What is the El Nino phenomenon?
El Nino and La Nina are opposing phases of the El Nino-Southern Oscillation (ENSO) cycle. The ENSO is a periodic climatic trend that involves temperature fluctuations in the eastern and central tropical Pacific Oceans, as well as changes in upper and lower-level wind patterns, sea level pressure, and tropical rainfall patterns over the Pacific basin. The warm phase of ENSO is typically referred to as El Nino, whereas the cold phase is referred to as La Nina. These deviations from average surface temperatures have the potential to have a substantial impact on global weather and climate conditions.
This article will help you to understand what the La Nina and El Nino phenomena are and how they affect Indian weather.
El Nino Meaning
In Spanish, El Nino means "small boy" or "Christ child". As it was initially seen by South American fishermen in the early 17th century, the phenomenon was given this name. Seas tended to become warm in the Pacific Ocean around December, which is why the name was picked. El Nino is a large-scale ocean-atmosphere climatic interaction associated with a recurrent increase of sea surface temperatures in the central and east-central Equatorial Pacific. It is linked to high pressure in the western Pacific. The El Nino effect has a negative influence on the Indian monsoons and, as a result, agriculture in India.
According to the work of Sir Gilbert Walker, climate scientists discovered that El Nino and the Southern Oscillation occur at the same time in the 1930s. A variation in air pressure over the tropical Pacific Ocean is known as the Southern Oscillation. The air pressure over the ocean lowers when coastal waters in the eastern tropical Pacific get warmer (El Nino). El Nino-Southern Oscillation is the name given to these two interconnected occurrences by climatologists (ENSO). The words El Nio and ENSO are now used interchangeably by most subject experts.
El Nino's Impact on India
The pressure distribution in a typical monsoon year (without El Nino) is as follows.
The pressure along Peru's coast in South America is higher than in the region bordering northern Australia and South East Asia.
As the Indian Ocean is warmer than the surrounding oceans, it has lower pressure. As a result, moisture-laden winds blow from the western Pacific to the Indian Ocean.
As the pressure on India's landmass is lower than that on the Indian Ocean, moisture-laden winds go farther from the ocean to the lands. The monsoons are disturbed if this typical pressure distribution is disrupted for any cause.
El Nino causes the chilly surface water off the Peruvian coast to warm. The regular trade winds are lost or alter their direction when the ocean is warm. As a result, moisture-laden winds from the western Pacific are steered towards Peru's coast (the region near northern Australia and South East Asia). It creates significant rainfall in Peru, during the El Nino, depriving the Indian subcontinent of its typical monsoon rains. The greater the temperature and pressure differential, the greater is the rainfall deficit in India.
La Nina Meaning
In Spanish, La Nina means "small girl", and it is also known as El Viejo, or "cold event". In the Eastern Pacific, the water temperature drops below average. As a result, a powerful high-pressure system has formed over the eastern equatorial Pacific. Low pressure is now present in the Western Pacific and off the coast of Asia. La Nina causes drought in Peru and Ecuador, major floods in Australia, high temperatures in the Western Pacific, Indian Ocean, and off the coast of Somalia, and abundant monsoon rains in India. La Nina conditions are really advantageous to the Indian monsoon. El Nino and La Nina weather patterns occur every 4–5 years on average. El Nino is more common than La Nina. Typically, the episodes last nine to twelve months.
Effects of El Nino and La Nina on Indian Climate
El Nino generates warm weather across the Indian subcontinent in the winter and dry conditions and a deficient monsoon in the summer. In contrast, La Nina causes a better-than-normal monsoon in India. During the El Nino years of 2002 and 2009, India had little rainfall, although the monsoon was typical during the El Nino years of 1994 and 1997. It signifies that India faced droughts during the monsoon for nearly half of the year due to El Nino in the summer. El Nino will harm crops such as paddy, maize, groundnut, guar, castor, tur, moong, and bajra.
El Nino: Measuring the Effects
Scientists, governments, and non-governmental organizations (NGOs) use a variety of technology, including scientific buoys, to collect data on the El Nino effect. A buoy is a floating object that serves as a navigational aid or warning signal for ships in the middle of the ocean. They are usually brightly coloured (fluorescent). Temperatures, currents, winds, and humidity are all measured by these buoys. The buoys provide data to academics and forecasters all across the world on a regular basis, allowing scientists to more correctly anticipate El Nino and visualize its evolution and influence around the planet.
The Oceanic Nino Index (ONI) is a tool for determining how much sea surface temperatures have deviated from normal. The major tool for determining, assessing, and forecasting each El Nino event is the Oceanic Nino Index, which is a measure of the departure from normal sea surface temperature in the east-central Pacific Ocean. El Nino occurrences range in severity from mild temperature rises (about 4-5° F) with relatively little local effects on weather and climate to extremely severe increases (14-18° F) linked to global climate change.
