Atmosphere

Class 9 | Social Science — Geography | Unit 3

Class 9 Unit 3 Geography

Unit 3 Atmosphere

Learning Objectives

• To understand the composition and structure of atmosphere
• To differentiate weather and climate
• To correlate the factors influencing weather and climate
• To recognize the classification of Clouds, wind and rainfall

Introduction

Earth is a unique planet where life is found. Can you imagine life on the earth without air? No. The air is essential for the survival of all forms of life. The blanket of air that surrounds the Earth is called the atmosphere. It is held close to the earth by gravitational attraction.

3.1 Composition of the Atmosphere

Atmosphere is a mixture of gases, water vapour and dust particles in different proportions. Nitrogen (78 percent ) and Oxygen (21 percent ) are permanent gases of the atmosphere. They constitute 99 percent of the total composition and their percentages always remain the same without any change. The remaining one percentage is occupied by Argon (0.93 percent), Carbon-di-oxide, (0.03 percent ), Neon (0.0018 percent ), Helium (0.0005 percent ), Ozone (0.00006 percent ) and Hydrogen (0.00005 percent ). Krypton, Xenon and Methane are also present in trace. Water vapour (0 - 0.4 percent ) is also found in the atmosphere, which plays an important role in predicting weather phenomenon. The other solid particles present in the atmosphere includes dust particles, salt particles, pollen grains, smoke, soot, volcanic ashes etc.,

Fact

In 1772 CE Daniel Rutherford discovered Nitrogen in atmosphere. In 1774 Joseph priestly discovered oxygen in atmosphere

Oxygen is most important for living organisms. Carbondi oxide absorbs heat and keeps the atmosphere warm by insulation and radiation. Nitrogen acts as a diluent and is chemically inactive. Ozone helps in protecting the earth from harmful ultra violet radiation. The solid particles in the atmosphere acts as nuclei on which water vapour condense to form precipitation.

3.2 Structure of the Atmosphere

The atmosphere is thick near the earth surface and thins out until it eventually merges with space. The five atmospheric layers are: Troposphere, stratosphere, Mesosphere, Thermosphere and Exosphere.

Troposphere

The lowest layer of the atmosphere is the troposphere. The Greek word 'tropos' means 'turn' or change. The layer extends up to 8 kilometers at the poles and up to 18 kilometers at the Equator. The temperature decreases with increasing height. Almost all weather phenomenon take place in this layer. Hence it is called weather making layer. The upper limit of the troposphere is called as tropopause.

Stratosphere

Stratosphere lies above the troposphere. It extends to a height of about 50km above earth surface. Since this layer is a concentration of ozone molecules, it is also referred as ozonosphere. The temperature increases with increase in height in this layer. Large jet planes normally fly here. The upper limit of the stratosphere is called as stratopause.

Mesosphere

Mesosphere extends between 50km and 80km. The temperature decreases with increasing height. Most of the meteors nearing the earth, get burned here. The upper most limit of the mesosphere is the mesopause.

Thermosphere

Thermosphere exists above the mesosphere. It extends to about 400 kilometer. The composition of gases in the lower thermosphere is more or less uniform, hence it is called "Homosphere". The upper portion of the thermosphere has uneven composition of gases and hence it is referred as "Heterosphere". Here the temperature increases with increasing height. Ionosphere is a layer of the thermosphere that contains Ions and free electrons. Radio waves transmitted from earth are reflected back to earth from this layer.

Fact

Magnetosphere lies beyond the exosphere. It is the earth's magnetic belt, where proton and electrons, coming out from the sun are trapped by the earth. The magnetic field extends to around 64,000 kilometer above the Earth.

Exosphere

The uppermost layer of the atmosphere is called exosphere. This layer is extremely rarefied with gases and gradually merges with the outer space. This zone is characterized by aurora Australis and aurora borealis.

Do you know?

Auroras are cosmic glowing lights produced by a stream of electrons discharged from the Sun's surface due to magnetic storms that are seen as unique multicoloured fireworks hanging in the polar sky during midnight.

3.3 Weather and Climate

Weather and climate are the terms that are related to the atmospheric conditions. Weather denotes the way the atmosphere behaves every day and climate reveals the average of weather conditions over relatively long periods of time. The difference between the two may be clearly understood with the following table.

Hots

Why is Troposphere called as weather making layer?

There are many factors that influence weather and climate.

