Solar Radiation, Heat Balance, and Temperature – Complete Guide For Class 11 Geography Chapter 8

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This chapter explores the fundamental concepts of solar radiation, the Earth’s heat balance, and temperature distribution. It delves into the factors that influence the intensity of solar radiation reaching the Earth’s surface, the processes involved in heating and cooling the atmosphere, and the factors that control the distribution of temperature across the globe.

Solar radiation is the primary source of energy that drives the Earth’s climate system. The way this energy is absorbed, reflected, and redistributed affects the temperature of the atmosphere and the oceans, which in turn influences weather patterns and climate zones. This chapter will examine the key concepts of solar radiation, heat balance, and temperature distribution.

Objectives Of Learning the chapter – Solar Radiation, Heat Balance, and Temperature

Now that we have explored the importance of the chapter, let’s outline the objectives of studying it.

• To understand the concept of solar radiation and its variability at the Earth’s surface.
• To explore the processes involved in the heating and cooling of the atmosphere.
• To analyze the factors that control the distribution of temperature across the globe.

Now let’s explore the various sections of the chapter.

Firstly, to understand solar radiation, let’s delve into the section “Solar Radiation” of the chapter “Solar Radiation, Heat Balance and Temperature.”

Solar Radiation

• Solar radiation refers to the energy emitted by the Sun, which is the primary source of heat and light for Earth.  
• The intensity of solar radiation reaching the Earth’s surface varies depending on several factors.

Variability of Insolation at the Surface of the Earth

The factors that cause these variations in insolation are

(i) the rotation of the earth on its axis; 

(ii) the angle of inclination of the sun’s rays; 

(iii) the length of the day; 

(iv) the transparency of the atmosphere; 

(v) the configuration of land in terms of its aspect.

The Passage of Solar Radiation through the Atmosphere: 

As solar radiation travels through the atmosphere, some of it is absorbed, scattered, and reflected by gasses, dust, and clouds, reducing the amount that reaches Earth’s surface.

Spatial Distribution of Insolation at the Earth’s Surface: 

Insolation is not distributed evenly across the Earth’s surface due to the curvature of the Earth, with the equatorial regions receiving more direct sunlight than the polar regions.

Now, to explore the processes that warm and cool the atmosphere, let’s focus on the “Heating and Cooling of the Atmosphere” section of the chapter “Solar Radiation, Heat Balance and Temperature.”

Heating and Cooling of the Atmosphere

The Earth’s atmosphere is heated by both solar radiation and terrestrial radiation.

The Earth’s atmosphere undergoes constant heating and cooling, primarily driven by solar radiation and terrestrial processes. Some key concepts in this process include:

• Terrestrial Radiation:
  • After absorbing solar energy, the Earth’s surface re-emits it in the form of terrestrial radiation (longwave radiation). This process heats the atmosphere from below, contributing to the overall temperature of the air.
• Heat Budget of the Planet Earth:
  • The Earth’s heat budget refers to the balance between incoming solar radiation and outgoing terrestrial radiation. The planet absorbs solar energy and radiates heat back into space to maintain this balance, ensuring that Earth’s climate remains relatively stable.

• Variation in the Net Heat Budget at the Earth’s Surface:
  • There is a variation in the net heat budget across different parts of the Earth’s surface. Areas near the equator receive more solar energy compared to the poles, resulting in temperature gradients that drive global wind patterns and ocean currents.

Now, to explore the factors that influence the distribution of temperature on Earth, let’s focus on the “Temperature” section of the chapter “Solar Radiation, Heat Balance and Temperature.”

Temperature

Temperature is a measure of the average kinetic energy of the molecules in a substance. The distribution of temperature across the Earth’s surface is influenced by several factors.

Factors Controlling Temperature Distribution

• Latitude: 

The angle at which solar radiation strikes the Earth’s surface varies with latitude, affecting the amount of heat absorbed.

• Altitude: 

Higher altitudes are generally cooler than lower altitudes due to the decrease in atmospheric pressure and density.

• Distance from the Sea: 

Coastal areas tend to have more moderate temperatures than inland areas due to the influence of ocean currents.

• Air-Mass Circulation: 

The movement of air masses can influence temperature distribution.

• Presence of Warm and Cold Ocean Currents: 

Ocean currents can transport heat from warm areas to cold areas, affecting temperature distribution.

• Local Aspects: 

Local factors such as topography, vegetation, and human activities can also influence temperature.

Distribution of Temperature

• The Earth’s temperature varies with latitude, altitude, and proximity to water bodies. 
• The equator is generally warmer than the poles, while higher altitudes are cooler than lower altitudes. 
• Coastal areas tend to have more moderate temperatures than inland areas.

Inversion of Temperature

Temperature inversion occurs when the normal vertical temperature gradient is reversed, causing a layer of cooler air to be trapped beneath a layer of warmer air. This phenomenon can lead to various meteorological effects, such as:

• Normally, air temperature decreases with altitude. However, during an inversion, temperature increases with altitude for a short distance. This can occur due to radiational cooling of the Earth’s surface, especially in valleys or during calm, clear nights.
• Inversions can trap pollutants near the ground, leading to smog and poor air quality in urban areas.

Finally, as we have gained comprehensive knowledge about the chapter “Solar Radiation, Heat Balance and Temperature”, let’s reflect on the overall learning value of this important lesson.

Overall Learning Value of the Chapter:

The chapter “Solar Radiation, Heat Balance and Temperature” provides essential knowledge about the Earth’s energy system and how it affects climate and weather patterns. By understanding solar radiation, terrestrial processes, and the factors that control temperature, students gain a deeper appreciation for the mechanisms that regulate Earth’s atmosphere. The concept of temperature inversion highlights the complexity of atmospheric processes and how they influence local weather and environmental conditions.