Which of the following statements concerning temperature is/are correct ? 1. In winter season isotherms in Northern Hemisphere are more or less circular on continents 2. Isotherms are parallel to latitude in Southern Hemisphere in oceans 3. Minimum temperature during winter is recorded in Northern Canada Select the correct answer using the code given below :
- (a)1 and 2 only
- (b)1 and 3 only
- (c)1, 2 and 3
- (d)2 only
Correct — A, statements 1 and 2 only. In the northern winter the continents lose heat far faster than the oceans, so intensely cold cells build up over the interiors of Asia and North America and the isotherms close around them into rough loops, which is what statement 1 describes. In the Southern Hemisphere the mid-latitudes are almost all ocean, with very little land to disturb the pattern, so temperature there is governed mainly by latitude and the isotherms run nearly parallel to the parallels — statement 2. Statement 3 is the one that fails: the coldest winter temperatures of the Northern Hemisphere are recorded in north-eastern Siberia, at Verkhoyansk and Oymyakon in Sakha, both of which have gone below minus 67 degrees Celsius, and not in northern Canada.
- (b)1 and 3 only — Keeps the Canada claim and discards the Southern Hemisphere one, getting both decisions wrong. The near-parallel run of isotherms over the southern oceans is one of the most consistently stated facts in the whole topic.
- (c)1, 2 and 3 — The all-correct option, tempting because statements 1 and 2 are indeed right and northern Canada certainly is cold. But cold is not the test — the record is, and the Northern Hemisphere cold pole sits in eastern Siberia.
- (d)2 only — Rightly rejects statement 3 but also drops statement 1. Closed, roughly circular isotherms over the northern continents in January are exactly the pattern that a winter isotherm map shows.
An isotherm joins places of equal temperature. If the Earth had a uniform surface, isotherms would run exactly along the parallels of latitude, because insolation is governed by the angle of the sun. Every departure from that neat pattern is caused by something other than latitude — chiefly the contrast between land and sea, which heat and cool at very different rates, and then ocean currents, altitude and prevailing winds. Land has a low specific heat and heats and cools quickly; water has a high specific heat, mixes to depth and changes temperature slowly.
That single contrast explains both correct statements at once. In the northern winter the huge landmasses cool sharply while the adjacent oceans stay comparatively warm, so the isotherms bend equatorward as they cross land and poleward as they cross the sea, and around the coldest continental interiors they close into loops. In the Southern Hemisphere between about thirty and sixty degrees there is hardly any land at all, so there is nothing to bend the pattern and the isotherms follow the parallels. On statement 3, the useful way to remember why Siberia and not Canada holds the record is continentality — north-eastern Siberia sits in a mountain-rimmed basin, far from any moderating ocean, and traps a pool of dense cold air through the winter. The lowest figure the World Meteorological Organization formally recognises for the Northern Hemisphere is lower still and also not Canadian: minus 69.6 degrees Celsius at an automatic station on the Greenland ice sheet in 1991.
- Isotherms would follow latitude exactly on a uniform Earth; the departures are caused mainly by the differing heating of land and water.
- In January the isotherms bend equatorward over the northern continents and poleward over the oceans, closing into loops over the coldest continental interiors.
- The Southern Hemisphere mid-latitudes are overwhelmingly oceanic, so isotherms there run nearly parallel to the latitudes.
- The Northern Hemisphere pole of cold is in Sakha, Russia — Verkhoyansk recorded minus 67.8 degrees Celsius in 1892 and Oymyakon minus 67.7 degrees Celsius in 1933.
- The annual range of temperature exceeds 60 degrees Celsius over north-eastern Eurasia, the most continental region on Earth.
Both correct statements come from the same cause — the different rates at which land and water heat and cool.
- Assuming the highest latitude must be the coldest place; continentality, not latitude alone, produces the extreme minima.
- Marking the all-correct option because two of three statements check out.
- Reversing the January bend — isotherms go equatorward over land and poleward over ocean in the northern winter, not the other way round.
Isotherm behaviour has been asked by both NDA and the civil services repeatedly, usually as a statement set about January maps, and the answer always turns on the same land-and-sea heating contrast.
Consider the following statements: Statement I: In January, in the Northern Hemisphere, the isotherms bend equatorward while crossing the landmasses, and poleward while crossing the oceans. Statement II: In January, the air over the oceans is warmer than that over the landmasses in the Northern Hemisphere. Which one of the following is correct in respect of the above statements?
- (a) Both Statement I and Statement II are correct and Statement II explains Statement I
- (b) Both Statement I and Statement II are correct but Statement II does not explain Statement I
- (c) Statement I is correct but Statement II is not correct
- (d) Statement I is not correct but Statement II is correct
Answer(a) Both Statement I and Statement II are correct and Statement II explains Statement I
Spells out the mechanism this NDA item leaves implicit — land cools faster than sea in January, and that single fact is what bends the isotherms and closes them into loops over the continents.
Which of the following is/are correct inference/inferences from isothermal maps in the month of January? 1. The isotherms deviate to the north over the ocean and to the south over the continent. 2. The presence of cold ocean currents, Gulf Stream and North Atlantic Drift make the North Atlantic Ocean colder and the isotherms bend towards the north. Select the answer using the code given below:
- (a) 1 only
- (b) 2 only
- (c) Both 1 and 2
- (d) Neither 1 nor 2
Answer(a) 1 only
The same January map, with an added trap about ocean currents — the Gulf Stream and the North Atlantic Drift are warm, not cold. Worth attempting straight after this card.
Match List–I with List–II and select the correct answer using the code given below the Lists : List–I (Koppen's Climatic Type) A. Tropical wet B. Mid-latitude desert C. Mediterranean D. Humid continental List–II (Letter Code) 1. Af 2. Cs 3. Df 4. BWk Code : A B C D
- (a) 1 4 2 3
- (b) 1 2 4 3
- (c) 3 2 4 1
- (d) 3 4 2 1
Answer(a) 1 4 2 3
The classification that formalises the temperature patterns this item describes — the humid continental type is precisely the strongly seasonal, land-dominated regime that produces closed winter isotherms.
- practice — not a real PYQ
Isotherms run more nearly parallel to the parallels of latitude in the Southern Hemisphere mainly because
- (a)the Southern Hemisphere receives more insolation
- (b)there is very little land in the southern mid-latitudes
- (c)the Southern Hemisphere has no ocean currents
- (d)the Earth's axis is tilted towards the south
Answer(b) there is very little land in the southern mid-latitudes — with almost no land to heat or cool rapidly, latitude alone governs the pattern.
- practice — not a real PYQ
The highest annual range of temperature on Earth is recorded over
- (a)the equatorial Atlantic
- (b)the north-eastern part of the Eurasian continent
- (c)the Sahara desert
- (d)the western coast of South America
Answer(b) the north-eastern part of the Eurasian continent — extreme continentality gives Siberia both very hot summers and the hemisphere's coldest winters.