• Distance from the equator
• Altitude
• Nearness to the sea
• Nature of the prevailing winds
• Mountain barrier
• Cloud cover
• Ocean currents
• Natural vegetation

Distance from the Equator

The sun's rays fall vertically on the equator. The rays are inclined on the regions away from the equator and near the poles due to the spherical shape of the earth. The vertical rays heat up the earth more than the inclined rays. Thus, the places near the equator are warmer than the places which are far away from the equator.

Activity Connect the following places with their latitudes and the temperature observed

Weather	Climate
Partly sunny	1. Weather is the study of atmospheric conditions for short duration over small areas.
Warm Climate	1. Climate is the study of the average weather condition observed over a long period of time for a larger area.
Windy	2. The weather changes very often ; hour to hour and day to day
Monsoon	2. Climate is more or less permanent and remains the same always.
Rainy	3. A place can experience different types of weather conditions in a day. Example, A day with hot morning can have a rainy noon.
Wet Climate	3. A place can experience almost the same type of climate
Chilly	4. Weather data is collected every day in the observatories
Extreme Climate	4. Climate is average of the weather data.
Stormy	5. Study of weather is called Meteorology
Cyclone	5. Study of climate is called Climatology

City	Latitude	Temperature [In August]
Kanyakumari – Tamil Nadu
Delhi-India
Moscow – Russia

Altitude:

Altitude refers to the height above mean sea level. The temperature decreases at the rate of 6.5°C per kilometer of height. This is called Normal lapse rate. So, places at the higher altitude have a lower temperature.

Activity Connect the following places with Altitude and the temperature

City	Altitude (height)	Temperature [In May]
MaduraiTamilnadu
Uthagamandalam – Tamilnadu
Simla -Himachal Pradesh

Nearness to the sea:

The climate of a place, varies according to its nearness to the sea. Places near the coast experience equable climate due to the influence of the winds from the sea. Places located inland, far from the sea, does not experience the moderating influence of the sea, such places experience a continental type of climate.

Fact

During the day, the land masses get heated more rapidly than the oceans. Heated air ascends and this causes low pressure on the adjoining ocean. Therefore, the wind blows from ocean to land in the afternoon. This is called sea breeze. Sea breeze helps in reducing the temperature of the coastal region especially during the summer season. During the night, the land cools more rapidly than the ocean. Cold air sinks and forms high pressure. The wind blows from land to sea during the night, this is called land breeze.

Nature of the Prevailing Winds

The wind changes the climate of a place based on, from where they blow. When wind blows from a warm region, it makes the place warm and cold, when blows from a colder region. The on-shore winds cause rainfall making the place cool whereas the off-shore winds bring dry weather.

Mountains barriers

The location of the mountains influence the climate of a place. The mountain chains act as natural barrier for the wind. Sometimes they prevent the entry of cold winds into the country or the escape of monsoon winds, thus having a great influence over the climate.

Do you know?

The windward is the side of a mountain which faces the prevailing wind. It receives heavy rainfall. The leeward side of the mountain is the side sheltered from the wind. It receives very less rainfall.

Cloud Cover

Clouds reflect a large amount of radiation from the sun. This prevents the entry of heat to the earth's surface. So, in areas generally of cloudless sky like the deserts, temperature is very high. On the other hand under cloudy sky, the temperature is low.

Ocean currents

The warm ocean currents raise the temperature of the nearby coastal areas, while the cold current lower the temperature of a place.

Natural vegetation

The trees release water vapour into the air and makes it cool. Thus forest areas have lower range of temperature throughout the year in contrast to non-forested areas.

3.4 Winds

The horizontal movement of air along the surface of the earth is called the "Wind" while the vertical movement of air is a called an "Air Current". The winds always blow from a high pressure area to a low pressure area. Wind is mostly named after the direction from which it blows. For example, the wind blowing from the east is known as the easterly wind or easterlies. An "anemometer" records wind speed while a "wind vane" measures the direction of the wind. The unit of measurement is kilometre per hour or knots

Types of Winds

Winds are generally classified into the following four major types:

• Planetary winds
• Periodic winds
• Variable wind
• Local wind

Planetary winds:

The winds which constantly blow in the same direction throughout the year are called the Planetary winds. They are also called as permanent winds or the prevailing winds. These winds include Trade winds, Westerlies and Polar Easterlies.

Trade Winds

Trade winds blow from the subtropical high pressure belt to the Equatorial low pressure belt in both the hemispheres. They blow with great regularity, force and in a constant direction throughout the year. These winds were very helpful to traders who depended on the winds while sailing in the seas. And so, they are named as Trade winds.

