FREE ESSAY ON EL NINO

EL NINO

El Nino has been a reoccurring phenomenon for centuries. Man has only started to realize
how much of the worlds weather is effected by it. The term El Nino refers to an irregular
warming of the seas surface. During the last 40 years there have been 10 significant El
Nino occurrences. Most affecting the coast of South America. Water temperatures increase
along the coast as far as the Galapagos islands. Weak events will raise the water
temperature 2 to 4 degrees Celsius and will have minor impact on fishing. However strong
events such as the 1982-83 event will disrupt climate conditions around the world as well
as local conditions. It has been linked to floods and droughts all over the world.
Hurricanes and tropical storms are also altered in their numbers by El Nino. Therefore it
would be very helpful for people if El Nino could be predicted and prepared for in some
form. 
During a El Nino cycle there are many biological changes. Due to a depressed thermocline
there is less photosynthetic activity resulting in a decrease in the primary life forms
that form the beginning of the food chain. The warmer waters that are brought by these
changing cycles hold less dissolved oxygen forcing fish to go deeper or venture
elsewhere. Due to a lack of data during El Nino occurrences it is not fully known if fish
populations are depleted solely due to exposure to El Nino. A decrease in their growth
and reproductive success has been observed by many surveys in coastal waters.
The link between climatic effects around the world and El Nino is now well established.
It has taken many years of studying to understand how the pieces of the puzzle, from
ocean currents to winds and heavy rains fit together. During the 1920s a scientist was on
assignment in India trying to predict the Asian monsoons. As he sorted through his
records he discovered a connection between barometer readings at stations on the eastern
and western sides of the Pacific. He noticed that when pressure rises in the west it
usually falls in the east and vice versa. He coined this term Southern Oscillation. When
it is on its high index state pressure is high on the eastern side of the Pacific and low
on the western side (figure 1). The east west pressure contrast drives easterly surface
winds. When it switches into low index (figure 2) the easterly surface winds weaken. The
biggest changes are over the western Pacific. West of the dateline the easterlies usually
completely di!
sappear during low index years, but east of the dateline they only weaken.
The surface winds that move the ocean currents are a major controller in weather. The
easterly winds that blow along the Ecuador and the southeasterly winds that blow along
the Peru and Ecuador coasts both tend to drag surface water with them. The Earth's
rotation then deflects the resulting surface currents northward in the Northern
Hemisphere and southward in the Southern Atmosphere. The surface waters are therefore
deflected away from the equator in both directions and away from the coastline. When the
surface water moves away, colder nutrient-rich water comes up from below to replace it.
This is known as upwelling. This nutrient rich water is the beginning of the food chain
as phytoplankton establish themselves in these waters.
When the easterlies are blowing at full strength, the upwelling of cold water along the
equatorial Pacific chills the air above it, making it too dense to rise high enough for
water vapor to condense and form clouds. As a result, this strip of ocean stays free of
clouds during normal years and rain in the equatorial belt is largely confined to the
extreme western Pacific near Indonesia.
But when the easterlies weaken and retreat eastward during early stages of an El Nino
event, the upwelling slows and the ocean warms. The moist air above the ocean also warms.
It becomes light enough to form deep clouds which produce heavy rain along the equador.
The change in ocean temperatures causes a major rain zone over the western Pacific to
shift eastward. Related adjustments in the atmosphere cause barometers to drop over the
central and eastern Pacific and rise over Indonesia and Australia. This results in a
further weakening and eastward retreat of the easterlies. In this way small changes in
the ocean and wind currents continue to amplify each other until a full blown El Nino
event occurs.
Dense tropical rain clouds alter the air flow 5 to 10 miles above sea level (ex. Rocks
distort the flow of a stream). These clouds create waves in the airflow that in turn
determine the positions of monsoons, the storms tracks and belts of strong winds above
the earth that separate warm and cold regions of the earth's surface.(referred to as jet
streams). The impacts of El Nino upon climate in temperature show up most clearly during
wintertime. Most El Nino winters are mild over western Canada and parts over the United
States, and wet over the southern United States from Texas to Florida. El Nino affects
temperature climates in all other seasons as well. But even during wintertime El Nino is
only one of a number of factors that influence temperature climates. El Nino years are
not always marked by tropical El Nino conditions the way they are in the tropics.
Scientists noticed that a monsoon season with low index conditions are often marked by
droughts in Australia, India, Indonesia and parts of Asia. Although scientists did not
realize the magnitude of what they were discovering they knew they had discovered only a
small portion of this phenomenon. It would require a knowledge of wind patters above
ground level (which were not recorded at that time) to continue to gain knowledge. In the
following decades researchers added new pieces to the emerging picture of Southern
Oscillation.
The march of the seasons is quite predictable. In contrast El Nino recurs at irregular
intervals ranging from two years to a decade, and no two events are ever exactly alike.
For example the 1982-83 El Nino caught scientists by surprise because unlike previous EL
Ninos it was not proceeded by a period of stronger easterlies on the equator. To further
confuse scientists this event also set in unusually late in the calendar year. In order
to guard against the possibility of being surprised by another El Nino scientists
continue to document as many past events as possible by piecing together bits of evidence
from many different sources such as sea surface temperatures, daily observations of
atmospheric pressure and rainfall and regarded as the strongest this centuries by many
experts. I t was not predicted and not even recognized by scientists during its early
stages. The economic impact were large. The Equador and Peru fishing industries suffered
heavily when there a!
nchovy harvest failed and their sardines unexpectedly moved south into Chilean waters. Up
to a 100 inches of rain fell in Equador and northern Peru. This transformed the coastal
desert into a grassland dotted with lakes. The new vegetation attracted swarms of
grasshoppers which fueled explosions in the toad and bird populations. The new lakes also
created a temporary habitat for fish that had migrated up stream from the sea and had
become trapped. Many of them were harvested by local residents as the lakes dried up. In
some of the flooded coastal estuaries, shrimp production records were set, but so did the
number of mosquito-borne malaria cases. 
Further to the west abnormal wind patterns shifted typhoons off their usual tracks and
sent them to the islands of Hawaii and Tahiti, which are unaccustomed to such severe
weather. They also caused the monsoon rains to fall over the central Pacific instead of
the western side which caused droughts and forest fires throughout Indonesia and
Australia. Many winter storms battered southern California and caused flooding throughout
the southern United States. Overall the loss to the world economy as a result to climate
changes resulted in 8$ billion.
Bibliography
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