Characteristics and Teleconnections of the Extreme Eastern and Central Pacific and Mixed El Niños

Document Type : Full length article


1 MSc Student of Meteorology, Space Physics Department, Institute of Geophysics, University of Tehran, Tehran, Iran

2 Associate Professor, Space Physics Department, Institute of Geophysics, University of Tehran, Tehran, Iran


The El Niño-Southern Oscillation (ENSO) cycle of alternating warm El Niño and cold La Niña events occurs when the tropical Pacific Ocean and its overlying atmosphere deviated from its natural state for at least several consecutive months (Neelin et al., 1998). The neutral phase of the El Niño-Southern Oscillation is derived by the strong zonally asymmetric state of the equatorial Pacific and is characterized by surface easterly trade winds along the equatorial Pacific, rising motion, deep convection and heavy rainfall over the western equatorial Pacific, westerly winds at upper levels and sinking motion over the eastern equatorial Pacific (Bjerknes, 1969). El Niño is characterized by weak and La Niña by strong zonal SST gradients, accompanied respectively by weakening and strengthening of the trade winds across the equatorial Pacific (McPhaden et al. 2006). As a result, compared to the neutral phase of the El Niño-Southern Oscillation, convective systems intensify in the western tropical Pacific and slightly shift to the west during La Niña events, but shift to the central and eastern tropical Pacific during El Niño events. Since this early recognition of the coupling between the atmosphere and the Pacific Ocean by Bjerknes (1966) and Bjerknes (1969), major advances have beenmade toward a comprehensive understanding of the physics of the El Niño-Southern Oscillation. This is particularly achived through development of complex climatemodels for realistic simulation of the El Niño-Southern Oscillation cycle (Bellenger et al., 2014), and great observational advances that have been made during the international Tropical Ocean-Global Atmosphere (TOGA) program conducted between 1985 and 1994 (McPhaden et al., 1998). El Niño or the warm phase of the El Niño-Southern Oscillation is a quasi-periodic natural phenomenon that occurs in the tropical Pacific Ocean. The El Niño-Southern Oscillation not only influences the climate of nearby regions, but it is the most important natural climate aggent contributing to the interannual climate variability over many regions across the globe, including North America (e.g. Yu et al., 2015; Guo et al., 2017), the Middle East (e.g. Alizadeh-choobari, 2017; Alizaeh-Choobari et al., 2018a, Alizaeh-Choobari et al., 2018b), East Asia (e.g. Feng and Li, 2011), Southeast Asia (e.g. Lee et al., 2017) and the Indian subcontinent (e.g. Kumar et al., 2006). Depending on the location of the maximum sea surface temperature in the eastern or central equatorial Pacific, the eastern Pacific El Niño or the central Pacific El Niño are identified, while a mixed event has also been diagnosed in the eastern and central Pacific El Niño events.
Materials and methods
In this study, using the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis Interim (ERA-Interim) monthly dataset with a horizontal resolution of 0.75º Í 0.75º, and the Extended Reconstructed Sea Surface Temperature version 5 (ERSSTv5) dataset, we determined the phase of ENSO and the type of El Niño events during the period 1979-2016. In addition, characteristics of the 1997-98 eastern Pacific El Niño, and the 2009-10 central Pacific El Niño and the 2015-16 El Niño are investigated as a mixed event of the eastern and central Pacific El Niño,.
Results and discussion
The results of this research indicateed that during the period 1979-2016, 1979-80, 1982-83, 1986-87, 1987-88, 1991-92, 1994-95, 1997-98, 2002-03, 2004-05, 2006-07, 2009-10, 2014-15 and 2015-16 have been the years for which three-month running means of the Oceanic Niño Index (ONI) for 5 consecutive periods became greater or equal to 0.5 degree Celcius, indicating the occurrence of El Niño in these years. To determine the eastern and central Pacific El Niños during the period 1979-2016, we used the empirical orthogonal function (EOF) by examining spatial correlation between sea surface temperature anomalies in the equatorial Pacific Ocean and results of the empirical orthogonal function. The 1997-98 and 2015-16 El Niño events are both categorized as extreme El Niño events. The 2009-10 El Niño is weaker than the other two events, but over the last century, it has been the strongest central Pacific El Niño event. Results indicated that the onset of all these three events was in June, while some differences are found between termination of the 1997-98 and 2015-16 El Niños, including different time of dissipation for these events. All these three events have shown characteristics of classic El Niño events, such that anomalous positive and negative sea surface temperature are seen in the eastern and western equatorial Pacific, respectively. Nevertheless, maximum positive sea surface temperature is formed in the eastern equatorial Pacific during the 1997-98 El Niño. This is different from the 2009-10 El Niño events with the maximum sea surface temperature in the central (near the dateline) equatorial Pacific. In fact, maximum positive sea surface temperature anomalies are expanded in the eastern and central equatorial Pacific during the 1997-98 and 2009-10 El Niño events, respectively. However, it extends from central to eastern equatorial Pacific during the 2015-16 El Niño. Intensities of the maximum sea surface temperature anomalies and mean sea level pressure have been greater during the 1997-98 El Niño compared to those during the 2009-10 event, indicating that central Pacific El Niños are generally less intense than eastern Pacific El Niño events. It is shown that positive sea surface temperature anomalies in the 2015-16 El Niño event cover a larger area extending from the central to the eastern equatorial Pacific. It is found that both sea surface temperature and mean sea level pressure anomalies in the equatorial Pacific were larger the 1997-98 eastern Pacific El Niño than those of the 2009-10 central Pacific El Niño. This suggests that the central Pacific El Niño events are generally weaker than the eastern Pacific El Niño events. In all of the three El Niño events, positive (negative) geopotential height anomalies at 300 hPa pressure level in the equatorial Pacific are collocated with positive (negative) sea surface temperature anomalies. Geopotential height anomalies in the upper levels over the tropical Pacific influence weather patterns of other regions. It is discussed that different geopotential height anomalies at upper levels of the equatorial Pacific during the three El Niño events have led to different teleconnections across the globe. For example, temperature anomalies in the Antarctic during the 2009-10 El Niño were opposite to those during the 1997-98 and 2015-16 El Niño events.  
Analysis of the ERA-Interim dataset with the horizontal resolution of 0.75º Í 0.75º for the period 1979-2016 indicated that the eastern, central and mixed El Niño events have generally different characteristics in the equatorial Pacific. As a result, teleconnection patterns of these events across the globe are also found to be different. 


