Understanding present and future dynamics of ENSO and the IOD
Project leaders: Drs Agus Santoso (CSIRO and UNSW) and Guojian Wang (CSIRO)
Staff: Drs Dave Bi and Benjamin Ng.
The El Niño Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) affect millions of human lives in the tropical belt and beyond. The likelihood of extreme weather events such as drought, heatwaves, floods, and cyclones is elevated during such events, particularly extreme ENSO and extreme positive IOD. Understanding their dynamics is of utmost importance as to enhance our capacity to predict their occurrences, especially their trends in a climate that is undergoing change.
Present outstanding issues on this topics are many, and these include: generation mechanism of ENSO diversity (mechanism of extreme El Niño and weak El Niño) and the associated diversity in ENSO teleconnections; uncertainty in projected change in future ENSO and the IOD; and the role of the Southern Hemisphere oceans, in the ENSO and the IOD life cycle.
The objectives of the project are to:
- understand how ENSO and IOD events are generated, in particular, how they attain extreme amplitude, how they interact with each other and with the Southern Hemisphere oceans
- examine the causes for decadal modulation of ENSO and IOD characteristics, and the potential role of Southern Hemisphere oceans
- project changes in ENSO and the IOD under greenhouse warming, as well as their interactions and teleconnection, and assess uncertainty in the projected change.
El Niño/Southern Oscillation inhibited by submesoscale ocean eddies
14 February 2022
A recent Nature Geoscience article, by Shengpeng Wang et al. (2022), identifies a pathway to resolve the long-standing overestimation of El Niño and La Niña amplitudes in climate simulations. The El Niño/Southern Oscillation is characterized by irregular warm (El Niño) and cold (La Niña) events in the tropical Pacific Ocean, which have substantial global environmental and socioeconomic impacts. These events are generally attributed to the instability of basin-scale air–sea interactions in the equatorial Pacific. However, the role of sub-basin-scale processes in the El Niño/Southern Oscillation life cycle remains unknown due to the scarcity of observations and coarse resolution of climate models.
Using a long-term high-resolution global climate simulation, the authors find that equatorial ocean eddies with horizontal wavelengths less than several hundred kilometres substantially inhibit the growth of La Niña and El Niño events. These submesoscale eddies are regulated by the intensity of Pacific cold-tongue temperature fronts. The eddies generate an anomalous surface cooling tendency during El Niño by inducing a reduced upward heat flux from the subsurface to the surface in the central-eastern equatorial Pacific; the opposite occurs during La Niña. This dampening effect is missing in the majority of state-of-the-art climate models.
Dr Wenju Cai, CSHOR Director, disecussed the study’s findings during a ABC Radio Central Brisbane interview.
Increased ENSO sea surface temperature variability under four IPCC emission scenarios
1 February 2022
Sea surface temperature (SST) variability of El Niño–Southern Oscillation (ENSO) underpins its global impact, and its future change is a long-standing science issue. In its sixth assessment, the IPCC reports no systematic change in ENSO SST variability under any emission scenarios considered. However, in a communication published yesterday in Nature Climate Change, Cai et al. (2022) present a comparison between the 20th and 21st century which shows a robust increase in century-long ENSO SST variability under four IPCC plausible emission scenarios.
La Niña and tropical rainforests
22 November 2021
Dr Wenju Cai, CSHOR Director, discusses the effect of La Niña on tropical rainforests with Carolyn Cowan, writing for Mongabay.com. The full story is at this link.
AGU book, El Niño Southern Oscillation in a Changing Climate, showcased at COP26
1 November 2021
AGU were invited to contribute four books to a special COP26 Virtual Book Showcase: El Niño Southern Oscillation in a Changing Climate was selected for this special books collection.
Predicting Tropical Pacific decadal climate variability and change
1 October 2021
Tropical Pacific decadal climate variability and change (TPDV) affects the global climate system, extreme weather events, agricultural production, streamflow, marine and terrestrial ecosystems, and biodiversity. Although major international efforts are underway to provide decadal climate predictions, there is still a great deal of uncertainty. A review article by Power et al. (Including Cai, W., Zhang, X., and Wang, G.) (2021), published in Science, critically synthesises what is known and not known about the characteristics and causes of TPDV, and the accuracy to which it can be simulated and predicted. The article concludes with recommendations to improve our understanding of and ability to predict TPDV.
Read the review article at this link.
Enhanced North Pacific impact on ENSO under greenhouse warming
20 September, 2021
A majority of El Niño Southern Oscillation (ENSO) events are preceded by the North Pacific Meridional Mode (NPMM), a dominant coupled ocean–atmospheric mode of variability. How the precursory NPMM forcing on ENSO responds to greenhouse warming remains unknown. Using climate model ensembles under high-emissions warming scenarios, the authors of a study recently published in Nature Climate Change (Jia et al., 2021), find an enhanced future impact on ENSO by the NPMM. This is manifested by increased sensitivity of boreal-winter equatorial Pacific winds and sea surface temperature (SST) anomalies to the NPMM three seasons before.
