These days, El Nino is a constant topic of conversation while talking about the Indian monsoon. It nearly seems as though the Indian monsoon's future rests on the unusual sea surface temperatures in the distant Pacific Ocean.
What is El Nino Southern Oscillation or ENSO?
El Nino (Christ child) is the term used to describe the unusual warming of surface waters in the West Pacific Ocean's equatorial area. It has a reputation for reducing monsoon rains.
“In the seventeenth century, fishermen began referring to the semi-regular arrival of exceptionally warm seas off the coastlines of Peru and Ecuador as "El Nino" (Christ child). Because these warmer waters often arrived around Christmas, which is why the name was picked. However, it may be argued that India, not South America, is where the scientific understanding of this phenomenon began. Henry Blanford, the Imperial Meteorological Reporter to the government of India, was inspired to hunt for an answer using atmospheric pressure readings after the failure of the Indian summer monsoon rains in 1876 and 1877, which led to the Great Famine. He found that the pressure was unusually high across broad portions of Asia, Australia, and the southern Indian Ocean in addition to being high over India.”
La Nina (Little Girl), the excessive cooling of the sea surface in the same region of the western Pacific Ocean, is the antithesis of El Nino. Rainfall over India is reported to be aided by it.
“La Nina was only identified in the 1980s, despite El Nino's discovery in the 1920s.”
A third phase exists, during which the sea surface temperature largely maintains its long-term average.
El Nino Southern Oscillation, or ENSO, is the collective name for these three oceanic phases.
Why do surface waters in the equatorial Pacific get abnormally warm or cold?
Not everything about ENSO and monsoons is very well understood, but scientists do have a fair idea of how this entire system works.
Ocean-Atmosphere System
It is crucial to remember that ENSO is more than just an ocean system, even though it is frequently discussed in terms of temperature fluctuations in sea surface waters. Oceanic and atmospheric factors interact to form ENSO.
The word ENSO really refers to a specific atmospheric condition that measures the difference in sea level air pressure across the western and eastern sides of the Pacific Ocean, known as the Southern Oscillation. The strength and direction of winds are other aspects of the atmosphere that are crucial to ENSO.
ENSO neutral condition
A persistent wind pattern termed the trade winds, which move from east to west at relatively low altitudes, is found in the tropical region, which is the area immediately above and below the equator. The Pacific Ocean's sea surface is quite warm due to sunlight exposure. These relatively warm waters, which also become lighter, are forced westward when the trade winds blow over the Pacific Ocean. As a result, the surface water in the eastern Pacific Ocean, which is close to the coast of South America, is forced to move west.
The surface water that is warmer keeps being pushed until it reaches landmasses in the Philippines and Indonesia. This process results in an accumulation of relatively warm waters around Indonesia, known as the Western Pacific warm pool, and comparatively cold waters in Ecuador and Peru. They cannot be pushed any further.
The air rises upward due to the warmer surface area. Additionally, this causes clouds to build and brings about a lot of rain. The monsoon system, which sends rain to India, is strengthened by the airflow.
El Nino
The trade winds occasionally become less strong for unknown causes. They are less able to force warmer surface water towards the Indonesian shore as a result. This results in a warmer-than-normal central and eastern Pacific Ocean near Ecuador and Peru. this El Nio period.
La Nina
The La Nina event results in the exact reverse. More warm water is pushed towards the Indonesian coast by stronger than usual trade winds, which also causes the eastern Pacific to be colder than usual. Although both phases normally last a year, La Nina tends to continue a little longer than El Nino.
ENSO and weather
In general, The globe warms during El Nino events while cooling during La Nina events. Typically, El Nino years are the decade's warmest year. 2016 was the warmest year on record and was a part of the strongest and longest EL Nino ever.
For instance, more warm surface water travels westward during the La Nina phase, causing deep cold water to upwell in the eastern Pacific, making it colder than usual. This body of chilly surface water has the capacity to absorb a small amount of heat from the atmosphere.
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