FAQs on El Nino
1. What is El Niño in simple terms?
El Niño is a naturally occurring climate pattern characterized by the unusual warming of surface waters in the eastern and central tropical Pacific Ocean. It is the "warm phase" of a larger phenomenon called the El Niño-Southern Oscillation (ENSO). This change in ocean temperature disrupts normal weather patterns, causing significant consequences for ecosystems, agriculture, and economies worldwide.
2. What are the key differences between El Niño and La Niña?
El Niño and La Niña are opposite phases of the ENSO cycle. The primary difference lies in the sea surface temperatures and their resulting atmospheric effects:
- Sea Surface Temperature: In an El Niño, the eastern Pacific Ocean is warmer than average. In a La Niña, the same region is cooler than average.
- Trade Winds: During El Niño, the east-to-west trade winds weaken or even reverse. During La Niña, these trade winds become stronger than usual.
- Rainfall Patterns: El Niño often brings increased rainfall to the eastern Pacific (e.g., Peru) and drought to the western Pacific (e.g., Indonesia and Australia). La Niña does the opposite, causing droughts in the eastern Pacific and heavy rainfall in the western Pacific.
- Upwelling: El Niño suppresses the upwelling of cold, nutrient-rich water off the coast of South America, whereas La Niña enhances it.
3. How does El Niño affect the Indian monsoon?
El Niño typically has a negative impact on the Indian summer monsoon. The warming of the central and eastern Pacific Ocean alters large-scale atmospheric circulation patterns, including the Walker Circulation. This shift can lead to suppressed rainfall and drought-like conditions over the Indian subcontinent. A strong El Niño event is often correlated with a deficient monsoon, which is critical for India's agriculture-dependent economy.
4. What is the role of the Southern Oscillation in the El Niño cycle?
The Southern Oscillation is the atmospheric component of the El Niño phenomenon (ENSO). It refers to the see-saw pattern of atmospheric pressure changes between the eastern and western tropical Pacific. During El Niño, the surface pressure is lower than average over the eastern Pacific (near Tahiti) and higher than average in the western Pacific (near Darwin, Australia). This pressure difference weakens the trade winds, linking the atmospheric change (oscillation) with the oceanic change (El Niño warming).
5. How does El Niño develop and what causes it?
El Niño is caused by a complex interaction between the ocean surface and the atmosphere in the tropical Pacific. It develops when the normally strong, westward-blowing trade winds weaken. This weakening allows the large mass of warm water, typically pooled in the western Pacific, to slosh back eastward towards the coast of South America. This eastward movement of warm water further warms the air above it, reducing the east-west temperature gradient and weakening the trade winds even more, creating a self-reinforcing cycle.
6. Beyond India, what are some examples of El Niño's global weather impacts?
El Niño's influence extends far beyond the Pacific, a phenomenon known as teleconnections. Key global impacts include:
- Australia & Indonesia: Increased risk of severe droughts and wildfires due to suppressed rainfall.
- South America: Heavy rains and flooding along the coasts of Peru and Ecuador.
- North America: Can lead to wetter and cooler conditions in the southern U.S. and warmer, drier conditions in the northern U.S. and Canada during winter.
- Africa: Can cause drought in Southern Africa and parts of the Sahel, while bringing heavier rainfall to East Africa.
7. Why is El Niño an important event with major economic and ecological consequences?
El Niño is critically important because its effects can be devastating. Economically, it disrupts agriculture through droughts and floods, leading to crop failures and food shortages. It also severely impacts fisheries, particularly the anchovy industry in Peru, by stopping the upwelling of nutrient-rich cold water. Ecologically, it can cause coral bleaching, forest fires, and shifts in marine and terrestrial habitats, affecting biodiversity on a global scale.
8. What is the typical duration and frequency of an El Niño event?
An El Niño event typically lasts for 9 to 12 months, though some prolonged episodes can extend up to two years. These events are not on a fixed schedule but tend to recur irregularly every 2 to 7 years. They usually develop during the northern spring (March-June), reach their peak intensity in the late autumn/winter (November-February), and then weaken during the following spring.
9. What are the 'normal' conditions in the Pacific when neither El Niño nor La Niña is present?
Under normal, or neutral, conditions, the trade winds blow strongly from east to west across the tropical Pacific. This pushes warm surface water towards the western Pacific (around Indonesia), causing sea levels there to be higher and the water warmer. In the eastern Pacific (around Peru), this movement allows cold, deep, nutrient-rich water to rise to the surface in a process called upwelling, which supports a rich marine ecosystem.
