Context: 

After 2016, El Niño is back in the Pacific Ocean, the National Oceanic and Atmospheric Administration (NOAA), USA, declared recently. 

Observations of NOAA: 

• The sea surface temperatures along the equatorial Pacific Ocean, especially along the various Niño regions, were showing signs of rapid warming. 
• The Niño 3.4 index value — the vital indicator confirming an event of El Niño — jumped from minus 0.2 degrees Celsius to 0.8 degrees Celsius between March and June this year. 
• An El Nino is now underway. The past three years have been dominated by the cooler La Nina pattern.

El Niño:

• El Niño is a naturally occurring climate pattern associated with warming of the ocean surface temperatures in the central and eastern tropical Pacific Ocean. 
• It occurs on average every two to seven years, and episodes usually last nine to 12 months.  
• Formation: 
  • It forms when the trade winds blowing east-to-west along the equatorial Pacific slow down or reverse as air pressure changes, although scientists are not entirely sure what kicks off the cycle.
  • Because the trade winds affect the sun-warmed surface waters, a weakening causes these warm western Pacific waters to slosh back into the colder central and eastern Pacific basins.
• Impacts: 
  • El Niño events are typically associated with increased rainfall in parts of southern South America, the southern United States, the Horn of Africa and central Asia.
  • In contrast, El Niño can also cause severe droughts over Australia, Indonesia, and parts of southern Asia.

La Niña:

• La Niña means Little Girl in Spanish. La Niña is also sometimes called El Viejo, anti-El Niño, or simply “a cold event.” 
• La Niña has the opposite effect of El Niño. During La Niña events, trade winds are even stronger than usual, pushing more warm water toward Asia. 
• Off the west coast of the Americas, upwelling increases, bringing cold, nutrient-rich water to the surface.
• These cold waters in the Pacific push the jet stream northward. This tends to lead to drought in the southern U.S. and heavy rains and flooding in the Pacific Northwest and Canada. 
• During a La Niña year, winter temperatures are warmer than normal in the South and cooler than normal in the North. La Niña can also lead to a more severe hurricane season.
• During La Niña, waters off the Pacific coast are colder and contain more nutrients than usual. 
• This environment supports more marine life and attracts more cold-water species, like squid and salmon, to places like the California coast.

News Source: Indian Express

DOWNLOAD PDF