Go to the Nature Climate Change publication via this link.
Changing El Niño–Southern Oscillation in a warming climate
18 August, 2021
A review article by Cai et al. (2021), published in Nature Reviews Earth & Environment, synthesises advances in observed and projected changes of multiple aspects of El Niño–Southern Oscillation (ENSO), including the processes behind such changes. The review finds that models which best capture key ENSO dynamics also tend to project an increase in future ENSO sea surface temperature (SST) variability and, thereby, ENSO magnitude under greenhouse warming, as well as an eastward shift and intensification of ENSO-related atmospheric teleconnections. Read the CSHOR post here.
Dr Guojian Wang’s science journey
14 April 2021
Dr Guojian Wang from the CSHOR team has shared a story on his science journey with the CSIRO blog. Read more about Guojian’s research into El Nino Southern Oscillation and the Indian Ocean Dipole, and what inspired him into a science carer, at this link.
CSHOR Session at AMOS 2021
CSHOR project leaders, Guojian Wang, Agus Santoso, Xuebin Zhang and Benjamin Ng are convening a session titled, ‘Southern hemisphere oceans and climate variability‘ at the AMOS 2021 Conference – online from 8 to 12 February 2021.
Abstract: The southern hemisphere oceans encompass many key elements of the Earth’s climate system, e.g., Indo-Pacific warm pool, Indonesian Throughflow, Super-gyre Circulation, and the vast Southern Ocean. Although more than 80% of the southern hemisphere is covered by ocean, the Amazonia, which has the largest rainforest in the world working as the lungs of the planet, and the Antarctic, which is covered by an average two-kilometre-thick ice sheet, can influence the Earth’s climate tremendously. All these components are influenced by climate variability in the region, including in the Indo-Pacific Oceans, such as the El Niño-Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) which exert significant impact on weather patterns, rainfall, air-sea fluxes, sea level, ocean density and circulations, ecosystems, and many others. How these modes of variability teleconnect in the southern hemisphere, and how they change under global warming, continue to be areas of active research.
Abstracts close on 6 November 2020.
Visit the conference website at this link.
Opposite response of strong and moderate positive Indian Ocean Dipole to greenhouse warming
1 December 2020
A new study by Cai, Yang and Wu et al. published today in Nature Climate Change shows that climate extremes seen in 2019-20 are likely to occur more frequently under greenhouse warming. Faster warming in the equatorial northwestern Indian Ocean favours atmosphere convection in the region. Equatorial nonlinear positive feedbacks responsible for the strong cooling in the equatorial eastern Indian Ocean are strengthened. Low-tropospheric warming which is faster than the surface warming is inconducive to Ekman pumping that drives warm anomalies. For further detail and a link to the full article, go to the CSHOR post at this link.
Book Release – ENSO in a changing climate
Update – on 29 December 2020, the book, ‘El Niño Southern Oscillation in a Changing Climate’, launched in November 2020, was highlighted in a Sydney Morning Herald article explaining El Niño and La Niña events.
El Niño is an unusual warming of the tropical Pacific that wreaks havoc on weather systems around the globe. It happens every few years and, like its cold counterpart La Niña, has profound effects on society and the environment. The irregular cycle between warm El Niño and cold La Niña events, referred to as El Niño Southern Oscillation, or ENSO, is the focus of a new book, El Niño Southern Oscillation in a Changing Climate, published by Wiley as part of the centennial celebration of the American Geophysical Union. The book is the first comprehensive examination of how ENSO cycle dynamics and impacts may change under the influence of rising greenhouse gas concentrations in the atmosphere.
Michael McPhaden (U.S. National Oceanic and Atmospheric Administration (NOAA) and CSHOR Advisory Committee Member), Agus Santoso (University of New South Wales (UNSW) and CSHOR project leader), and Wenju Cai (CSIRO and CSHOR Director), served as editors of the book.
Read the Editors’ Vox on the Eos website at this link.
La Niña event expected in 2020/21
28 September 2020
Dr Agus Santoso was interviewed by Peter Hannam for the Sydney Morning Herald/The Age about an emerging La Niña in 2020. The article reports that the Bureau of Meteorology is expected to declare a La Niña event is under way in the Pacific, underscoring climate influences that point to a wetter than usual end to 2020 across northern and eastern Australia. The article is available here.
