CL-IX Unit-III Climate-SM - CBSE

CLASS
IX
CBSE–i
UNIT-3
GEOGRAPHY
CLIMATE
STUDENTS' MANUAL
Shiksha Kendra, 2, Community Centre, Preet Vihar, Delhi-110 092 India
CBSE-i
GEOGRAPHY
CLIMATE
STUDENTS' MANUAL
CLASS
IX
UNIT-3
Shiksha Kendra, 2, Community Centre, Preet Vihar, Delhi-110 092 India
The CBSE-International is grateful for permission to reproduce
and/or translate copyright material used in this publication. The
acknowledgements have been included wherever appropriate and
sources from where the material may be taken are duly mentioned. In
case any thing has been missed out, the Board will be pleased to rectify
the error at the earliest possible opportunity.
All Rights of these documents are reserved. No part of this publication
may be reproduced, printed or transmitted in any form without the
prior permission of the CBSE-i. This material is meant for the use of
schools who are a part of the CBSE-International only.
Preface
Education plays the most important role in acquiring professional and social skills and a positive attitude to face thechallenges of
life. Curriculum is a comprehensive plan of any educational programme. It is also one of the means of bringing about qualitative
improvement in an educational system. The Curriculum initiated by Central Board of Secondary Education-International
(CBSE-i) is a progressive step in making the educational content responsive to global needs. It signifies the emergence of a fresh
thought process in imparting a curriculum which would restore the independence of the learner to pursue the learning process
in harmony with the existing personal, social and cultural ethos.
The CBSE introduced the CBSE-i curriculum as a pilot project in few schools situated outside India in 2010 in classes I and IX and
extended the programme to classes II, VI and X in the session 2011-12. It is going to be introduced in classes III, VII and for Senior
Secondary classes with class XI in the session 2012-13.
The Senior Secondary stage of education decides the course of life of any student. At this stage it becomes extremely important
for students to develop the right attitude, a willingness to learn and an understanding of the world around them to be able to
take right decisions for their future. The senior secondary curriculum is expected to provide necessary base for the growth of
knowledge and skills and thereby enhance a student's potential to face the challenges of global competitiveness. The CBSE-i
Senior Secondary Curriculum aims at developing desired professional, managerial and communication skills as per the
requirement of the world of work. CBSE-i is for the current session offering curriculum in ten subjects i.e. Physics Chemistry,
Biology, Accountancy, Business-Studies, Economics, Geography, ICT, English, Mathematics I and Mathematics II. Mathematics
at two levels caters to the differing needs of students of pure sciences or commerce.
The Curriculum has been designed to nurture multiple intelligences like linguistic or verbal intelligence, logical mathematical
intelligence, spatial intelligence, sports intelligence, musical intelligence, inter-personal intelligence and intra-personal
intelligence.
The Core skills are the most significant aspects of a learner's holistic growth and learning curve. The objective of this part of the
core of curriculum is to scaffold the learning experiences and to relate tacit knowledge with formal knowledge. This involves
trans-disciplinary linkages that would form the core of the learning process. Perspectives, SEWA (Social Empowerment through
Work and Action), Life Skills and Research would be the constituents of this 'Core'. The CBSE-i Curriculum evolves by building
on learning experiences inside the classroom over a period of time. The Board while addressing the issues of empowerment with
the help of the schools' administering this system strongly recommends that practicing teachers become skilful and lifelong
learners and also transfer their learning experiences to their peers through the interactive platforms provided by the Board.
The success of this curriculum depends upon its effective implementation and it is expected that the teachers will make efforts to
create better facilities, develop linkages with the world of work and foster conducive environment as per recommendations
made in the curriculum document.
I appreciate the effort of Dr. Sadhana Parashar, Director (Training), CBSE and her team involved in the development of this
document. I specially appreciate the efforts of (Late) Dr. Srijata Das for working tirelessly towards meeting deadlines.
The CBSE-i website enables all stakeholders to participate in this initiative through the discussion forums. Any further
suggestions on improving the portal are always welcome.
Vineet Joshi
Chairman, CBSE
Acknowledgements
Advisory
Conceptual Framework
Shri Vineet Joshi, Chairman, CBSE
Dr. Sadhana Parashar, Director (Training), CBSE
Shri G. Balasubramanian, Former Director (Acad), CBSE
Ms. Abha Adams, Consultant, Step-by-Step School, Noida
Dr. Sadhana Parashar, Director (Training), CBSE
Ideators
Dr. Anju Srivastava
Ms. Varsha Seth
Ms. Sarita Manuja
Prof. Chand Kiran Saluja
Mr. N. K. Sehgal
Ms. Preeti Hans
Ms. Sunita Tanwar
Dr. Usha Sharma
Dr. Uma Chaudhry
Ms. P Rajeshwary
Ms. S. Radha Mahalakshmi
Ms. Renu Anand
Ms. Anita Sharma
Ms. Suganda Vallli
Ms. Neelima Sharma
Dr. Rajesh Hassija
Mr. Mukesh Kumar
Material Production Groups
English :
Ms. Gayatri Khannaa
Ms. Renu Anand
Ms. P. Rajeshwary
Ms. Sarabjit Kaur
Hindi :
Ms. Sunita Joshi
Ms. Babita Singh
Ms. Veena Sharma
Sh. Akshay Kumar Dixit
Core- SEWA
Ms. Vandna
Ms. Nishtha Bharati
Ms. Seema Bhandari
Ms. Seema Chopra
Ms. Madhuchhanda
Ms. Reema Arora
Ms. Neha Sharma
Chemistry
Ms. Charu Maini
Ms. S. Anjum
Physics:
Ms. Novita Chopra
Ms. Meenambika Menon
Biology :
Ms. Pooja Sareen
Ms. Neeta Rastogi
Core- Prespectives
Ms. Madhuchhanda,
RO(Innovation)
Ms. Varsha Seth,
Consultant
Ms. Neha Sharma
Mathematics :
Dr. K.P. Chinda
Dr. Ram Avtar
Mr. Mahendra Shankar
Mr. J.C. Nijhawan
Ms. Rashmi Kathuria
Ms. Reemu Verma
Ms. Arti
Ms. Himani Ashija
Economics:
Ms. Anubha Malhotra
Ms. Vintee Sharma
Ms. Chaitali Sengupta
Core-Research
Ms. Renu Anand
Ms. Gayatri Khanna
Dr. N. K. Sehgal
Ms. Anita Sharma
Ms. Rashmi Kathuria
Ms. Neha Sharma
Ms. Neeta Rastogi
Ms. Manjushtha Bose
Ms. Varsha Manku
Dr. K. L. Chopra
ICT:
Mr. Yogesh Kumar
Ms. Nancy Sehgal
Ms. Purvi Srivastava
Ms. Babita Mahajan
Ms. Ritu Arora
Ms. Swati Panhani
Ms. Chanchal Chandna
Geography:
Ms. Meena Bharihoke
Ms. Parul Tyagi
Ms. Sudha Tyagi
Ms. Sonia Jarul
Ms. Neena Phogat
Mr. Nisheeth Kumar
History:
Ms. Sajal Chawala
Ms. Jyoti Sharma
Ms. Kamma Khurana
Ms. Shalini Chatarvedi
Mr. Dalia Haldar
Ms. Preeti Gupta
Political Science:
Dr. Sangeetha Mathur
Ms. Ananya Roy
Ms. Sunita Rathee
Ms. Amarjit Kaur
Ms. Nishu Sharma
Ms. Manisha Anthwal
Ms. Mamta Talwar
Chief Co-ordinator : Ms. Kshipra Verma, EO
Coordinators:
Ms. S. Radha Mahalakshmi, E O
Sh. R. P. Sharma
Consultant (Science)
Ms. Monika Munjal Gandhi
(Coordinator)
Mr. Navin Maini, RO (Tech)
Ms. Neelima Sharma,
Consultant (English)
Mr. Sanjay Sachdeva, DO
Shri Al Hilal Ahmed, AEO
Ms. Deepa Shukla
Consultant (Biology)
Shri R. P. Singh, AEO
Ms. Reema Arora
Consultant (Chemistry)
Contents
1.
