1. The impact of El Niño on the Indian summer monsoon depends not only on its strength but also on the timing of its development.
2. A positive Indian Ocean Dipole can, in some years, weaken the adverse impact of El Niño on the Indian monsoon.
Which of the statements given above is/are correct?
Statement 1 – Correct: El Niño does not affect the monsoon in a fixed mechanical way. The timing of warming relative to the core monsoon months is important, which is why forecast outcomes may differ across years.
Statement 2 – Correct: A positive Indian Ocean Dipole can sometimes offset, at least partly, the suppressing effect of El Niño on Indian monsoon rainfall. This is a classic UPSC conceptual trap because it tests interaction, not isolated definition.
ENSO Phases: El Niño is the warm phase of ENSO, while La Niña is the cool phase.
IOD Measurement: IOD is measured using the sea surface temperature contrast between the western and eastern equatorial Indian Ocean.
Reason (R): The advance of the monsoon usually occurs in surges.
Assertion (A) – Correct: The southwest monsoon does not cover India in one uninterrupted sweep. It advances progressively across regions.
Reason (R) – Correct: IMD explicitly notes that the monsoon advances northward usually in surges.
Link between A and R – Correct explanation: Because the advance occurs in surges, pauses and renewed progress are normal. Hence the reason directly explains the assertion.
1. Niño 3.4 region — Central and eastern equatorial Pacific
2. Positive Indian Ocean Dipole — Western equatorial Indian Ocean warmer than eastern equatorial Indian Ocean
3. Break monsoon — Complete cessation of rainfall over the whole of India
How many of the above pairs are correctly matched?
Pair 1 – Correct: The Niño 3.4 region is the primary area used by meteorologists to monitor ENSO (El Niño-Southern Oscillation). It spans the central and eastern equatorial Pacific (specifically 5°N-5°S, 120°-170°W). Warming here signifies an El Niño, while cooling signifies a La Niña.
Pair 2 – Correct: A Positive IOD occurs when the sea surface temperature in the western Indian Ocean (near Africa) is higher than normal, while the eastern part (near Sumatra/Indonesia) is cooler. This phase is typically beneficial for the Indian monsoon.
Pair 3 – Incorrect: Break monsoon does not mean zero rainfall over the entire country. It refers to weakening of monsoon conditions and a shift in rainfall distribution. This leads to a sharp decrease in rain over the North Indian Plains, but causes heavy rainfall in the mountainous regions and Northeast India.
Option (a) – Incorrect: Surface heating over the Deccan Plateau is not the direct cause of heavy rainfall on the windward slope. The main mechanism here is topographic uplift.
Option (b) – Correct: Moist monsoon winds are forced to ascend along the Western Ghats, producing heavy rainfall through orographic lifting.
The heavy rainfall on the windward side of the Western Ghats is a classic example of orographic rainfall, also called relief rainfall.
The Western Ghats form a continuous mountain barrier that lies across the path of the Arabian Sea branch of the southwest monsoon. When moisture-laden winds from the sea reach these mountains, they are forced to rise along the slopes.
As the air rises, it expands and cools adiabatically. This cooling reduces the air’s capacity to hold water vapour, causing condensation and resulting in heavy rainfall on the windward side, especially along the western slopes.
After crossing the peaks, the winds descend on the eastern, or leeward, side. By this stage, they have already lost most of their moisture. As they descend, they become warmer and drier, creating a rain shadow region over the Deccan Plateau.
Option (c) – Incorrect: Jet streams influence monsoon circulation at a broader scale, but they do not directly explain the heavy rainfall on the windward side of the Ghats.
Option (d) – Incorrect: Retreating monsoon is associated mainly with the post-southwest monsoon phase, not with the main southwest monsoon rainfall along the west coast.
1. Arabian Sea branch
2. Bay of Bengal branch
3. Western Ghats
4. Meghalaya Plateau
Which of the following is the correct sequence of interaction from moisture source to topographic intensification in the case of very heavy rainfall over northeastern India?
Fact 1 – Arabian Sea branch: Not the main branch responsible for very heavy rainfall over northeastern India. Its major topographic interaction is with the Western Ghats.
Fact 2 – Bay of Bengal branch: Correct source branch for northeastern India. It travels northward and northeastward, carrying abundant moisture.
Fact 3 – Western Ghats: Not relevant to the rainfall intensification over northeastern India in this context. This is the trap location.
Fact 4 – Meghalaya Plateau: Correct topographic feature linked with intense rainfall in northeastern India because of uplift of moisture-laden winds.