Affect of El Nino and La Nina on the weather

MINTU SARMA

There are multiple places around the world having rare natural phenomena such as magnetic hill in Ladakh, mystery spot (Santa Cruz California) , the appearance of “Bigfoot” in America, low-frequency hum in the desert area in Taos (New Maxico), unidentified flying object (UFO) to mention a few.  Some of them have been explained scientifically and some are still dangling between myth and fact. Such a mystery had cropped up in the year of 1600 AD when fishermen on the west Peru coast noticed unusual warming of seawater during Christmas days. They had believed divine force behind it and named it as El Nino.  El Nino is a Spanish word that means “the little boy or Christ-child”.
El Nino is periodic warming in sea surface temperature across the central and east-central equatorial Pacific and La Nina is the antithesis to it. Both the phenomena significantly influence weather over a vast area, from South America to India. El Nino associated with dry weather and drought over India and Australia, on the contrary La Nina associated with good monsoon rain, less heat and cold wave. The word “La Nina” also originates from Spanish which means “the little girl”. These two weather driving phenomena occur in between the Peru coast (Eastern pacific) and the East coast of Australia (Western Pacific). The tread wind is a major factor in the occurrence of these phenomena. We are aware that the sun’s rays strike Earth’s surface most directly at the equator. This area receives a constant 12 (twelve) hours of direct sunlight of a day. As the rays hit directly for a longer time, the equatorial area (central Pacific) is heated more, and sea surface temperature (SST) rises accordingly.
In normal condition the strong treat wind which is known as equatorial easterly also blows from the East to the West, pushes the warm seawater to the East coast of Australia and starts accumulates near the coast. The evaporation from warm water help in cloud formation and ultimately good precipitation occurs near the East Coast and surrounding areas. The moister laden warm air raises up to the tropopause and gets cool and dry leaving all the moister content. The equatorial westerlies (the wind from the west to the east) in the troposphere bring this cold air above the Peru coast and move down. The descending of cold air at the Peru coast and ascending of warm air at the East Australian coast creates a cycle. This cycle is called the walker cycle or walker cell in the name of Sir Gilbert Walker who discovered this phenomenon.
In El Nino condition, the tread wind becomes weak and the warm seawater gets back to the Peru coast and accumulates. Due to this accumulation level of the sea surface increases up to 90 cm and helps in forming rain-bearing clouds due to rapid evaporation. Subsequently, heavy precipitation takes place that creates flood and havoc brings uncertainty to the fishing industry. On the other hand drought-like situation prevails in Australia as well as in India as the flow of monsoon wind is affected by this phenomenon. La Nina’s condition is like normal condition, the strong tread wind pushes warm seawater to Australia’s East coast and warm water begins to deplete near the Peru coast. This depletion is filled by cold seawater from the lower level of sea replace. The up whirling of cold water brings a lot of nutrition that attracts fishes. The nutrition entices the fishes and unfortunately trapped in the fishing net.   The fishing community on the Peru coast is blessed by the La Nina condition as it helps in their economical growth directly. In general El Nino and La Nina repeat within 6 to 7 years.
Though 2020 was a COVID cursed year, but it was a good year for Indian weather. According to the India Meteorological Department (IMD), it was a La Nina year. La Nina seemed to have played an influencing role in the country’s weather 2020. Last year India experienced above normal rainfall, below the normal temperature in winter and less occurrence of heat wave. The country received 109 percent rainfall of long period average (LPA). The monsoon wind arrived in Kerala on 1st June which is the normal date of onset. Southwest monsoon covered the whole country on June 26th against the normal date of July 8th. It retreated from west Rajasthan and parts of Punjab on September 28th, 11 days after the normal withdrawal date. In general North-East monsoon brings rain to Tamil Nadu, parts of Andhra Pradesh, Kerala and Karnataka from October to December. Last year during winter also country received good rainfall, in other words SW monsoon and NE monsoon were good in 2020. La Nina conditions are likely to prevail for the next 6 (six) month according to IMD source. Can we expect the reflection of weather 2020 in 2021 also? IMD is yet to forecast it. It is very much clear that the weather forecast is a very challenging task due to the complex web of different thermodynamic active parameters in the atmosphere over the various orographic surface.
India is an agricultural country and agriculture basically depends on the monsoon rain. Good monsoon brings good harvesting and increases GDP share up to 16%. Planning and policies for agriculture are simply useless without good monsoon rain. Irrigation can never be a backbone for the vast agriculture sector in a developing country like India. Calculated weather prediction has the potential to flourish the country’s agricultural scenario. Since El Nino and La Nina are the two most influencing factors in weather, thorough research on it would be a boon for the country. The research and development (R & D) wing of IMD needs to stride with time to develop a perfect forecasting model especially for India which would bring heyday to Indian cultivators. It may be a unique contribution to the nation to make India as Vishwa Guru of this planet.
(The writer is a Research Scholar, Gauhati University. Email: sarmamintu9@gmail.com)