Prelims · Geography · 27 questions

Climate & atmosphere

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Prelims 2020 · Q93

Hard

With reference to Ocean Mean Temperature (OMT), which of the following statements is/are correct?

1.OMT is measured up to a depth of 26°C isotherm which is 129 meters in the south-western Indian Ocean during January – March.
2.OMT collected during January – March can be used in assessing whether the amount of rainfall in monsoon will be less or more than a certain long-term mean.

Select the correct answer using the code given below:

Answer & explanation

Answer: (b) 2 only

Statement 2 is right and statement 1 is wrong. OMT (the average temperature of the ocean from the surface down to the 26°C isotherm) in the south-western Indian Ocean during January–March helps predict whether the coming monsoon rainfall will be above or below average, but the 26°C isotherm there lies at about 59 m, not 129 m.

✗ 1. OMT is the mean temperature of the layer from the surface down to the 26°C isotherm, which is the first half of the statement. But the January–March climatic mean depth of that isotherm in the south-western Indian Ocean is about 59 m, not 129 m.
✓ 2. The January–March south-western Indian Ocean OMT is a better qualitative predictor of Indian summer monsoon rainfall than sea surface temperature; it correctly signals above-average or below-average rain about 80% of the time, against 60% for SST.

Remember · OMT = mean temperature from the surface to the 26°C isotherm; south-western Indian Ocean OMT in January–March forecasts monsoon rain (isotherm depth about 59 m there).

Sources

Venugopal et al., 'Statistical Evidence for the Role of Southwestern Indian Ocean Heat Content in the Indian Summer Monsoon Rainfall', Scientific Reports 8:12092 (2018), open-access copy on PubMed Central (NIH) ↗ “Here, we show that the southwestern Indian OMT down to the depth of the 26 °C isotherm during January–March is a better qualitative predictor of the ISMR than SST. … The January–March climatic mean D 26 is 59 m and the corresponding OHC is 50 kJ cm −2 in this region.”

Question and answer: UPSC's official GS Paper I (2020, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink ·

Prelims 2020 · Q99

Medium

Consider the following statements:

1.Jet streams occur in the Northern Hemisphere only.
2.Only some cyclones develop an eye.
3.The temperature inside the eye of a cyclone is nearly 10°C lesser than that of the surroundings.

Which of the statements given above is/are correct?

Answer & explanation

Answer: (c) 2 only

Only statement 2 is correct. Jet streams blow in both hemispheres, and the eye of a tropical cyclone is warmer, not colder, than its surroundings; but an eye forms only once a cyclone has organised and intensified.

✗ 1. Jet streams exist in both hemispheres. The polar jet lies between about 50° and 60° latitude in the northern and the southern hemispheres alike.
✓ 2. An eye develops only when the inner spiral bands close into an eyewall, which usually happens around the time winds reach hurricane force. Weak tropical systems and temperate (extra-tropical) cyclones generally have no eye.
✗ 3. The eye is the region of lowest surface pressure and, aloft, the warmest air; a tropical cyclone has a warm core, so the eye is warmer than its surroundings, not cooler.

Remember · Jet streams occur in both hemispheres. A cyclone's eye forms only in mature tropical cyclones, and it is a calm, warm-cored centre.

Sources

US National Weather Service / NOAA JetStream: The Jet Stream ↗ “The polar jet is located between the 50°-60° latitude lines in both the northern and southern hemispheres.”
NOAA Hurricane Research Division FAQ: life cycle of a hurricane ↗ “the inner bands will close off into an eyewall, surrounding a central calm area known as the eye. This usually happens around the time wind speeds reach hurricane force. … The eye is the region of the lowest pressure at the surface and the warmest temperatures at the top.”

Question and answer: UPSC's official GS Paper I (2020, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink ·

The same topic in Mains

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