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Q27 (IAS/2025) Geography › World Physical Geography › Atmospheric heat balance Answer Verified

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?

Result
Your answer: —  ·  Correct: A
Explanation

Both statements are correct, and Statement II correctly explains Statement I.

In January, the isotherms deviate to the north over the ocean and to the south over the continent.[3] This confirms Statement I – isotherms bend poleward (northward) over oceans and equatorward (southward) over landmasses in the Northern Hemisphere during January.

The presence of warm ocean currents, Gulf Stream and North Atlantic drift, make the Northern Atlantic Ocean warmer and the isotherms bend towards the north.[1] Over the land the temperature decreases sharply and the isotherms bend towards south in Europe.[1] This demonstrates that oceans are warmer than landmasses in January, confirming Statement II.

The causal relationship is clear: The isotherms deviate equatorward over the continents (due to continentality) as the cold polar winds are able to penetrate southwards into the interiors.[4] The warmer ocean temperatures cause isotherms to bend poleward over oceans, while colder continental temperatures cause them to bend equatorward over land. Therefore, Statement II (warmer oceans) directly explains the isotherm pattern described in Statement I.

Sources
  1. [1] FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 8: Solar Radiation, Heat Balance and Temperature > Distribution of Temperature > p. 71
  2. [2] FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 8: Solar Radiation, Heat Balance and Temperature > Distribution of Temperature > p. 71
  3. [3] FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 8: Solar Radiation, Heat Balance and Temperature > Distribution of Temperature > p. 71
  4. [4] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 21: Horizontal Distribution of Temperature > Northern Hemisphere > p. 290
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Don’t just practise – reverse-engineer the question. This panel shows where this PYQ came from (books / web), how the examiner broke it into hidden statements, and which nearby micro-concepts you were supposed to learn from it. Treat it like an autopsy of the question: what might have triggered it, which exact lines in the book matter, and what linked ideas you should carry forward to future questions.
Q. Consider the following statements : Statement I : In January, in the Northern Hemisphere, the isotherms bend equatorward while crossing t…
At a glance
Origin: From standard books Fairness: High fairness Books / CA: 10/10 · 0/10

This is a classic 'NCERT-reward' question. It tests the fundamental concept of differential heating of land and water directly from the 'Distribution of Temperature' section in Class XI NCERT. If you analyzed the January isotherm map (Fig 8.1) in the book, this was a free hit.

How this question is built

This question can be broken into the following sub-statements. Tap a statement sentence to jump into its detailed analysis.

