The Southern Oscillation is a seesaw pattern between which of these two oceans?

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Correct — B, the Pacific and the Indian Ocean. The Southern Oscillation is a see-saw in sea-level atmospheric pressure between the two ends of the equatorial belt: when pressure is high over one, it is low over the other, and after a few years the pattern reverses. It is measured as the Southern Oscillation Index (SOI), the pressure difference between Tahiti in the south-central Pacific and Port Darwin in northern Australia — and Indian geography texts, NCERT included, place Port Darwin on the Indian Ocean side, which is why the pattern is described here as a Pacific-Indian Ocean see-saw. Sir Gilbert Walker identified it in the 1920s while he was Director-General of Observatories in India, precisely because he was hunting for a predictor of monsoon failure.

Why the other options are wrong — (a) The Atlantic has its own climate see-saws — the North Atlantic Oscillation and the Atlantic Niño — but they are separate phenomena with separate indices. Neither pressure pole of the Southern Oscillation, Tahiti or Darwin, lies anywhere near the Atlantic.  (c) The Atlantic is not involved at all. The Indian Ocean does have its own east-west see-saw, but that is a sea-surface temperature index called the Indian Ocean Dipole, not the Southern Oscillation.  (d) Option (b) is the description used in the standard Indian school geography, so a valid pairing does exist and 'none of the above' is not available.

Concept: El Niño and the Southern Oscillation are two halves of one system. El Niño is the oceanic half — an abnormal warming of the eastern equatorial Pacific off Peru and Ecuador. The Southern Oscillation is the atmospheric half — the pressure see-saw that rides on it. Coupled, they are called ENSO, and the east-west overturning of air along the equator that they modulate is the Walker circulation. The Southern Oscillation Index is pressure at Tahiti minus pressure at Darwin: strongly negative in El Niño years, positive in La Niña years.

State PCS 2025 Q78 — Geography PYQ with Answer

State PCS 2025 Q78 — Geography PYQ with Answer