El Niņo Basics

Introduction:

This page explains just about everything one needs to know about the forces driving El Niņo and its history. What is El Niņo? provides a definition and an animated picture of the 1997/98 El Niņo. What are the Trade Winds? and Positive and Negative Feedback give some scientific information and theory as to some of the causes and effects of El Niņo. How does El Niņo stop? and How long might this El Niņo Last? provide information about when this El Niņo will die out and the science behind it. Demise of the 1997-98 El Niņo describes how the strength of the current El Niņo is diminishing and might bring La Niņa conditions in its wake. Volcanoes and El Niņo provides and alternate theory about El Niņo. The History of El Niņo explains where the name El Niņo originates and the first people to realize it and its effect. And finally Heat change involved with El Niņo describes the power and amount of energy involved with an El Niņo. At the bottom of the page, along with the bottom frame, is a link to view the bibliography for this and all other pages.

To see the definition of selected words, put your mouse pointer over them.

What is El Niņo?

El Niņo is a disruption of the ocean atmosphere system in the tropical Pacific having important consequences for the weather around the globe. The disruptions involve large scale weakening of the trade winds and warming of the surface layers in the eastern and central equatorial Pacific.


Animated picture of El Niņo

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What are the Trade Winds?

To have more of an understanding of El Niņo, it is necessary to be familiar with the "); write("Trade Winds:
"); write("The Trade Winds are a part of the global wind pattern, which is divided into three wind belts. "); write("(1) Polar Easterlies: 60-90 degrees N and S. (2) Prevailing Westerlies: 30-60 degrees N and S, (Westerlies). (3) Tropical Easterlies: 0-30 degrees N and S, (Trade Winds).
"); write("


"); write("Above is a diagram of the global wind patterns and the direction in which the wind blows in the different belts. The Trade Winds (between 30N and 30S) blow from the East to the West. "); write("During an El Niņo, the trade winds slacken, causing upwelling to shut off, which leads increased ocean temperature."); write("

Close this window to return to El Niņo Basics.
"); write(""); } terms.document.close(); } // -->trade winds. The trade winds are another type of global winds present in the equatorial regions of the earth.

The earth is heated by the sun, and more strongly in the tropical regions. This hot air rises, and is replaced with cooler air. The "); write("Coriolis Effect:
"); write("The Coriolis effect is a force which deflects air and wind, from its path. "); write("This force is the result of the earth's rotation."); write("


"); write("In the above image, you can see that objects in the northern hemisphere deflect to the right, while objects in the southern hemisphere deflect to the left."); write(" The famous example of this is flushing a toilet bowl. In the northern hemisphere, the water will always drain clockwise, while in the southern hemisphere it will always drain counter-clockwise."); write("

Close this window to return to El Niņo Basics.
"); write(""); } terms.document.close(); } // --> Coriolis effect then curves these winds. In the Northern Hemisphere, they flow to the right and in the Southern Hemisphere, to the left. Therefore wind is blowing westward over the topical Pacific and water is pushed westward.

This causes warm surface water in the west to pile up. For example, sea surface temperatures are about 8o C higher in the west, compared to the relatively cool temperatures off the South American coast. Also, the water in the west is about 50 inches higher than the east. Water in the east is also cooler because of "); write("Upwelling:
"); write("Upwelling, in relating to ocean dynamics, is the upward motion of sub-surface water towards the surface of the ocean."); write("This is often the source of cold, nutrient rich water. Strong upwelling occurs along the equator where easterly winds are present."); write("Upwelling can occur along coastlines, and is extremely important for fishing along California and Peru."); write("

"); write("Now look closely at the above image. The diagram shows that as the surface water is being pushed away from the coast,"); write("this water is being replaced with sub-surface water. This water is cooler than the surface water. These conditions described are "); write("present in non El Niņo years. During an El Niņo, the suface water is not displaced as much, and upwelling of cold water shuts off."); write("

Close this window to return to El Niņo Basics.
"); write(""); } terms.document.close(); } // --> upwelling. As is pictured below, the warm water at the top of the sea, which is also pushed west, is replaced with colder water from the deeper ocean levels.

Upwelling
Picture of Upwelling

But during El Niņo, the trade winds relax in the central and western Pacific. This causes high atmospheric sea level pressures to develop in the Western tropical Pacific and Indian Ocean, also, low sea level pressures develop in the Southeastern tropical Pacific. The change in pressure causes the amount of upwelling of cold water to decline. This tends to make the water in the Eastern Pacific (off the western South American Coast) warmer. This is now referred to as El Niņo.

