Causes of the El Niño and La Niña Amplitude Asymmetry in the Equatorial Eastern Pacific

2010 ◽  
Vol 23 (3) ◽  
pp. 605-617 ◽  
Author(s):  
Jingzhi Su ◽  
Renhe Zhang ◽  
Tim Li ◽  
Xinyao Rong ◽  
J-S. Kug ◽  
...  
Keyword(s):  
Data Assimilation ◽  
Mixed Layer ◽  
El Niño ◽  
El Nino ◽  
La Niña ◽  
Eastern Pacific ◽  
Ocean Data Assimilation ◽  
La Nina ◽  
Nonlinear Advection ◽  
Far Eastern

Abstract The amplitude asymmetry between El Niño and La Niña is investigated by diagnosing the mixed-layer heat budget during the ENSO developing phase by using the three ocean assimilation products: Simple Ocean Data Assimilation (SODA) 2.0.2, SODA 1.4.2, and the Global Ocean Data Assimilation System (GODAS). It is found that the nonlinear zonal and meridional ocean temperature advections are essential to cause the asymmetry in the far eastern Pacific, whereas the vertical nonlinear advection has the opposite effect. The zonal current anomaly is dominated by the geostrophic current in association with the thermocline depth variation. The meridional current anomaly is primarily attributed to the Ekman current driven by wind stress forcing. The resulting induced anomalous horizontal currents lead to warm nonlinear advection during both El Niño and La Niña episodes and thus strengthen (weaken) the El Niño (La Niña) amplitude. The convergence (divergence) of the anomalous geostrophic mixed-layer currents during El Niño (La Niña) results in anomalous downwelling (upwelling) in the far eastern equatorial Pacific, which leads to a cold nonlinear vertical advection in both warm and cold episodes.

scholarly journals Dipole Structure of Mixed Layer Salinity in Response to El Niño‐La Niña Asymmetry in the Tropical Pacific

2019 ◽  
Vol 46 (21) ◽  
pp. 12165-12172 ◽  
Author(s):  
Cong Guan ◽  
Shijian Hu ◽  
Michael J. McPhaden ◽  
Fan Wang ◽  
Shan Gao ◽  
...  
Keyword(s):  
Mixed Layer ◽  
El Niño ◽  
El Nino ◽  
Tropical Pacific ◽  
La Niña ◽  
Dipole Structure ◽  
La Nina ◽  
The Tropical Pacific

scholarly journals Pengaruh Central Pacific dan eastern Pacific El Nino terhadap variabilitas curah hujan di Sulawesi

2018 ◽  
Vol 15 (2) ◽  
pp. 73
Author(s):  
Budi Prasetyo ◽  
Nikita Pusparini
Keyword(s):  
Data Assimilation ◽  
El Niño ◽  
El Nino ◽  
Climate Prediction ◽  
Eastern Pacific ◽  
Central Pacific ◽  
Eastern Pacific El Niño ◽  
Ocean Data Assimilation ◽  
Ep El Niño ◽  
Climate Prediction Center

Pulau Sulawesi dipengaruhi oleh fenomena Central Pacific (CP) dan Eastern Pacific (EP) El Niño. Curah hujan Sulawesi mencakup ketiga pola hujan yang ada di Indonesia yaitu Monsunal, equatorial, dan lokal. Variabilitas ketiga pola curah hujan tersebut akan memberikan respon yang berbeda terhadap pengaruh dari kedua tipe El Niño tersebut. Maka, Kajian ini akan membahas pengaruh dari kedua tipe El Niño  terhadap curah hujan Sulawesi. Penelitian ini Menggunakan data curah hujan bulanan berasal dari Climate Prediction Center (CPC) National Oceanic and Atmospheric Administration (NOAA), Suhu Permukaan Laut (SPL) bulanan dari System Ocean Data Assimilation (SODA) versi 2.2.4 dan oceanic Niño Indeks (ONI) dengan periode  Januari 1950 hingga Desember 2010 (60 tahun). Perhitungan statistik sederhana berupa perata-rataan, korelasi, dan analisa komposit digunakan dalam kajian ini. Penentuan tipe El Niño menggunakan tiga buah indeks yang berbeda. Hasilnya diperoleh bahwa Curah hujan Sulawesi berkurang saat kedua tipe El Niño. Penurunan curah hujan akibat EP El Niño berkisar antara 5 – 20 mm sedangkan akibat CP El Niño berkisar antara 2-12 mm. Wilayah Sulawesi dengan pola curah hujan monsunal merupakan wilayah yang mengalami penurunan curah hujan terbesar akibat kedua tipe El Niño tersebut, kemudian diikuti dengan pola curah hujan equatorial dan terakhir Lokal.