Atmosphere and World Climate
1
2.
Atmosphere: Composition and Structure
2
3.
Insolation and Temperature
4
4.
Pressure Belts and Wind Patterns
8
5.
Precipitation and its Types
21
6.
World Climate and its Types
24
CLIMATE
INTRODUCTION
Warm Up Activity
EXTENT OF THE ATMOSPHERE
The atmosphere is a blanket of gases and suspended liquids and solids that entirely envelops the Earth. It extends as far as 9600 km above the Earth’s surface. This gaseous
cover of the Earth is held around it by gravitational attraction. The density of the atmosphere decreases rapidly with altitude. About 97 per cent of the air is concentrated in
the lower 29 km. The weight of the upper layer is exerted on the lower layers.
ATMOSPHERIC LAYERS
There are many layers of atmosphere. There is a lot
of difference in their properties. These layers are not
separated from one another. The properties of layers
change slowly. The main layers are:
1.
Troposphere – The lowest layer of the atmosphere is called troposphere. This word consists
of two words – Tropo and sphere. Tropo means
‘changing’. Hence, Troposphere is that layer in
which the temperature changes upward on ac-
Fig 3.1: Showing Layers of the
Atmosphere
count of convection current. The height of this layer at equator is 16 km and at
poles 7 km. The troposphere is higher in summer than in winter. It contains most
1
of the atmospheric air (75%). The highest amount of water vapour, water particles
and dust is found in this layer. Change of weather takes place all through the year.
2.
Tropopause – The upper layer of Troposphere is called Tropopause. It is a thin
layer and its height changes according to latitudes. In fact this is a transitional zone
which connects the lower troposphere with the upper Stratosphere.
3.
Stratosphere – Stratosphere lies above Tropopause. The temperature in the lower
part of this sphere does not change with altitude. The temperature is nearly constant upward to about 20 km and then increases, owing to absorption of ultraviolet
radiation by ozone.
4.
Ozonosphere – There is a layer in stratosphere at a height of 18 km to 46 km which
has a high concentration of ozone gas. This is why it is called Ozonosphere. A
property of ozone is that it absorbs ultraviolet rays. Had there been no layer of
ozone in the atmosphere, the ultraviolet rays would have reached the surface of
the Earth and blinded all the living beings and left their skins burnt. A thicker
layer of ozone would also be harmful because this would absorb all the ultraviolet
rays. A small amount of ultra violet rays is useful to man. It provides him with vitamins. The temperature of this layer is high because of the absorption of
ultraviolet rays.
5.
Ionosphere – This layer is above Ozonosphere. It is estimated that it spreads above
60 km. Due to the radiation of the sun, the free electrons and the atoms of gas are
found in it. This helps in the conduction of electricity in this sphere. The Ionosphere reflects Radio Wave. Had there been no ionosphere, the radio waves would
have travelled out of the Earth into the sky and would not have come back. It is
due to this ionosphere that the radio waves travel in a curved path and that radio
transmission is received by us.
6.
Mesosphere: This layer of the atmosphere is spread over stratosphere.
2
7.
Exosphere: This is the last layer of atmosphere located above ionosphere and extends to beyond 400 km above the Earth. Gases are very sparse due to the lack of
gravitational force. The density of this layer is very less.
Watch a video on weather Instruments
Elements of weather and climate
Weather: - It is the state of the atmosphere at a given time, at any one place. It combines
temperature, pressure, wind and rainfall conditions of a small area for a short period of
time.
Climate: - It deals with the average condition at a specific place of over a relatively
longer period of time. It contains the elements of Temperature, Pressure, Wind, Humidity and Rainfall into consideration.
1.
Temperature:- It expresses intensity of heat. Almost the whole of heat on the
Earth is received from the sun. The amount of heat is greatest near the equator
and starts decreasing as we move away from the equator. Isotherms are drawn to
represent temperature on the map, they are imaginary lines joining places of
same temperature. Temperature is measured by an instrument called the thermometer.
2.
Air Pressure:- It is the pressure exerted by the weight of air on the Earth’s surface. Atmospheric pressure is related to the temperature of the air. Unequal distribution of temperature over the Earth’s surface causes difference in atmospheric pressure which, in its turn, causes winds. The air always moves from high
pressure areas to low pressure areas.
3.
Moisture: Water vapour present in the air is called its moisture. Condensation of
water vapour takes place under favourable circumstances; clouds are formed and
precipitation takes place.
3
ATMOSPHERE: TEMPERATURE
The source of Atmospheric heat – The main source of atmospheric heat is the sun. A
little heat is obtained from the interior parts of the Earth but it is insignificant.
Warm Up Activity (video on mechanism of the seasons)
SOLAR RADIATION (INSOLATION)
Insolation is the incoming solar radiation. It is received in the form of short waves. The Earth’s surface receives this radiant energy at the rate of two
calories per square centimeter per minute. It is this
amount of energy received from the sun that acts as
the driving force for all the atmospheric as well as
biological processes on the Earth.
Factors affecting the receipt of insolation on
Fig 3.2: Showing vertical rays and
slanting rays
Earth’s surface:
The insolation does not reach the Earth directly and uniformly. Its amount varies from
place to place. Radiation at a place depends upon the following factors:
4
1.
Inclination of Solar Radiations – The
Earth is round and is inclined at an
angle of 66½0 to its orbital plane. The
insolation is therefore, not vertical at
all places. Vertical rays provide more
heat than the inclined ones. There are
two reasons for vertical rays being
more responsible for greater heat than
the inclined ones: (i) vertical rays occupy less area than inclined ones.
Fig3.3: Showing Seasons- Solstices and
Equinoxes
Hence vertical rays have to heat a smaller area than the inclined ones. (ii) Vertical
rays have to pass through smaller distance than the inclined ones. Atmosphere absorbs less heat from the vertical than the inclined rays. That is why the days with a
longer duration of sunlight in higher latitudes give less heat than those with less
duration of sunlight in lower latitudes.
2.
Duration of the Day – The Earth is inclined at an angle of 66 ½o at its orbital plane.
It rotates around its axis and revolves around the sun. The circle of illumination
passes through the two poles of the Earth on March 21st and September 23rd. This
makes day and night equal on these dates
on the Earth. In all other positions, the circle of illumination does not pass through
the poles with the result that the days and
nights are not equal.
