CHAPTER 3 Atmosphere and Climate Class 9th Understanding Society India and Beyond

 

CHAPTER 3

Atmosphere and Climate

Class 9

 

 

Question: Give definition of atmosphere

Answer: A blanket of air surrounding the Earth, called the atmosphere. It is pulled down around the Earth by gravity, and is a mixture of gases in various proportions.

 

Question: What is the importance of atmosphere?

Answer: We can understand the importance of atmosphere with help of facts given below.

     (i)            It is vital for the survival of all living beings on the Earth.

   (ii)            The atmosphere shields us from the harmful radiation coming from the Sun, including ultraviolet radiation.

 (iii)            It regulates the Earth’s temperature by trapping some of the Sun’s energy and prevents it from escaping back into space.

 (iv)            The atmosphere is a key component of the Earth’s weather and climate systems, influencing factors such as temperature, humidity, and air pressure.

 

Question: What do you mean by gravity?

Answer: Gravity is a fundamental physical force of attraction between objects that have mass or energy such as the Sun and the Earth.

Question: What do you mean by gravity of Earth?

Answer: The force of attraction that the Earth’s mass exerts on the objects that are on or close to its surface is referred to as gravity of Earth.

Question: Explain the Composition of the Atmosphere.

Answer: The Earth’s atmosphere is composed of a mixture of various gases.

Nitrogen (78%) and Oxygen (21%) are the two primary and most abundant gases that are essential to life on the Earth.

Carbon Dioxide (0.04%) Argon (0.93%) helium, neon, krypton, xenon, ozone, and hydrogen are some other gases present in the atmosphere, but are found in lesser quantities.

The atmosphere also consists of water vapour and tiny dust particles.

 

Question: Write a note on water vapour.

Answer: Water vapour is one of the important elements of atmosphere. The amount of water vapour in the atmosphere varies from place to place. It generally ranges from 0.1 per cent to 0.4 per cent. It plays a significant role in cloud formation and precipitation.

 

Question: Define Altitude.

Answer: The height of a location above mean sea level is called altitude, usually measured in metres or feet. The mean sea level is considered zero.

 

Question: Discuss the Structure of the Atmosphere.

Answer: The atmosphere has a layered structure.

These layers are defined on the basis of changes in temperature and density with increasing altitude.

The density of air is highest near the Earth’s surface and decreases with altitude.

The major layers extending from the Earth’s surface to outer space are Troposphere, Stratosphere Mesosphere Thermosphere and Exosphere. These are illustrated below.

 

Question: What are the main features of troposphere?

Answer: Main features of troposphere are given below.

     (i)            The troposphere is the most important layer of the atmosphere,

   (ii)            The average height of troposphere is about 12 kilometres.

 (iii)            In this layer, temperature decreases with increasing altitude.

 (iv)            The air we breathe exists here, along with most of the water vapour and clouds.

   (v)            Nearly all the weather phenomena, such as rainfall, fog, and hail, occur in this layer.

 (vi)            Temperature decreases with altitude only in the troposphere and mesosphere.

(vii)            The troposphere is separated from the stratosphere by a transition zone known as the tropopause.

 

Question: What are the main features of Stratosphere?

Answer: Main features of stratosphere are given below.

     (i)            The stratosphere lies above the troposphere

   (ii)            This layer extending up to 50 kilometres.

 (iii)            This layer is ideal for flying aeroplanes because it is free of clouds and other weather disturbances.

 (iv)            A notable feature of the stratosphere is that it contains a layer of ozone gas, which shields us by filtering the Sun’s harmful radiation, including ultraviolet radiation.

   (v)            The stratopause marks the boundary between the stratosphere and the mesosphere.

 

Question: What are the main features of Mesosphere?

Answer: Main features of Mesosphere are given below.

     (i)            Above the stratosphere lies the third layer of the atmosphere, the mesosphere.

   (ii)            It extends up to a height of 80 kilometres.

 (iii)            In this layer, temperature decreases with increasing altitude.

 (iv)            Most meteorites entering from space burn up in the mesosphere.

 

Question: What are the main features of Thermosphere?

Answer: Main features of Thermosphere are given below.

 In the thermosphere, temperature rises very rapidly with increasing altitude, as the gas molecules in this layer absorb the X-rays and short-wave ultraviolet radiation of the Sun.

     (i)            The thermosphere extends from 80 to 700 km.

   (ii)            It also helps with radio transmission by reflecting radio waves transmitted from the Earth back towards it.

 (iii)            Ionosphere is a part of the thermosphere.

 (iv)            Additionally, the northern and southern lights (auroras) also occur in the thermosphere.

 

Question: What are the main features of Exosphere?

Answer: Main features of Exosphere are given below.

     (i)            The uppermost layer of the atmosphere is known as the exosphere.

   (ii)            It characterised by very thin air.

 (iii)            Light gases like helium and hydrogen float into space from this layer due to weak gravity.

 

Question: Explain‘Aurora Borealis and Aurora Australis ? 

Answer: The word ‘aurora’ originates from Latin, meaning ‘dawn’ or ‘morning light.’  It is named after the Roman goddess Aurora, the goddess of dawn.

