El Niño Southern Oscillation (ENSO)

by

Brian Bossak

• LAST REVIEWED: 15 April 2021
• LAST MODIFIED: 29 May 2015
• DOI: 10.1093/obo/9780199874002-0113

Introduction

El Niño Southern Oscillation (ENSO) is a coupled ocean–atmosphere phenomenon in the Pacific Ocean that has widespread meteorological and ecological impacts on the Earth’s surface. Although observed for many years, the currently accepted definition of the ENSO phenomenon was largely shaped by a Trenberth’s publication in 1997. ENSO affects both sea-surface temperatures and large-scale climate features, resulting in shifting rainfall, tropical storm, ecologic, and health-related patterns. This article explores publications related to ENSO definitions, climate effects, association with tropical cyclones, water and food security, human health, vector-borne disease, and other social impacts of ENSO. The author would like to thank Meredith Phillips for assistance with an early draft and Michele Bolduc for extremely valuable editorial and reference locating assistance.

General Overviews

Historically, the Southern Oscillation and El Niño were generally considered separate events (e.g., Walker 1928); however, as climate understanding increased throughout the 20th century, the two phenomena became associated as a coupled climate event, and cycles began being termed “ENSO” beginning in the 1960s. Allan, et al. 1996; Jin 1996; and Neelin, et al. 1998 provide broad overviews of ENSO for a wide audience; however, Clarke 2008 offers more technical information for the advanced reader. Julian and Chervin 1978 began to shape the way in which the phenomenon was considered. McCreary and Anderson 1991 provides a useful overview of the types of models used to visualize ENSO cycles. Torrence and Webster 1999 provides an accessible review of 125 years of ENSO data to show the types of data used to monitor ENSO and discuss how ENSO conditions are dynamic (perhaps even more so under global warming, discussed in ENSO under Global Climate Change).

• Allan, Robert J., Janette A. Lindesay, and David E. Parker. El Niño Southern Oscillation and Climatic Variability. Collingwood, Australia: CSIRO, 1996.

  Comprehensive text that provides an overview of ENSO for a wide audience. Includes a synthesis of the literature, a review of different theories, and an extensive discussion of the global impacts of the phenomenon. Text comes with a CD-ROM containing monthly mean sea level pressure (MSLP) and sea-surface temperature (SST) data from 1871 to 1994.

• Clarke, Allan J. An Introduction to the Dynamics of El Niño and the Southern Oscillation. Burlington, MA: Elsevier, 2008.

  Technical introduction to ENSO for the graduate student or researcher. Includes sections on the history of ENSO research and observations, ocean and atmospheric dynamics, approaches to prediction, and effects on marine and bird life.

• Jin, Fei-Fei. “Tropical Ocean-Atmosphere Interaction, the Pacific Cold Tongue, and the El Niño-Southern Oscillation.” Science 274 (1996): 76–78.

  DOI: 10.1126/science.274.5284.76

  Presents a simple paradigm of the tropical Pacific basin, covering the basic physics of the ocean–atmospheric interactions producing ENSO and the Pacific cold tongue and the basic features of the climate states of the Atlantic and Indian Ocean basins.

• Julian, Paul R., and Robert M. Chervin. “A Study of the Southern Oscillation and Walker Circulation Phenomenon.” Monthly Weather Review 106 (1978): 1433–1451.

  DOI: 10.1175/1520-0493(1978)106<1433:ASOTSO>2.0.CO;2

  Begins with a survey of over fifty years of data (1920s through the late 1970s) on the Southern Oscillation (SO) to show the importance of the phenomenon. Uses the NCAR 5° global atmospheric model to simulate the SO and to suggest areas for future research.

• McCreary, Julian P., Jr., and David L. T. Anderson. “An Overview of Coupled Ocean-Atmosphere Models of El Niño and the Southern Oscillation.” Journal of Geophysical Research: Oceans 96 (Suppl. S) (1991): 3125–3150.

  DOI: 10.1029/90JC01979

  A useful review of coupled ocean–atmosphere models of ENSO arranged in a hierarchy of increasing dynamical complexity. Discusses the utility and limitations of various models, including conceptual and simple models, intermediate models, and coupled general circulation models (GCMs).

• Neelin, J. David, David S. Battisti, Anthony C. Hirst, et al. “ENSO Theory.” Journal of Geophysical Research 103.C7 (1998): 14261–14290.

  DOI: 10.1029/97JC03424

  Details the ocean–atmosphere interactions underlying the ENSO phenomenon using data from the 1985–1994 Tropical Ocean-Global Atmosphere (TOGA) study, including the possible mechanisms that cause the irregularity of ENSO and the strengths and weaknesses of current models.

• Torrence, Christopher, and Peter Webster. “Interdecadal Changes in the ENSO–Monsoon System.” Journal of Climate 12 (1999): 2679–2690.

  DOI: 10.1175/1520-0442(1999)012<2679:ICITEM>2.0.CO;2

  Examines the significant changes that both El Niño Southern Oscillation (ENSO) and Indian monsoon have undergone over the last 125 years. Authors’ results are robust with respect to different data sets and analysis methods.

• Walker, Gilbert. “World Weather.” Monthly Weather Review 56.5 (1928): 167–170.

  DOI: 10.1175/1520-0493(1928)56<167:WW>2.0.CO;2

  A classic article based on the author’s presidential address to the Royal Meteorological Society. Provides a useful survey of early research on the Southern Oscillation for a historical background.