In its simplest definition, "El Nino" refers to an abnormal warming

of the topmost layers of the eastern Pacific Ocean, which generally occurs

at irregular intervals of 3-7 years. The name "El Nino" dates back to

late 19th century folklore, referring to a weak ocean counter-current off

the coast of western South America, called "corriente del nino". This

warm counter-current flowed opposite to the colder equator-ward flowing

"Peru Current" that is normally seen over offshore waters. The "corriente

del nino" usually arrives in late December, shorty after Christmas,

replacing the normally chilly water, with warmer, equatorial water. This

annual event was shorted to just "El Nino", which is Spanish for "the

infant boy" ... a direct reference to the baby Jesus.

The "El Nino" is typically short-lived, but every few years the

warming is *intense* and longer lasting, often accompanied by heavy rains.

The cause of "El Nino" is not known for sure. The westward blowing trade

winds are an important contributer, as they push surface ocean water away

from the western South American coast, which causes "upwelling" of colder,

nutrient rich water from down deep. This enhances the Peruvian fishing crop,

especially anchovies. Warm water also piles up over the western, south

Pacific. Sea level can be 20" higher in Indonesia than at Ecuador and can

be as much as 14 deg warmer. The warm, moist conditions further enhance

T-storms over the western south-Pacific, while the eastern Pacific remains dry.

When the trades winds relax, the warm waters spread back to the east

and an "El Nino" begins. What causes this relaxation of the trade winds?

This is not an easy answer. During the non-El Nino years, surface baro-

metric pressures tend to be low over the warmer equatorial, western Pacific

waters, where warm air is rising and diverging aloft. Over the equatorial,

eastern Pacific, cool air is sinking and the winds are converging aloft,

leading to higher surface pressure. When an "El Nino" begins, there is a

reversal of air pressure across the Pacific Ocean, with pressures rising

in the west and falling in the east. This air pressure reversal is called

"the Southern Oscillation." Back in 1924, Sir Gilbert Walker was given

credit for discovering this phenomenon, while monitoring the air pressure

at Darwin, Australia and at the south Pacific island of Tahiti. He noted

that when the pressure is high at Darwin, it is low at Tahiti, and vice

versa. It is not clear which comes first. Oceanographers tend to believe

that the eastward spreading of warm water is initiated by the relaxation

of the trade winds. Meteorologists tend to believe that the warming surface

waters, which alter air pressure patterns, eventually cause the trade winds

to relax. This can be put into the "chicken and the egg" debate folder.

It is most likely a *complex* interaction between the relatively quickly

changing atmosphere and the much slower responding ocean. In an *intense*

El Nino, the normal westward blowing trade winds reverse direction and blow

eastward, driving warm surface ocean water over a much larger area of the

Pacific than during an ordinary El Nino. Today, this type of event is

called "ENSO" ... which is an acronym standing for "El Nino-Southern Oscillation."

Once an ENSO event is underway and the trade winds have relaxed or

possibly even reversed direction, it is believed that as the warmer surface

water from the equatorial western Pacific spreads eastward, evaporation rates

increase. The overlying warm and moist air rises, increasing the likelihood

of T-storms. The updrafts from these equatorial thunderstorms inject energy

in the form of moisture up to the tropopause, which is the boundary between

the troposphere (where we live and where all weather occurs) and the

stratosphere (where the protective ozone layer can be found). This causes

the subtropical jet stream to energize and can act as a "conveyor belt" of

moisture from the equator, passing south of Hawaii and up into western North

America and has been called the "Pineapple Connection." This subtropical

jet stream often extends over TX and the southeastern U.S., producing cool

and wet weather. Furthermore, the strength of the sub-tropical jet stream

causes the polar jet stream to alter its course, leading to what is called

"climatic abnormalities." Scientists have discovered that an ENSO event has

reliable "teleconnections". A teleconnection is a *direct link* between

changes in weather patterns in widely separated regions on the planet, often

thousands of miles apart. For example, temps will run warmer than normal

through the winter over Alaska and western Canada, as well as in the Canadian

maritimes and Japan. Wetter than normal conditions will usually be found

across the southern U.S. from TX to FL, over the U.S. Rockies, as well as

over parts of South America. Severe drought usually sets in over much of

Australia and Indonesia, ne-South America and South Africa, and disrupts the

monsoon over India. Many other areas can have vastly differing effects from

one El Nino to another. For example, the El Nino of 1982-83 caused $2 billion

in damage due to flooding and mudslides in the Pacific Coast, Rocky Mtn and

Gulf coastal states, but saved $500 million in fuel bills in the east, where

we had our warmest winter in 25 years. However, during the 1976-77 El Nino,

California suffered through a severe drought, while the Midwest and eastern

U.S. had one of the century's coldest winters. The extent of thunderstorm

activity across the equatorial Pacific and the ensuing strength of the

subtropical jet stream has the final say in what *type* of pattern becomes

established. The 1982-83 ENSO event has been the strongest and most

devastating of the century ... and perhaps the worst in recorded history.

In addition to the aforementioned flooding in the western and southern U.S.,

there were weather-related disasters on nearly every other continent.