Four False Color Views of Ocean Surface Height of the Pacific Ocean

El Niño and La Niña

Photograph

By: National Aeronautics and Space Administration (NASA)

Date: 1997

Source: NASA. "Four False Color Views of Ocean Surface Height of the Pacific Ocean." 1997.

About the Organization: TOPEX/Poseidon is part of NASA's Mission to Planet Earth, a long-term research program to study the Earth as a global system, with particular emphasis on gathering data about how oceans influence global climate. The Jet Propulsion Laboratory manages the U.S. portion of the TOPEX/Poseidon mission for NASA.

INTRODUCTION

El Niño and La Niña refer to an irregular cycle of shifting climactic conditions in the tropical Pacific Ocean. El Niño and La Niña affect the dynamics of both the ocean and the atmosphere throughout the planet.

In the 1880s, South American fisherman gave the name El Niño, which means little boy in Spanish, to the climactic condition. They noticed the oceanic changes associated with El Niño around Christmas celebrations centered on a Christ-child figure. La Niña, or little girl, is a name given in opposition to El Niño. The alternating climactic conditions have also been called El Niño/Southern Oscillation or ENSO by oceanographers.

In normal conditions, the Trade Winds blow from east to west across the tropical Pacific Ocean. Friction between the winds and the ocean effectively pulls water toward the western side of the Pacific. The sea surface is about 1.6 feet (0.5 m) higher near Indonesia than it is near South America. As the Trade Winds pull water away from the eastern side of the Pacific, cool water from deep in the ocean rises to the surface in a process called upwelling. The upwelled water is cold and rich in nutrients. Microscopic ocean plants called phytoplankton flourish in this water. In turn, fish and other predators graze on the phytoplankton. As a result, the Eastern Pacific Ocean along the coast of Peru has extremely diverse ecosystems and rich fisheries.

As the warm Trade Winds pull the ocean water to the west, they heat it. A lot of evaporation occurs in the warmed water on the western side of the Pacific Ocean. This results in heavy rains near Indonesia and relatively dry conditions near Peru. La Niña conditions occur when the Trade Winds intensify across the Tropical Pacific. This leads to very strong upwelling near South America and very cold ocean waters along the coast of Peru extending westward toward the center of the Pacific Ocean. Under La Niña conditions, the weather near Indonesia and Australia tends to be extremely wet, and very dry conditions persist in the western part of South America.

When El Niño conditions arise, the Trade Winds relax. Less water is pulled from the east side of the Pacific toward the west. Upwelling of cold, nutrient-rich water decreases, leading to oceanic conditions that do not favor phytoplankton growth. Lacking adequate food supply, the fish and other predators decline in number. With the decrease in the strength of the Trade Winds, warm water from the western side of the Pacific flows eastward. This shifts the site of evaporation towards the east. Rainfall follows evaporation, so El Niño conditions bring heavy rains to the coast of Peru and result in droughts and fires in Indonesia and Australia.

El Niño conditions occur irregularly every four to seven years. Understanding the processes that control El Niño required the collaboration of atmospheric scientists and oceanographers. In the first part of the twentieth century, atmospheric scientists noticed an oscillation in the atmospheric pressure in the eastern and western Pacific Ocean. In most cases pressure was low in the west and high in the east. However, in some years the pressure differential seemed to abate and these years were associated with lighter than normal monsoons in eastern parts of Asia.

In the 1950s, atmospheric scientist Jacob Bjerknes proposed that the pattern of oscillating atmospheric pressure might be linked to the ocean. This idea was explored in the 1970s as oceanographers began to make systematic measurements of sea surface height and temperatures. Eventually, in the 1980s, David Halpern of NOAA pieced together the first array of moored sensors across the Pacific Ocean to continually measure ocean temperatures and to relay the information to researchers via satellite. In addition, oceanographic and atmospheric scientists began collaborating to build coupled models of the atmosphere and the ocean in order to develop the ability to predict the onset of El Niño. Wind and ocean temperature measurements as well as NASA ocean surface height measurements are used to make predictions about changes to El Niño and La Niña patterns and severity.

The image presented shows NASA and other agencies monitoring of ocean surface height. The data was obtained from NASA's TOPEX/Poseidon satellite and transmitted as false color images (presented here in gray scale). The shaded areas represent various ocean heights correlated to heat intensity.

PRIMARY SOURCE

SURFACE HEIGHT OF THE PACIFIC OCEAN

See primary source image.

SIGNIFICANCE

Although the exact impacts of El Niño and La Niña are still under study, the data suggests strong correlations between these phenomena and changes to weather and atmospheric patterns. For example, the results of the 1982–1983 El Niño were serious. Australia experienced extreme wildfires and drought. Africa also suffered from a severe drought. On the other hand, Peru and Ecuador were subjected to extremely heavy rains, resulting in flooding and mudslides. Estimates held the El Niño responsible for the loss of 2,100 lives and $13 billion in damage worldwide.

Following the 1982–1983 El Niño, scientists recognized the importance of accurately predicting El Niño. An international effort resulted in the Tropical Ocean-Global Atmosphere (TOGA) program, which deployed moored and satellite-tracked ocean temperature sensors in the Pacific Ocean. TOGA was replaced by the Tropical Ocean-Atmosphere (TAO) array of moored sensors in 1995, which has set of bands of moored ocean temperature sensors throughout the Pacific Ocean.

In 1986, using coupled ocean and atmospheric computer models along with the data collected from TOGA and from ocean viewing satellites, scientists predicted an El Niño event. The El Niño arrived as predicted and lasted until 1988.

In 1997, models predicted an El Niño. Although as severe as that of 1982, a variety of preparations occurred throughout the world. Farmers in Brazil planted drought resistant crops while Californians improved flood systems and acquired additional flood insurance. People living in the Galápagos Islands improved roads and water systems.

Currently, the Pacific Ocean is under constant monitoring for signs of El Niño. Predictions are constantly updated and given the sophistication of their coupled atmospheric and ocean models. Along with the high-quality data from satellites and moored sensors, scientists feel fairly certain that they can predict and El Niño more than a year before the actual conditions occur.

FURTHER RESOURCES

Books

Philander, S. George. Our Affair with El Niño: How We Transformed an Enchanting Peruvian Current into a Global Climate Hazard. Princeton, N.J.: Princeton University Press, 2004.

Web sites

"El Niño and La Niña: Tracing the Dance of Ocean and Atmosphere." National Academy of Sciences. 〈http://www7.nationalacademies.org/opus/elnino.html〉 (accessed March 15, 2006).

"El Niño Theme Page." National Oceanic & Atmospheric Administration (NOAA), U.S. Department of Commerce. 〈http://www.pmel.noaa.gov/tao/elnino/nino-home.html〉 (accessed March 15, 2006).