El Nino, La Nina and El Nino Modoki - Explained
EL Nino :
- The term "El Niño" originates from Spanish, meaning "the Christ Child," and was coined by fishermen residing along the coasts of Ecuador and Peru. It is used to describe the phenomenon of warming in the central and eastern Pacific Ocean.
- El Nino is the name given to the occasional development of warm ocean surface waters along the coast of Equador and Peru.
- When this warming Occurs the usual Upwelling of cold , nutrient rich deep ocean water is significantly reduced.
- El Nino Normally occurs around Christmas and usually lasts for a few weeks to few months.
Normal Years:
- In a normal year, a surface low pressure develops in the region of northern Australia and Indonesia and a high pressure system over the coast of Peru.
- As a result, the trade winds over the Pacific Ocean move strongly from east to west.
- The easterly flow of the trade winds carries warm surface waters westward, bringing convective storms (thunderstorms) to Indonesia and coastal Australia.
- Along the coast of Peru, cold bottom cold nutrient rich water wells up to the surface to replace the warm water that is pulled to the west.
Normal Conditions :
- Eastern Pacific == Coast of Peru and Ecuador == Cold Ocean Water == Good for Fishing.
- Western Pacific == Indonesia and Australia == Warm Ocean Water == Plenty of rains.
Walker Circulation ( Occurs During Normal Years )
- The Walker circulation (walker cell) is caused by the pressure gradient force that results from a high pressure system over the eastern Pacific ocean, and a low pressure system over Indonesia.
- The Walker cell is indirectly related to upwelling off the coasts of Peru and Ecuador. This brings nutrient-rich cold water to the surface, increasing fishing stocks.
During El Nino Year :
- Air Pressure Changes: During an El Niño event, air pressure decreases over the central and eastern Pacific Ocean and increases over the western Pacific. This reversal of pressure patterns is part of the larger climate phenomenon known as the Southern Oscillation.
- Weak High Pressure in Western Pacific: The normal low-pressure system in the western Pacific is replaced by a weaker high-pressure system. This change in pressure gradient is a characteristic feature of El Niño.
- Trade Wind Reduction and Weak Walker Cell: The weakening of the pressure gradient results in reduced trade winds. The Walker Circulation, which is a pattern of atmospheric circulation in the tropical Pacific, weakens during El Niño. The Walker Cell refers to the east-west circulation along the equator, and it may even reverse during intense El Niño events.
- Equatorial Counter Current and Warm Water Accumulation: The weakening of the trade winds allows the equatorial counter current, which flows eastward along the equator, to accumulate warm ocean water along the coasts of Peru and Ecuador. This accumulation of warm water disrupts the typical oceanic circulation patterns.
- Upwelling Disruption and Warm Water: The accumulation of warm water in the eastern Pacific during El Niño disrupts the normal upwelling of cold, nutrient-rich water along the coast of Peru. This has significant effects on marine ecosystems and can impact fisheries.
- Climate Effects: The disruption of normal atmospheric and oceanic patterns leads to various climatic impacts:
- Droughts in Western Pacific: The weakening of the Australian monsoon during El Niño can lead to droughts in regions that typically receive rainfall from this monsoon.
- Rains in Equatorial South America: The warmer sea surface temperatures off the coast of South America lead to increased convection and rainfall in the region, often causing flooding.
- Central Pacific Storms: El Nino can enhance the development of convective storms and hurricanes in the central Pacific.
El Nino Condition :
- Eastern Pacific == Coast of Peru and Ecuador == Warm Ocean Water == Fishing industry suffers.
- Western Pacific == Indonesia and Australia == Cold Ocean Water == Drought.
Effects of El Nino :
- The warmer waters had a devastating effect on marine life existing off the coast of Peru and Ecuador.
- Fish catches off the coast of South America were lower than in the normal year (Because there is no upwelling).
- Severe droughts occur in Australia, Indonesia, India and southern Africa.
- Heavy rains in California, Ecuador, and the Gulf of Mexico.
How El Nino Impacts Monsoon Rainfall in India:
- El Nino and Indian Monsoon Relationship: El Niño is a climate phenomenon characterised by warmer-than-normal sea surface temperatures in the central and eastern equatorial Pacific Ocean. This warming can disrupt global weather patterns, including the Indian monsoon. The Indian monsoon is a seasonal wind pattern that brings about 80% of India's annual rainfall, crucial for agriculture and water resources.
- Impact on Indian Monsoon: El Nino tends to weaken the Indian monsoon, leading to reduced rainfall in many parts of the country. This can result in drought conditions, water shortages, and a decrease in agricultural productivity. The weakening of the monsoon can be attributed to changes in atmospheric circulation patterns caused by the altered sea surface temperatures associated with El Niño.