Statement 1
In January in the Northern Hemisphere, do isotherms bend equatorward while crossing landmasses and poleward while crossing oceans?
Origin: Direct from books Fairness: Straightforward Book-answerable
From standard books
FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 8: Solar Radiation, Heat Balance and Temperature > Distribution of Temperature > p. 71
Presence: 5/5
“In January the isotherms deviate to the north over the ocean and to the south over the continent. This can be seen on the North Atlantic Ocean. The presence of warm ocean currents, Gulf Stream and North Atlantic drift, make the Northern Atlantic Ocean warmer and the isotherms bend towards the north. Over the land the temperature decreases sharply and the isotherms bend towards south in Europe. It is much pronounced in the Siberian plain. The mean January temperature along 60° E longitude is minus 20° C both at 80° N and 50 N latitudes. The mean monthly temperature for January is over 27° C, in equatorial oceans over 24° C in the tropics and 2° C - 0° C in the middle latitudes and –18° C to –48° C in the Eurasian continental interior.”
Why this source?
  • Explicitly states that in January isotherms deviate north over oceans and south over continents (i.e., poleward over oceans, equatorward over land).
  • Gives the North Atlantic/Gulf Stream example showing warm ocean currents cause poleward bending of isotherms.
  • Provides continental examples (Europe, Siberian plain) where rapid land cooling causes equatorward bending.
Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 21: Horizontal Distribution of Temperature > Northern Hemisphere > p. 290
Presence: 5/5
“• The isotherms are closer on the eastern margins as the temperature gradient is high because of the less moderating effect of the oceans (westerlies flow from west to east).• The isotherms deviate to the north over the ocean. For example, the presence of warm Gulf Stream and North Atlantic drift make the Northern Atlantic warmer and the isotherms show a poleward shift indicating that the currents are able to carry high temperatures poleward.• The isotherms deviate equatorward over the continents (due to continentality) as the cold polar winds are able to penetrate southwards into the interiors.• Lowest temperatures are recorded over northern Siberia and Greenland (due to continentality). • During July, it is summer in the northern hemisphere and winter in the southern hemisphere.”
Why this source?
  • Directly asserts isotherms deviate to the north over the ocean and equatorward over the continents.
  • Explains mechanism: warm currents carry heat poleward over oceans; continentality allows cold polar winds to penetrate southward over land.
Statement 2
In January in the Northern Hemisphere, is the air over the oceans warmer than the air over the landmasses?
Origin: Direct from books Fairness: Straightforward Book-answerable
From standard books
FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 8: Solar Radiation, Heat Balance and Temperature > Distribution of Temperature > p. 71
Presence: 5/5
“In January the isotherms deviate to the north over the ocean and to the south over the continent. This can be seen on the North Atlantic Ocean. The presence of warm ocean currents, Gulf Stream and North Atlantic drift, make the Northern Atlantic Ocean warmer and the isotherms bend towards the north. Over the land the temperature decreases sharply and the isotherms bend towards south in Europe. It is much pronounced in the Siberian plain. The mean January temperature along 60° E longitude is minus 20° C both at 80° N and 50 N latitudes. The mean monthly temperature for January is over 27° C, in equatorial oceans over 24° C in the tropics and 2° C - 0° C in the middle latitudes and –18° C to –48° C in the Eurasian continental interior.”
Why this source?
  • Specifies that in January isotherms deviate north over oceans and south over continents, indicating relatively warmer ocean air.
  • Names warm currents (Gulf Stream, North Atlantic drift) that make the North Atlantic warmer in January.
  • Notes that over land temperature decreases sharply in winter (e.g., Europe, Siberia).
Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 21: Horizontal Distribution of Temperature > Northern Hemisphere > p. 290
Presence: 5/5
“• The isotherms are closer on the eastern margins as the temperature gradient is high because of the less moderating effect of the oceans (westerlies flow from west to east).• The isotherms deviate to the north over the ocean. For example, the presence of warm Gulf Stream and North Atlantic drift make the Northern Atlantic warmer and the isotherms show a poleward shift indicating that the currents are able to carry high temperatures poleward.• The isotherms deviate equatorward over the continents (due to continentality) as the cold polar winds are able to penetrate southwards into the interiors.• Lowest temperatures are recorded over northern Siberia and Greenland (due to continentality). • During July, it is summer in the northern hemisphere and winter in the southern hemisphere.”
Why this source?
  • Explains poleward (northward) shift of isotherms over northern oceans due to warm currents, signifying warmer ocean temperatures.
  • Contrasts with equatorward isotherm shift over continents as cold polar winds penetrate inland, making land colder.
Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 21: Horizontal Distribution of Temperature > Northern Hemisphere > p. 289