Activity Find the correlation between the Trade Winds and the location of prominent deserts like Sahara, Atacama etc.

Westerlies

Westerlies are the permanent winds that blow from the tropical high pressure belt to the sub polar low pressure belt in both the hemispheres. They blow from South West to North East in the northern hemisphere and North West to South East in the southern hemisphere. The velocity of westerlies become so vigorous and fast to be called Roaring Forties at 40 degree, Furious Fifties at 50 degree and Screaming Sixties at 60 degree latitudes.

Polar Easterlies:

Polar easterlies are cold and dry polar winds that blow from the polar high pressure belt to the sub polar low pressure belt. These are weak winds blowing from North East direction in the Northern Hemisphere and South East direction in the Southern Hemisphere.

Fact

G.G.Coriolis The rotation of the Earth causes deflection of winds from their original path, called the "Coriolis effect". Winds are deflected to the right in the northen hemisphere and to the left in the southern hemisphere which is known as "Ferrel's law". This was profounded by William Ferrel. He used "Coriolis force" named after G.G Coriolis (1792-1843) for proving Ferrel's Law.

Periodic winds

The periodic winds are the seasonal winds that change their direction periodically. These winds are caused by the differential heating of land and ocean. Winds which reverse their direction with the change of seasons are called monsoons. Tropical Monsoon winds of Indian subcontinent is a best example.

Variable wind

Cyclones

The term cyclone is a Greek word meaning "coil of a snake". Cyclones are centres of low pressure where, winds from the surrounding high pressure area converge towards the centre in a spiral form. Due to the rotation of the earth, the cyclonic winds in the northern hemisphere move in anti clock wise direction, where as they move in clockwise direction in the southern hemisphere.

Cyclones can be classified into

• Tropical cyclones
• Temperate cyclones
• Extra tropical cyclones

Tropical cyclones:

Tropical cyclones are known as 'cyclones' in Indian ocean, 'typhoons' in the western pacific ocean, 'hurricanes' in the Atlantic and eastern Pacific ocean, 'baguios' in Phillipines and 'willy willy' in Australia, Taifu in japan. Tropical cyclones often cause heavy loss of life and property on the coasts and become weak after reaching the landmasses.

Fact

Super Cyclone A violent cyclone that hit Odisha, on Friday, 29 October 1999, was one of the most devastating and strongest storm to hit the Indian coast. Winds of up to 260 kph raged for over 36 hours. The winds caused a seven-metre tidal wave that swept more than 20 km inland and brought massive destruction and death to a number of coastal districts in the state of Odisha. It is estimated that more than 10 million people in 12 coastal belt districts were affected by the cyclone. More than 10,000 people lost their lives.

Do you know?

Deliberations for naming cyclones in the Indian ocean region began in 2000 and a formula was agreed upon in 2004. Eight countries in the region Bangladesh, India, Maldives, Myanmar, Oman, Pakistan, Srilanka, and Thailand contributed a set of names which our assigned sequentially whenever a cyclonic storm develops.

Temperate cyclones:

Temperate cyclones are formed along a front where hot and cold air masses meet in mid-latitudes between 35 degree and 65 degree North and South . Temperate cyclones do not become weak like the tropical cyclones on reaching the land. Temperate cyclone commonly occurs over the North Atlantic Ocean, North West Europe, Mediterranean basin. Mediterranean basin's temperate cyclones extend up to Russia and India in winter. In India it is as called western disturbances.

A front is the boundary separating warm and cold air masses. One type of airmass is usually denser than the other, with different temperatures and humidity. This meeting of airmass causes rain, snowfall, hail storm, thunder storm, lightining cold days, hot days, and windy days.

Extra tropical cyclones:

Extra tropical cyclones occur in the latitudes between 30° and 60° in both the hemispheres. They are also called as mid-latitude cyclones. They collect energy from temperature differences which are found in higher latitudes. Extra tropical cyclones produce mild showers to heavy gales, thunderstorms, blizzards, and tornadoes.

Hots

Cuddalore and Nagapattinam are always affected by cyclones. Why?

Anticyclones:

Anticyclones are the opposite of cyclones. Here an area of high pressure region is found in the centre surrounded by low pressure on all sides. The wind from the high pressure region move outwards to the low pressure regions in a spiral form. Anticyclones are often accompanied by cold and heat waves.

Local Winds:

Local winds are the winds that blow only in a particular locality for a short period of time, The effect of these local winds are experienced only in that particular area. Such as land and sea breeze, mountain and valley breeze. They are mostly seasonal and have local names like....

