (2,3°C). 1988 (-1,9°C), 1991 (1,6°C), 1992 (1,8°C), 1997 (2,5°C), 1998 (2,3°C), 1999/2000 (-1,6°C) y 2002 (1,5°C). Se observa que, en general, el NDC para cada año del período tiene una relación directa con El Niño y La Niña, ya que la línea de tendencia polinómica de segundo orden ha cambiado poco.Palabras clave: Temperatura del Océano Pacífico, ENSO, número de días de lluvia, Climatologia. 

scholarly journals Droughts and floods over the upper catchment of the Blue Nile and their connections to the timing of El Niño and La Niña events

2014 ◽  
Vol 18 (3) ◽  
pp. 1239-1249 ◽  
Author(s):  
M. A. H. Zaroug ◽  
E. A. B. Eltahir ◽  
F. Giorgi
Keyword(s):  
El Niño ◽  
El Nino ◽  
La Niña ◽  
Blue Nile ◽  
La Nina ◽  
The Pacific ◽  
Extreme Flood ◽  
Droughts And Floods ◽  
Relationship Of ◽  
The Impact

Abstract. The Blue Nile originates from Lake Tana in the Ethiopian Highlands and contributes about 60–69% of the main Nile discharge. Previous studies investigated the relationship of sea surface temperature (SST) in the Pacific Ocean (Niño 3.4 region) to occurrence of meteorological and hydrological droughts in the Nile Basin. In this paper we focus on the dependence of occurrence of droughts and floods in the upper catchment of the Blue Nile on the timing of El Niño and La Niña events. Different events start at different times of the year and follow each other, exhibiting different patterns and sequences. Here we study the impact of these timing and temporal patterns on the Blue Nile droughts and floods. The comparison between the discharge measurements (1965–2012) at the outlet of the upper catchment of the Blue Nile and the El Niño index shows that when an El Niño event is followed by a La Niña event, there is a 67% chance for occurrence of an extreme flood. Furthermore, we also found that 83% of El Niño events starting in April–June resulted in droughts in the upper catchment of the Blue Nile. Although the current study is limited by the reduced number of samples, we propose that observations as well as global model forecasts of SST during this season could be used in seasonal forecasting of the Blue Nile flow.

scholarly journals Internal tides in the Solomon Sea in contrasted ENSO conditions

2019 ◽  
Author(s):  
Michel Tchilibou ◽  
Lionel Gourdeau ◽  
Florent Lyard ◽  
Rosemary Morrow ◽  
Ariane Koch Larrouy ◽  
...  
Keyword(s):  
El Niño ◽  
El Nino ◽  
Tidal Energy ◽  
Dominant Mode ◽  
La Niña ◽  
Internal Tides ◽  
Western Boundary ◽  
Boundary Current ◽  
Surface Cooling ◽  
La Nina

Abstract. The Solomon Sea is a place of intense Low Latitudes Western Boundary current transiting to the equator where mesoscale activity is superimposed on internal tides. In this marginal sea, the cumulated effects of these dynamical constraints result in water mass transformation as observed by in situ observations. The objective of this paper is to document the M2 internal tides in the Solomon Sea and their impacts based on two regional simulations with and without tides. Because the Solomon Sea is under the influence of ENSO, the characteristics of the internal tides are analyzed for two contrasted ENSO conditions: the 1997–1998 El Niño and the 1999 La Niña. The generation, propagation and dissipation of the internal tides are sensitive to changes in stratification and mesoscale activity between El Niño and La Niña. Mode 1 is the dominant mode to propagate baroclinic tidal energy within the Solomon Sea, but the El Niño conditions, with stratification closer to the surface, are favorable for the propagation of mode 2. The la Niña case with a high level of mesoscale activity favors the appearance of incoherent internal tides. These results illustrate the complexity in predicting internal tides in order to access meso and submesoscale signatures from altimetric missions, including the future SWOT mission. Diapycnal mixing induced by the internal tides is efficient in eroding the salinity maximum of the upper thermocline water, and in cooling the surface temperature interacting with the atmosphere. Such effects are particularly visible far from the strong currents, where particles may experience the tidal effects during a longer time. Nevertheless, the impacts are different when considering particular ENSO conditions. The interaction of internal tides with the surface mesoscale activity reduces surface cooling during El Niño 1998, but increases surface warming during La Niña 1999, with possible impacts on regional air sea interaction.

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