El Niño

Explanation

Statement 1 is correct. El Niño is defined by anomalous warming of sea surface temperatures (SSTs) in the central and eastern equatorial Pacific. This warming disrupts the Walker Circulation — the large-scale atmospheric overturning cell driven by the temperature contrast between the warm western Pacific and the cooler eastern Pacific. When this circulation weakens, the rising-air limb (associated with heavy rainfall) shifts eastward toward the central Pacific, leaving regions such as southern Africa, the Indian subcontinent, and Australia under descending, dry air — resulting in below-normal rainfall. This teleconnection mechanism is the physical basis for El Niño-induced drought in the Global South. Statement 2 is incorrect and inverts the documented teleconnection. Southern Africa (including Zimbabwe) experiences below-normal rainfall and prolonged dry spells during El Niño episodes — not above-normal rainfall. Zimbabwe's current drought-preparedness response, including grain reserves and promotion of drought-tolerant crops, is precisely because El Niño is associated with moisture deficits, not surpluses, in this region. Statement 3 is correct. Rain-fed agricultural systems in the Global South — where smallholder and subsistence farmers depend entirely on seasonal rainfall — are especially vulnerable during El Niño years. The delayed onset of the rainy season shortens the effective growing window; reduced and erratic rainfall lowers soil moisture; and together these stresses drive crop failures, livestock losses, and cascading food insecurity. This is a well-established pattern across southern Africa and parts of South and Southeast Asia during El Niño events.

Explanation

All three pairs are correctly matched. Western Disturbances are extratropical weather systems that originate in the Mediterranean region and travel eastward, bringing winter precipitation to north-western India — particularly to the Indo-Gangetic plains and the Himalayan foothills. This winter rainfall is critical for wheat cultivation in states like Punjab, Haryana, and Uttar Pradesh, as it replenishes soil moisture during the grain-filling phase. The ENSO (El Niño–Southern Oscillation) teleconnection to South Asian winter weather is well-documented: during El Niño years, the jet stream and atmospheric circulation patterns are altered, reducing the frequency and intensity of Western Disturbances that reach north-western India. This suppression of Western Disturbance activity results in lower winter precipitation, warmer-than-normal temperatures across northern India, and greater drought risk for rabi crops — especially rain-fed pulses and oilseeds. The teleconnection between El Niño and suppressed Western Disturbance activity is a standard concept in Indian climatology.

Explanation

Statement 1 is correct. A positive Indian Ocean Dipole (+IOD) is defined by anomalously warm sea-surface temperatures in the western Indian Ocean and cooler-than-normal temperatures in the eastern Indian Ocean. This temperature gradient strengthens westerly winds over the Indian Ocean and enhances convection and moisture transport toward the Indian subcontinent, including potential support for northeast monsoon activity over the South Peninsula — though its effects are not uniform across all districts. Statement 2 is incorrect. The MJO is an eastward-propagating (not westward) pulse of enhanced tropical convection. It originates over the Indian Ocean/Africa region and moves eastward across the Indian Ocean, Maritime Continent, and into the Pacific. This direction of propagation is a defining feature that distinguishes the MJO from westward-moving equatorial waves. By influencing the distribution of moisture, clouds, and rising air, the MJO modulates the intensity of monsoon activity and the formation of low-pressure systems. Statement 3 is correct. El Niño (the warm phase of ENSO) is associated with a weakening of the Walker Circulation and generally suppresses Indian monsoon rainfall by reducing moisture supply and large-scale ascent over the Indian Ocean. However, a simultaneously positive IOD can partially offset El Niño's suppressing influence — since the IOD is an Indian-Ocean-internal mode that independently enhances convection over the western Indian Ocean. The net outcome for South Peninsula rainfall therefore depends on the relative dominance of these competing and sometimes reinforcing large-scale signals.