‘Aurora’ is refers to the colourful display of light seen in the sky near the poles.  The ‘solar wind’ is charged particles emitted by the Sun. Upon reaching the Earth’s atmosphere ‘solar wind’ is directed towards the magnetic poles. As these particles interact with different atmospheric gases, each gas glows with a particular colour. This phenomenon is known as the Aurora Borealis in the Northern Hemisphere and the Aurora Australis in the Southern Hemisphere.

 

Question: The air above us exerts a significant force on our bodies, and yet we do not feel it. Why?

Answer: The air above us exerts a significant force on our bodies, and yet we do not feel it. This is because air presses on us from all sides, and our bodies exert a counter-pressure in response. The pressure inside our bodies is also equal to the atmospheric pressure and cancels the pressure from outside.

 

Question: Differentiate between Weather and Climate

Answer: difference between weather and climate is given below.

Weather  

The term weather refers to the hour-to-hour and day-to-day conditions of the atmosphere.

Weather can vary significantly from day-to-day.

Climate  

The average weather conditions of a place over a longer period of time refer to the climate of the place. Climate refers to the sum total of weather conditions and variations over a large area for an extended period of time, usually thirty years or more.

 

Question: Which type of weather is irritable and which type of weather may make one cheerful?

Answer: Hot or humid weather may make one irritable, Pleasant or breezy weather may make one cheerful..

 

Question: What are the elements of Weather and Climate

Answer: Various elements influence weather and climate. These are temperature, precipitation, humidity, wind, and atmospheric pressure. These elements can change under varying conditions.

 

Question: Why Insolation is an important factor affecting temperature distribution?

Answer: Insolation is an important factor affecting temperature distribution. The amount of insolation decreases from the equator towards the poles. Hence, the temperature decreases from the equator towards the poles.

 

Question: Define Insolation.

Answer: The incoming solar energy from the Sun that is intercepted by the Earth.

 

Question: Define humidity?

Answer: Humidity refers to the presence of water vapour in the air, creating moisture. When water evaporates from land and different water bodies, it becomes water vapour. When the levels of water vapour in the air are high, it leads to humidity.

 

Question: When air gets warmer what happens to humidity level? What are the results of higher humidity levels?  

Answer: As the air gets warmer, its capacity to hold water vapour increases. This process leading to higher humidity levels in air.

Effects (results) of higher humidity level in air

     (i)            Clothes take longer to dry.

   (ii)            Sweat evaporates more slowly.

 (iii)            We feel very uncomfortable.

Question: What is precipitation?

Answer: Precipitation occurs when a part of the atmosphere becomes saturated with water vapour, which condenses and ‘precipitates’, or falls on the Earth due to gravity.

Question: Write about the types of precipitation?

Answer: Precipitation has many types such as drizzle, rain, snowfall, sleet and hail.

Question: What are the main factors that affect precipitation?

Answer: The main factors that affect precipitation in are given below.

(1) prevailing winds, (2) mountains, and (3) seasons.

Question: Write a note on rain?

Answer: When precipitation falls on the the Earth in liquid form, it is called rain.

Rain is the most common form of precipitation

It lowers the temperature of a place.

A long absence of rainfall results in a dry climate.

Most of the groundwater is collected from rainwater.

 

Question: Define Atmospheric pressure. Write main characteristics of Atmospheric pressure.

Answer:

Definition of Atmospheric pressure

The pressure exerted by the weight of air on the Earth’s surface is called air pressure.

Characteristics of Atmospheric pressure

     (i)            As we go higher in the atmosphere, pressure falls rapidly.

   (ii)            It is highest at sea level and decreases with altitude.

 (iii)            Horizontally, the distribution of air pressure is influenced by the air’s temperature at a given place.

 

Question: Differentiate between low air pressure area and high air pressure area.

Answer:

Low-pressure area

In areas with high temperatures, air heats up and rises. This creates a low-pressure area.

Low pressure is associated with cloudy skies and wet weather.

High-pressure area

In areas with lower temperatures, air is cold. It is therefore heavy and sinks, creating a high-pressure area.

High pressure is associated with clear and sunny skies.

 

Question: Define wind.

Answer: Air always moves from high-pressure areas to low-pressure areas. The movement of air from a high-pressure area to a low-pressure area is called wind. It can be gentle or strong.

 

Question: What is the cause of wind? By which the direction of wind is influenced? How can we get names of winds?

Answer: Wind is caused by air flowing from high-pressure to low-pressure areas.

Its direction is influenced by the Earth’s rotation.

Winds are named after the direction they blow from, for example, the wind blowing from the west is called westerly.

ind Speed (km/hr) Common Effects

Question: Create a table to explain wind speeds and their common effects.

 

Answer:

Wind speeds and their common effects

WIND	SPEED IN KM/HOURS	COM COMMON EFFECTS
Calm	0–1	Calm, smoke rises vertically.
Light breeze	6–11	Wind can be felt on the face. Leaves rustle. An ordinary vane moves by winds.
Strong breeze	39–49	Large branches sway in the wind. Umbrellas are difficult to use.
Storm	103–117	It is very rarely experienced. Usually accompanied by widespread damage.

