UPSC Prelims 2024 Q4: Geography – Atmosphere & Climatology
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
Explanation
January Isotherms — Ocean vs Continent Deflection
| Statement | Claim | Verdict | Why |
|---|---|---|---|
| 1 | Isotherms deviate northward (poleward) over ocean and southward (equatorward) over continent in January | TRUE | In January (NH winter), continents cool rapidly but oceans retain heat. Warm oceans → isotherms bend poleward (north) over oceans. Cold continents → isotherms bend equatorward (south) over land. This is called the land-sea thermal contrast effect on isotherms. |
| 2 | Gulf Stream and North Atlantic Drift make the North Atlantic Ocean colder in winter | FALSE | The Gulf Stream and North Atlantic Drift are warm ocean currents flowing from the Gulf of Mexico northeastward. They transport tropical warmth to NW Europe and the North Atlantic, making the region WARMER than expected at those latitudes - not colder. This is why Western Europe has mild winters. |
Isotherm Deflection Summary (January, NH):
| Location | Ocean/Land | Temperature relative to latitude | Isotherm bends |
|---|---|---|---|
| North Atlantic | Ocean (warm current) | Warmer than expected | North/Poleward |
| North America | Continent (cold winter) | Colder than expected | South/Equatorward |
| North Pacific | Ocean (Kuroshio current) | Warmer than expected | North/Poleward |
Answer: (a) 1 only.
Why each option is right or wrong
- (a) CORRECT. Only Statement 1 is correct. Isotherms do deflect poleward over warm oceans and equatorward over cold winter continents in January. Statement 2 is wrong — Gulf Stream warms, not cools, the North Atlantic.
- (b) Incorrect. 'Only 2' would mean Gulf Stream cools the North Atlantic — the exact opposite. Gulf Stream + North Atlantic Drift bring warm tropical water northward, giving Western Europe its mild winters.
- (c) Incorrect. 'Both 1 and 2' would require Gulf Stream to make the North Atlantic colder. Gulf Stream is a warm current that raises North Atlantic temperatures significantly above latitudinal norms.
- (d) Incorrect. 'Neither' would mean isotherms do NOT deflect differently over oceans and continents — they do. Ocean-continent thermal contrast is a fundamental cause of isotherm deflection patterns.
Key point
In January: isotherms bend POLEWARD (north) over warm oceans, EQUATORWARD (south) over cold continents. Gulf Stream = WARM current = makes North Atlantic WARMER, not colder.
Remember
In January, isotherms deflect poleward over oceans (warmer) and equatorward over continents (colder). Gulf Stream makes the North Atlantic warmer, not colder — isotherms bend north over it.
Common mistakes
- Confusing the direction of Gulf Stream's effect — it warms the North Atlantic and NW Europe, which is why London is milder than Moscow despite similar latitudes.
- Mixing up January and July isotherm patterns — in July (NH summer), the deflection reverses (land heats more than ocean).
- Not knowing the ocean-continent rule: in winter, oceans are warmer than continents at same latitude → isotherms bulge poleward over oceans.
Exam tip
Isotherm rule: Ocean in winter = warmer than land → isotherms bend POLEWARD over ocean. Ocean in summer = cooler than land → isotherms bend EQUATORWARD over ocean. Gulf Stream = warm current = bends January isotherms NORTHWARD over North Atlantic.
Sources
- NCERT Class 11 Geography — Chapter 13: Water (Ocean Currents)
- NCERT Physical Geography — Isotherms and Temperature Distribution