Explanation

Statement 1 is correct. The Madden–Julian Oscillation (MJO) is a well-established intraseasonal climate mode that travels eastward along the equatorial region roughly every 30–60 days. Its active phase, when it passes over the Indian Ocean and South Asian region, enhances atmospheric convection and can intensify monsoon rainfall, while its suppressed phase does the opposite. Statement 2 is correct. A positive Indian Ocean Dipole occurs when the western Indian Ocean is anomalously warmer than the eastern Indian Ocean. This configuration draws moisture-laden winds towards the Indian peninsula and East Africa, increasing the likelihood of above-normal rainfall over India. A negative IOD does the reverse. Statement 3 is incorrect. El Niño warms the central and eastern Pacific, which shifts the Walker Circulation eastward, enhancing convection over the eastern Pacific and the Maritime Continent (the Indonesia–Philippines region) while simultaneously suppressing convection over the Indian Ocean and the Indian subcontinent. This typically leads to below-normal monsoon rainfall over India — the opposite of what Statement 3 claims.

Explanation

Statement 1 is correct: El Niño — a warming of the Central Pacific — is well-established as a driver of weakened southwest monsoon rainfall over India; this is a foundational teleconnection in Indian climate science. Statement 2 is incorrect: the Pacific Decadal Oscillation (PDO) correlates *negatively* with Indian monsoon rainfall, much like the El Niño–La Niña cycle. A warm (positive) phase of the PDO tends to suppress Indian monsoon rainfall, not reinforce it. Statement 3 is correct: studies have shown that when El Niño and the PDO are 'in phase' (i.e., both in their warm, monsoon-suppressing phases), their effects on the Indian monsoon reinforce each other, producing a stronger suppression than either would alone; when they are out of phase, their effects partially offset one another.

Explanation

All three statements correctly describe ENSO mechanics and related teleconnections. Statement 1 accurately captures the core El Niño signal: anomalously warm SSTs in the central and eastern equatorial Pacific suppress convection over Indonesia and the western Pacific (reflected in above-average OLR — indicating suppressed convection — over Indonesia and the Philippines), and this Walker Circulation disruption is the primary mechanism through which El Niño weakens the Indian monsoon by reducing moisture convergence over the Indian subcontinent. Statement 2 correctly identifies the Indian Ocean Dipole as a distinct but coupled ocean-atmosphere mode: a positive IOD is defined by warmer-than-normal SSTs in the western equatorial Indian Ocean and cooler-than-normal SSTs in the eastern equatorial Indian Ocean (near Indonesia). This pattern strengthens moisture inflow into India from the west and tends to partially compensate for El Niño's suppressing effect on the monsoon — making a co-occurring positive IOD a moderating influence. Statement 3 correctly describes the Niño3.4 index and the symmetric La Niña definition: anomalously cool sustained SSTs in the same Niño3.4 region (5°N–5°S, 170°W–120°W) define a La Niña, which tends to enhance Indian monsoon precipitation through the opposite Walker Circulation response. All three statements reflect established ENSO science validated by the CPC, NOAA, and Australia's Bureau of Meteorology monitoring frameworks.

Explanation

El Niño is the warm phase of the El Niño–Southern Oscillation (ENSO) cycle. During El Niño, the Walker Circulation — the east-west atmospheric convection cell over the tropical Pacific — weakens or reverses: trade winds slacken, warm water pools in the central and eastern Pacific, and the zone of deep convection (rainfall) shifts eastward toward the central Pacific and South America's Pacific coast. This suppresses rainfall over the western Pacific rim, including South-East Asia and Australia, and over Southern Africa, producing drought conditions in major crop-growing regions. Statement 1 is correct — drought risk rises in South-East Asia and Southern Africa, while enhanced rainfall is typical along the Pacific coast of equatorial South America. Statement 2 is correct — the weakening of the Walker Circulation and the anomalous warming of the central-eastern Pacific are the defining physical mechanism of El Niño. Statement 3 is incorrect: India's southwest monsoon is historically weakened, not strengthened, during El Niño years. El Niño suppresses convection over the Indian Ocean–Bay of Bengal system and reduces the land-sea pressure gradient that drives monsoon onset, increasing the risk of deficit rainfall over India. The current event itself is described as causing a 'regional monsoon patchwork with significant shortfalls' across multiple parts of India.

