By Vani Manocha
El Niño is a local warming of surface waters which takes place in the entire equatorial zone of the central and eastern Pacific Ocean and which affects the atmospheric circulation and direction of winds world-wide
In a normal year, trade winds push warm ocean currents westward from the eastern and central Pacific towards Indonesia and Australia. The warmer water heats the air, causing rain clouds to form over Asia
In an El Nino year, trade winds weaken or reverse direction and warm waters and rain clouds shift eastward. Thus, Asia is left dry
During La Nina, unusually strong, eastward-moving trade winds and ocean currents bring cold water to the surface, a process known as upwelling. La Niña is characterised by lower-than-normal air pressure over the western Pacific
It usually peaks around Christmas, hence the name of the phenomenon, El Niño, Spanish for Christ Child. La Niña refers to the "cold" equivalent of El Niño
The atmospheric variations which arise as a result of El Niño and La Niña events are together called the Southern Oscillation. It is also the East-West balancing movement of air masses between the Pacific and the Indo-Australian areas
El Niño is a permanent feature of the Pacific Ocean and occurs on average every 4 to 5 years, sometimes less (2 to 3 years), sometimes more (8 to 11 years). The phenomenon proper lasts 12 to 18 months, also a recent very unusual event lasted from mid-1990 to mid-1995
Its influence on climate is global and it can trigger severe floods and droughts. The notorious famine, that occurred in 1877 and resulted in the deaths of over nine million people in China and eight million in India, was triggered by El Niño. Year 2002, 2004, 2009, 2012 were other drought periods in India when EL Nino surfaced