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General Studies 2026 GS Paper I 10 marks 150 words Compulsory Explain

GS Paper I — Q4

What is the Fujiwhara effect? Explain its impact on the movement and intensity of tropical cyclones. (Answer in 150 words) 10

हिंदी में प्रश्न पढ़ें

फुजिह्वारा प्रभाव क्या है? उष्णकटिबन्धीय चक्रवातों के संचलन तथा तीव्रता पर पड़ने वाले इसके प्रभाव को समझाइए। (उत्तर 150 शब्दों में दीजिए)

Q4 of the 2026 UPSC Mains General Studies GS Paper I, as printed
The question as printed in the 2026 General Studies paper
Evaluate your answer to this question → See all 2026 General Studies questions

Model answer

Written by UPSC Answer Check against this question's marking rubric, to the 150-word length. UPSC does not publish answers for Mains — this is one way to score well, not an official key.

The Fujiwhara effect, identified by Japanese meteorologist Sakuhei Fujiwhara in 1921, occurs when two nearby tropical cyclones (typically within ~1,400 km) orbit around a common vortex centre. It is driven by mutual vorticity interaction, where each storm’s cyclonic circulation advects the other, generating counterclockwise co-rotation in the Northern Hemisphere.

Impact on Movement: The mutual steering leads to erratic track deflections rather than standard trajectories. Depending on relative size and distance, the interaction results in mutual binary orbiting, slingshot repulsion, the absorption and dissipation of the smaller system, or a complete merger into a single larger vortex.

Impact on Intensity: The proximity disrupts symmetric low-level inflow and upper-level outflow while creating competition for shared ambient moisture and ocean thermal energy. The induced vertical wind shear generally weakens one or both cyclones, though unpredictable intensification can occasionally happen.

Commonly observed in Pacific typhoon pairs, this phenomenon severely complicates track, intensity, and landfall forecasting.

What "Explain" is asking you to do

Make the working of something clear — what sets it off, what follows from what, and what it produces. Explain is the Commission's mechanism word: it dominates the technical papers and the “explain why” stems, where the marks sit in the causal chain and not in the label.

Structure that answers it

State what it is → the initiating condition → the chain of cause, step by step → an instance where it plays out → what the chain produces

Where marks are lost

Describing what something looks like instead of why it works that way. Naming the stages without linking them reads as description too.

All UPSC directive words, compared →

How this answer will be evaluated

Approach

Framework: Geography: explain the mechanism, then location follows. explain: definition/context > points in order > small example > short close Full marks: Clear definition, accurate mechanism, distinct points on movement and intensity.

Key points expected

  • Definition: interaction of two cyclonic vortices
  • Mechanism: mutual rotation around common center
  • Impact on movement: altered track/deflection
  • Impact on intensity: intensification or weakening

Evaluation rubric

Each sub-part is marked on its own, against the marks and word limit printed on the paper.

  1. The answer Define the effect and detail its impact on cyclone movement and intensity. 10 marks · 150 words

    explain— definition/context → points in order → small example → short close

    Must cover

    • Definition: interaction of two cyclonic vortices
    • Mechanism: mutual rotation around common center
    • Impact on movement: altered track/deflection
    • Impact on intensity: intensification or weakening

    Loses marks

    • Describing only the visual appearance without physics
    • Confusing with general Coriolis effect
    • Ignoring the 'intensity' aspect of the question

    Earns more

    • Mention of 'binary interaction' or 'merger'
    • Reference to conservation of angular momentum
    • Distinction between close and distant encounters

    Extra mark

    • 30-second sketch of two spirals merging
    • Specific example (e.g., 2015 Typhoon Meari)

Practice this exact question

Write your answer and it is marked point by point against the model answer above — what you covered, what you missed, what you got wrong.

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