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El Nino

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					EL NINO

Fishermen who ply the waters of the Pacific off the coast of Peru and Ecuador have known for
centuries about the El Niño. Every three to seven years during the months of December and
January, fish in the coastal waters off of these countries virtually vanish, causing the fishing
business to come to a standstill. South American fishermen have given this phenomenon the
name El Niño, which is Spanish for "the Boy Child," because it comes about the time of the
celebration of the birth of the Christ Child. During an El Niño, the physical relationships
between wind, ocean currents, oceanic and atmospheric temperature, and biosphere break
down into destructive patterns that are second only to the march of the seasons in their
impacts to weather conditions around the world.


El Niño: A temperature anomaly
The vast tropical Pacific Ocean receives more sunlight than any other region on Earth. Much
of this sunlight is stored in the ocean in the form of heat. Typically, the Pacific trade winds
blow from east to west, dragging the warm surface waters westward, where they accumulate
into a large, deep pool just east of Indonesia, and northeast of Australia. Meanwhile, the
deeper, colder waters in the eastern Pacific are allowed to rise to the surface, creating an east-
west temperature gradient along the equator known as the thermocline tilt.

 What is El Niño?
El Niño: a temperature anomaly .The trade winds tend to lose strength with the onset of
springtime in the northern hemisphere. Less water is pushed westward and, consequently,
waters in the central and eastern Pacific begin to heat up (usually several degrees Fahrenheit)
and the thermocline tilt diminishes. But the trade winds are usually replenished by the Asian
summer monsoon, and the delicate balance of the thermocline tilt is again maintained.

Sometimes, and for reasons not fully understood, the trade winds do not replenish, or even
reverse direction to blow from west to east. When this happens, the ocean responds in a
several ways. Warm surface waters from the large, warm pool east of Indonesia begin to
move eastward. Moreover, the natural spring warming in the central Pacific is allowed to
continue and also spread eastward through the summer and fall. Beneath the surface, the
thermocline along the equator flattens as the warm waters at the surface effectively act as a
300-foot-deep cap preventing the colder, deeper waters from upwelling. As a result, the large
central and eastern Pacific regions warm up (over a period of about 6 months) into an El
Niño. On average, these waters warm by 3° to 5°F, but in some places the waters can peak at
more than 10°F higher than normal (up from temperatures in the low 70s Fahrenheit, to the
high 80s).

In the east, as temperatures increase, the water expands, causing sea levels to rise anywhere
from inches to as much as a foot. But in the western Pacific, sea level drops as much of the
warm surface water flows eastward. During the 1982-83 El Niño, this drop in sea level
exposed and destroyed upper layers of coral reefs surrounding many western Pacific islands.

During normal years, when there is a steep thermocline tilt, the cold, deep currents flowing
from Antarctica up the west coast of South America are allowed to upwell, bringing essential
nutrients that would otherwise lie at the bottom. Phytoplankton living near the surface depend
upon these nutrients for survival. In turn, fish and mammals depend upon phytoplankton as
the very foundation of the marine food chain. As previously explained, the warm surface
waters of an El Niño prevent this upwelling, effectively starving the phytoplankton population
there and those animals higher up the food chain that depend upon it. Fishermen in Peru and
Ecuador generally suffer heavy losses in their anchovy and sardine industries.

At Christmas Island, as a result of the sea level rise during the 1982-83 El Niño, sea birds
abandoned their young and flew out over a wide expanse of ocean in a desperate search for
food. Along the coast of Peru during that same time period, 25 percent of the adult fur seal
and sea lion populations starved to death, and all of the pups in both populations died. Similar
losses were experienced in many fish populations.

Meanwhile, over a six-month period about 100 inches of rainfall fell in Ecuador and northern
Peru--ordinarily a desert region. Vegetation thrived and the region grew lush with grasslands
and lakes, attracting swarms of grasshoppers and, subsequently, birds and frogs that fed on the
grasshoppers. Many fish that had migrated upstream during the coastal flooding became
trapped in the drying lakes and were harvested by local residents. Shrimp harvests were also
very high in some of the coastal flood regions, but so too was the incidence of malaria cases
due to thriving mosquito populations.

El Niño's impacts on weather patterns
El Niño's effects are not limited to the tropical regions off the western coasts of Peru and
Ecuador. Its effects are felt all over the world, where the disruption of normal local weather
patterns can have tragic and/or profound economic consequences. As warm water migrates
eastward, increased heat and moisture rises into the atmosphere, altering the weather patterns
in neighboring regions, which in turn can ripple out to affect still other region weather
patterns around the globe. For instance, a severe El Niño will enhance the jet stream over the
western Pacific and shift it eastward, leading to stronger winter storms over California and the
southern United States, with accompanying floods and landslides. In contrast, El Niño can
also cause severe droughts over Australia, Indonesia, and parts of southern Asia.

While El Niño is known to lower the probability of hurricanes in the Atlantic, it increases the
chances of cyclones and typhoons in the Pacific. The 1982-83 El Niño is estimated by NOAA
to have caused some $8 billion in damages due to floods, severe storms, droughts and fires
around the world.

				
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