scholarly journals Spatial Analysis of the Yellowfin Tuna (Thunnus albacares) Fishery, and its Relation to El Niño and La Niña Events in the Tropical Eastern Pacific

2002 ◽  
Vol 30 (1) ◽  
Author(s):  
Juan Antonio de Anda-Montañez ◽  
Susana Martínez-Aguilar ◽  
Alberto Amador-Buenrostro ◽  
Adriana Muhlia-Almazán
Keyword(s):  
Spatial Analysis ◽  
El Niño ◽  
El Nino ◽  
Yellowfin Tuna ◽  
La Niña ◽  
Eastern Pacific ◽  
Thunnus Albacares ◽  
Tropical Eastern Pacific ◽  
La Nina

The NCEP GODAS Ocean Analysis of the Tropical Pacific Mixed Layer Heat Budget on Seasonal to Interannual Time Scales

2010 ◽  
Vol 23 (18) ◽  
pp. 4901-4925 ◽  
Author(s):  
Boyin Huang ◽  
Yan Xue ◽  
Dongxiao Zhang ◽  
Arun Kumar ◽  
Michael J. McPhaden
Keyword(s):  
Data Assimilation ◽  
Mixed Layer ◽  
Heat Budget ◽  
La Niña ◽  
Sst Variability ◽  
Ocean Data Assimilation ◽  
La Nina ◽  
Mixed Layer Heat Budget ◽  
Data Assimilation System ◽  
The Tropical Pacific

Abstract The mixed layer heat budget in the tropical Pacific is diagnosed using pentad (5 day) averaged outputs from the Global Ocean Data Assimilation System (GODAS), which is operational at the National Centers for Environmental Prediction (NCEP). The GODAS is currently used by the NCEP Climate Prediction Center (CPC) to monitor and to understand El Niño and La Niña in near real time. The purpose of this study is to assess the feasibility of using an operational ocean data assimilation system to understand SST variability. The climatological mean and seasonal cycle of mixed layer heat budgets derived from GODAS agree reasonably well with previous observational and model-based estimates. However, significant differences and biases were noticed. Large biases were found in GODAS zonal and meridional currents, which contributed to biases in the annual cycle of zonal and meridional advective heat fluxes. The warming due to tropical instability waves in boreal fall is severely underestimated owing to use of a 4-week data assimilation window. On interannual time scales, the GODAS heat budget closure is good for weak-to-moderate El Niños. A composite for weak-to-moderate El Niños suggests that zonal and meridional temperature advection and vertical entrainment/diffusion all contributed to the onset of the event and that zonal advection played the dominant role during decay of the event and the transition to La Niña. The net surface heat flux acts as a damping during the development stage, but plays a critical role in the decay of El Niño and the transition to the following La Niña. The GODAS heat budget closure is generally poor for strong La Niñas. Despite the biases, the GODAS heat budget analysis tool is useful in monitoring and understanding the physical processes controlling SST variability associated with ENSO. Therefore, it has been implemented operationally at CPC in support of NOAA’s ENSO forecasting.

scholarly journals The Role of Reversed Equatorial Zonal Transport in Terminating an ENSO Event

2016 ◽  
Vol 29 (16) ◽  
pp. 5859-5877 ◽  
Author(s):  
Han-Ching Chen ◽  
Zeng-Zhen Hu ◽  
Bohua Huang ◽  
Chung-Hsiung Sui
Keyword(s):  
El Niño ◽  
El Nino ◽  
Equatorial Pacific ◽  
La Niña ◽  
Eastern Pacific ◽  
Enso Events ◽  
Mature Phase ◽  
La Nina ◽  
Eastern Equatorial Pacific ◽  
Equatorial Thermocline