Butterfly effect and a self-modulating El Niño response to global warming
3 September 2020
In an article published online today in Nature we show that like a butterfly effect, an infinitesimal random perturbation to identical initial conditions induces vastly different initial ENSO variability, which systematically affects its response to greenhouse warming a century later. In experiments with higher initial variability, a greater cumulative oceanic heat loss from ENSO thermal damping reduces stratification of the upper equatorial Pacific Ocean, leading to a smaller increase in ENSO variability under subsquent greenhouse warming. This self-modulating mechanism operates in two large ensembles generated using two different models, each commencing from identical initial conditions but with a butterfly perturbation; it also operates in a large ensemble generated with another model commencing from different initial conditions and across climate models participating in the Coupled Model Intercomparison Project. Thus, if the greenhouse-warming-induced increase in ENSO variability is initially suppressed by internal variability, future ENSO variability is likely to be enhanced, and vice versa. This self-modulation linking ENSO variability across time presents a different perspective for understanding the dynamics of ENSO variability on multiple timescales in a changing climate. Go to the CSHOR post for a link to the article and to related news items.
Abellán, E., McGregor, S., England, M. H., & Santoso, A. (2017). Distinctive role of ocean advection anomalies in the development of the extreme 2015–16 El Niño. Climate Dynamics. https://doi.org/10.1007/s00382-017-4007-0.
Bordbar, M. H., M. H. England, A. Sen Gupta, A. Santoso, A. S. Taschetto, T. Martin, W. Park, M. Latif (2019). Uncertainty in near-term global surface warming linked to tropical Pacific climate variability. Nature Communications, 10:1990. https://doi.org/10.1038/s41467-019-09761-2.
Bi, D., Wang, G., Cai, W., Santoso, A., Sullivan, A., Ng, B., & Jia, F. (2022). Improved simulation of ENSO variability through feedback from the equatorial Atlantic in a pacemaker experiment. Geophysical Research Letters, 49, e2021GL096887. https://doi.org/10.1029/2021GL096887.
Cai, W., McPhaden, M. J., Grimm, A. M., Rodrigues, R. R., Taschetto, A. S., Garreaud, R. D., . . . Vera, C. (2020). Climate impacts of the El Niño–Southern Oscillation on South America. Nature Reviews Earth & Environment, 1(4), 215-231. https://doi.org/10.1038/s43017-020-0040-3.
Cai, W., Ng, B., Geng, T. Wu, L., Santoso, A., McPhaden, M. J. (2020). Butterfly effect and a self-modulating El Niño response to global warming. Nature, 585, 68–73. https://doi.org/10.1038/s41586-020-2641-x.
Cai, W., Ng, B., Wang, G., Santoso, A., Wu, L., and Yang, Kai (2022). Increased ENSO sea surface temperature variability under four IPCC emission scenarios. Nature Climate Change. https://doi.org/10.1038/s41558-022-01282-z.
Cai, W., Santoso, A., Collins, M. et al. (Including Wang, G. and Ng, B.) (2021). Changing El Niño–Southern Oscillation in a warming climate. Nature Reviews Earth and Environment. https://doi.org/10.1038/s43017-021-00199-z.
Cai, W., A. Santoso, G. Wang, L. Wu, M. Collins, M. Lengaigne, S. Power, and A. Timmermann (2020). Chapter 13: ENSO Response to Greenhouse Forcing. AGU Monograph: ENSO in a Changing Climate. McPhaden, M., A. Santoso, W. Cai (Eds.), Wiley. https://doi.org/10.1002/9781119548164.ch13.
Cai, W., G. Wang, B. Dewitte, L. Wu, A. Santoso, K. Takahashi, Y. Yang, A. Carreric, and M. J. McPhaden (2018b). Increased variability of Eastern Pacific El Niño under greenhouse warming. Nature, 564, 201-206. https://doi.org/10.1038/s41586-018-0776-9.
Cai, W., Wang, G., Gan, B., Wu, L., Santoso, A., Lin, X., Chen, Z., Jia, F., & Yamagata, T. (2018). Stabilised frequency of extreme positive Indian Ocean Dipole under 1.5 °C warming. Nature Communications, 9(1), 1419. https://www.nature.com/articles/s41467-018-03789-6.
Cai, W., Wang, G., Santoso, A., Lin, X., & Wu, L. (2017). Definition of Extreme El Niño and Its Impact on Projected Increase in Extreme El Niño Frequency. Geophysical Research Letters, 44(21), 11,184-111,190. http://dx.doi.org/10.1002/2017GL075635.
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Cai, W., Yang, K., Wu, L., Huang, G., Santoso, A., Ng, B., Wang, G. and Yamagata, T. (2021). Opposite response of strong and moderate positive Indian Ocean Dipole to global warming. Nature Climate Change, 11, 27–32. https://doi.org/10.1038/s41558-020-00943-1.
Geng, T., Cai, W., & Wu, L. (2020). Two types of ENSO varying in tandem facilitated by nonlinear atmospheric convection. Geophysical Research Letters, 47. https://doi.org/10.1029/2020GL088784.