• Foehn (Alps-Europe)
• Sirocco (North coast of Africa)
• Chinook (Rockies-North America)
• Loo (Thar Desert- India)
• Mistral (Mediterranean sea in France)
• Bora (Mediterranean sea in Italy)

3.5 Clouds

According to their height, clouds are classified into the following types

• High clouds (6 to 20 kilometer Height)
• Middle clouds (2.5kilometer to 6kilometer Height)
• Low clouds (ground surface to 25 kilometer height)

These major types of clouds are further divided into different types on the basis of shape and structure.

High clouds

Cirrus: Detached clouds in the form of white delicate fibrous silky filaments formed at the high sky (8000 meters to 12000 meters) are called Cirrus clouds. These clouds have Ice crystals and are dry and do not give rainfall.

Cirro-cumulus: White patched, sheet or layer like clouds composed of ice crystals.

Cirro-stratus: Smooth milky transparent whitish clouds composed of tiny ice crystals.

Do you know?

During sunset cirrus clouds look colourful hence they are called as "Mare's Tails".

Middle clouds

Alto-stratus: Thin sheets of grey or blue coloured clouds in uniform appearance. consisting of frozen water droplets

Alto-cumulus: clouds fitted closely together in parallel bands, called as 'Sheep clouds' or wool pack clouds.

Nimbo stratus: These are clouds of dark colour very close to the ground surface associated with rain, snow or sleet.

Do you know?

The only sphere which contains all clouds in the atmosphere is troposphere

Low clouds

Strato-cumulus:- Grey or whitish layer of non-fibrous low clouds found in rounded patches at an height of 2500 to 3000 metres, associated with fair or clear weather

Stratus:- Dense, low lying fog-like clouds associated with rain or snow

Cumulus:- Dome-shaped with a flat base often resembling a cauliflower, associated with fair weather

Cumulo-nimbus:- Fluffy thick towering thunderstorm cloud capable of producing heavy rain, snow, hailstorm or tornadoes

Precipitation

Falling down of condensed water vapour in different forms is called Precipitation. When the dew point is reached in the cloud water droplets become saturated and start to fall. Hence, they fall on the earth as Precipitation. The climatic conditions/ factors influencing the forms of precipitation mainly are: Temperature. Altitude Cloud type. Atmospheric conditions. Precipitation process. The main forms of precipitation include drizzle, rain, sleet, snow, hail etc.

Drizzle

Falling of numerous uniform minute droplets of water with diameter of less than 0.5 mm is called drizzle from low clouds. Sometimes drizzles are combined with fog and hence reduce visibility.

Rain

Rain is the most widespread and important form of precipitation in places having temperature above the freezing point. It occurs only when there is abundant moisture in the air. The diameter of a rain drop is more than 5mm.

Sleet

Sleet refers to a precipitation, in the form of pellets made up of transparent and translucent ice. This precipitation is a mixture of snow and rain

Snow

Snow is formed when condensation occurs below freezing point. It is the precipitation of opaque and semi opaque ice crystals. When these ice crystals collide and stick together, it becomes snowflakes.

Hails

Hails are chunks of ice (greater than 2cm in diameter) falling from the sky, during a rainstorm or thunderstorm. Hailstones are a form of solid precipitation where small pieces of ice fall downwards. These are destructive and dreaded forms of solid precipitation because they destroy agricultural crops and human lives.

Fact

Any thunderstorm which is associated with fall of hail stones is known as hailstorm. Hailstorm is one of the most feared weather phenomenon because it has the potential to destroy plant, trees, crops, animals and human life.

3.6 Rainfall

Rainfall is the most predominant type of Precipitation. Moisture laden air masses raise upwards, forms clouds and bring rainfall. Based on the mechanisms of raising the air, there are three types of rainfall.

1. Convectional rainfall
2. Frontal or cyclonic rainfall
3. Orographic rainfall.

1. Convectional rainfall (or) 4'o' Clock rainfall

Earth surface is intensely heated through solar radiation during the day time. When the air near the earth surface is heated, it rises and expands. This heating results is the formation of convectional air currents. Thus the ascending moist air cools, condenses and results in convectional rainfall. Convectional rainfall occurs regularly in the equatorial region in the evenings. It is also experienced in tropical, sub-tropical and temperate regions in the summer months and on warmer days.