- Droughts and El Nino Events: there is a historical pattern of major droughts in India coinciding with El Niño events. The warmer Pacific waters during El Niño disrupt the typical atmospheric circulation that drives the monsoon, leading to decreased rainfall and potentially severe droughts. The years 2002 and 2009 are notable examples of El Niño-associated droughts in India.
- Complex Factors: While El Niño is a significant driver of monsoon variability, other factors like the Indian Ocean Dipole (IOD) also play a role. The IOD is another sea surface temperature anomaly in the Indian Ocean that can either amplify or counteract the effects of El Niño on the Indian monsoon. This complexity is why not every El Niño event leads to a drought in India.
- Economic Impact: The Indian economy heavily relies on agriculture, and the performance of the monsoon greatly affects crop yields. Severe droughts due to El Niño can lead to reduced agricultural production, particularly of crops like rice, sugarcane, cotton, and oilseeds. This can result in higher food prices, which contribute to inflation. Additionally, decreased agricultural output can impact the livelihoods of millions of farmers and labourers.
- GDP Growth: The agricultural sector's contribution to India's GDP is substantial, around 14%. A poor monsoon due to El Niño-induced drought can lead to lower agricultural output, which in turn affects the overall GDP growth of the country. This is because a weaker agricultural sector can have ripple effects on related industries and economic activities.
El Nino Southern Oscillation :
- The El Nino-Southern Oscillation (ENSO) is a complex climatic phenomenon that involves the interaction between the ocean and the atmosphere in the tropical Pacific Ocean.
- It is characterised by irregular and periodic shifts in sea surface temperatures, atmospheric pressure patterns, and wind patterns.
- The warming phase of the sea temperature is known as El Niño and the cooling phase as La Nina.
Southern Oscillation Index and Indian Monsoons :
The see-saw pattern of meteorological changes is observed between the Eastern Pacific and Western Pacific. This entails high pressure over the equatorial Eastern Pacific coinciding with low pressure over the equatorial Western Pacific, and vice versa. This pressure oscillation creates a vertical circulation along the equator, with upward motion over low pressure areas and downward motion over high pressure regions, a phenomenon known as the Walker Circulation.
The positioning of the low-pressure system, particularly over the Western Pacific, fosters favourable monsoon rainfall conditions in India. However, when this configuration shifts eastward, as observed during El Niño years, it leads to diminished monsoon rainfall in India. El Niño and the Southern Oscillation (SO) are closely linked, and collectively they form an ENSO event.
The Southern Oscillation does not adhere to a fixed periodicity; rather, its cycle ranges from two to five years. The Southern Oscillation Index (SOI) is employed to gauge the intensity of the Southern Oscillation. This index quantifies the pressure difference between Tahiti in French Polynesia (representing the Central Pacific Ocean) and Port Darwin in northern Australia (representing the Eastern Pacific Ocean). The positive and negative values of the SOI—derived from the Tahiti minus Port Darwin pressure difference—serve as indicators of favorable or unfavourable rainfall conditions in India.
La Nina:
- The term "La Nina," meaning 'little girl' in Spanish, is also referred to as El Viejo or the 'cold event.'
- La Nina sees cooler than average sea surface temperatures in the equatorial Pacific region.
- It occurs when ocean temperatures in the equatorial Pacific drop to lower-than-normal levels.
- During this cool phase, Trade winds are stronger than usual, pushing warmer water towards western Pacific ocean .
Impacts of La Nina :
- Abnormally Heavy Monsoons in India and Southeast Asia: La Niña can lead to increased rainfall during the monsoon season in these regions, potentially causing flooding and other water-related issues.
- Cool and Wet Winter Weather in Southeastern Africa: La Niña tends to bring cooler and wetter conditions to southeastern Africa during the rainy season, which can affect agriculture and local ecosystems.
- Wet Weather in Eastern Australia: La Niña can enhance rainfall in eastern Australia, leading to wetter conditions and potentially reducing the risk of drought in those areas.
- Cold Winter in Western Canada and Northwestern United States: La Niña tends to result in colder-than-average winter temperatures in these regions, possibly leading to increased snowfall and colder conditions overall.
- Winter Drought in the Southern United States: La Niña is associated with a higher likelihood of drier-than-normal conditions in the southern United States during the winter months, which can contribute to drought concerns.
El Nino Modoki :
- El Nino Modoki is a coupled ocean-atmosphere phenomenon in the tropical Pacific.
- It is different from another coupled phenomenon in the tropical Pacific namely, El Nino.
- Conventional El Niño is characterised by strong anomalous warming in the eastern equatorial Pacific.
- Whereas, El Nino Modoki is associated with strong anomalous warming in the central tropical Pacific and cooling in the eastern and western tropical Pacific.
The Following Picture depicts all all the Phenomena we discussed above :
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