El Nino and La Nina

A new study projects that climate change will significantly impact El Nino and La Nina weather patterns by approximately 2030.

It is a climate pattern that describes the unusual warming of surface waters in the eastern tropical Pacific Ocean.
This is associated with increased rainfall along the western coast of South America and a decrease in rainfall over the Indian subcontinent.
It also leads to westerly winds instead of the generally occurring easterly winds.
Discovery

Peruvian fishermen first recognised El Nino off the coast of Peru for the appearance of unusually warm water.
The Spanish immigrants called it El Nino, meaning “the little boy” in Spanish.
Features
The El Nino event is not a regular cycle; they are not predictable and occur irregularly at two- to seven-year intervals.
How does El Nino impact monsoon rainfall in India?

El Nino and Indian monsoons are inversely related.
El Nino years in India have witnessed extreme heat and below-average rainfall levels during monsoon.
In 2014, an El Nino year, India received 12 per cent deficient rainfall from June to September.

After the El Nino event, weather conditions usually return to normal.
However, in some years, the trade winds can become extremely strong, and an abnormal accumulation of cold water can occur in the central and eastern Pacific. This event is called a La Nina.
In other words, It is the reverse phenomenon of El Nino.
The temperatures over the eastern Pacific Ocean decrease, along with a decrease in rainfall. Also, the rain over the Indian subcontinent increases, along with augmentation of the strength of surface-level easterly winds.
Impacts

La Nina tends to lead to milder winters in Northern Europe and colder winters in southern/western Europe, leading to snow in the Mediterranean region.
It is continental North America where most of these conditions are felt.
La Nina causes drought in the South American countries of Peru and Ecuador.
It usually positively impacts the fishing industry of western South America.
In the western Pacific, La Nina increases the potential for landfall in those areas most vulnerable to their effects, especially in continental Asia and China.
It also leads to heavy floods in Australia and high temperatures in Western Pacific, Indian Ocean, off the Somalian coast and comparatively better monsoon rains in India.

ENSO is a global phenomenon affecting the temperature and precipitation of many regions around the globe, including the Indian subcontinent.
It is a recurring climate pattern involving changes in the temperature of waters in the central and eastern tropical Pacific oceans.
The most important factor with the ENSO is the ability of the scientists to predict its occurrence, thereby indicating the amount of rainfall and temperature in the region.

About
It is a multiyear cooling of the surface temperature of the equatorial Pacific Ocean, which can cause droughts, fierce winds and heavy rainfall. According to the World Meteorological Organisation (WMO), the current La Nina is projected to span three consecutive northern hemisphere winters.

Atmospheric carbon dioxide
Increasing atmospheric carbon dioxide can cause a weakening of future simulated El Nino-Southern Oscillation (ENSO) sea surface temperature variability.
Temperature extremes

Future El Nino events will lose heat to the atmosphere more quickly due to the evaporation of water vapour.
Also, in the future there will be a reduced temperature difference between the eastern and western tropical Pacific, inhibiting the development of temperature extremes during the ENSO cycle.
Weakening of Tropical Instability Waves
There can be a weakening of Tropical Instability Waves (TIWs) in the projected future which can cause a disruption of the La Nina event.

TIWs are a dominant feature of monthly variability in the equatorial Pacific and Atlantic Ocean.

Content Source: The Hindu