Presence: 4/5
“• During January, it is winter in the northern hemisphere & summer in the southern hemisphere.• The western margins of continents are warmer than their eastern counterparts since the Westerlies are able to carry high temperatures (from the oceans) into the landmasses.”
Why this source?
  • States January is winter in the northern hemisphere and that westerlies carry warmth from oceans onto western continental margins.
  • Implies ocean-sourced air keeps coastal/sea-adjacent air relatively warmer than interior land in winter.
Statement 3
In the Northern Hemisphere in January, is the isotherm pattern of bending equatorward over land and poleward over oceans explained by the oceans being warmer than the land?
Origin: Direct from books Fairness: Straightforward Book-answerable
From standard books
FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 8: Solar Radiation, Heat Balance and Temperature > Distribution of Temperature > p. 71
Presence: 5/5
“In January the isotherms deviate to the north over the ocean and to the south over the continent. This can be seen on the North Atlantic Ocean. The presence of warm ocean currents, Gulf Stream and North Atlantic drift, make the Northern Atlantic Ocean warmer and the isotherms bend towards the north. Over the land the temperature decreases sharply and the isotherms bend towards south in Europe. It is much pronounced in the Siberian plain. The mean January temperature along 60° E longitude is minus 20° C both at 80° N and 50 N latitudes. The mean monthly temperature for January is over 27° C, in equatorial oceans over 24° C in the tropics and 2° C - 0° C in the middle latitudes and –18° C to –48° C in the Eurasian continental interior.”
Why this source?
  • Explicitly states that in January isotherms deviate north (poleward) over oceans and south (equatorward) over continents.
  • Attributes the poleward ocean deviation to warm ocean currents (Gulf Stream/North Atlantic drift) making the ocean warmer than adjacent land.
  • Contrasts sharp land cooling (continental interior) causing equatorward bending over land.
Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 21: Horizontal Distribution of Temperature > Northern Hemisphere > p. 290
Presence: 5/5
“• The isotherms are closer on the eastern margins as the temperature gradient is high because of the less moderating effect of the oceans (westerlies flow from west to east).• The isotherms deviate to the north over the ocean. For example, the presence of warm Gulf Stream and North Atlantic drift make the Northern Atlantic warmer and the isotherms show a poleward shift indicating that the currents are able to carry high temperatures poleward.• The isotherms deviate equatorward over the continents (due to continentality) as the cold polar winds are able to penetrate southwards into the interiors.• Lowest temperatures are recorded over northern Siberia and Greenland (due to continentality). • During July, it is summer in the northern hemisphere and winter in the southern hemisphere.”
Why this source?
  • Says isotherms shift poleward over oceans because warm currents carry higher temperatures poleward.
  • Explains equatorward deviation over continents by continentality: cold polar winds penetrate southwards into interiors.
Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 21: Horizontal Distribution of Temperature > Generally follow the parallels (latitudes) > p. 288
Presence: 3/5
“• Isotherms have a close correspondence with the parallels mainly because the same amount of insolation is received by all the points located on the same latitude.• The isotherms are irregular over the northern hemisphere due to an enhanced land-sea contrast.• The thermal equator (ITCZ) generally lies to the north of the geographical equator (this is because most of the land surface is in the northern hemisphere).”
Why this source?
  • Identifies irregular isotherms in the Northern Hemisphere as resulting from enhanced land–sea temperature contrast.
  • Supports the conceptual mechanism that differing land and ocean temperatures drive the observed isotherm bends.
Pattern takeaway: UPSC is prioritizing 'Statement-Explanation' formats for core concepts. They don't just want you to know *that* isotherms bend; they want you to confirm *why* (differential heating). Physical Geography requires understanding the mechanism, not just the outcome.
How you should have studied
  1. [THE VERDICT]: Sitter. Directly lifted from **NCERT Class XI Fundamentals of Physical Geography, Chapter 8 (p. 71)**.
  2. [THE CONCEPTUAL TRIGGER]: **Climatology > Horizontal Distribution of Temperature**. Specifically, the behavior of isotherms during Solstices (January vs July).
  3. [THE HORIZONTAL EXPANSION]: Memorize the **July pattern** (Isotherms bend poleward on land, equatorward on oceans); **Southern Hemisphere** behavior (isotherms are straight/parallel due to lack of landmass); **Thermal Equator** position (shifts north in July); and **Inversion of Temperature** prerequisites (long winter nights, clear skies, still air).
  4. [THE STRATEGIC METACOGNITION]: Do not just read the text; **trace the isotherm lines** on the maps provided in NCERT (Fig 8.1 and 8.2). Visualizing the 'kink' over the North Atlantic (Gulf Stream effect) locks the concept in memory better than rote learning.
Concept hooks from this question
📌 Adjacent topic to master
S1
👉 Land–Sea Contrast (Continentality vs Maritime Influence)
💡 The insight