Herold, N., & Santoso, A. (2017). Indian Ocean warming during peak El Niño cools surrounding land masses. Climate Dynamics. https://doi.org/10.1007/s00382-017-4001-6.
Holgate, C.; Evans, J. P.; Taschetto, A. S; Sen Gupta, A.; Santoso, A. (2022). The impact of interacting climate modes on east Australian precipitation moisture sources. Journal of Climate, pp. 1 – 31, https://doi.org/10.1175/JCLI-D-21-0750.1.
Holmes, R. M., McGregor, S., Santoso, A., & England, M. H. (2018). Contribution of Tropical Instability Waves to ENSO Irregularity. Climate Dynamics. https://doi.org/10.1007/s00382-018-4217-0.
Hu, S., Sprintall, J., Guan, C., McPhaden, M. J., Wang, F., Hu, D., & Cai, W. (2020). Deep-reaching acceleration of global mean ocean circulation over the past two decades. Science Advances, 6(6), eaax7727. https://doi.org/10.1126/sciadv.aax7727.
Jia, F., Cai, W., Wu, L., Gan, B., Wang, G., Kucharski, F., . . . Keenlyside, N. (2019). Weakening Atlantic Niño–Pacific connection under greenhouse warming. Science Advances, 5(8), eaax4111. https://advances.sciencemag.org/content/5/8/eaax4111?rss=1.
Jia, F., Cai, W., Gan, B. Di Lorenzo, E. (2021). Enhanced North Pacific impact on El Niño/Southern Oscillation under greenhouse warming. Nature Climate Change. https://doi.org/10.1038/s41558-021-01139-x.
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Karamperidou, C., M. F. Stuecker, A. Timmermann, K.-S. Yun, S.-S. Lee, F.-F. Jin, A. Santoso, M. J. McPhaden, and W. Cai (2020). Chapter 21: ENSO in a Changing Climate: Challenges, Paleo-Perspectives, and Outlook. AGU Monograph: ENSO in a Changing Climate. McPhaden, M., A. Santoso, W. Cai (Eds.), Wiley. https://doi.org/10.1002/9781119548164.ch21.
Kajtar, J. B., Santoso, A., Collins, M., Taschetto, A. S., England, M. H., & Frankcombe, L. M. (2021). CMIP5 intermodel relationships in the baseline Southern Ocean climate system and with future projections. Earth’s Future, 9, e2020EF001873. https://doi.org/10.1029/2020EF001873.
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Li, S., Cai, W., & Wu, L. (2021). Weakened Antarctic dipole under global warming in CMIP6 models. Geophysical Research Letters, 48, e2021GL094863. https://doi.org/10.1029/2021GL094863.
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Makarim, S., J. Sprintall, Z. Liu, W. Yu, A. Santoso, X.-H. Yan, R. D. Susanto (2019). Previously unidentified Indonesian Throughflow pathways and freshening in the Indian Ocean during recent decades. Scientific Reports, 9:7364. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6517581/.
Mao, Y., Zou, Y., Alves, L. M., Macau, E. E. N., Taschetto, A. S., Santoso, A., & Kurths, J. (2022). Phase coherence between surrounding oceans enhances precipitation shortages in Northeast Brazil. Geophysical Research Letters, 49, e2021GL097647. https://doi.org/10.1029/2021GL097647.
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Wang, G. J., Cai, W. J., Gan, B. L., Wu, L. X., Santoso, A., Lin, X. P., Chen, Z. H., & McPhaden, M. J. (2017). Continued increase of extreme El Niño frequency long after 1.5 degrees C warming stabilization. Nature Climate Change, 7(8), 568-572. https://www.nature.com/articles/nclimate3351.
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Wang, G., Cai, W., & Santoso, A. (2021). Simulated thermocline tilt over the tropical Indian Ocean and its influence on future sea surface temperature variability. Geophysical Research Letters, 48, e2020GL091902. https://doi.org/10.1029/2020GL091902.
Wang, G., Cai, W., Yang, K., Santoso, A., & Yamagata T. (2020). A unique feature of the 2019 extreme positive Indian Ocean Dipole event. Geophysical Research Letters, 47. https://doi.org/10.1029/2020GL088615.
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Yeh, S.-W., Wang, G., Cai, W., & Park, R. J. (2022). Diversity of ENSO-related surface temperature response in future projection in CMIP6 climate models: Climate change scenario versus ENSO intensity. Geophysical Research Letters, 49, e2021GL096135. https://doi.org/10.1029/2021GL096135.
Zhong, W. X., Zheng, X. T., & Cai, W. J. (2017). A decadal tropical Pacific condition unfavorable to central Pacific El Niño. Geophysical Research Letters, 44(15), 7919-7926. https://doi.org/10.1002/2017GL073846.