El Nino/La Nina - Essay Example

To begin with the concept El Nino refers to the warming of the Pacific ocean water surface primarily along the coast of Ecuador, Peru, Chile and the great broader basin found in the equatorial pacific. The Pacific ocean water temperatures in the equatorial region is usually 29° c in the west and 23° c in the first three months before the start of the El Niño phenomena as was the case in 1997.The difference of 6-7° c between the east and the west in sea surface is a representation of the balance between the westwards blowing wind near the sea surfaces and the temperatures in the upper 300meters of the ocean from the deep waters.

El Niño phenomena occurs after every 3-7 years(Barnabé and Regine,2000 p 30 ) and the surface temperatures in the western and eastern equatorial pacific ocean usually drops by I° c and rise by either 2 or 3° c. During the El Niño events in 1997-98,the sea surface temperatures in the eastern equatorial pacific increased by 5-6° c ,thus creating a uniform surface temperature in the regions lying along the equator and the entire band with of the pacific, that forms nearly the a half of the circumference of the earth.

The El Niño phenomena are at its climax in the months of December. . In the eastern region of the equator, a layer of 75 meters of warm water occurs above the thermoclines.Then the eastwards flow of warm water and high sea surface temperatures are accompanied by clouds formation and rainfall. Thus in the tropical pacific, the El Nino phenomena represents reduced rainfall in the western pacific and high temperatures in the eastern pacific. La Nina phenomena on the other hand refers to the cold phase of the Oscillation of the sea surface temperatures in the Eastern tropic Pacific Ocean.

La Nina often occurs after the collapse of an El Nino event .For example after the 1997-8 El Nino event in May 1998, a cold event began to develop thus La Nina is the opposite event of El Nino. During la Nina conditions, the easterly trade winds and westwards flowing equatorial current in the pacific equatorial region are very strong and warm than in usual (Chang, 2002, p 122). The currents move the warmer waters with surface temperatures of more than 29° c to the westwards thus creating a 150-200metres thickness of warm water layer in the western tropical pacific.

In the eastern equatorial pacific, the sea surface temperatures are below 23° c and the thickness of the upper layer lies between 25-50 meters. The thermocline which constitutes a 100meters thickness layer that separates the warm upper ocean from the cold deep ocean slopes upwards from the west to the east direction (Vasseu and Kevin, 2007, p 3). As a result of the thermocline sloping, in the east-west direction, the sea level along the equator becomes roughly 0.5 meters higher in the west than in the east.

In the equator sea patterns are characterised by the easterly winds. Thus in the tropics where air occurs over the sea surface of