Role of El Nino and Southern Oscillation (ENSO)

The word EI-Nino means ‘Child Christ’ because this current appears around Christmas in December. EI-Nino is a complex weather system that generally appears once in every three to seven years. It brings drought, floods and other weather extreme events in different parts of the world.

The system involves oceanic and atmospheric phenomena with the appearance of   warm currents off the coast of Peru in the Eastern Pacific and affects weather in many places including India. EI-Nino is merely an extension of the warm equatorial current which replaces, temporarily, cold Peruvian current or Humbolt current. This current increases the temperature of water off the Peruvian coast by 10°C. This results in the distortion of usual equatorial atmospheric circulation and irregularities in the evaporation of sea water.

As warm water appears off the coast of Peru, it creates a low pressure circulation there. This causes easterly winds to weaken and, therefore, El Nino has been generally known to suppress monsoon rainfall in India, since it is the easterly wind that form water bearing clouds to Indian monsoon rainfall.

ENSO (El Nino Southern Oscillation) refers to the oscillation between the El Nino and the La Nina. ENSO shifts irregularly back and forth between El Nino and La Niña every two to seven years. La Nina is the opposite of El Nino i.e. during La Nina water off the coast of Peru cools by a margin. During La Nina, easterly winds strengthen and there is higher than average rainfall during Indian monsoon period.

Indian Monsoon

El Nino Modoki
It is different from traditional El Nino as the sea surface temperature (SST) warming is largely in the central equatorial pacific region instead of in the eastern equatorial pacific region. It is also known as Central Pacific El Nino or warm pool El Nino, first recorded in 1986. The traditional ENSO linked more closely with the tropical Indian Ocean whereas the El Nino modoki is with Southern Indian Ocean.