1. Details of Module and its structure Module Detail Subject Name Geography Course Name Geography 01 (Class XI, Semester - 1) Module Name/Title Solar Radiation and Heat Budget – Part 1 Module Id kegy_20901 Pre-requisites Basic understanding of the composition and structure of the atmosphere Objectives After reading this lesson, learners will be able to know about: Explain the importance of insolation and establish relationship between angle of incidence of sun’s rays and the intensity of heat received from them at a place; Explain the different processes involved in heating and cooling of the atmosphere (conduction, convection, radiation and advection). Explain the heat budget with the help of a diagram; Differentiate between solar radiation and terrestrial radiation. Keywords Insolation, Radiation, Conduction, Convection, Latent heat, Adiabatic changes in temperature 2. Development Team Role Name Affiliation National MOOC Coordinator (NMC) Prof. Amarendra P. Behera CIET, NCERT, New Delhi Program Coordinator Dr. Mohd. Mamur Ali CIET, NCERT, New Delhi Course Coordinator (CC) / PI Prof. Aparna Pandey DESS, NCERT, New Delhi Course Co-Coordinator / Co-PI Dr. Archana CIET, NCERT, New Delhi Subject Matter Expert (SME) Hema Gupta BBPS,Dwarka Sector 12, New Delhi Review Team Dr. Preeti Tiwari Shivaji College, New Delhi
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1. Details of Module and its structure
Module Detail
Subject Name Geography
Course Name Geography 01 (Class XI, Semester - 1)
Module Name/Title Solar Radiation and Heat Budget – Part 1
Module Id kegy_20901
Pre-requisites Basic understanding of the composition and structure of theatmosphere
Objectives After reading this lesson, learners will be able to knowabout:
Explain the importance of insolation and establishrelationship between angle of incidence of sun’s raysand the intensity of heat received from them at aplace;
Explain the different processes involved in heatingand cooling of the atmosphere (conduction,convection, radiation and advection).
Explain the heat budget with the help of a diagram; Differentiate between solar radiation and terrestrial
radiation.
Keywords Insolation, Radiation, Conduction, Convection, Latent heat,Adiabatic changes in temperature
2. Development Team
Role Name Affiliation
National MOOC Coordinator (NMC)
Prof. Amarendra P. Behera CIET, NCERT, New Delhi
Program Coordinator Dr. Mohd. Mamur Ali CIET, NCERT, New DelhiCourse Coordinator (CC) / PI Prof. Aparna Pandey DESS, NCERT, New DelhiCourse Co-Coordinator / Co-PI Dr. Archana CIET, NCERT, New DelhiSubject Matter Expert (SME) Hema Gupta BBPS,Dwarka Sector 12, New
DelhiReview Team Dr. Preeti Tiwari Shivaji College, New Delhi
Table of Contents:
Introduction
Solar Radiation
Variability of Insolation at the Surface of the Earth
Heating and cooling of atmosphere
Terrestrial Radiation
Heat Budget of the Earth
Variation in the Net Heat Budget at the Earth’s Surface
Introduction
The earth receives almost all of its energy from the sun. The earth in turn radiates back to
space the energy received from the sun. As a result, the earth neither warms up nor does it get
cooled over a period of time. Thus, the amount of heat received by different parts of the earth
is not the same. This variation causes pressure differences in the atmosphere. This leads to
transfer of heat from one region to the other by winds. This chapter explains the process of
heating and cooling of the atmosphere and the resultant temperature distribution over the
earth’s surface.
Solar Radiation
The earth’s surface receives most of its energy in short wavelengths. The energy received by
the earth is known as incoming solar radiation which in short is termed as insolation. As the
earth is a geoid resembling a sphere, the sun’s rays fall obliquely at the top of the atmosphere
and the earth intercepts a very small portion of the sun’s energy. On an average the earth
receives 1.94 calories per sq. cm per minute at the top of its atmosphere.
Table: Length of the Day in Hours and Minutes on winter and Summer Solstices in the
Northern Hemisphere
4. Transparency of Atmosphere:
The atmosphere is largely transparent to short wave solar radiation. Incoming solar radiation
passes through the atmosphere before striking the earth’s surface. The amount of cloud cover
and its thickness, dust and water vapour, which determine the transparency of the
atmosphere, affect the reflection, absorption and transmission of solar radiation.
5. Altitude and Aspect:
Places at a higher altitude receive more insolation as the density of the atmosphere decreases
with height. Less energy is therefore lost to the atmosphere. The direction of the slope and its
angle control the amount of solar radiation received locally. Slopes more exposed to the sun
receive more solar radiation than those away from the sun’s direct rays. South facing slopes
receive more insolation in the Northern Hemisphere. In the Southern Hemisphere, it is the
north-facing slopes that receive more insolation.
Spatial Distribution of Insolation at the Earth’s Surface
The insolation received at the surface varies from about 320 Watt/m2 in the tropics to about
70 Watt/m2 in the poles. Maximum insolation is received over the subtropical deserts, where
the cloudiness is the least. Equator receives comparatively less insolation than the tropics.
Generally, at the same latitude the insolation is more over the continent than over the oceans.
In winter, the middle and higher latitudes receive less radiation than in summer
Heating and Cooling of Atmosphere
There are different processes by which heat is gained and lost, and transferred within the
atmosphere and between the atmosphere and the Earth. These processes are:
The earth after being heated by insolation transmits the heat to the atmospheric layers near to
the earth in long wave form. The air in contact with the land gets heated slowly and the upper
layers in contact with the lower layers also get heated. This process is called conduction.
Conduction takes place when two bodies of unequal temperature are in contact with one
another, there is a flow of energy from the warmer to cooler body. The transfer of heat
continues until both the bodies attain the same temperature or the contact is broken.
Conduction is important in heating the lower layers of the atmosphere.
Fig. 04 show how aerosols can reflect solar radiation back into space altering the earth’s
radiation balance ,this affect is measured by rephelometters.
The air in contact with the earth rises vertically on heating in the form of currents and furthertransmits the heat of the atmsphere. This process of vertical heating of the atmosphere is
known as convection. The convective transfer of energy is confined only to the troposphere.