Ahrens, C.D. (2012). Meteorology Today: An Introduction to Weather, Climate, and the Environment, Cengage Learning.
Alizadeh-Choobari, O. (2017). Contrasting global teleconnection features of the eastern Pacific and central Pacific El Niño events, Dynamics of Atmospheres and Oceans, 80: 139-154.
Alizadeh-Choobari, O.; Adibi, P. and Irannejad, P. (2018a). Impact of the El Niño–Southern Oscillation on the climate of Iran using ERA-Interim data, Climate Dynamics, 51: 2897-2911.
Alizadeh-Choobari, O. and Najafi, M.S. (2018b). Climate variability in Iran in response to the diversity of the El Niño-Southern Oscillation, International Journal of Climatology, 38: 4239-4250.
Andreoli, R.V.; Oliveira, S.S.; Kayano, M.T.; Viegas, J.; Souza, R.A.F. and Candido, L.A. (2016). The influence of different El Niño types on the South American rainfall, International Journal of Climatology, 37(3): 1374-1390.
Ashok, K.; Behera, S.K.; Rao, S.A.; Weng, H. and Yamagata, T. (2007). El Niño Modoki and its possible teleconnection, Journal of Geophysical Research: Oceans, 112, C11007.
Ashok, K.; Iizuka, S.; Rao, S.A.; Saji, N.H. and Lee, W.J. (2009). Processes and boreal summer impacts of the 2004 El Niño Modoki: An AGCM study, Geophysical Research Letters, 36, L04703.
Barsugli, J.J. and Sardeshmukh, P.D. (2002). Global atmospheric sensitivity to tropical SST anomalies throughout the Indo-Pacific basin, Journal of Climate, 15(23): 3427-3442.
Bellenger, H.; Guilyardi, E.; Leloup, J.; Lengaigne, M. and Vialard, J. (2014). ENSO representation in climate models: from CMIP3 to CMIP5, Climate Dynamics, 42: 1999-2018.
Berrisford, P.; Dee, D.P.; Fielding, K.; Fuentes M.; Kallberg, P.; Kobayashi, S. and Uppala, S.M. (2009). The ERA-Interim archive: Era Report Series,1.Era report series. ECMWF, Reading.
Bjerknes, J. (1969). Atmospheric teleconnections from the equatorial Pacific, Monthly weather review, 97(3): 163-172.
Cai, W.; Borlace, S.; Lengaigne, M.; Van Rensch, P.; Collins, M.; Vecchi, G. ... and England, M.H. (2014). Increasing frequency of extreme El Niño events due to greenhouse warming, Nature Climate Change, 4(2): 111-116.
Cai, W.; Santoso, A.; Wang, G.; Yeh, S.W.; An, S.I.; Cobb, K.M. ... and Lengaigne, M. (2015). ENSO and greenhouse warming, Nature Climate Change, 5(9): 849-859.
Feng, J. and Li, J. (2011). Influence of El Niño Modoki on spring rainfall over south China, Journal of Geophysical Research: Atmospheres, 116, D13102.
Fu, C.; Diaz, H.F. and Fletcher, J.O. (1986). Characteristics of the response of sea surface temperature in the central Pacific associated with warm episodes of the Southern Oscillation, Monthly Weather Review, 114(9): 1716-1739.
Guo, Y.; Ting, M.; Wen, Z. and Lee, D.E. (2017). Distinct patterns of tropical Pacific SST anomaly and their impacts on North American climate, Journal of Climate, 30(14): 5221-5241.
Holton, J.R. (2004). An Introduction to Dynamic Meteorology, Burlington, MA: Elsevier.
Jiménez-Muñoz, J.C.; Mattar, C.; Barichivich, J.; Santamaría-Artigas, A.; Takahashi, K.; Malhi, Y. ... and Van Der Schrier, G. (2016). Record-breaking warming and extreme drought in the Amazon rainforest during the course of El Niño 2015–2016, Scientific reports, 6: 1-12.
Kao, H.Y. and Yu, J.Y. (2009). Contrasting eastern-Pacific and central-Pacific types of ENSO, Journal of Climate, 22(3): 615-632.
