• There is a 66 per cent chance of the La Nina weather pattern, characterised by cold temperatures in the Pacific Ocean, emerging during September-November, a US government forecaster said.

• India is set to receive monsoon rainfall that is above the average as a La Nina weather pattern forms in August and September, promising to boost farm output and growth in Asia’s third-biggest economy.

• El Nino and La Nina are two opposing climate patterns that break these normal conditions. 

• Scientists call these phenomena the El Nino-Southern Oscillation (ENSO) cycle. 

• El Nino and La Nina can both have global impacts on weather, wildfires, ecosystems, and economies.

What is El Nino and La Nina?

• El Nino and La Nina events are a natural part of the global climate system. 

• They occur when the Pacific Ocean and the atmosphere above it change from their neutral (‘normal’) state for several seasons.

• It occurs on average every two to seven years, and typically lasts nine to 12 months. 

• El Nino, which is the warming of the waters in the Pacific Ocean near South America, is generally associated with the weakening of monsoon winds and dry weather in India.

• It influences weather and storm patterns in different parts of the world. But it takes place in the context of a climate being changed by human activities. 

• It is associated with increased rainfall in the Horn of Africa and the southern US, and unusually dry and warm conditions in Southeast Asia, Australia and southern Africa. 

• La Nina, which is the opposite of El Nino, typically brings good rainfall during the monsoon season.

• These changes in the Pacific Ocean and its overlying atmosphere occur in a cycle known as the El Nino–Southern Oscillation (ENSO). 

• The term ‘El Nino’ translates from Spanish as ‘the boy-child’. Peruvian fishermen originally used the term to describe the appearance, around Christmas, of a warm ocean current off the South American coast. 

• It is now the commonly accepted term to describe the warming of the central and eastern tropical Pacific Ocean. 

• La Nina means Little Girl in Spanish. 

• La Nina is also sometimes called El Viejo, anti-El Nino, or simply “a cold event” and is the opposite ENSO phase to El Nino.

Ocean temperature influences weather

• Weather patterns are heavily influenced by ocean temperatures. 

• Warmer ocean waters tend to create more clouds and, subsequently, increased rainfall in those areas. This phenomenon is particularly evident in the Pacific Ocean near the equator, where the sun heats the water’s surface significantly.

• Under typical conditions, a low-pressure system forms near northern Australia and Indonesia, while a high-pressure system develops off the coast of Peru. These pressure systems result in strong trade winds blowing from east to west across the Pacific Ocean, pushing warm surface waters toward the west. 

• Consequently, convective storms, including thunderstorms, are more likely to develop over Indonesia and coastal Australia.

(The author is a trainer for Civil Services aspirants.)