UPSC Prelims 2025 Q27: Geography – Atmosphere & Climatology
- (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
Explanation
January isotherms in the Northern Hemisphere
In January it is winter in the Northern Hemisphere.
Land loses heat quickly and becomes colder than the ocean at the same latitude.
| Surface | January temperature | How the isotherm bends |
|---|---|---|
| Landmass | Colder (rapid radiation loss) | Bends equatorward — you must go south to find the same temperature |
| Ocean | Warmer (high specific heat, warm currents like the Gulf Stream) | Bends poleward — the same temperature is found farther north |
Statement I — correct. This is the classic January isotherm pattern.
Statement II — correct, and it is the reason. Warmer air over oceans pushes isotherms poleward; colder land pulls them equatorward.
In July the pattern reverses: land is warmer, so isotherms bend poleward over land.
Answer: (a) Both Statement I and Statement II are correct and Statement II explains Statement I.
Why each option is right or wrong
- (a) CORRECT. Oceans are warmer than land in January, which is exactly why isotherms bend poleward over oceans and equatorward over land.
- (b) Incorrect. Statement II is not a separate fact; it is the direct cause of the bending.
- (c) Incorrect. Statement II is true: in a Northern Hemisphere winter, oceans hold heat longer than land.
- (d) Incorrect. Statement I is the standard January isotherm pattern shown in NCERT.
Key point
January (NH winter): land colder → isotherms bend equatorward over land, poleward over oceans. July reverses it.
Remember
In January, isotherms bend equatorward over cold land and poleward over warm oceans.
Common mistakes
- Mixing up the January and July patterns; in July, land is warmer and isotherms bend poleward over it.
- Thinking isotherms are straight lines along latitudes; land–sea contrast bends them.
- Forgetting specific heat — water heats and cools slowly, so oceans stay warmer in winter.
Exam tip
Isotherms bend towards the colder side's equivalent. Cold land in January drags the line south, toward the Equator.
Sources
- NCERT Class XI — Fundamentals of Physical Geography, Ch 9 (Solar Radiation, Heat Balance and Temperature)
- G.C. Leong — Certificate Physical and Human Geography (Climate)