January isotherms over land and ocean — UPSC Prelims PYQ 2025

Consider the following statements

1. Statement I: In January, in the Northern Hemisphere, the isotherms bend equatorward while crossing the landmasses, and poleward while crossing the oceans.
2. 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?

1. Both Statement I and Statement II are correct and Statement II explains Statement I
2. Both Statement I and Statement II are correct but Statement II does not explain Statement I
3. Statement I is correct but Statement II is not correct
4. Statement I is not correct but Statement II is correct

Explanation

Both Statement I and Statement II are correct and Statement II explains Statement I

• In January, the Northern Hemisphere experiences winter, with significant temperature contrasts between land and oceans. During winter, landmasses cool more rapidly than oceans due to differences in heat capacity. Isotherms reflect these temperature gradients, bending to reflect colder temperatures over land and warmer temperatures over oceans.
• Specifically, isotherms shift equatorward (southward) over landmasses, indicating colder temperatures, and poleward (northward) over oceans, indicating warmer temperatures, due to the moderating effect of oceans. Oceans have higher heat capacity than land, retaining heat longer and moderating temperatures. In January, Northern Hemisphere oceans (e.g., the North Atlantic and Pacific) remain warmer than landmasses, which lose heat rapidly due to their lower heat capacity and radiative cooling.

Answer: (a) Both Statement I and Statement II are correct and Statement II explains Statement I; Difficulty Level: Medium