Continentality allows stronger seasonal cooling over land, shifting isotherms equatorward, while maritime influence moderates temperatures over oceans.

High-yield for questions on horizontal temperature distribution and seasonal contrasts; links to monsoon dynamics, temperature range, and regional climate types. Knowing this helps answer questions on isotherm patterns, thermal anomalies, and climate classification.

📚 Reading List :
  • FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 8: Solar Radiation, Heat Balance and Temperature > Distribution of Temperature > p. 71
  • Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 21: Horizontal Distribution of Temperature > Northern Hemisphere > p. 290
  • Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 21: Horizontal Distribution of Temperature > Temperature Anomaly > p. 287
🔗 Anchor: "In January in the Northern Hemisphere, do isotherms bend equatorward while cross..."
📌 Adjacent topic to master
S1
👉 Ocean Currents and Poleward Heat Transport
💡 The insight

Warm currents (e.g., Gulf Stream, North Atlantic drift) transport heat poleward and cause isotherms to bend toward higher latitudes over oceans.

Important for explaining deviations in standard latitudinal temperature patterns and for questions on regional climate moderation; connects to ocean circulation, heat budget, and impacts on coastal climates.

📚 Reading List :
  • FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 8: Solar Radiation, Heat Balance and Temperature > Distribution of Temperature > p. 71
  • FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 13: Movements of Ocean Water > Major Ocean Currents > p. 112
  • Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 21: Horizontal Distribution of Temperature > Northern Hemisphere > p. 290
🔗 Anchor: "In January in the Northern Hemisphere, do isotherms bend equatorward while cross..."
📌 Adjacent topic to master
S1
👉 Isotherms vs Parallels and Thermal Anomalies
💡 The insight

Isotherms generally follow parallels but show irregular deviations where thermal anomalies (land-sea contrasts, currents) exist.

Useful for map interpretation and descriptive answers about temperature distribution; links to concepts of thermal equator, temperature anomaly, and interpreting climate maps in prelims and mains.

📚 Reading List :
  • Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 21: Horizontal Distribution of Temperature > Generally follow the parallels (latitudes) > p. 288
  • Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 21: Horizontal Distribution of Temperature > Temperature Anomaly > p. 287
🔗 Anchor: "In January in the Northern Hemisphere, do isotherms bend equatorward while cross..."
📌 Adjacent topic to master
S2
👉 Isotherm deviation and interpretation
💡 The insight

Northward bends of isotherms over oceans and equatorward bends over continents directly reveal relative warmth of ocean air versus land air in January.

High-yield for map-reading and climate distribution questions; links temperature patterns to seasonal conditions and helps explain regional anomalies. Mastery enables quick answers on where and why temperatures are relatively higher or lower during seasons.

📚 Reading List :
  • FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 8: Solar Radiation, Heat Balance and Temperature > Distribution of Temperature > p. 71
  • Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 21: Horizontal Distribution of Temperature > Northern Hemisphere > p. 290
🔗 Anchor: "In January in the Northern Hemisphere, is the air over the oceans warmer than th..."
📌 Adjacent topic to master
S2
👉 Continentality versus maritime moderation
💡 The insight

Continental interiors cool strongly in winter while oceans moderate temperature, producing larger land–ocean contrasts in January.

Essential for explaining seasonal temperature ranges, pressure systems, and wind patterns (e.g., winter highs over Siberia). Frequently tested in physical geography and climate essays and linked to monsoon/pressure belt topics.

📚 Reading List :
  • Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 21: Horizontal Distribution of Temperature > ity (far from the moderating effect of the seas). > p. 288
  • Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 21: Horizontal Distribution of Temperature > Northern Hemisphere > p. 290
🔗 Anchor: "In January in the Northern Hemisphere, is the air over the oceans warmer than th..."
📌 Adjacent topic to master
S2
👉 Ocean currents and heat transport (Gulf Stream effect)
💡 The insight

Warm ocean currents (Gulf Stream, North Atlantic Drift) transport heat poleward and raise sea-surface and overlying air temperatures in winter.