 

Question: Can local winds also affect the weather and climate of a place? Explain with example.

Answer: Yes, local winds also affect the weather and climate of a place. For example, the land breeze and the sea breeze affect the weather and climate of coastal region. They are essential in creating moderate climatic conditions in the coastal region.

 

Question: Discussed sea breeze and land breeze.

OR

Question: Differentiate between sea breeze and land breeze.

Answer: Sea breeze and land breeze are a type of local winds. Different between sea breeze and land breeze are given below.

Sea breeze

It is a local wind that blows from sea to land during the day, especially in the afternoon, when the land becomes relatively warmer than the sea. This results in the formation of a low-pressure region over land, and so the wind starts blowing from the sea.

Land breeze

It is a local wind that blows from land to sea during the night, resulting from differential surface cooling between the land and the sea. Land cools faster than sea at night. Since the difference in temperatures and air pressure between the sea and the land is low, the wind speed is low.

 

You may have observed that weather conditions often fluctuate, sometimes even within a single day. However, based on generalized monthly atmospheric conditions, or a common pattern over a few weeks or months—such as the days being cool or hot, windy or calm, cloudy or bright, and wet or dry—the year is divided into seasons.

 

 

Question: How many seasons has recognised by The Indian Meteorological Department (IMD) in India? Write their names and timing of seasons.

Answer: The Indian Meteorological Department (IMD) has recognised four distinct seasons in India:

     (i)            Winter: The winter season generally lasts from December to early April.

   (ii)            Summer or pre-monsoon: The summer or pre-monsoon season spans from April to June, or up to July in north-western India.

 (iii)            Monsoon or rainy (Advancing monsoon): The monsoon season generally spans from June to September.

 (iv)            Post-monsoon (Retreating monsoon): The post-monsoon season lasts from October to December.

 

Question: Write the characteristics of winter season in India.

Answer: Main characteristics of winter Season in India are given below.

     (i)            The winter season generally lasts from December to early April.

   (ii)            The coldest months of the year are December and January, when the average temperature in the north-west is around 10–15°C.

 (iii)            Temperatures increase towards the equator, reaching around 20–25°C in mainland India’s south-east.

 

Question: Write the characteristics of summer or pre-monsoon season in India.

Answer: Main characteristics of summer or pre-monsoon Season in India are given below.

     (i)            The summer or pre-monsoon season spans from April to June or up to July in north-western India.

   (ii)            In western and southern regions, the hottest month is April; in northern regions, it is May.

 (iii)            The average temperature across most of inland India ranges from 32–40°C.

 

Question: Write the characteristics of Monsoon or rainy season (Advancing monsoon)in India.

Answer: Main characteristics of Monsoon or rainy season (Advancing monsoon) in India are given below.

     (i)            The monsoon season generally spans from June to September.

   (ii)            This season is dominated by the humid south-west summer monsoon, which slowly sweeps across the country in late May or early June.

 (iii)            Monsoon rain begins to recede from north India at the beginning of October, and South India typically receives more rainfall during this time.

 

Question: Write the characteristics of Post-monsoon (Retreating monsoon season in India.

Answer: Main characteristics of Post-monsoon (Retreating monsoon season in India are given below.

     (i)            The post-monsoon season lasts from October to December.

   (ii)            In north-western India, October and November are usually cloudless.

 (iii)            The Himalayan states, being more temperate, experience two additional seasons, autumn and spring.

 

Question: How many traditionally seasons in India. Explain with a suitable table?

 

Answer: Traditionally, India experiences six seasons. Each season about two months long—spring, summer, monsoon, early autumn, late autumn, and winter. These seasons are based on the astronomical division of the 12 months into six parts. The traditional Indian calendar also reflects these seasons through its arrangement of months. These seasons and their duration may vary across different parts of the country. The table given below is showing the details of these six seasons.

Table Traditional Indian seasons

 

Seasons (Ritu)	Months according to Indian Calendar	Months according to Gregorian Calendar
Vasant	Chaitra –Vaishakha	March –April
Grishma	Jyeshtha – Ashadha	May- June
Varsha	Shravana- Bhadrapada	July –August
Sharad	Ashvina – Kartika	September –October
Hemanta	Margashirsha – Pausha	November –December
Shishira	Magha – Phalguna	January – February

 

Question: Which type of music associates with specific seasons?

Answer: Hindustani Classical music associates certain Ragas with specific seasons.

Question: What is the meaning of word ‘Monsoon’.

Answer: It refers to the seasonal reversal in the wind direction during a year.

The sailors who came to India during ancient times were among the first to notice the phenomenon of monsoon. They benefited from the reversal of the wind system as they travelled by sailing ships at the mercy of the winds. The Arabs, who had also come to India as traders, named this seasonal reversal of the wind system ‘monsoon’, derived from the Arabic word mausim, which literally means season.

Question: The climate of India is strongly influenced by which type of winds?

Answer: The climate of India is strongly influenced by monsoon winds.