3.
The distance between the sun and the
Earth – The distance between the sun and
the Earth is not constant but goes on
changing.. More solar radiation is received
5
Fig 3.4: Showing Perihelion and Aphelion positions
by the Earth when the Earth is closer (in Perihelion) and less solar radiation when
the Earth is the farthest.
4.
Atmospheric Transparency – Dust particles, water vapours and some gases
present
in
the
air
absorb,
reflect
and
scatter
insolation.
If
the
radiation of the obstructing particles is smaller than the wavelength of the insolation, the light is scattered.
5.
The effect of Land and Sea – The reception of insolation is not uniform over land
and water bodies. Even at one latitude all the land areas do not receive equal
amount of insolation. For example, the ice cover of an area reflects 70 to 90% of the
insolation falling upon it. A small amount of insolation is therefore left to heat it.
VERTICAL DISTRIBUTION OF TEMPERATURE
The rate of the fall of temperature is called Normal
Lapse Rate. The value of normal lapse rate is 2oC
per 300 metres of height. In other words there is a
fall of 2oC with every rise in a height of 300 metres.
This rate is limited up to tropopause. Above it, the
temperature is almost stationary.
Temperature also falls as we move towards higher
latitudes but the normal lapse rate is about 1000
Fig3.5: Showing fall and rise of temperature as per the height of the atmosphere
times that of the fall of temperature according to latitudes. The normal lapse rate is not
fixed. It changes according to temperature, time and place. One thing is very clear from
normal lapse rate that the lower part is warmer than the upper part of the atmosphere.
HORIZONTAL DISTRIBUTION OF TEMPERATURE
The temperature across latitudes and distribution is shown by isotherms. An Isotherm
is an imaginary line joining places having equal temperatures; reduced to sea level. The
Earth can be divided into three temperature zones:
6
1.
Torrid Zone – The sun is vertical at the
equator but it also shifts on either sides
of the equator. The zone situated between these latitudes is called Torrid
Zone.
2.
Temperate Zone – The zone situated
between the torrid and frigid zones is
called Temperate zone. It extends from
23 ½ oN to 66 1/2 oN in the northern
and 23 ½ oS to 66 ½ oS in the southern
hemispheres. Summers and winters are
Fig 3.6: Showing heat zones of the Earth
distinct seasons in these zones.
3.
Frigid Zone – There is at least one day in a year beyond 66 ½ o N and 66 ½ oS upto
poles, when the night or day is at least of 24 hours duration. The sun rays are very
much inclined in these zones and make the zones very cold. This type of zone is
found in both the hemispheres.
Watch a Video on temperature Inversion experiment
INVERSION OF TEMPERATURE
Temperature inversion under certain circumstances: the normal observed decrease of
temperature with increased altitude might be reversed; temperature may actually increase for several hundred meters. This is called temperature inversion. Some inversions take place 1000 or 2000 meters above the surface of the Earth where a layer of
warmer air interrupts the normal decrease in temperature with altitude. Such inversions tend to stabilize the air, causing less turbulence and discouraging both precipitation and the development of storms.
7
Fig 3.7: (Left) Temperature inversion caused by subsidence of air. (Right) Lapse rate associated with the column of air (A) in the left-hand drawing.
Upper air inversions may occur when air settles slowly from the upper atmosphere.
Such air is compressed as it sinks and rises in temperature, becoming more stable and
less buoyant. Inversions caused by descending air are common at about 30—35° north
and south latitudes.
AIR PRESSURE AND WINDS
Though air is very light but it has weight. It also exerts pressure on the Earth’s surface.
The weight of air on unit area of the Earth is called Air Pressure. Atmospheric pressure
is measured by an instrument called barometer. The pressure is expressed in centimeters or millimeters of mercury.
Students will be shown video on atmospheric pressure
VERTICAL DISTRIBUTION OF AIR PRESSURE
As air pressure is the weight of a column of air at a point, pressure decreases with altitude above sea level. At high altitudes the air pressure is less. The lower layers are of
greater density as they are compressed by layers above them.
8
HORIZONTAL DISTRIBUTION OF AIR PRESSURE
The distribution of solar radiation, the axial rotation of the Earth, land-sea distribution,
etc. affect the air pressure on the Earth. It would be convenient to study an ideal condition for air-pressure. Suppose the Earth is covered with water or land uniformly. In
such an ideal condition the rotation of the Earth and the incoming insolation creates a
number of pressure belts.
1.
Doldrums – It is situated at the Equator. Sun rays are mostly vertical between 5oN
and 5oS. The air being heated becomes light and continues to rise. This decreases
air pressure in this belt. The air pressure is also low because of excess of water vapours. The air is mostly calm, as its speed is very low. It is because of the generally
calm air that this belt is known as doldrums. This condition of air is found only
upto a small height above which the winds blow at a higher speed.
2.
Sub-tropical High pressure belts – This belt extends between 300 – 350 North and
South of equator. The air which continuously rises at the equator descends
in these latitudes and increases the
pressure of air. There is another reason
for high pressure in these belts. The
winds above tropopause blow towards
the poles that the axial rotate on the
Earth produces centrifugal force which
Fig 3.8: Showing major pressure belts
makes the air descend in these belts.
3.
Sub-polar low pressure belts – These belts are situated between 600 to 650 in the
southern and Northern hemispheres. Due to axial rotation of the Earth, the air is
blown away from the poles and it causes low pressure areas at the poles. The poles
are however very cold and the air being cold is very heavy. The effect of cold is
9
greater than that of axial rotation. This creates high pressure in areas near the
poles.
4.
Polar High Pressure Belts – This belt surrounds the poles. Due to intense cold at
the poles, the air becomes very cold and develops a high pressure belt around the
poles.
The positions of belts described above are correct at the equinoxes only. In other seasons all these belts shift from their position. The shift of wind belts will be described later. In fact, the distribution of pressure on the Earth’s surface is not so simple as it appears from the ideal conditions assumed to describe the pressure belts.
In Northern Hemisphere, land and water are distributed in alternate order. Hence,
pressure belts disappear at many places and pressure cells are found in their places.
Water has a great expanse in Southern Hemisphere. Pressure cells are therefore not
dominant in that hemisphere. In winter many high pressure cells are found on the continents in Northern Hemisphere but low pressure cells are common in ocean areas.
HORIZONTAL DISTRIBUTION OF AIR PRESSURE
Fig 3.9: Showing distribution of air pressure
(in millibars) in January
Fig 3.10:- Showing distribution of pressure (in
millibars) in July
10
Egg in the Bottle
This is a dramatic way of demonstrating the effects of air pressure by putting a hard
boiled egg into a bottle with a small opening and getting it out in one piece.
Get a boiled egg and remove the shell. Use a bottle where the egg cannot go through
the opening. The air in the bottle has no outlet; it will resist any pressure on the egg
to slip in, unless you change the air pressure inside.
Drop a burning match into the bottle just before you put the egg on the top of the
bottle. When the flame goes out, the air cools and contracts, forming a vaccum or
low pressure. The egg will fall inside, by itself. The greater pressure outside the bottle forces the egg into the bottle.
