Draft 3: El Nino

This Progress Report submitted by Cassie Burns and Maria Gausman [e-mail:burns.ce@pg.com, gausman.mm@pg.com] on 4/5/03.

El Nino/La Nina Outline

Second edition

What is El Nino?

El Nino is possibly the world's most dramatic and measurable force of climate change. The term, El Nino, means "the boy child" or "Christ Child"
and was named by Peruvian fishermen. They noticed this phenomenon arrived near the time of Christmas.

El Nino is an ocean circulation pattern that interrupts the normal circulation of water in the Pacific Ocean every 2 to 7 years.
In a normal Non-El Nino year, strong trade winds along the equator drive the warm Pacific surface water toward the west (Australia and Indonesia)
which causes cooler water to well up along the equator.

So What Does That Mean?

This upwelling of cooler water is the cause of lower Non-El Nino temperatures - the high pressure cell above the east Pacific pushes low-level winds along the coast of
South America (eg Peru, Chile). The trade winds push warm surface water away from the coast and cool water upwells.
The trade winds also push surface water away from the equator and toward the southwest, which causes cooler water to well up along the equator, also.
In a Non-El Nino year, South America doesn't see a whole lot of rain - this is because cooler surface waters are a bad source for water vapor for the atmosphere.
(Ruddiman, William F.)

Oceanic Circulation patterns are not the only factor of El Ninos. Atmospheric circulation is also involved with this phenomenon.
During the 1920's, Gilbert Walker discovered changes in atmospheric pressure between western Pacific and the island of Tahiti.
He noticed that high pressures occurring at Australia correlated with low pressures in Tahiti and vice versa. A high surface pressure indicates a sinking of air
and a low atmospheric pressure indicates a rising of air and moist conditions. These opposite changes in pressure are termed the Southern Oscillation.
The linking of the ocean circulation system and the atmospheric circulation system is called ENSO or El Nino Southern Oscillation.

During a normal time, trade winds drive the warm surface water in the Pacific westerly and the bulge of water that piles up acts as a source of moisture for evaporation
and heavy precipitation in Australia and Indonesia - also, some of the warm rising air cools, moves eastward, and sinks in the east-central Pacific. This is the cause for the normal cool and dry conditions
of South America.
(Ruddiman, William F.)

National Oceanic Atmospheric Administration

So, You ask, What happens when there is an El Nino?

National Oceanic Atmospheric Administration

At the time of an El Nino, the strong trade winds in the eastern Pacific are not able to push water to the west, therefore the warm water in the west Pacific
flows back eastward. This warm water replaces the usual cooler upwelling waters in the central and eastern Pacific. This warm water becomes a source of latent heat
and moisture for rains to occur. Floods are one effect of this rainfall. The waters actually reach temperatures between 1C & 5C higher than normal. The cooler conditions
in the western Pacific causes high pressures and dry conditions (like in Australia). The warming also brings changes in weather patterns worldwide. (Ruddiman, William F.)

Sea Surface Temperatures from El Nino 1997-1998 Occurrence

I've heard of La Nina too - tell me a little more about it

La Nina, meaning the girl, is essentially the opposite phenomenon. This occurs when El Nino tries to go back to the normal state and actually go past the normal state.
The cold water up-welling exceeds "typical" boundaries, and unusually cool surface temperatures occur in the east Pacific.
This cools the Pacific ocean, and weather patterns again change in different ways.

The Southern Oscillation Index (SOI) is the difference in air pressure in Tahiti and Darwin. Sustained negative values are indicative of an El Nino event, and vice versa for La Nina.
The Australian Bureau of Meteorology calculates the SOI with the following equation:

SOI =[(Pdiff - Pdiffav)/SD(Pdiff)]*10


Pdiff=(average Tahiti MSLP for the month) - (average Darwin MSLP for the month),

Pdiffav=long term average of Pdiff for the month in question, and

SD(Pdiff)=long term standard deviation of Pdiff for the month in question.

The SOI ranges from about 35 to about +35. SOI values are reported on monthly durations when looking for trends.

The SOI can:

1. Predict possible up-coming El Nino/La Nina

2. Record past El Nino/La Nina

3. Record intensity. Strongly negative SOI trends indicate more intense El Nino.

Intensity has also been characterized by using Sea Surface Temperatures (SST).

Buoy stations all over the Pacific record SST daily.

The greater the temperature anomolly over the duration of an El Nino/La Nina, the more intense the event.

There are a lot of scientific and government agencies all over the globe devoted to improving their capabilites for predicting El Nino.

Why do so many people care about predicting El Nino?

The changes in weather patterns can be devastating. Below is a map indicating typical El Nino weather patterns globally.

Prediction: Seismic activity does trigger El Nino/La Nina events. We are predicting that occurrences of volcanic activity and earthquakes recorded along the Pacific Plate will correlate positively with occurrences of El Nino. Such volcanic activity and agitation introduces enough heat to the Pacific Ocean to alter the typical cool verses warm water patterns.

Prediction: The intensities of El Ninos/La Ninas have increased. We predict that the intensities of El Ninos/La Ninas have increased over the past few centuries. To prove this, we will examine historical records including tree ring data, coral band data, and glacial data.

More on Predictions coming soon!!!

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