Explanation

Statement 1 is correct: during El Niño years, altered wind patterns and air pressure near the equator cause cyclones in the Bay of Bengal to form at lower latitudes, closer to the equator. This shifts their most likely landfall zone southward — toward Andhra Pradesh and Tamil Nadu — rather than the usually more vulnerable Odisha and West Bengal coasts. Statement 2 is correct: El Niño's defining feature is anomalous warming of surface waters in the equatorial and central Pacific Ocean, and its teleconnections ripple across the globe — including unusual warming of the North Indian Ocean, which provides additional oceanic heat energy that fuels rapid intensification of cyclones. Statement 3 is false on a critical conceptual point: the Niño 3.4 region is located in the equatorial Pacific Ocean, not the North Indian Ocean. It is the standard benchmark region for measuring El Niño intensity based on sea-surface temperature anomalies there. The 26°C sea-surface temperature threshold at 50–100 m depth is the general condition conducive to cyclone formation, but it applies to the cyclone's formation zone (the North Indian Ocean), not to the Niño 3.4 region itself. Conflating the measurement region (Pacific) with the cyclone-formation region (Indian Ocean) is a common conceptual error.

Explanation

Statement 1 is correct. The Niño 3.4 region in the central-equatorial Pacific is the internationally recognised primary index area used to define and monitor ENSO phases; positive sea-surface temperature anomalies there signal El Niño conditions. Statement 2 is incorrect. El Niño is associated with a weakening (not strengthening) of the Walker Circulation. During El Niño, the warm pool shifts eastward into the central-eastern Pacific, suppressing convection over the Indian Ocean and the Maritime Continent, which typically results in weakened or deficient Indian summer monsoon rainfall — making El Niño years drought-prone for India, not flood-prone. Statement 3 is correct. El Niño is a natural climate pattern recurring every two to seven years; it is well-established in climate science that El Niño conditions heighten the risk of extreme heatwaves, wildfires, and altered precipitation patterns across multiple continents.

Explanation

Pair 1 is correctly matched: the Niño 3.4 region is the specific zone of the central equatorial Pacific Ocean (roughly 5°N–5°S, 120°W–170°W) whose sea-surface temperature anomalies serve as the standard index for measuring El Niño's strength. Pair 2 is correctly matched: one of the most well-established ENSO teleconnections is the suppression of the Indian summer monsoon — El Niño typically weakens the Walker Circulation and the monsoon trough, increasing the probability of below-normal rainfall and drought over India. Pair 3 is incorrectly matched: La Niña is the COLD phase of ENSO, characterised by below-normal sea-surface temperatures in the central and eastern Pacific. It is El Niño (not La Niña) that is the warm phase. This is a classic conceptual distinction that UPSC tests — confusing the two phases of ENSO.

Explanation

El Niño is defined by the anomalous warming of sea-surface temperatures in the central and eastern equatorial Pacific, and it forms the warm phase of the El Niño–Southern Oscillation (ENSO) system — Statement 1 is correct. Statement 2 is incorrect: El Niño is teleconnected to below-normal (deficit) rainfall over India, not above-normal; the suppression of the Walker Circulation during El Niño weakens the Indian summer monsoon, historically leading to drought conditions in the subcontinent — which is precisely why Indian state governments issue warnings about El Niño-driven rainfall deficits. Statement 3 is correct: the Southern Oscillation Index (SOI), computed as the standardised pressure anomaly difference between Tahiti and Darwin (Australia), is the canonical atmospheric indicator of ENSO state and is used by meteorologists to track and forecast monsoon conditions across South and Southeast Asia.