To get the egg out, you have to change the pressure again. Turn the bottle upside
down so that the egg falls into the neck. Tip back your head and blow vigorously into the inverted bottle. When you remove you lips, the egg will pop out quickly.
11
WINDS AND AIR PRESSURE
A study of the distribution of air pressure reveals that the air pressure is not uniformly
distributed over the Earth’s surface. In order to destroy this uneven distribution of pressure, Winds are caused. In other words, winds are caused due to uneven distribution of
pressure. Wind is the air which moves in any direction parallel to the surface of the
Earth. Wind moves from High Pressure areas towards Low Pressure Areas. The rate of
change of air pressure between two places is called Pressure Gradient.
Direction of the wind – Winds blows in the direction of pressure gradient. The Earth
on account of its rotation produces a force known as Coriolis force after the name of the
Mathematician Coriole. This force displaces the wind from the direction of the wind
gradient. Ferrel formulated a law to deduce the direction of winds in the Northern and
Southern Hemispheres. It is known as Ferrel’s law.
The axial rotation of the Earth has no effect on the direction of winds in the equatorial
areas but as we move towards higher latitudes, the effect of axial rotation is increasingly
felt. This effect is maximum at the poles.
Types of Wind
Winds are of three types on the surface of the
Earth:
1.
1.
Primary or Planetary Winds
2.
Secondary or Periodic Winds
3.
Tertiary or Local Winds
Fig 3.11 Showing permanent winds
movement
Primary or Planetary Winds: They are also called as permanent winds because
they blow throughout the year. They blow regularly from high pressure belts to
low pressure belts. Hence, planetary winds are divided into three categories according to Pressure belts and Temperature Zones.
12
a)
Trade Winds: These are winds which blow from the subtropical high pressure regions to the equatorial low pressure region. These winds are constant
in their track, thus, the name, trade, which in latin means constant direction.
b)
Westerlies: The winds blowing from the sub-tropical high pressure belts towards the sub-polar low pressure belts are called Westerlies. They are normally prevalent from 30o-40o to 60o-65o latitudes and prevail in westerly direction. They move from south-west in Northern Hemisphere, to the NorthWest in the Southern Hemisphere.
c)
Polar Winds: The winds blowing from the polar high pressure belts towards
the sub-polar low pressure belts are known as Polar Winds.
2)
Secondary or Periodic Winds: The winds which change their direction periodically, or as per season are called Periodic Winds. The unequal heating and cooling of
the Earth’s surface is mainly responsible for these winds. They are also of three
types.
a)
Monsoon
Winds:
They are the most
significant
seasonal
winds and they have
a special impact on
the Indian climatic
conditions. The word
‘Monsoon’ has been
derived
from
the
Fig 3.12: Showing monsoon winds
Arabic word ‘mausim’ which means season. These winds blow from sea to the land during the
summer and from land to the sea during winter season. The Monsoon winds
13
blow over India, Pakistan, Bangladesh, Mayanmar, Sri Lanka, Arabian Sea,
Bay of Bengal, South-East Asia, China and Japan.
Land and Sea Breeze: During
day time when the sun shines,
land gets more heated than the
adjoining sea and develops low
pressure. Sea breeze starts blowing from high pressure area of
the sea to the low pressure area
of land.
Fig 3.13: showing land and sea breeze
At night, land becomes cooler than the sea due to rapid radiation. This results
in high pressure over the land and low pressure over the sea. Air starts blowing from land to sea and is known as land breeze.
b)
Mountain
and
Valley
Breeze:
These winds blow in mountainous
regions.
During
the
day
time
mountain slope is heated more
than the valley floor. The air from
the valley blows up the slope in the
form of valley breeze. After sunset,
the pattern is reversed, resulting in
sliding of the cold dense air from
higher elevations to Valleys, called
as Mountain Breeze.
3.
Fig 3.14 Showing mountain and valley
breeze
Tertiary or Local Winds: In several parts of the world, winds with special
attributes blow over limited areas and have local significance. These winds are
14
called as Local winds. They affect small areas and are restricted to the lowest levels
of the troposphere.
Material Required:
A cylindrical cardboard oatmeal box
Construction paper (blue and white)
Red and white crepe paper streamers
Glue
String
Scissors
Hole punch
Cut the bottom of a cylindrical cardboard oatmeal box.
Cover the box with blue construction paper and then glue on
white construction paper stars.
Cut some red and white crepe paper streamers and glue or staple them to
one end of the wind sock.
Punch four holes along the top of the wind sock.
15
Cut two pieces of string about a foot long. Tie the strings to the wind
sock (tie the opposite ends of a string to holes on opposite sides of the
cylinder).
Tie a longer piece of string to the smaller pieces - you'll hang the wind
sock from this piece of string.
Hang your wind sock from your window or porch.
It will give the idea to students about the direction of wind.
AIR MASSES AND FRONTS
An air mass is usually defined as a large body of air whose physical properties, namely
temperature and moisture content are almost uniform horizontally over hundreds of
square kilometers. There are two broad categories of air masses:
1.
Continental air masses (c): Those which develop over continents and have low
moisture content.
2.
Maritime air masses (m): Those which have their source regions over the oceans.
Maritime air masses have high moisture content.
3.
Tropical(T) and Polar (P) air mass: Tropical air masses are warm and polar air
masses are cold. They are further subdivided into four types:
Pc-Polar continental
Pm-Polar maritime
Tc-Tropical continental
Tm-Tropical maritime
16
Fronts: When two air masses having different properties move toward each other or
converge, the sharp boundary zone between the two is called a Front.
Fig 3.16 Showing Temperate Fronts
Fig 3.15 Showing continental air mass
Warm Front: When a warmer and lighter air mass moves against a cold and more dense
air mass, the former rides up over the latter and is called as Warm Front.
Cold Front: When a cold air mass forces its way under a mass of warmer air and pushes
the latter upward, the front will be called a Cold Front.
Meeting of warm and cold air masses in the Temperate zone gives birth to Temperate
cyclones along the front of warm and cold air masses.
CYCLONES
The word ‘Cyclone’ is derived from a Greek word ‘cyclosis’ meaning ‘coils of a snake’.
A cyclone is a whirl in the atmosphere with wind circulating around it in anti-clockwise
direction in the Northern Hemisphere and clockwise direction in the southern hemisphere. Cyclones can be divided into two types base on their origin, their nature and the
weather associated with them.

Temperate cyclones

Tropical cyclones
17
Temperate Cyclones: The temperate cyclones develop in the middle latitudes where the
sub-tropical warm air masses and polar cold air masses converge along a front.
Fig 3.17 Showing formation of temperate cyclones
Video on Tropical cyclones
Tropical Cyclones: Tropical cyclones originate in the zones of inter-tropical convergence where the trade winds from both the hemisphere converge. They occur in the
seasons when the zone of convergence of trade winds is deflected farthest from the
equator. They usually originate in the warm western parts of the Atlantic and Pacific
oceans in both the hemispheres.
Fig 3.23 Showing formation of Tropical Cyclones
18
ATMOSPHERE
Water in the atmosphere occurs in all the three states of matter-solid, liquid and gas.
Water vapour is an important component of the atmosphere and its quantity varies
from place to place.
