El Nino-Southern Oscillation (ENSO) Cycle

Explanation :

Context: The La Nina weather phenomenon is back in the central and eastern equatorial Pacific Ocean after nearly a decade’s absence, the World Meteorological Organization (WMO) said in its latest Global Seasonal update released on October 29, 2020.

El Nino-Southern Oscillation (ENSO)

• El Nino and La Nina are opposite phases of what is known as the El Nino-Southern Oscillation (ENSO) cycle.
• The ENSO cycle is a scientific term that describes the fluctuations in temperature between the ocean and atmosphere in the east-central Equatorial Pacific (approximately between the International Date Line and 120 degrees West).
• La Nina is sometimes referred to as the cold phase of ENSO and El Nino as the warm phase of ENSO.
• These deviations from normal surface temperatures can have large-scale impacts not only on ocean processes, but also on global weather and climate.
• El Nino and La Nina episodes typically last nine to 12 months, but some prolonged events may last for years.
• While their frequency can be quite irregular, El Nino and La Nina events occur on average every two to seven years.
• Typically, El Nino occurs more frequently than La Nina.

El Nino

• El Nino means ‘The Little Boy’, or ‘Christ Child’ in Spanish. El Nino was originally recognized by fishermen off the coast of South America in the 1600s, with the appearance of unusually warm water in the Pacific Ocean.
• The name was chosen based on the time of year (around December) during which these warm waters events tended to occur.
• It refers to the large-scale ocean-atmosphere climate interaction linked to a periodic warming in sea surface temperatures across the central and east-central Equatorial Pacific.
• Typical El Nino effects are likely to develop over North America during the upcoming winter season.
• Those include warmer-than-average temperatures over western and central Canada, and over the western and northern United States. Wetter-than-average conditions are likely over portions of the U.S. Gulf Coast and Florida, while drier-than-average conditions can be expected in the Ohio Valley and the Pacific Northwest.
• The presence of El Nino can significantly influence weather patterns, ocean conditions, and marine fisheries across large portions of the globe for an extended period of time.

La Nina

• La Nina means ‘The Little Girl’ in Spanish. La Nina is also sometimes called ‘El Viejo’, ‘anti-El Nino’, or simply ‘a cold event’.
• La Nina episodes represent periods of below-average sea surface temperatures across the east-central Equatorial Pacific.
• The effect of La Nina impacts on global climate tend to be opposite those of El Nino.
• In the Tropics, ocean temperature variations in La Nina also tend to be opposite to those of El Nino.
• During a La Nina year, winter temperatures are warmer than normal in the Southeast and cooler than normal in the Northwest.