Crucial for understanding regional climate moderation, anomalous warmth in oceanic regions, and impacts on weather systems; appears in map-based and cause–effect questions.

📚 Reading List :
  • FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 8: Solar Radiation, Heat Balance and Temperature > Distribution of Temperature > p. 71
  • Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 26: Tropical Cyclones > The Sea Surface Temperature (SST) Is Higher In The Northern Hemisphere > p. 368
🔗 Anchor: "In January in the Northern Hemisphere, is the air over the oceans warmer than th..."
📌 Adjacent topic to master
S3
👉 Land–sea temperature contrast (continentality vs. maritime effect)
💡 The insight

Northern Hemisphere January isotherm bending arises because continental interiors cool more strongly than adjacent oceans, producing a pronounced land–sea temperature contrast.

High-yield for geography questions: explains seasonal temperature distributions, extreme continental ranges (e.g., Siberia), and why isotherms deviate from parallels. Connects to monsoon dynamics, climate classification, and regional weather patterns; useful for interpreting temperature maps and current-effects questions.

📚 Reading List :
  • Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 21: Horizontal Distribution of Temperature > Generally follow the parallels (latitudes) > p. 288
  • FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 12: Water (Oceans) > Factors Affecting Temperature Distribution > p. 103
🔗 Anchor: "In the Northern Hemisphere in January, is the isotherm pattern of bending equato..."
🌑 The Hidden Trap

The **Southern Hemisphere Anomaly**: In the Southern Hemisphere, isotherms are almost parallel to the latitudes (straight) because there is very little landmass to cause differential heating deviations. Also, look out for the **July Pattern**, which is the exact inverse: Isotherms bend poleward over land and equatorward over oceans.

⚡ Elimination Cheat Code

**The 'Warm Push, Cold Pull' Rule**: Think of a specific temperature line (e.g., 10°C). If the ocean is *warmer* (winter), you must go further North (towards the pole) to find 10°C air—so the line bends Poleward. If the land is *colder*, you must come South (towards the equator) to find 10°C—so the line bends Equatorward. Basic logic of Specific Heat Capacity solves this without rote memorization.

🔗 Mains Connection

**Mains GS-1 (Geography) & GS-3 (Environment)**: This same 'Land-Sea Contrast' mechanism is the engine behind the **Indian Monsoon**. The differential heating that bends isotherms also creates the low-pressure cell over the Tibetan Plateau/NW India, pulling the SW Monsoon winds. Understanding isotherms is understanding the heartbeat of the Monsoon.

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SIMILAR QUESTIONS

NDA-I · 2010 · Q5 Relevance score: 2.42

Statement I : Winds are deflected to their right in the northern hemisphere and to their left in the southern hemisphere. Statement II : The Earth’s axis is inclined.

NDA-I · 2011 · Q99 Relevance score: 2.41

Statement I : In the northern hemisphere the ocean currents flowing from equator towards the north pole and from pole towards the equator are deflected to their right Statement II : This happens due to rotation of the Earth on the axis from west to east

IAS · 2024 · Q2 Relevance score: 2.29

Consider the following statements : Statement-I : Thickness of the troposphere at the equator is much greater as compared to poles. Statement-II : At the equator, heat is transported to great heights by strong convectional currents. Which one of the following is correct in respect of the above statements ?

CDS-II · 2010 · Q5 Relevance score: 1.95

Statement I : Wind is deflected to the right in northern hemisphere and to the left in southern hemisphere from its normal course. Statement II : Earth rotates from west to east.

CDS-II · 2024 · Q81 Relevance score: 1.91

Consider the following statements: 1. Ocean currents are dominated by huge surface gyres that are driven by the global surface wind pattern. 2. Equatorial currents move cold water westward and then poleward along the east coasts of continents. With regard to the statements given above, which of the following is correct?