Warm up activity (Watch video on atmospheric moisture)
HUMIDITY
The presence of water vapours in air is called humidity.
Absolute humidity - It is the amount of vapours present in a certain volume of air. It is
expressed in grains per cubic or grams per
cubic centimeter. For example, if there are 9
grains of water vapours in a cubic metre of
water at a certain time, the absolute humidity is 9 grains per cubic metre. Absolute humidity is not much used because the volume
of air increases when it rises and decreases
when the air descends. Hence, it is a practice
Fig 3.18 Showing Relative Humidity
to use relative humidity in place of absolute
humidity.
Relative humidity – The capacity of air to hold moisture depends upon its temperature.
If we increase the water vapour of a certain amount of air at a fixed temperature, the air
will initially hold the water vapours but after a limit it will stop absorbing more water
vapours. In other words, the air gets saturated. In this condition the air will not absorb
more water vapours than those which the air contains. If the temperature of air is increased it will start taking more water vapours but it will again be saturated after taking
19
a certain amount of water vapours. The temperature at which air gets saturated is called
the dew point.
EVAPORATION
The process through which water (liquid) changes into vapours (gas) is called evaporation. This process takes place almost at all temperatures. There is a lot of turbulence accompanied by sound when boiling takes place.
CONDENSATION
The process through which the water vapours change
into liquid is called Condensation. With the rise of
temperature the capacity of air to hold and absorb water
vapours also increases but with the fall of temperature
the capacity to hold and absorb water decreases. If the
temperature of water mass goes on falling, the capacity
to hold water vapours goes on decreasing. If we reduce
Fig 3.19 showing condensation
the temperature of the airmass to such an extent that with a slight fall the air fails to
hold water vapours which begins to be condensed, the temperature is called Dew Point
and the air at this temperature is called Saturated.
FORMS OF CONDENSED WATER VAPOURS
Condensation of water vapour into tiny droplets of water may take different forms depending on the temperature at which condensation takes place and the level at which
condensation occurs. They are of many types. Dew –Frost –Haze –Mist and Fog
CLOUDS
Clouds are the numerous small drops or particles of water, frost, or ice which form a
large mass of air. These particles which flow in the air at different heights are called fog
at the surface of the Earth. The clouds are found upto a height of 12,000 metres but they
20
do not occur in stratosphere because there is no water vapour in it. It extends upto
troposphere.
Classification of Clouds
Clouds can be classified on many basis. It is usually done on the basis of the height of
the clouds and their appearance from the Ground.
Cloud Chart
Cloud Group
Cloud Height
Cloud Types
High Clouds = Cirrus
Above 6,000 metre
Cirrus Cirrostratus Cirrocumulus
Middle Clouds = Alto
2200 metres to 6000 metres
Altostratus Altocumulus
Low Clouds = Stratus
Up to 2200 metres
Stratus Stratocumulus Nimbostratus
Video on types and causes of Precipitation
PRECIPITATION
Precipitation is the process by which condensed water vapour falls to the ground in the
form of Rainfall or in other forms. Rain drops of smaller size fall down as drizzle. Rainfall and drizzle occur when the temperature of air is above the freezing point.
Snow – When the water vapours of the air are condensed in the air having temperature
below freezing point, the water vapours change directly into a solid form. The bigger
particles fall on Earth’s surface in the form of snow flakes.
Hail – Hail falls from cumulus clouds. For hail it is necessary that the cold front between the warm and cold air masses should pass over that area or very strong clouds
coalesce into bigger drops and the up thrust of a strong wind takes them to a height
21
where these big drops are condensed into ice-pellets. The conditions are then favourable for the formation of hail. The ice-pellets rise still higher and grow larger and change
into ice-crystals.
Sleet – When snow accompanies hail, it is known as Sleet. In fact sleet is only a stage in
the development of rainfall. The mixture of Hail and Rain is known as sleet in America
but in Britain these are the solidified and remelted water drops that are known as sleet.
Rainfall – Precipitation in the form of drops of water is called rainfall. The drops of rain
are generally larger than those drizzle. On the basis of its origin, precipitation is of three
main following types:
Convectional Rainfall
The cold air in contact with a hot surface of the Earth is also warmed. On heating it expands, becomes lighter than the surroundings and rises. To fill the place of the rising
air, cold air from the surroundings rushes in. Later on even the incoming air is also
warmed and rises. In this way convection currents are formed.
The rising air continues to rise till its temperature becomes equal to that of the surrounding
air. If water vapour of the rising air is condensed before the air reaches that height, the
latent heat released from the condensation further heats the rising air. The rising air being
heated more than before rises to still higher
heights. Due to condensation the vapours condense into heavy rainfall. As this rainfall is
Fig 3.21 Showing Conventional rainfall
caused by convection process. It is known as convectional rainfall.
22
Orographical Rainfall
When the humid winds from the
seas strike a mountain situated in
the interior far from the coast, the
humid winds rise up the slope by
the push of the strike which is at
right angle to the mountain. The ascent of the wind cools it and condensation starts. The water vapours on
condensation provide rainfall. This
Fig 3.22 Showing Orographic Rainfall
rainfall is called Orographical Rainfall.
Cyclonic Rainfall
When hot and humid airmass meets a cold one, the warm air tries to enter the cold air
at the frontal area but the cold air pushes the warm one from below. This moves the
warm air on to the cold airmass and warm air begins to ascend. The water vapours of
the warm humid airmass are condensed in the
ascent of airmass and rainfall occurs. This rainfall is caused due to the convergence of air
masses.
Frontal Rainfall
This is a low pressure area at the centre of cyclones. The air from the surrounding high pressure area moves encircling towards the centre.
Fig 3.23 Showing Frontal Rainfall
This air does not find place to stay at the centre
due to the cyclonic rotation and therefore has to rise in the atmosphere. Condensation
by ascent causes rainfall.
23
CLASSIFICATION OF CLIMATE
Watch a Video on Climate Types
There is a great diversity in the information associated with the concept of climate. It is
necessary to select significant climatic characteristics and a systematic way to classify
the climate. All the classifiers of world climatic system have used precipitation and
temperature to achieve this goal. The earliest known climatic classification scheme originated with the ancient Greeks; from that time onwards the scheme of climate classification has been transferred from scholar to scholar.
The Thornthwaite System of Classifying Climates
It was the first system of classifying climates on a local scale. Developed by an American climatologist, C. Warren Thornthwaite, the Thornthwaite system establishes moisture availability at the sub-regional scale. It is the system preferred by those examining
climates on a local scale.
The Thornthwaite system is based on the concept of Potential Evapotranspiration (potential ET), which approximates the water use of plants with an unlimited water
supply. Potential ET is a theoretical value that increases with Increasing Temperature,
winds, and length of daylight and decreases with increasing humidity. Actual evapotranspiration (actual ET), which reflects actual water use by plants, can be supplied during the dry season by soil moisture if the soil is saturated, the climate is relatively cool,
and/or the day lengths are short. Thus, measurements of actual ET relative to potential
ET and available soil moisture are the determining factors for most vegetation and crop
growth.
The Thornthwaite system recognizes three climate zones based on potential ET values:
Low-latitude climates, with potential ET greater than 130 centimeters (51 in.);
24
Middle- latitude climates, with potential ET less than 130 but greater than 52.5
centimeters (20.5 in.);
High-Latitude climates, with potential ET less than 52.5 centimeters.