2. Cyclonic rainfall (or) Frontal

Cyclonic precipitation occurs during cyclones when air masses are made to converge and move upward so that adiabatic cooling occurs. Cyclonic rainfall occurs in tropical as well as temperate regions. When warm and cold air masses converge, condensation and precipitation takes place on the boundary between warm and cold air masses called as Frontal rainfall.

3. Orographic rainfall (or) Relief rainfall

Orographic rainfall, also called relief rainfall, is caused when air is forced to rise against a high mountain. The mountain barriers lying across the direction of air flow, forces the moisture laden air to rise along the mountain slope. This results in the cooling of the air, which leads to the formation of clouds and rain. This rainfall is called Orographic rainfall. The side of the mountain facing the wind is called the windward side and receives heavy rainfall. It is called the rainfed region. The other side of the mountain that does not face the wind is called the leeward side and receives less rainfall becomes rain shadow region.

Do you know?

Mawsynram is the wettest place of India as it is located in the windward side of the Purvachal hills, whereas Shillong lies on the leeward side and thus receives less rainfall. This is the same, in the case of Mumbai and Pune.

3.7 Humidity

Humidity is an important aspect of the atmosphere because it affects both weather and climate. The amount of water vapour present in the atmosphere is referred to as humidity. Humidity of the atmosphere is high when it has large quantities of water vapour. The amount of water vapour in the atmosphere is called absolute humidity.

Do you know?

When the relative humidity of the air is 100 percent , the air is said to be saturated. Saturated air will not absorb any more water vapour. The temperature at which air gets saturated is called dew point. Humidity of the atmosphere is measured by the wet and dry bulb thermometer also called the Hygrometer Absolute humidity is expressed in terms of grams of water vapour present per cubic metre of air. Relative humidity is expressed in percentage.

Recap

• Atmosphere is a thin layer of gases that surrounds the earth.
• The major gases in the atmosphere are Nitrogen (78 percent ) and oxygen (21 percent )
• Five Layers of the atmosphere are Troposphere, stratosphere, mesosphere, thermosphere and exosphere
• Atmosphere gets heated through conduction.
• Wind is the horizontal movement of air
• Wind blows from high pressure belt to low pressure belt.
• The 4 types of winds are permanent (planetary), periodic, local and variable winds.
• Cyclone is an area of low pressure surrounded by high pressure
• Anticyclone is an area of high pressure area surrounded by low pressure.
• Clouds: A visible mass of Condensed water vapour floating in the air
• All precipitation occurs from clouds
• According to height clouds are classified into High clouds, Middle clouds and low-clouds
• The main forms of precipitation are drizzle, rain, snow, sleet, hail etcetera.

EXERCISE

Exercise 1. Choose The Best Answers

1. is the most important gas for the survival of living organisms.

a. Helium b. carbon-di-oxide c. oxygen d. methane

2. The lowest layer of the atmosphere is

a. Troposphere b. Stratosphere c. Exosphere d. Mesosphere

3. reflects radio waves.

a. Exosphere b. Ionosphere c. Mesosphere d. Stratosphere

4. The process of change of state of water from gaseous to liquid state is called

a. Precipitation b. evaporation c. transpiration d. condensation.

5. The is the chief energy source of the Earth.

a. Sun b. Moon c. Stars d. Clouds.

6. All types of clouds are found in the

a. Troposphere b. Ionosphere c. Mesosphere d. Exosphere

7. clouds are called 'Sheep clouds'

a. Alto-cumulus b. Alto-Stratus c. Nimbo - stratus d. Cirro-stratus.

8. The Monsoons are

a. Prevailing winds b. Periodic winds c. local winds d. none of the above.

9. Dew in the form of ice crystals is called

a. frost b. fog c. mist d. sleet.

10. is called the eye of the storm/ cyclone.

a. Pressure b. wind c. cyclones d. snow.

11. The vertical movement of air is called

a. Wind b. storm c. Air current d. drift. Exercise (2). Match the following

1. Meteorology	— wind speed
2. Climatology	— direction of wind
3. Anemometer	— cirrus
4. Wind Vane	— study of climate
5. Mare's Tail	— study of weather
6. Leeward side	— Australia
7. Willy willy	— rain shadow region

