EL-NINO

EL-NINO

• In the sheltered side of the tropical land mass, upwelling of deep ocean water under the influence of trade wind is a constant phenomenon.
•  Trade wind moves the water westerly. If the trade wind strengths, the warm tropical water accumulates on the west side of the Pacific.
•  This event is followed by the winds losing their driving force; upwelling lessens, the mass of warm western Pacific water moves eastward across the ocean to accumulate along the coast of America.
•  This sequence of events is known as El-Nino. 
• El-Nino is the Spanish word (little boy), refers to the Child Christ named for its frequent coincidence with Christmas season.
• It is an erratic climate abnormality over the equatorial Pacific which strongly affects tropical and mid-latitude countries
•  It is the complete reversal of climate and water circulation pattern. 
• The exact cause of El-Nino is still in doubt.
•  But certain processes identified with its appearance. They are increase in surface water temperature of eastern tropical pacific; Southward displacement of Doldrum - inter tropical convergence zone; 
• Trade wind fails to strength in spring

Southern ocean oscillation: Change in the ocean atmosphere system. It alters the wind and weather pattern across the tropical Pacific.

•  Atmospheric pressure increases on one side of the pacific, decreases on the other, and then reverses is known as Southern ocean oscillation
• In normal condition, trade wind blows the surface water westward away from the adjacent continental margins. 
• The deep water moves towards surface to replace it, bringing with it a mass of nutrients to the surface. Such upwelling along Peruvian coast, support Peruvian anchovy fisheries.
•  Each year in October, the trade winds slacken; the upwelling is reduced and the mass of western Pacific water moves eastward across the ocean to accumulate along the coast of America.
•  Normally trade wind picks up again in early spring, when the surface water once again blown westward across the ocean.
• In the region of 30° lat N & S, the surface winds are easterly, and the wind alofts are easterly, moves water from west to east -called jet streams because they are narrow rivers of high speed winds.
•  During El-Nino, the resulting temperature anomalities may cause these jet streams to be even stronger and may set off another mechanisms called a teleconnection bringing flood to central Europe and draught to South Africa, Northern Australia, South east Asia and Indonesia.
•  El-Nino is a joyous event because the rain transformed the desert in to the garden. 1997-98 El-Nino is the strongest ever recorded.

Effects of El-Nino

• Fishery along peru - chile coast devasted: Tuna and anchovy moves away from the coastal fishing ground.
•  Because the plankton on which the fish feeds need cold water, High mortality in sea bird; 
• Mortality and bleaching of corals observed in the coast of central America and Florida;
•  Frequency of hurricane increases in the south pacific, Heavy rain in eastern pacific, especially western South America Draught in western pacific and Australia; 
• Walker speculated that the increased in under water volcanic activity as a result of plate tectonics may warm the ocean, which in turn warmed the air.
•  This may cause major changes in atmospheric pressure, triggering the change in air and sea conditions linked to El-Nino.

ENSO

• Though Southern ocean oscillation and El-Nino are isolated phenomenon, they take place in a particular region is referred as ENSO.
•  The pressure centres associated with this oscillation lies over Easter island in the eastern Pacific and Indonesia in the western Pacific. 
• In normal condition, trade winds are strong and constant.
•  Thus High pressure system lies over - Easter island; 
• Low pressure system lies over - Indonesia. 
• Whereas in reversed condition, high pressure system lies over - Indonesia; Low pressure system lies over Easter island.
•  The effect of ENSO are harmful.
•  Heavy rains may cause floods, where such rains are rare. Drought and famine to areas, where such rains are normal

• La-Nino

• Between El-Nino, surface temperature of off Peru will drop below normal is called as la-nino. 
• It is also a Spanish word refers to 'the girl'.
•  It is an unusual cold ocean surface current.
•  It occurs over a large area of equatorial Pacific Ocean. 
• It has been observed in n average over every four years.
•  Large scale meterological effect observed during la-Nino are strengthening of trade wind and abnormal accumulation of cold water in the central and eastern Pacific;
•  Stronger currents and stronger upwelling, Decrease in surface water temperature of eastern tropical Pacific while warmer than normal in the west.