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Positive and Negative Feedback

In global systems science, the terms positive and negative feedback do not necessarily mean good or bad. They are two different kinds of natural processes that effect a system. The processes effecting El Niņo always seem to add to its strength. Therefore it is referred to as "); write("Positive Feedback:
"); write("In Positive Feedback, the change to the system is always increased. "); write("Whereas negative feedback keeps systems at current levels, positive feedback causes systems to break down. "); write("A thunderstorm is an example of positive feedback."); write("As sunlight evaporates water, warm moist air rises. "); write("This air condenses to form clouds, which causes heat to be released. "); write("Warm air rises further, forming thunderheads. Updrafts cause rain, hail, and lightning."); write("As more air ries, more water condenses, creating more energy in the system. This is positive feedback."); write("There is little difference between this and El Nino. All positive feedback process cannot last forever. "); write("Once all its energy is spent, the system ends, but the larger system continues to function."); write("

Close this window to return to El Niņo Basics.
"); write(""); } terms.document.close(); } // -->positive feedback. Changes in a positive feedback system always increase. As seen in El Niņo, the warming of water in the Pacific creates weaker winds; weaker winds create more ocean to warm even more, which in turn makes even weaker winds. Fortunately, the process has comes to an end. This is different from "); write("Negative Feedback:
"); write("In negative feedback, the cange to a system is always reduced. "); write("Negative feedback tends to maintain systems at proper working levels. "); write("An example of negative feedback is sweating. As your body heats up, your sweat glands in your skin "); write("to open and release water. The evaporation of sweat carries heat away, "); write("which cools your body. When your body no longer needs to discharge heat, your pores close, "); write("and your skin returns to normal. In this way, your body temperature is maintained "); write("within a range not dangerous to your body."); write("

Close this window to return to El Niņo Basics.
"); write(""); } terms.document.close(); } // -->negative feedback. On the contrary, negative feedback is a system that is always diminishing.

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How does El Niņo stop?

El Niņo does eventually stop growing. When El Niņo grows into the middle or eastern part of the Pacific, it creates Rossby waves that drift towards Asia. A Rossby wave is similar to a tidal wave. Like a tidal wave, massive amounts of water flow pretty much in the same direction rather quickly. In a Rossby wave, the upper part of the ocean moves very slowly, about 100 times slower than walking, and slides one way, while the lower part slides the other way. During an El Niņo, these waves, after months of traveling, hit the coast and reflect back, creating a Kelvin wave. This Kelvin wave slowly heads back to where the Rossby wave was first made. The change in temperature a Kelvin wave carries cancels out with the original temperature changes El Niņo creates. If a Kelvin wave brings back too much cool water, La Niņa is formed. This takes approximately 12-18 months to happen, therefore, El Niņo lasts between 12-18 months per occurrence.

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How long might this El Niņo last?

Many climate models are now predicting that normal conditions are slowly beginning to return, and in fact, a few are even predicting a La Niņa might follow this El Niņo. The United Nations reported that the 1997/98 was the strongest El Niņo ever recorded, easily surpassing the former "champion", the 1982/83 El Niņo. As of February, the volume of warm water was down 40% from its peak in November. With this decrease of volume, the area of warm water decreased to about 1.5 times, from 3.75 times, the size of the continental US. The World Meteorological Organization said that El Niņo is likely to be severely weakened after May, but the warm water pool will still continue to dominate climate patterns until mid-1998.

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Demise of the 1997-98 El Niņo

Since the beginning of May 1998, the warm water in the Pacific has begun to cool off. These findings are in line with most forecast models.


Animated picture of El Niņo declining strength

On an average, the pool of warm water has decreased by almost 2 degrees C since May. One buoy located along the equator and 125oW had decreased almost 6oC during the same time period. Along with this cooling, there is a strong possibility that this El Niņo will bring La Niņa conditions. On the image above, a pool of cool water is forming as the warm water is receding. Other El Niņos which showed rapidly declining temperatures didn't develop into La Niņas, but the 1982/83 El Niņo did bring a weak La Niņa. Although the magnitude of a possible La Niņa is unknown, many models are now predicting further cooling which will create weak La Niņa conditions.

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Volcanoes and El Niņo

There is an alternate theory on what might cause El Niņo. Some scientists theorize that volcanic activity might at least be partly responsible for El Niņo. The theory was created from a discovery of the largest cluster of volcanoes in the world. Discovered in 1993, the cluster is the size of New York State and is 600 miles northwest of Easter Island. Although there is no proof, and many scientists dismiss it, the idea is plausible enough to warrant more research. In 1995, undersea eruptions and quakes preceded the onset of El Niņo.

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History of El Niņo

Originally, Peruvian fishermen noticed a warm, southward, ocean current occurred almost annually around Christmas. They coined the term El Niņo, meaning "Christ child" or "the little one", because of its annual Christmas occurrence. El Niņo then came to mean the unusually strong warming that disrupted fish and bird populations every few years. Finally, during the 1960’s, it was realized that the local Peruvian occurrence became synonymous with a larger scale, climactically important, warming event.

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Heat change involved with El Niņo

The heat involved during an El Niņo occurrence is astounding! For example, through January and July of 1997, the average ocean temperature change was 1.62oC. Using this number, along with the density of sea water (1030 kg/m3), the heat capacity of sea water (4000J/kg/K), and the area of the region, it was determined that the quantity of energy increased by 3.5 x 1022 J! To put this figure into terms more understandable, this figure will be compared to human engineering feats. One of the most powerful man made devices was the H-bomb, which is equal to one kiloton of TNT. One kiloton of TNT creates about 4.18x 1012 J. Therefore, 8 x 109 kilotons, or 400,000 20-megaton bombs is equivalent to 3.5 x1022 J. This figure is assuming that all of the energy produced is directly absorbed by water. Another comparison is with a power plant. 3.5 x 1022 J creates about 1.5 PW, since 1W = 1J/second. A very large power plant can create 1000 MW. About 1,500,000 power plants of this size, working non-stop for 8 months, would be needed to create 3.5 x 1022 J.

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