Koppen’s Climate Classification
It is the most widely used climate classification, based on temperature and precipitation
patterns. It has been developed by Wladimir Koppen, who was a Botanist and Climatologist from Germany. Koppen recognized that major vegetation associations reflect
the area's climate. Hence, his climate regions were formulated to coincide with welldefined vegetation regions, and each climate region was described by the natural vegetation most often found there.
The Koppen system, as modified by later climatologists, divides the world into six major Climate Categories. The first four are based on the annual range of temperatures:
humid tropical climates
(A) humid mesothermal (mild winter) climates
(C) humid microthermal (severe winter) climates
(D) and polar climates
(E) Another category, the arid and semiarid climates
(BW and BS), identifies regions that are characteristically dry based on both temperature and precipitation values. The final category, highland climates
(H) identifies mountainous regions where vegetation and climate vary rapidly as
a result of changes in elevation and exposure.
Climate categories of the Koppen classification include enough differences in the
ranges, total amounts, and seasonality of temperature and precipitation to produce the
13 distinctive climate types.
25
Fig 3.24 Showing Schematic representation of Koppen’s Climatic Classification
Tropical Humid Climate: Tropical humid climate exist between Tropic of Cancer and
Tropic of Capricorn. The sun being overhead throughout the year and the presence of
Inter Tropical Convergence Zone (ITCZ) make the climate hot and humid. Annual
range of temperature is very low and annual rainfall is high. The tropical group is divided into three types, namely (i) Af- Tropical wet climate; (ii) Am - Tropical monsoon
climate; (iii) Aw- Tropical wet and dry climate.
Tropical Wet Climate (Af)
It is found near the equator. The major areas are the Amazon Basin in South America,
western equatorial Africa and the islands of East Indies. The region receives significant
amount of rain fall throughout the year with thundering in the afternoon. The temperature remains uninformly high. Tropical Evergreen forests with dense canopy cover and
large biodiversity are found in this climate.
Tropical Monsoon Climate (Am)
Tropical monsoon climate (Am) is found over the Indian sub-continent, North Eastern
part of South America and Northern Australia. Heavy rainfall occurs mostly in summer. Winter is dry.
26
Tropical Wet and Dry Climate (Aw)
Tropical wet and Dry climate occurs North and South of Af type climate regions. Extensive Aw climate is found to the North and south of the Amazon forest in Brazil and its
adjoining parts.
Dry Climates: B
Dry climates are characterized by very low rainfall that is not adequate for the growth
of plants. These climates cover a very large area of the planet extending over large latitudes from 15° - 60° north and south of the equator. At low latitudes, from 15° - 30°,
they occur in the area of subtropical high where subsidence and inversion of temperature do not produce rainfall. Dry climates are divided into Steppe or Semi-Arid Climate
(BS) and Desert Climate (BW). They are further subdivided as subtropical steppe (BSh)
and subtropical desert (BWh) at latitudes from 15° - 35° and mid-latitude steppe (BSk)
and mid-latitude desert (BWk) at latitudes between 35° - 60°.
Subtropical Steppe (BSh) and Subtropical Desert (BWh) Climates
Subtropical steppe (BSh) and subtropical desert (BWh) have common precipitation and
temperature characteristics. Located in the transition zone between humid and dry climates, subtropical steppe receives slightly more rainfall than the desert, adequate
enough for the growth of sparse grasslands. Rainfall in both the climates is highly variable.
Warm Temperate (Mid-Latitude) Climates-C
Warm temperate (mid-latitude) climates extend from 30° - 50° of latitude mainly on the
Eastern and western margins of continents. These climates generally have warm summers with mild winters. They are grouped into four types: (i) Humid subtropical, i.e.
dry in winter and hot in summer (Cwa); (ii) Mediterranean (Cs); (iii) Humid subtropical, i.e. no dry season and mild winter (Cfa); (iv) Marine west coast climate (Cfb).
27
Humid Subtropical Climate (Cwa)
Humid subtropical climate occurs poleward of Tropic of Cancer and Capricorn, mainly
in North Indian plains and South China interior plains. The climate is similar to Aw
climate except that the temperature in winter is warm.
Mediterranean Climate (Cs)
As the name suggests, Mediterranean climate occurs around Mediterranean sea, along
the west coast of continents in subtropical latitudes between 30° - 40° latitudes e.g. Central California, Central Chile, along the coast in South Eastern and south western Australia. These areas come under the influence of sub tropical high in summer and westerly wind in winter. Hence, the climate is characterised by hot, dry summer and mild,
rainy winter.
Humid Subtropical (Cfa) Climate
Humid subtropical climate lies on the Eastern parts of the continent in subtropical latitudes. In this region the air masses are unstable and cause rainfall throughout the year.
They occur in Eastern United States of America, Southern and Eastern China, Southern
Japan, northeastern Argentina, coastal South Africa and Eastern coast of Australia. The
annual averages of precipitation vary from 75-150 cm.
Marine West Coast Climate (Cfb)
Marine west coast climate is located pole ward from the Mediterranean climate on the
west coast of the continents. The main areas are: Northwestern Europe, west coast of
North America, North of California, Southern Chile, South Eastern Australia and New
Zealand. Due to marine influence, the temperature is moderate and in winter, it is
warmer than its latitude.
28
Cold Snow Forest Climates (D)
Cold snow forest climates occur in the large continental area in the northern hemisphere between 40°-70° north latitudes in Europe, Asia and North America. Cold snow
forest climates are divided into two types: (i) Df- cold climate with humid winter; (ii)
Dw- cold climate with dry winter.
Cold Climate with Humid Winters (Df)
It occurs poleward of marine west coast climate and mid latitude steppe. The winters
are cold and snowy.
Cold Climate with Dry Winters (Dw)
Cold climate with dry winter occurs mainly over NorthEastern Asia. The development
of pronounced winter anticyclone and its weakening in summer sets in monsoon like
reversal of wind in this region.
Polar Climates (E)
It is found beyond 70° latitude poleward. Polar climates consist of two types: (i) Tundra
(ET); (ii) Ice Cap (EF). The Tundra Climate (ET) is so called after the types of vegetation,
like low growing mosses, lichens and flowering plants. This is the region of permafrost
where the sub soil is permanently frozen. (EF) The ice cap climate (EF) occurs over interior Greenland and Antarctica. Even in summer, the temperature is below freezing
point. This area receives very little precipitation.
Highland
It is found in parts of Bolivia and Paraguay in South America, Sudan and South of Central Africa. The Annual rainfall in this climate is considerably less than that in Af and
Am climate types and is variable also. The wet season is shorter and the dry season is
longer with the drought being more severe. Temperature is high throughout the year
29
and diurnal ranges of temperature are the greatest in the dry season. Deciduous forest
and tree-shredded grasslands occur in this climate.
Fig 3.25 Showing Koppens Climatic Classification
30
GLOSSARY
Insolation: Incoming solar radiation in the form of shortwave.
Adiabatic Lapse Rate: It is the rate of change of temperature of the airmass by raising
or lowering (when no heat is added or subtracted) through Condensation, Evaporation
and Radiation.