Exercise (3). Answer the following Briefly

1. Define atmosphere

2. Mention the factors that affect the climate?

3. Write short note on Lapse rate.

4. What are the processes responsible for heating the atmosphere?

5. Mention the Planetary wind system of the earth.

6. Write short note on: a. Trade winds. b. Roaring Forties

7. How are clouds formed?

8. What are the different types of rainfall?

9. Write short notes on: a. drizzle b. rain c. sleet d. snow e. heat

10. How are Cyclones Classified?

Exercise (4). Give reason

1. Cyclones cause huge loss of life and property.

2. Cloudy days are warmer than cloudless days.

3. Fog is dangerous for traffic.

4. Convectional rainfall is also called 4'0 clock rain.

5. Polar Easterlies are cold and dry. Why it is so?

Exercise (5). Distinguish between the following

1. Weather and climate

2. Land breeze and sea breeze

3. Windward side and Leeward side.

4. Tropical cyclone and Temperate cyclones.

Exercise (6). Paragraph Questions

1. Write a paragraph about the structure of the atmosphere.

2. Explain the different types of Permanent winds.

3. How are clouds classified? Explain them.

4. How are cyclones formed? How are they classified?

5. Explain the different forms of precipitation

Exercise (7). Activity

1. Preparing chart of clouds at various atmospheric layers.
2. Collecting Proverbs clouds and rain related Proverbs
3. Poem on 'clouds', 'rain'
4. Report writing observe the clouds for a week. Write your report about the shape and colours ofclouds.
5. Working models a) Rain Gauge b) Wind vane
6. Preparing bar diagram Collect the data of temperature of Kanyakumari, Delhi, Allahabad, and Itanagar for a day.Also collect the data of rainfall received by Jaisalmer (Rajasthan), Mawsynram (Meghalaya), Nagapattinam, Coimbatore for a day.
7. Become a budding Meterologist: Record the local weather condition of your place for a week.

ICT Corner

Melting point

Steps

1. Use the URL to download the 'Glaciers' flash file.
2. Select the 'Glacier type' from bottom and change them using arrows to see the different land forms affected by it.
3. Select 'Anatomy of Glaciers' from top of the page and animate the activity to observe the glacier formation.
4. Select 'Glacier Erosion' and press 'Move Glacier' button to observe erosion made by glaciers.

Website URL: https://ees.as.uky.edu/sites/default/files/elearning/module13swf.swf

Unit 4 Hydrosphere

Learning Objectives

• To understand the importance of water
• To learn about fresh water
• To know about the relief features of the ocean floor
• To study about the movements of ocean water
• To learn about marine resources and the need for conservation

Introduction

We know that, our planet Earth consists of four spheres. They are the Lithosphere, Atmosphere, Hydrosphere and Biosphere. In the earlier chapters, we have studied about the Lithosphere and Atmosphere. We shall now learn the other two spheres namely the Hydrosphere and the Biosphere.

Book-back Exercises — Questions & Answers

Answers generated strictly from the Samacheer Kalvi textbook content. Attempt each question first, then click "Show Answer" to check.

1. Choose The Best Answers

1. _____ is the most important gas for the survival of living organisms.

a) Helium b) carbon-di-oxide c) oxygen d) methane

Answer: c) oxygen

Explanation: Oxygen is most important for living organisms.

2. The lowest layer of the atmosphere is _____.

a) Troposphere b) Stratosphere c) Exosphere d) Mesosphere

Answer: a) Troposphere

Explanation: The lowest layer of the atmosphere is the troposphere.

3. _____ reflects radio waves.

a) Exosphere b) Ionosphere c) Mesosphere d) Stratosphere

Answer: b) Ionosphere

Explanation: Radio waves transmitted from earth are reflected back to earth from the Ionosphere layer.

4. The process of change of state of water from gaseous to liquid state is called _____.

a) Precipitation b) evaporation c) transpiration d) condensation

Answer: d) condensation

Explanation: When the dew point is reached in the cloud, water droplets become saturated through condensation.

5. The _____ is the chief energy source of the Earth.

a) Sun b) Moon c) Stars d) Clouds

Answer: a) Sun

Explanation: Earth surface is intensely heated through solar radiation during the day time.

6. All types of clouds are found in the _____.

a) Troposphere b) Ionosphere c) Mesosphere d) Exosphere

Answer: a) Troposphere

Explanation: The only sphere which contains all clouds in the atmosphere is troposphere.

7. _____ clouds are called 'Sheep clouds'.

a) Alto-cumulus b) Alto-Stratus c) Nimbo-stratus d) Cirro-stratus

Answer: a) Alto-cumulus

Explanation: Alto-cumulus clouds fitted closely together in parallel bands are called 'Sheep clouds' or wool pack clouds.

8. The Monsoons are _____.

a) Prevailing winds b) Periodic winds c) local winds d) none of the above

Answer: b) Periodic winds

Explanation: Winds which reverse their direction with the change of seasons are called monsoons. The periodic winds are the seasonal winds that change their direction periodically.

