"WMO warns of intensifying El Niño driving extreme global weather patterns"
El Niño
Warm ENSO phase; SSTs in Niño 3.4 region exceed mean by +0.5°C for five overlapping three-month periods.
Southern Oscillation Index (SOI)
Measures pressure difference between Tahiti and Darwin; negative SOI signals El Niño conditions.
El Niño is the warm phase of the El Niño–Southern Oscillation (ENSO), a naturally recurring ocean-atmosphere coupled system centred in the tropical Pacific Ocean. Scientifically, El Niño is defined when sea surface temperatures (SSTs) in the Niño 3.4 region of the central-eastern equatorial Pacific exceed the climatological mean by +0.5°C for five consecutive overlapping three-month periods. The ENSO cycle — encompassing El Niño, La Niña, and neutral phases — recurs roughly every two to seven years and is one of the most powerful drivers of interannual climate variability on Earth. The atmospheric counterpart, the Southern Oscillation, is measured by the Southern Oscillation Index (SOI), which turns negative during El Niño events, reflecting weakened pressure gradients between the eastern and western Pacific.
India's Southwest Monsoon (June–September) delivers approximately 75% of the country's annual rainfall, with a Long Period Average (LPA) of roughly 887 mm. The monsoon's vigour is intimately tied to ENSO dynamics: El Niño weakens the land-sea temperature gradient between the Indian subcontinent and the Indian Ocean, suppressing the moisture-laden winds that drive monsoon precipitation. Historically, roughly 60% of strong El Niño years have coincided with below-normal monsoon rainfall in India — defined as less than 90% of LPA — though the relationship is probabilistic, not deterministic. Modulating factors such as the Indian Ocean Dipole (IOD) and the Madden-Julian Oscillation (MJO) can offset or amplify El Niño's suppressive effect.
Under normal Pacific conditions, strong easterly trade winds push warm surface water westward toward the Indo-Pacific Warm Pool, allowing cold, nutrient-rich water to upwell along the South American coast. This sustains the Walker Circulation — a zonal atmospheric loop in which air rises over the warm western Pacific and subsides over the cooler eastern Pacific. During El Niño, trade winds weaken or even reverse; warm water migrates eastward; the Walker Circulation shifts and weakens; and subsidence spreads over the Indian Ocean, suppressing convection and reducing monsoon rainfall over South Asia.
The Indian Ocean Dipole (IOD) is a separate but interacting ocean-atmosphere phenomenon. In its positive phase, the western Indian Ocean warms relative to the eastern Indian Ocean, enhancing moisture flux toward the Indian subcontinent and partially counteracting El Niño's suppressive effect. A negative IOD, conversely, compounds El Niño's damage. …
Consider the following statements:
1.In the tropical zone, the western sections of the oceans are warmer than the eastern sections owing to the influence of trade winds.
2.In the temperate zone, westerlies make the eastern sections of oceans warmer than the western sections.
Which of the statements given above is/are correct?
In the South Atlantic and South-Eastern Pacific regions in tropical latitudes, cyclone does not originate. What is the reason?
Which of the following statements about El Niño is/are correct?
1.El Niño is defined when SSTs in the Niño 3.4 region exceed the climatological mean by +0.5°C for five consecutive overlapping three-month periods.
2.The Southern Oscillation Index (SOI) turns positive during El Niño conditions.
3.El Niño weakens the Walker Circulation by causing trade winds to slow or reverse.
Select the correct answer using the codes below:
Consider the following pairs regarding the Indian Ocean Dipole (IOD):
1.Positive IOD — Western Indian Ocean warmer than eastern; buffers El Niño's suppressive effect on Indian monsoon
2.Negative IOD — Eastern Indian Ocean warmer than western; compounds El Niño's suppressive effect on Indian monsoon
3.Positive IOD — Reduces moisture flux toward Indian subcontinent
Which of the pairs given above is/are correctly matched?
Assertion (A): During El Niño years, the Indian Summer Monsoon tends to be below normal.
Reason (R): El Niño strengthens the Walker Circulation, increasing convection over the Indian Ocean and enhancing monsoon rainfall.
Which one of the following is correct?
With reference to the Madden-Julian Oscillation (MJO), consider the following statements:
1.The MJO propagates westward across the tropics.
2.The MJO governs intra-seasonal variability within the Indian Summer Monsoon.
3.An active MJO phase over the Indian Ocean can temporarily revive monsoon activity even during an El Niño year.
Which of the statements given above is/are correct?
Which of the following best describes the 'Walker Circulation' under normal (non-El Niño) conditions in the tropical Pacific?
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