Chapter 8: Solar Radiation, Heat Balance And Temperature
Source: NCERT Official Textbook
The spatial distribution of insolation is highest over subtropical deserts and decreases towards the poles. The chapter then details the mechanisms of atmospheric heating and cooling: conduction, convection, advection, and most importantly, terrestrial radiation—the long-wave radiation from the Earth that heats the atmosphere from below.
This leads to the concept of the Earth’s heat budget, a state of balance where 100 units of incoming solar energy are ultimately reflected or radiated back to space, preventing perpetual warming or cooling. The surplus heat in the tropics is redistributed towards the poles via atmospheric and oceanic circulations.
Finally, the chapter examines the factors controlling temperature distribution: latitude, altitude, distance from the sea, air masses, and ocean currents. It analyses global temperature patterns using isotherms, noting the pronounced effects of continentality and warm ocean currents like the Gulf Stream.
The phenomenon of temperature inversion, where temperature increases with height, is also explained, along with its effects like fog formation and frost protection in valleys.
Topics Covered:
Section A: Descriptive Questions
- What is insolation? Explain the concept briefly. (Pg. 1) Page 67
- What are the main factors that cause variations in insolation at the Earth’s surface? (Pg. 1-2) Page 67-68
- Describe the spatial distribution of insolation across the Earth’s surface. (Pg. 2) Page 68
- What is advection and how does it influence weather, especially in middle latitudes? (Pg. 2) Page 68
- Explain the heat budget of the Earth. How is the incoming solar energy balanced? (Pg. 3) Page 69
- What does Figure 8.3 indicate about the latitudinal variation in net radiation balance? (Pg. 4) Page 70
- Explain how distance from the sea moderates temperature. (Pg. 4) Page 70
- Describe the major features of global temperature distribution in January. (Pg. 5) Page 71
- What is temperature inversion? Describe an ideal condition for it to occur. (Pg. 7) Page 73
Section B1: Objective MCQs
When is the earth at its farthest point from the sun (aphelion)? (Pg. 1)
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Reference: NCERT Page 67
Why do slant sun rays (at higher latitudes) result in less net energy per unit area? (Pg. 2)
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Reference: NCERT Page 68
Over which areas is maximum insolation received? (Pg. 2)
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Reference: NCERT Page 68
What is the primary process by which the atmosphere is heated from below? (Pg. 2-3)
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Reference: NCERT Page 68-69
What is the term for the percentage of solar radiation reflected back by the Earth and its atmosphere? (Pg. 3)
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Reference: NCERT Page 69
Which of the following is NOT a factor controlling the temperature distribution of a place? (Pg. 4)
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Reference: NCERT Page 70
Why do places at higher altitudes generally have lower temperatures? (Pg. 4)
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Reference: NCERT Page 70
In January, why do isotherms bend northward over the North Atlantic Ocean? (Pg. 5)
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Reference: NCERT Page 71
What is a common consequence of a surface temperature inversion? (Pg. 7)
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Reference: NCERT Page 73
(Exercise) The sun is directly overhead at noon on 21st June at: (Pg. 7)
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Reference: NCERT Page 73
(Exercise) The atmosphere is mainly heated by the: (Pg. 7)
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Reference: NCERT Page 73
(Exercise) The main reason the earth experiences highest temperatures in the subtropics rather than at the equator is: (Pg. 8)
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Reference: NCERT Page 74
Section B2: Factual One-Liners
The energy received by the earth from the sun is termed ______. (Pg. 1) Page 67
Reveal Answer
The red colour of the rising/setting sun and blue sky are results of ______ of light. (Pg. 2) Page 68
Reveal Answer
The transfer of heat through direct contact between two bodies is called ______. (Pg. 2) Page 68
Reveal Answer
The process of vertical heating of the atmosphere through rising air currents is ______. (Pg. 2) Page 68
Reveal Answer
Out of 100 units of insolation, roughly ______ units are absorbed by the Earth’s surface. (Pg. 3) Page 69
Reveal Answer
The rate of decrease of temperature with increasing height is called the ______. (Pg. 4) Page 70
Reveal Answer
Lines joining places of equal temperature on a map are called ______. (Pg. 5) Page 71
Reveal Answer
The highest range of temperature (>60°C) is found over the ______ part of Eurasia. (Pg. 7) Page 73
Reveal Answer
In hilly areas, cold air flowing down slopes to collect in valleys is called air ______. (Pg. 7) Page 73
Reveal Answer
(Exercise) Pair the term ‘Albedo’ with its correct definition. (Pg. 8) Page 74