Airmass: A body of air that is relatively uniform in its characteristics for distances of
hundreds to thousands of square kilometers.
Temperature Inversion: The situation in which the temperature of the static atmosphere increases with height increases instead of decreasing.
Doldrums: Equatorial belt of calm areas near the centre of the Earth formed due to intense heating and rising of the air.
Horse Latitude: Also called as subtropical high latitude, which lies between 30° N and
South latitude. In olden times horse traders use to throw their horses in the sea to reduce the weight of the ship for being able to sail in very calm conditions.
Roaring Forties: Name given to strong westerly winds of Southern Hemisphere between the latitudes 40° to 50°.
Coriolis Force: A force generated from the rotation of the Earth. It causes moving objects to be deflected to the right in the northern hemisphere and to the left in the southern hemisphere. Coriolis force does not exist on the equator.
Inter-tropical Convergence Zone (ITCZ): The belt where air blowing from subtropical
high pressure to equatorial low pressure converges caused by rising motion of general
circulation.
Geostrophic Winds: The airflow that results when the pressure gradient force balances
the Coriolis effect and the gradient force; results in air flowing parallel to isobars.
31
Anticyclone: Any enclosed area of relatively high pressure in the centre and high pressure outside, rotating generally clockwise in the Northern Hemisphere and counter
clockwise in the southern hemisphere.
Cyclone: Any enclosed area of relatively low pressure, rotating generally counterclockwise in the northern hemisphere and clockwise in the Southern Hemisphere.
El Nino: Also called as child of Christ in Spanish language. It is the phenomenon where
the cold Humboldt Current flowing in the southwestern coast of Ecuador and Peru
changes into warm current that bring torrential rainfall in those areas and drought in
India and South East Asian countries.
La Nina: The condition in this is opposite to El Nino. In this the tropical pacific trade
winds become very strong and an abnormal accumulation of cold waters occur in the
central and Eastern Pacific Ocean.
Rozby Waves: Upper- tropospheric, midlatitude waves with wave length of hundreds
to thousands of kilometers.
Monsoons: Derived from Arabic word ‘Mawsim’ means seasonal reversal of wind system.
Katabatic: A local circulation of mountain regions, in which air moves down slope, typically at night when the air adjacent to the surface increases in density as it cools.
Cold Front: A narrow zone separating two air mass types in which the colder air mass
is actively displacing the warmer air mass.
Occluded Front: A surface front that results in the late stage of a multitude wave cyclone's life cycle after the cold front has overtaken the warm front; results in warm sector
being wedged upward between cold air behind the cold front and cool air ahead of the
warm front.
32
Temperate Cyclone: It has low pressure at the centre and increasing pressure outward.
It has varying shapes such as near circular, elliptical or wedge, therefore, it is also called
Low or Troughs or Mid Latitude Depressions.
Evapotranspiration: The sum of evaporation and transpiration from plants and Earth
surface into the atmosphere.
Absolute Humidity: The mass of water vapour per cubic meter of air.
Relative Humidity: The ability of an air to hold the water vapour at a specific temperature.
Ultraviolet Radiation: It is a part of electromagnetic radiation from the sun. It is harmful for the skin and may cause skin cancer if subjected for a longer period of time.
Green House Effect: Irreversible increase in Earth's surface atmospheric temperatures
caused by increasing green house gas concentrations.
33
WORKSHEETS
WORKSHEET–1
I.
Give one word for the following:
1.
Layer in which most of the weather phenomena occur._________________
2.
Rate at which temperature decreases with altitude in the troposphere._______________
II.
3.
Layer which absorbs ultra-violet radiation._____________________
4.
The topmost layer of the atmosphere._______________________
5.
Layer providing ideal flying conditions._____________________
Distinguish between Weather and Climate.
WEATHER
CLIMATE
1.
1.
2.
2.
3.
3.
III. Describe the principle elements of weather and climate.
a.
_____________________________________________________________________
34
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
b.
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
c.
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
IV. Look at the picture and answer the following questions.
1.
What is troposphere? What is its
importance?
_______________________________
_______________________________
_______________________________
_______________________________
____________________________________________________________________
____________________________________________________________________
35
2.
How is it that the lowest temperatures at the tropopause are vertically over
the equatorrather than over the poles?
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
36
WORKSHEET–2
I.
On the basis of the given picture answer the following questions:
What is being depicted in the picture
______________________________________________________________________
Which season is experienced on March 21st in northern hemisphere
______________________________________________________________________
In June and December, the sun is overhead at the tropics of Cancer and Capricorn respectively. Examine how this is brought about and show what effect it
has on the differences in:
____________________________________________________________________________
1. Temperature
_________________________________________________________________________
_________________________________________________________________________
37
2. Length of day and night between Summer and Winter in Northern Hemisphere
_________________________________________________________________________
_________________________________________________________________________
II.
Fill in the blanks:
1.
Temperature is measured by an instrument called the __________________
2.
The process of horizontal transfer of heat by winds is called______________
3.
Normal lapse rate of temperature is ___________________
4.
Transfer of heat by contact between two bodies is called_______________
5.
______________is a process by which heat is transferred through space.
III. Answer the following questions briefly:
1.
What is insolation? List the factors that affect distribution of insolation & explain any one of them?
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
2.
What are isotherms? What is its importance?
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
38
3.
Explain inversion of temperature with the help of the following diagram.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
39
WORKSHEET–3
I.
Look at the picture given below and answer the questions:
a.
What causes shifting of pressure belts according to seasons?
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
b.
Where do you find maximum and minimum deflection of winds by coriolis
effect?
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
c.
What is the direction of westerlies blowing in the Northern Hemisphere?
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
40
II.
Give one word for the following:

Winds flow over vast area of the continents and oceans__________________

Certain winds which reverse their direction periodically with season are
called _______________

A surface wind which blows from the sea to the land in the afternoon and
evening are called as _____________________

Hot and dry winds which blows from the west in the months of May and
June____________

Cold north-west wind that blows into the western Mediterranean basin from
higher elevations.______________
III. Look at the map given below and answer the following questions:
 Why high pressure does develop over the continents and low pressure on the oceans in winter season in Asia?
_________________________________________
_________________________________________
________________________________________
 Why do winds blow from sea to the land during summer season?
_________________________________________
_________________________________________
_________________________________________
41
IV. Look at the picture to identify and explain the process.
_________________________________________________________________________
_________________________________________________________________________
_________________________________________________________________________
42
WORKSHEET–4
I.
Look at the graph showing Decadal occurrences of Tropical Cyclones in Tonga and
answer the following questions:
How do you say that the intensity of cyclones has increased since the 1960’s
in Toga?
_____________________________________________________________________
_____________________________________________________________________
What are the effects of these cyclones on humans life.
_____________________________________________________________________
_____________________________________________________________________
II.
Name the four types of air masses.
_________________________________________________________________________
_________________________________________________________________________
_________________________________________________________________________
43
_________________________________________________________________________
III. Fill in the blanks:
1.
The word cyclone is derived from a Greek word__________________
2.
Air pressure is measured by an instrument called_________________
3.
Warm
dry
wind
blows
down
the
Eastern
flanks
of
the
Rockes_________________
4.