Abstract This study shows the sudden basinwide reversal of anomalous equatorial zonal transport above the thermocline at the peaking phase of ENSO triggers rapid termination of ENSO events. The anomalous equatorial zonal transport is controlled by the concavity of anomalous thermocline meridional structure across the equator. During the developing phase of ENSO, opposite zonal transport anomalies form in the western-central and central-eastern equatorial Pacific, respectively. Both are driven by the equatorial thermocline anomalies in response to zonal wind anomalies over the western-central equatorial ocean. At this stage, the anomalous zonal transport in the east enhances ENSO growth through zonal SST advection. In the mature phase of ENSO, off-equatorial thermocline depth anomalies become more dominant in the eastern Pacific because of the reflection of equatorial signals at the eastern boundary. As a result, the meridional concavity of the thermocline anomalies is reversed in the east. This change reverses zonal transport rapidly in the central-to-eastern equatorial Pacific, joining with the existing reversed zonal transport anomalies farther to the west, and forms a basinwide transport reversal throughout the equatorial Pacific. This basinwide transport reversal weakens the ENSO SST anomalies by reversed advection. More importantly, the reversed zonal transport reduces the existing zonal tilting of the equatorial thermocline and weakens its feedback to wind anomalies effectively. This basinwide reversal is built in at the peak phase of ENSO as an oceanic control on the evolution of both El Niño and La Niña events. The reversed zonal transport anomaly after the mature phase weakens El Niño in the eastern Pacific more efficiently than it weakens La Niña.

Interannual Variations of the Tropical Ocean Instability Wave and ENSO

2008 ◽  
Vol 21 (15) ◽  
pp. 3680-3686 ◽  
Author(s):  
Soon-Il An
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Thermal Flux ◽  
La Niña ◽  
Instability Wave ◽  
Cold Tongue ◽  
Tropical Ocean ◽  
Ocean Data Assimilation ◽  
La Nina

Abstract Using ocean data assimilation products, variability of eastern Pacific Ocean tropical instability waves (TIWs) and their interaction with the El Niño–Southern Oscillation (ENSO) were analyzed. TIWs are known to heat the cold tongue through horizontal advection. Conversely, variability of the cold tongue influences TIW variability (TIWV). During La Niña, TIWs are more active and contribute to anomalous warming. During El Niño, TIWs are suppressed and induce an anomalous cooling. TIWV thus acts as negative feedback to ENSO. Interestingly, this feedback is stronger during La Niña than during El Niño. To investigate this negative/asymmetric feedback, a simple parameterization for the horizontal thermal flux convergence due to TIWs was incorporated into a simple ENSO model. The model results suggested that asymmetric thermal heating associated with TIWs can explain the El Niño–La Niña asymmetry (with larger-amplitude El Niños).

scholarly journals ENSO Impact on Kelvin Waves and Associated Tropical Convection

2013 ◽  
Vol 70 (11) ◽  
pp. 3513-3532 ◽  
Author(s):  
Gui-Ying Yang ◽  
Brian Hoskins
Keyword(s):  
El Niño ◽  
El Nino ◽  
Tropical Convection ◽  
Kelvin Waves ◽  
La Niña ◽  
Eastern Pacific ◽  
Substantial Impact ◽  
La Nina ◽  
Central Eastern ◽  
The Impact

Abstract The impact of El Niño–Southern Oscillation (ENSO) on atmospheric Kelvin waves and associated tropical convection is investigated using the ECMWF Re-Analysis, NOAA outgoing longwave radiation (OLR), and the analysis technique introduced in a previous study. It is found that the phase of ENSO has a substantial impact on Kelvin waves and associated convection over the equatorial central-eastern Pacific. El Niño (La Niña) events enhance (suppress) variability of the upper-tropospheric Kelvin wave and the associated convection there, in both extended boreal winter and summer. The mechanism of the impact is through changes in the ENSO-related thermal conditions and the ambient flow. In El Niño years, because of SST increase in the equatorial central-eastern Pacific, variability of eastward-moving convection, which is mainly associated with Kelvin waves, intensifies in the region. In addition, owing to the weakening of the equatorial eastern Pacific westerly duct in the upper troposphere in El Niño years, Kelvin waves amplify there. In La Niña years, the opposite occurs. However, the stronger westerly duct in La Niña winters allows more NH extratropical Rossby wave activity to propagate equatorward and force Kelvin waves around 200 hPa, partially offsetting the in situ weakening effect of the stronger westerlies on the waves. In general, in El Niño years Kelvin waves are more convectively and vertically coupled and propagate more upward into the lower stratosphere over the central-eastern Pacific. The ENSO impact in other regions is not clear, although in winter over the eastern Indian and western Pacific Oceans Kelvin waves and their associated convection are slightly weaker in El Niño than in La Niña years.

scholarly journals Importance of El Niño reproducibility for reconstructing historical CO<sub>2</sub> flux variations in the equatorial Pacific