Kim, W.; Yeh, S.W.; Kim, J.H.; Kug, J.S. and Kwon, M. (2011). The unique 2009–2010 El Niño event: A fast phase transition of warm pool El Niño to La Niña, Geophysical Research Letters, 38: L15809.
Kug, J.S.; Jin, F.F. and An, S.I. (2009). Two types of El Niño events: cold tongue El Niño and warm pool El Niño, Journal of Climate, 22(6): 1499-1515.
Kumar, K.K.; Rajagopalan, B.; Hoerling, M.; Bates, G. and Cane, M. (2006). Unraveling the mystery of Indian monsoon failure during El Niño, Science, 314(5796): 115-119.
Lee, B.P.Y.; Davies, Z.G. and Struebig, M.J. (2017). Smoke pollution disrupted biodiversity during the 2015 El Niño fires in Southeast Asia, Environmental Research Letters, 12(9): 094022.
Marjani, S.; Alizadeh-Choobari, O. and Irannejad, P. (2019). Frequency of extreme El Niño and La Niña events under global warming, Climate Dynamics, 53: 5799-5813.
McPhaden, M.J. (1999). El Niño the child prodigy of 1997–98, Nature, 398: 559-562.
McPhaden, M.J.; Busalacchi, A.J.; Cheney, R.; Donguy, J.; Gage, K.S.; Halpern, D.; Ji, M.; Julian, P.; Meyers, G.; Mitchum, G.T.; Niiler, P.P.; Picaut, J.; Reynolds, R.W.; Smith, N. and Takeuchi, K. (1998). The Tropical Ocean-Global Atmosphere observing system: a decade of progress, Journalof Geophysical Research, 103: 14169-14240.
McPhaden, M.J.; Zebiak, S.E. and Glantz, M.H. (2006). ENSO as an integrating concept in Earth science, Science, 314: 1740-1745.
Neelin, J.D. (2011). Climate change and climate modeling,  Cambridge: Cambridge University Press.
Paek, H.; Yu, J.Y. and  Qian, C. (2017). Why were the 2015/2016 and 1997/1998 extreme El Niños different?, Geophysical Research Letters, 44(4): 1848-1856.
Sarachik, E.S. and Cane, M.A. (2010). The El Nino-southern oscillation phenomenon, Cambridge University Press.
Walker, G.T. and Bliss, E.M. (1932). World weather V, Memoirs of the Royal Meteorological Society, 4(36): 53-84.
Wang, C.; Deser, C.; Yu, J.Y.; DiNezio, P. and Clement, A. (2017). El Niño and southern oscillation (ENSO): a review, In Coral Reefs of the Eastern Tropical Pacific: Springer, Dordrecht, 85-106.
Wang, G. and Hendon, H.H. (2007). Sensitivity of Australian rainfall to inter–El Niño variations, Journal of climate, 20(16): 4211-4226.
Yeh, S.W.; Cai, W.; Min, S.K.; McPhaden, M.J.; Dommenget, D.; Dewitte, B.; ... and Kug, J.S. (2018). ENSO atmospheric teleconnections and their response to greenhouse gas forcing, Reviews of Geophysics, 56(1): 185-206.
Yu, B.; Zhang, X.; Lin, H. and Yu, J.Y. (2015). Comparison of wintertime North American climate impacts associated with multiple ENSO indices, Atmosphere-ocean, 53(4): 426-445.
Yu, J.Y. and Zou, Y. (2013). The enhanced drying effect of Central-Pacific El Niño on US winter, Environmental Research Letters, 8(1): 014019.
Yu, J.Y.; Zou, Y.; Kim, S.T. and Lee, T. (2012). The changing impact of El Niño on US winter temperatures, Geophysical Research Letters, 39(15): L15702.
Yu, J.Y. and Kim, S.T. (2013). Short Communication Identifying the types of major El Niño events since 1870, International Journal of Climatology, 33(8): 2105-2112.
Yu, J.Y.; Kao, H.Y. and Lee, T. (2010). Subtropics-related interannual sea surface temperaturevariability in the central equatorial Pacific, Journal of Climate, 23(11): 2869-2884.
Zhou, T.; Wu, B. and Dong, L. (2014). Advances in research of ENSO changes and the associated impacts on Asian-Pacific climate, Asia-Pacific Journal of Atmospheric Science, 50(4): 405-422.