IAS Prelims Geography Q.6–2025 | January Isotherms, Land–Sea Contrast & Ocean Currents
Authentic Classroom Explanation by IAS Monk
📌 Question
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
✅ Correct Answer: (a)
🎯 Theme of the Question
Climatology | Temperature Distribution | Isotherms | Land–Sea Contrast | Ocean Currents (NH Winter)
🧠 Classroom Explanation
Step 1: What are isotherms?
Isotherms are lines joining places with equal temperature on a map.
Normally, they roughly follow latitudes, but they “wiggle” because Earth is not a uniform heating plate.
Step 2: Why do isotherms bend more in January?
In January (NH winter):
- Land cools very fast (low specific heat, rapid radiation loss)
- Oceans cool slowly (high specific heat, mixing, heat storage)
So, the temperature contrast between continent vs ocean becomes sharp.
✅ Statement I Analysis
“Isotherms bend equatorward over land and poleward over oceans.”
✔️ Correct.
Logic:
- Over cold land, temperatures drop → to find the same temperature line, you must move towards equator
→ hence isotherms bend equatorward over continents. - Over relatively warm oceans, temperatures remain higher → same temperature line shifts towards poles
→ hence isotherms bend poleward over oceans.
✅ Statement II Analysis
“In January, the air over oceans is warmer than that over land in NH.”
✔️ Correct.
This is the classic land–sea thermal contrast in winter:
- Land becomes a cold plate
- Ocean becomes a heat bank
🔗 Does Statement II explain Statement I?
✅ Yes, perfectly.
Because ocean stays warmer and land becomes colder, the equal-temperature lines are forced to curve:
- Poleward over warm oceans
- Equatorward over cold continents
Hence, (a) is correct.
🧭 Map-Based Visual Anchor (Quick Mental Picture)
Think North Atlantic in January:
- Warm currents (Gulf Stream + North Atlantic Drift) keep ocean warmer
- Western Europe becomes warmer than expected for its latitude
➡️ Isotherms “bulge” northward over the Atlantic.
Meanwhile:
- Eurasian interiors (Siberia) become intensely cold
➡️ Isotherms “dip” southward over land.
🧠 Memory Hook
“Land freezes fast, sea remembers heat.”
So isotherms:
- DIP over land (towards equator)
- BULGE over oceans (towards pole)
🔍 Curiosity Corner
Why is London milder than parts of Canada at the same latitude?
Because winter isotherms are “pulled” northward over the Atlantic by:
- Ocean heat storage
- Warm currents
- Prevailing westerlies carrying maritime air inland
UPSC loves this triangle: Currents + Westerlies + Land–Sea contrast.
📘 Enrichment Note
Three big controllers of January isotherms (NH):
- Land–Sea contrast (primary)
- Ocean currents (warm/cold)
- Prevailing winds (westerlies transport ocean warmth)
This is why January maps show stronger “zig-zag” patterns than July.
🎯 Prelims Strategy Insight
In Assertion–Reason questions:
- If Reason gives a direct physical cause, it’s usually (a).
Here it’s clean: ocean warmer than land → isotherm bending.
🧩 One-Line Ready Recall
January NH: Isotherms dip south over land, bulge north over oceans because oceans stay warmer.
🧭 IAS Monk Whisper
Land forgets summer quickly; the sea carries its memory like a quiet lantern.