Ocean Science ◽  
2020 ◽  
Vol 16 (6) ◽  
pp. 1431-1442
Author(s):  
Michio Watanabe ◽  
Hiroaki Tatebe ◽  
Hiroshi Koyama ◽  
Tomohiro Hajima ◽  
Masahiro Watanabe ◽  
...  
Keyword(s):  
Data Assimilation ◽  
El Niño ◽  
El Nino ◽  
Correction Term ◽  
Co2 Flux ◽  
Equatorial Pacific ◽  
The Other ◽  
Ocean Temperature ◽  
Ocean Data Assimilation ◽  
La Nina

Abstract. Based on a set of climate simulations utilizing two kinds of Earth system models (ESMs) in which observed ocean hydrographic data are assimilated using exactly the same data assimilation procedure, we have clarified that the successful simulation of the observed air–sea CO2 flux variations in the equatorial Pacific is tightly linked to the reproducibility of coupled physical air–sea processes. When an ESM with a weaker ENSO (El Niño–Southern Oscillations) amplitude than that of the observations was used for historical simulations with ocean data assimilation, the observed equatorial anticorrelated relationship between the sea surface temperature (SST) and the air–sea CO2 flux on interannual to decadal timescales could not be represented. The simulated CO2 flux anomalies were upward (downward) during El Niño (La Niña) periods in the equatorial Pacific. The reason for this was that the non-negligible correction term in the governing equation of ocean temperature, which was added via the ocean data assimilation procedure, caused an anomalous, spurious equatorial upwelling (downwelling) during El Niño (La Niña) periods, which brought more (less) subsurface layer water rich in dissolved inorganic carbon (DIC) to the surface layer. On the other hand, in the historical simulations where the observational data were assimilated into the other ESM with a more realistic ENSO representation, the correction term associated with the assimilation procedure remained small enough so as not to disturb an anomalous advection–diffusion balance for the equatorial ocean temperature. Consequently, spurious vertical transport of DIC and the resultant positively correlated SST and air–sea CO2 flux variations did not occur. Thus, the reproducibility of the tropical air–sea CO2 flux variability with data assimilation can be significantly attributed to the reproducibility of ENSO in an ESM. Our results suggest that, when using data assimilation to initialize ESMs for carbon cycle predictions, the reproducibility of the internal climate variations in the model itself is of great importance.

The Role of Ekman Ocean Heat Transport in the Northern Hemisphere Response to ENSO

2008 ◽  
Vol 21 (21) ◽  
pp. 5688-5707 ◽  
Author(s):  
Michael A. Alexander ◽  
James D. Scott
Keyword(s):  
Mixed Layer ◽  
North Atlantic ◽  
El Niño ◽  
North Pacific ◽  
El Nino ◽  
La Niña ◽  
Ekman Transport ◽  
Layer Model ◽  
The North ◽  
La Nina

Abstract The influence of oceanic Ekman heat transport (Qek) on air–sea variability associated with ENSO teleconnections is examined via a pair of atmospheric general circulation model (AGCM) experiments. In the mixed layer model (MLM) experiment, observed sea surface temperatures (SSTs) for the years 1950–99 are specified over the tropical Pacific, while a grid of mixed layer models is coupled to the AGCM elsewhere over the global oceans. The same experimental design was used in the Ekman transport/mixed layer model (EKM) experiment with the addition of Qek in the mixed layer ocean temperature equation. The ENSO signal was evaluated using differences between composites of El Niño and La Niña events averaged over the 16 ensemble members in each experiment. In both experiments the Aleutian low deepened and the resulting surface heat fluxes cooled the central North Pacific and warmed the northeast Pacific during boreal winter in El Niño relative to La Niña events. Including Qek amplified the ENSO-related SSTs by ∼⅓ in the central and northeast North Pacific, producing anomalies comparable to those in nature. Differences between the ENSO-induced atmospheric circulation anomalies in the EKM and MLM experiments were not significant over the North Pacific. The sea level pressure (SLP) and SST response to ENSO over the Atlantic strongly projects on the North Atlantic Oscillation (NAO) and the SST tripole pattern in observations and both model experiments. The La Niña anomalies, which are stronger than during El Niño, include high pressure and positive SSTs in the central North Atlantic. Including Ekman transport enhanced the Atlantic SST anomalies, which in contrast to the Pacific, appeared to strengthen the overlying atmospheric circulation.

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