Gunin Borah
(The writer is a faculty of Geography in Biswanath College, Chariali. He can be reached at borah.gunin@gmail.com)
La-Nina is the periodic cooling part of the Pacific Ocean, affecting weather patterns worldwide. It is an oceanic atmospheric phenomenon, which is a colder counterpart of El-Nino. La-Nina is a part of the broader El-Nino Southern Oscillation (ENSO) climate pattern. The name 'La-Nina' originated from the Spanish word for 'The Girl'. It is defined as a complex weather pattern that occurs every few years, as a result of variation in ocean temperature in the equatorial Band of the Pacific Ocean. The phenomena of La-Nina is usually associated with more tropical cyclones, greater rainfall and colder than average temperatures in the Equatorial Pacific Ocean. The events typically last about a year.
La-Nina has an extensive effect on weather worldwide, especially in North America. During the La-Nina period, sea surface temperature across the Eastern Equatorial part of the central Pacific Ocean becomes lower than normal. It also impacts the Atlantic and Pacific hurricane seasons, in which the number of Tropical cyclones increases in the Atlantic basin because, of low wind shear and warmer sea surface temperatures.
La Nina spells temperatures way below normal in the northern hemisphere. The regional weather agencies have predicted a rather frigid winter this year in northern India. It leads to colder winter in the northern hemisphere, causes droughts in the southern US, and heavy rain, flooding in the Pacific North Northwest and Canada.
The meteorologists, weather observers predict that North India could see temperature under three degrees Celsius with cold La Nina winds blowing from the pacific. The weather is changing and the chill is setting in most parts of the country. This is going to get severe in the coming months as the weather observers have predicted a harsh winter in Northern India after the region saw one of the worst phases of heatwave earlier this year.
While climate change has been playing havoc, unleashing extreme weather events, the prediction of the temperature likely to fall to as low as three degrees Celsius in Northern parts of the country in January and February is due to the La Nina effect. When weather conditions are normal in the Pacific Ocean, the winds guiding the ocean currents, or trade wind blow west along the equator. This takes warm water from South America towards Asia. To replace that warm water, cold water rises from the depths of the ocean. El-Nino and La-Nina are two opposing climate patterns that break these normal conditions.
El-Nino weakens the trade winds, pushing the warmer current back East, towards the West coast of America. This leads to an above-normal ocean temperature in a large area along the equator. The heat from the ocean goes out into the atmosphere, leading to warmer air temperature, in the Pacific and subsequently, to warmer global air temperatures.
La-Nina creates an opposite climate pattern. The heatwave from the ocean come into the atmosphere, leading to the colder air temperatures in the Pacific and consequently colder global air temperature. El-Nino and La-Nina, the two events occur every two to seven years and in normal conditions, El-Nino occurs more frequently than La-Nina.
At the beginning of October 2021, last year the US-based National Oceanic and Atmospheric Administration (NOAA) had warned of a Double-Dip La-Nina, saying that it is expected to last through the early spring season of 2022. For the upcoming winter season, which extends from December 2021 through February 2022, there is an 87 per cent chance of La-Nina.
The latest forecast and weather observations indicate that North India is likely to shiver with mercury dipping under three degrees Celsius this winter. The weather phenomenon has already led to unexpected heavy rain in October causing a dip in the normal temperatures in parts of North India.
India has been witnessing extreme weather conditions over the past months. Various causes have led to this, including warming of the oceans, delayed withdrawal of the monsoon, and of course, the usual culprit- 'Climate Change'. When the Southwest Monsoon withdraws from the country on October 25, 2021, it was the seventh most delayed retreat since 1975, according to the Indian Meteorological Department (IMD). In the past, the South West Monsoon has been delayed five times in the span of a decade, starting in 2010 and then followed by 2016, 2017, 2020 and 2021.
After witnessing the worst phase of intense heat and heavy rainfall last year, India is now gripped by freezing cold. Most parts of Central and Northern India have already seen a significant drop in minimum temperature in December last.
La-Nina is responsible for bringing cold air from Siberia, and South China to the Indian subcontinent, which results in a North-South low-pressure system when it interacts with the tropical heating condition here. The cold conditions associated with these troughs can envelop the Southern parts of India as well as can extend to the southern states of Tamil Nadu. However, they don't affect the Northeastern part of India.
In the winter months, the La-Nina causes a very cold wave-like Jet stream to flow across Afghanistan, Iran, and Hindu Kush mountains. These strong and cold winds impact the degree of cold in India.