_______________ is the pressure exerted by the weight of air on the Earth’s
surface.
5.
_______________ is the important factor which influences atmospheric pressure.
IV. Distinguish between Tropical Cyclones and Temperate Cyclones
Tropical Cyclones
V.
Temperate Cyclones
Study the given diagram and answer the following questions:
44
a)
What are air masses?
_____________________________________________________________________
_____________________________________________________________________
b)
How do they influence the area over which they move?
_____________________________________________________________________
_____________________________________________________________________
c)
What are two types of Air masses?
_____________________________________________________________________
_____________________________________________________________________
45
WORKSHEET–5
Q.1 Multiple Choice Questions
Read the questions given below and write the correct option number in the brackets.
1.
2.
3.
Specific humidity is measured.
a)
In grams of water vapour per cubic metre of air.
b)
In grams of water vapour per kilogram of air.
c)
In cubic centimeters of water vapour per cubic metre of air.
d)
In cubic centimeters of water vapour per kilogram of air.
(
)
(
)
Condensation occurs in the air when
a)
Air descends
b)
Air gets cooled
c)
Air gets heated
d)
Air remains stable
When condensation occurs on the Earth’s surface as droplets of water, it is
called
4.
a)
Dew
b)
Mist
c)
Fog
d)
White frost
(
)
Which of the following regions receive precipitation throughout the year?
a)
Equatorial region
b)
West coast of continents in the westerly wind belt.
46
c)
Monsoon region
d)
East coast of continents in the trade wind belt.
(
)
Q.2 Fill in the blanks:
a)
Absolute humidity is expressed as grams per cubic meter.
b)
Relative humidity is expressed in percentage
c)
Air containing moisture to its full capacity at a given temperature is said to be
saturated.
d)
Sleet is frozen rain drops and refrozen melted snow water,
e)
Precipitation in the form of hard rounded pellets is known as hail.
Q.3 Study the diagram given below and answer the following questions:
1.
one
Give
word
for the fol-
lowing.
2.
Process
by
which
water
is
form________________
47
transformed
from
liquid
to
gaseous
3.
Process of change of state from gaseous to liquid or solid state.
_____________________
What is surface runoff?
__________________________________________________________________
__________________________________________________________________
What is transpiration?
__________________________________________________________________
__________________________________________________________________
Q.4 Complete the table given below:
Cloud Group
Cloud Height
Cloud Types
High Clouds = _______ Above _________ feet Cirrus ________ Cirrocumulus
Middle Clouds =_____ _____feet to_____ feet Altostratus ___________
Low Clouds =________ Up to_______ feet
48
Stratus ________ Nimbostratus
WORKSHEET–6
I.
Look at the picture and answer the following questions.
a)
What is saturation point?
_____________________________________________________________________
b)
What is Dew point?
_____________________________________________________________________
c)
How is the above given diagram is related to Relative Humidity?
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
49
II.
Look at the clues given below and fill up the Cross word
1.
A rainfall caused by convectional ascent of warm and humid air to great
heights _________________
2.
A rainfall caused by ascending of moist air and adiabatic cooling caused by
convergence of two extensive air masses_________________
3.
A precipitation commonly found on the windward sides of mountains_________________
4.
Condensation of water vapour in the air in the form of water droplets and ice
and their falling on the ground_________________
5.
Precipitation in the form of rounded pellets_________________
6.
Frozen rain drops with melted snow water_________________
7.
Precipitation in form of drops of water_________________
8.
Millions of minute droplets of water or tiny crystals of ice formed by the condensation of water vapour in free air_________________
9.
Cloud with its base at a very near the ground_________________
10.
A kind of fog in which visibility is more than one kilometer but less than
2km_________________
50
51
WORKSHEET–7
Q.1 Give a single term for each of the following.
a)
Low pressure belt in the equatorial region.________________
b)
Winds which blow form the sub-tropical high pressure belt towards the subpolar low pressure.__________________
c)
Wind which blows from sea to land._________________
d)
Wind which blows down the mountain slope.______________________
e)
Air mass which originates over tropical oceans. ____________________
f)
Sharp boundary zone, between two air masses.______________________
Q.2 Look at the map showing the temperature and pressure conditions around the
world in summer season and answer the given questions.
52
 Where is the highest temperature and lowest pressure located in Troppical
region. Is there change in the position of isolines compared to summer season.
Give reason. Why?
______________________________________________________________________
______________________________________________________________________
______________________________________________________________________
 Where are the high pressure areas over seas and oceans in the Northern
Hemisphere and why?
______________________________________________________________________
______________________________________________________________________
______________________________________________________________________
Q.3 Make a Climograph from the given data.
Temp
Jan
Feb
Mar April May June July Aug
Sep
Oct
Nov
Dec
oC
14.3
16.2
20.8
34.4
31.4
26.3
20.6
15.4
R.Fall
Jan
Feb
Mar April May June July Aug
Sep
Oct
Nov
Dec
mm
13.8
10.4
29.8
00
0.7
4.5
11.3
25.0
29.7
30.8
13.1
33.6
00
34.6
00
CLIMOGRAPH
53
00
WORKSHEET–8
Q.I Multiple Choice Questions
Read the questions given below and write the correct option number in the
brackets
1.
2.
3.
4.
Koppen’s scheme of classification of climates is based on
a)
Temperature and pressure
b)
Temperature and humidity
c)
Temperature and rainfall
d)
Pressure and winds
(
)
(
)
(
)
Equatorial type of climate is represented by Koeppen by symbol
a)
Af
b)
Am
c)
Cf
d)
Df.
Which of the following regions is an example of mid-latitude desert?
a)
Kalahari
b)
Atacama
c)
Tibet
d)
Arabia
Which of the following regions experiences CF type of climate?
a)
Japan
b)
British Isles
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c)
North-Eastern United States
d)
Central Chile
(
)
QII. Give a brief account of Koeppens classification of climates.
_________________________________________________________________________
_________________________________________________________________________
_________________________________________________________________________
QIII. What are the similarities between tropical desert type (BWh) and subtropical
steppe (BSh) type of climate.
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_________________________________________________________________________
_________________________________________________________________________
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WORKSHEET–9
Q.1 Identify the climatic type from the details given below:
a.
Cool summers (100 -150C) and cold winter (less than 00 C) with no dry season_________________
b.
Warm summers (200 C) and cool winter (100 C) with dry season in summer_____________________.
c.
Hot summers (300C ) and warm winters (200 C) with moderate rainfall in
summer only_________________.
d.
Warm summers (150 C) and cool winter (50C) with no dry season
______________________.
Q2. Describe the main features of equatorial type (Af) climates.
_________________________________________________________________________
_________________________________________________________________________
_________________________________________________________________________
_________________________________________________________________________
_________________________________________________________________________
_________________________________________________________________________
Q3. What are the six major climatic types of Koeppen?
_________________________________________________________________________
_________________________________________________________________________
_________________________________________________________________________
_________________________________________________________________________
_________________________________________________________________________
_________________________________________________________________________
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CENTRAL BOARD OF SECONDARY EDUCATION
Shiksha Kendra, 2, Community Centre, Preet Vihar, Delhi-110 092 India