9. Dew in the form of ice crystals is called _____.

a) frost b) fog c) mist d) sleet

Answer: a) frost

Explanation: Refer to the chapter text for this answer.

10. _____ is called the eye of the storm/cyclone.

a) Pressure b) wind c) cyclones d) snow

Answer: Refer to the chapter text for this answer.

11. The vertical movement of air is called _____.

a) Wind b) storm c) Air current d) drift

Answer: c) Air current

Explanation: The horizontal movement of air along the surface of the earth is called the "Wind" while the vertical movement of air is a called an "Air Current".

2. Match the following

2. Match the Following

1. Meteorology	— wind speed
2. Climatology	— direction of wind
3. Anemometer	— cirrus
4. Wind Vane	— study of climate
5. Mare's Tail	— study of weather
6. Leeward side	— Australia
7. Willy willy	— rain shadow region

Answers: 1-study of weather, 2-study of climate, 3-wind speed, 4-direction of wind, 5-cirrus, 6-rain shadow region, 7-Australia

3. Answer the following Briefly

1. Define atmosphere

Answer: The blanket of air that surrounds the Earth is called the atmosphere. It is held close to the earth by gravitational attraction.

2. Mention the factors that affect the climate?

Answer: The factors that influence weather and climate are distance from the equator, altitude, nearness to the sea, nature of the prevailing winds, mountain barrier, cloud cover, ocean currents, and natural vegetation.

3. Write short note on Lapse rate.

Answer: The temperature decreases at the rate of 6.5°C per kilometer of height. This is called Normal lapse rate. So, places at the higher altitude have a lower temperature.

4. What are the processes responsible for heating the atmosphere?

Answer: Refer to the chapter text for this answer.

5. Mention the Planetary wind system of the earth.

Answer: The planetary winds include Trade winds, Westerlies and Polar Easterlies. These are the permanent winds that blow throughout the year in the same direction.

6. Write short note on: a. Trade winds. b. Roaring Forties

Answer: a. Trade winds blow from the subtropical high pressure belt to the Equatorial low pressure belt in both hemispheres. They blow with great regularity, force and constant direction throughout the year. b. The velocity of westerlies become so vigorous and fast to be called Roaring Forties at 40 degree latitude.

7. How are clouds formed?

Answer: When moisture laden air masses raise upwards, they cool down and condense to form clouds. Water vapour condenses on dust particles, salt particles, pollen grains and other solid particles present in the atmosphere.

8. What are the different types of rainfall?

Answer: Based on the mechanisms of raising the air, there are three types of rainfall: Convectional rainfall, Frontal or cyclonic rainfall, and Orographic rainfall.

9. Write short notes on: a. drizzle b. rain c. sleet d. snow e. hail

Answer: a. Drizzle: Falling of numerous uniform minute droplets of water with diameter of less than 0.5 mm. b. Rain: Most widespread precipitation with raindrops having diameter more than 5mm. c. Sleet: Precipitation in the form of pellets made up of transparent and translucent ice. d. Snow: Precipitation of opaque and semi opaque ice crystals formed below freezing point. e. Hail: Chunks of ice greater than 2cm in diameter falling during thunderstorms.

10. How are Cyclones Classified?

Answer: Cyclones can be classified into Tropical cyclones, Temperate cyclones and Extra tropical cyclones based on their characteristics and formation.

4. Give reason

1. Cyclones cause huge loss of life and property.

Answer: Tropical cyclones often cause heavy loss of life and property on the coasts. They bring strong winds, tidal waves and massive destruction as seen in the Super Cyclone that hit Odisha in 1999.

2. Cloudy days are warmer than cloudless days.

Answer: Clouds reflect a large amount of radiation from the sun. In areas of cloudless sky like deserts, temperature is very high, while under cloudy sky, the temperature is low.

3. Fog is dangerous for traffic.

Answer: Sometimes drizzles are combined with fog and hence reduce visibility, making it dangerous for traffic.

4. Convectional rainfall is also called 4'0 clock rain.

Answer: Convectional rainfall occurs regularly in the equatorial region in the evenings. It is also experienced in tropical, sub-tropical and temperate regions in the summer months and on warmer days.

5. Polar Easterlies are cold and dry. Why it is so?

Answer: Polar easterlies are cold and dry polar winds that blow from the polar high pressure belt to the sub polar low pressure belt. They originate from the polar regions which are cold.