Explanation

All three pairs are correctly matched. El Niño is characterised by anomalously warm sea surface temperatures in the central and eastern tropical Pacific; this warming weakens the Walker Circulation, which typically suppresses convection over the Indian Ocean and reduces monsoon rainfall over the Indian subcontinent — a well-established teleconnection documented by the India Meteorological Department and global climate science. The delayed dairy flush season in India is a downstream agricultural consequence: El Niño-driven temperature rise and irregular rainfall shrink fodder availability and intensify cattle water stress, which suppresses milk yields and shifts the peak supply period later in the season. ENSO teleconnection is the precise scientific concept describing how the El Niño-Southern Oscillation (ENSO) in the Pacific remotely drives weather anomalies — rainfall deficits, heat waves, dry spells — across South Asia, East Africa, and other distant regions through atmospheric circulation bridges. Each pair correctly links the phenomenon to its established mechanism.

Explanation

All three pairs are correctly matched. First, El Niño is officially declared when the sea surface temperature (SST) anomaly in the central-eastern tropical Pacific Ocean exceeds +0.5°C above the long-term average — this is the standard WMO/NOAA threshold. Second, the core mechanism of El Niño involves the release of heat that has accumulated in the upper layers of the Pacific Ocean into the overlying atmosphere; because ocean heat content is vast, this process significantly warms global average surface temperatures. Third, El Niño is well-documented to act as a 'risk multiplier' through teleconnections — large-scale atmospheric circulation changes driven by the SST anomaly — that intensify heatwaves, tropical cyclones, and extreme precipitation events across multiple continents beyond what historical baselines would predict. All three pairs therefore correctly capture the declaration threshold, the physical mechanism, and the downstream weather effects of El Niño.

Explanation

Statement 1 is correct. El Niño — the warm phase of the El Niño–Southern Oscillation (ENSO) — involves a periodic warming of sea surface temperatures in the central and eastern tropical Pacific. This weakens the Walker Circulation (the east–west atmospheric circulation over the tropical Pacific), which in turn drives teleconnections: cascading, often distant impacts such as droughts in South Asia and Australia, floods in parts of the Americas, and amplified heatwaves across multiple continents. These teleconnections are the defining feature of ENSO's global footprint. Statement 2 is incorrect. El Niño typically adds only about 0.1°C–0.2°C to the annual global mean temperature — a modest increment on top of the much larger background warming trend driven by greenhouse-gas accumulation. It is therefore a temporary amplifier, not the dominant driver of multi-degree warming; confusing the magnitude of ENSO's increment with that of long-term anthropogenic warming reflects a fundamental misunderstanding of their respective roles. Statement 3 is correct. Because El Niño intensifies heat, drought and heavy-rainfall extremes across affected regions, it compounds public health vulnerabilities: heat stress and heat-related illness rise during heatwaves; disrupted agriculture raises malnutrition and food insecurity; altered hydrology expands the breeding habitat of disease vectors (mosquitoes transmitting malaria, dengue etc.); and poor air quality from wildfires worsens respiratory outcomes. ENSO is therefore widely recognised as a health-system risk multiplier.

Explanation

Statement 1 is correct. El Niño — the warm phase of ENSO — involves anomalous warming of sea surface temperatures in the central and eastern tropical Pacific. Its teleconnections produce asymmetric regional effects: drought and reduced rainfall across much of South and Southeast Asia (and Australia), while enhanced convection and heavy rainfall affect the Pacific coast of South America, including Peru and Ecuador. This divergent pattern is a defining feature of ENSO teleconnections. Statement 2 is incorrect. El Niño does not suppress or offset anthropogenic (human-driven) global warming; it amplifies it. The additional heat released from the tropical Pacific into the atmosphere adds to the warming already caused by greenhouse gases, temporarily elevating global mean surface temperatures above the underlying human-driven trend. It is La Niña — the cool phase of ENSO — that tends to slightly dampen global mean temperatures in a given year. Conflating El Niño's thermal role with a cooling or offsetting effect is a common misconception. Statement 3 is correct. El Niño's food-price impacts are not confined to post-harvest periods. Because global commodity markets are forward-looking, the anticipation of crop shortfalls — driven by El Niño-linked drought or flood forecasts — can trigger price volatility well before harvests are completed. Market uncertainty itself generates price spikes, compounding actual supply disruptions once they materialise. This market-expectations mechanism is a recognized feature of how climate shocks transmit into food systems.