UPSC Prelims Practice Questions — ‘El Nino may occur after July; clear picture to emerge after April’
Q1. Which one of the following is the primary monitoring region whose sea-surface temperature anomalies are used to classify El Niño and La Niña events?
- A. Niño 1+2 region
- B. Niño 3 region
- C. Niño 3.4 region
- D. Niño 4 region
Q2. With reference to the India Meteorological Department's operational definition, El Niño is best described as:
- A. A sustained warming of the central equatorial Pacific Ocean by at least 0.5°C above average for five consecutive overlapping three-month periods
- B. A sustained warming of the western equatorial Pacific Ocean by at least 1.0°C above average for three consecutive months
- C. A sustained cooling of the central-eastern equatorial Pacific Ocean by at least 0.5°C below average for five consecutive months
- D. An anomalous warming of the equatorial Indian Ocean coupled with weakening of the Somali Jet over six consecutive months
Q3. With reference to the El Niño–Southern Oscillation (ENSO) and the Indian monsoon, consider the following statements:
1. As per IMD, El Niño is identified when the central equatorial Pacific records sea-surface temperatures at least 0.5°C above average for five consecutive overlapping three-month seasons.
2. ENSO-neutral conditions are those in which Pacific sea-surface temperature anomalies lie within ±0.5°C of the long-term average.
3. La Niña refers to anomalous warming of the central equatorial Pacific Ocean.
4. Historically, about six out of every ten El Niño years have coincided with below-normal southwest monsoon rainfall over India.
Which of the statements given above are correct?
- As per IMD, El Niño is identified when the central equatorial Pacific records sea-surface temperatures at least 0.5°C above average for five consecutive overlapping three-month seasons.
- ENSO-neutral conditions are those in which Pacific sea-surface temperature anomalies lie within ±0.5°C of the long-term average.
- La Niña refers to anomalous warming of the central equatorial Pacific Ocean.
- Historically, about six out of every ten El Niño years have coincided with below-normal southwest monsoon rainfall over India.
- A. 1 and 2 only
- B. 2 and 3 only
- C. 1, 2 and 4
- D. 1, 3 and 4
Q4. The atmospheric east-west overturning circulation across the equatorial Pacific, whose weakening is associated with El Niño events, is named after which one of the following scientists?
- A. Sir Gilbert Walker
- B. Jacob Bjerknes
- C. Klaus Wyrtki
- D. Carl-Gustaf Rossby
Q5. With reference to the IMD's February 2026 weather briefing on ENSO and the 2026 outlook, consider the following statements:
1. ENSO-neutral conditions were stated to be likely to persist until around July 2026, with a probability of a shift to El Niño thereafter.
2. A clearer picture of El Niño formation was expected to emerge only after April 2026, on account of the boreal spring predictability barrier.
3. The Niño 3.4 region in the equatorial Pacific is used as the primary index for ENSO classification.
4. El Niño is characterised by anomalous cooling of the central-eastern equatorial Pacific Ocean.
Which of the statements given above is/are NOT correct?
- ENSO-neutral conditions were stated to be likely to persist until around July 2026, with a probability of a shift to El Niño thereafter.
- A clearer picture of El Niño formation was expected to emerge only after April 2026, on account of the boreal spring predictability barrier.
- The Niño 3.4 region in the equatorial Pacific is used as the primary index for ENSO classification.
- El Niño is characterised by anomalous cooling of the central-eastern equatorial Pacific Ocean.
- A. 1 and 2 only
- B. 3 only
- C. 4 only
- D. 2 and 4 only