5. Distinguish between the following

1. Weather and climate

Answer: Weather denotes the way the atmosphere behaves every day while climate reveals the average of weather conditions over relatively long periods of time. Weather changes very often but climate is more or less permanent.

2. Land breeze and sea breeze

Answer: Sea breeze blows from ocean to land in the afternoon when land heats more rapidly than oceans. Land breeze blows from land to sea during night when land cools more rapidly than ocean.

3. Windward side and Leeward side.

Answer: The windward is the side of a mountain which faces the prevailing wind and receives heavy rainfall. The leeward side of the mountain is sheltered from wind and receives very less rainfall.

4. Tropical cyclone and Temperate cyclones.

Answer: Tropical cyclones become weak after reaching landmasses and cause heavy loss on coasts. Temperate cyclones are formed where hot and cold air masses meet in mid-latitudes and do not become weak like tropical cyclones on reaching land.

6. Paragraph Questions

1. Write a paragraph about the structure of the atmosphere.

Answer: The atmosphere is thick near the earth surface and thins out until it merges with space. The five atmospheric layers are Troposphere, Stratosphere, Mesosphere, Thermosphere and Exosphere. Troposphere is the lowest layer where all weather phenomena occur. Stratosphere contains ozone and extends to 50km. Mesosphere extends between 50-80km where meteors burn up. Thermosphere extends to 400km and contains the Ionosphere. Exosphere is the uppermost layer that merges with outer space.

2. Explain the different types of Permanent winds.

Answer: The three types of permanent winds are Trade winds, Westerlies and Polar Easterlies. Trade winds blow from subtropical high pressure to equatorial low pressure belt with great regularity. Westerlies blow from tropical high pressure to subpolar low pressure belt and become vigorous at 40°, 50° and 60° latitudes. Polar Easterlies are cold dry winds blowing from polar high pressure to subpolar low pressure belt. These winds constantly blow in the same direction throughout the year.

3. How are clouds classified? Explain them.

Answer: According to height, clouds are classified into High clouds (6-20km), Middle clouds (2.5-6km) and Low clouds (ground to 2.5km). High clouds include Cirrus, Cirro-cumulus and Cirro-stratus made of ice crystals. Middle clouds include Alto-stratus and Alto-cumulus with frozen water droplets. Low clouds include Strato-cumulus, Stratus, Cumulus and Cumulo-nimbus associated with various weather conditions. Each type has distinct characteristics based on shape, structure and composition.

4. How are cyclones formed? How are they classified?

Answer: Cyclones are centres of low pressure where winds from surrounding high pressure areas converge towards the centre in spiral form. Due to earth's rotation, cyclonic winds move anti-clockwise in northern hemisphere and clockwise in southern hemisphere. Cyclones are classified into Tropical cyclones, Temperate cyclones and Extra tropical cyclones. Tropical cyclones form over warm oceans and become weak on land. Temperate cyclones form where hot and cold air masses meet. Extra tropical cyclones occur between 30°-60° latitudes in both hemispheres.

5. Explain the different forms of precipitation

Answer: Precipitation is falling down of condensed water vapour in different forms. The main forms include drizzle (minute droplets less than 0.5mm diameter), rain (widespread form with droplets over 5mm), sleet (mixture of snow and rain as ice pellets), snow (opaque ice crystals formed below freezing point), and hail (chunks of ice greater than 2cm diameter). The form of precipitation depends on temperature, altitude, cloud type and atmospheric conditions. These different forms occur based on the climatic conditions during condensation and falling process.

📝 Summary

1. The atmosphere is a mixture of gases where Nitrogen (78 percent) and Oxygen (21 percent) are permanent gases constituting 99 percent of the total composition, with the remaining one percentage occupied by Argon (0.93 percent), Carbon dioxide (0.03 percent), and other trace gases.
2. The atmosphere consists of five distinct layers: Troposphere (lowest layer extending 8-18 kilometers), Stratosphere (up to 50km with ozone concentration), Mesosphere (50-80km where meteors burn), Thermosphere (up to 400km), and Exosphere (uppermost layer).
3. The troposphere is called the weather making layer because almost all weather phenomena take place in this layer, with temperature decreasing as height increases.
4. The stratosphere is also called ozonosphere due to its concentration of ozone molecules, which helps protect Earth from harmful ultraviolet radiation, and temperature increases with height in this layer.
5. The ionosphere, located in the thermosphere, contains ions and free electrons that reflect radio waves transmitted from Earth back to the surface, enabling long-distance radio communication.