GEOGRAPHY (VII)-LESSON-4 AIR (LESSON NOTES)

GEOGRAPHY(VII)-LESSON-4

AIR

(LESSON NOTES)

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v ATMOSPHERE

Ø A huge blanket of air that surrounds the earth is called as atmosphere. It is very important for human beings because-

§  It provides us the air we breathe and

§  It protects us from the harmful effects of the ultraviolet sun’s rays.

§  This mass of air also made the temperature of the earth live able. Without atmosphere the Earth’s temperature is very high or very low.

v COMPOSITION OF THE ATMOSPHERE

Ø In the atmosphere there are many gases and tiny dust particles. Heavy gases are near to the Earth while light gases are in higher areas. The most important gases in the atmosphere are-

§  Nitrogen (78%)

§  Oxygen(20.9%)

§  Argon (0.93%)

§  Carbon dioxide (0.003%)

§  Other gases-Helium, ozone, and hydrogen are found in lesser quantities.

 

v IMPORTANCE OF GASES

Ø Nitrogen- It is very important for plants. Their survival depends on this gas. They take this gas with the help of bacteria.

Ø Oxygen-It is very essential for humans and animals. They breathe in oxygen which is produced by green plants during photosynthesis.

Ø Carbon dioxide- Green plants take in carbon dioxide which is released by humans and animals. Thus, there is a mutual relation between the plants and the humans or animals. Hence, we should protect plants and trees for our own benefit.

 

v STRUCTURE OF THE ATMOSPHERE

Ø Our atmosphere is divided into five layers starting from the earth’s surface.

Ø TROPOSPHERE-

§  The first layer is the Troposphere which average height is 13 km.

§  The troposphere is the layer in which the air we breathe exist.

§  All weather phenomena like rainfall, hailstorm etc occurs here.

Ø STRATOSPHERE-

§  The second layer is the Stratosphere which extends up to 50 km.

§  It provides the ideal condition for flying aeroplanes as it is free from weather phenomena.

§  It also contains a layer of ozone gas which protect us from harmful sunrays.

Ø MESOSPHERE

§  The third layer is the Mesosphere which extends up to the height of 80 km.

§  Meteorites burn up in this layer on entering from the space.

Ø THERMOSPHERE

§  The fourth layer is the Thermosphere which extends from 80 km to 400 km.

§  Ionosphere is also the part of this layer.

§  It helps in radio transmission as radio waves transmitted from the earth are reflected back to the earth by this layer.

Ø EXOSPHERE

§  The uppermost layer of the atmosphere is Exosphere which has very thin air like helium and hydrogen.

§  It mixes up with space.

v WEATHER AND CLIMATE

Ø WEATHER—Day to day or Hour-to-hour changes in the atmospheric condition is known as weather. For example-sunny day, cold day, warm day, or windy day etc.

Ø CLIMATE- The average weather conditions of a particular area for a long period of time is called as climate. For example extreme climate, moderate climate etc.

v TEMPERATURE

Ø The degree of hotness and coldness of the air is called temperature. It is measure by thermometer in degree(º) Celsius or Fahrenheit. On the Celsius scale water boiled at 100 º c and freeze at 0 ºc.

Ø The temperature of the atmosphere changes not only between day and night but also from season to season. The distribution of temperature on the Earth is depends on the insolation.

§  Insolation is the incoming solar energy intercepted by the earth.

§  The amount of insolation decreases from the equator towards the poles.

Ø Temperature in cities is much higher than that of villages because concrete and metals in buildings and the asphalts of roads observe the heat during day and release in night. High buildings also trap the warm air which increase the temperature.

v AIR PRESSURE

Ø The pressure exerted by the weight of air on the earth’s surface is called as air pressure. We can’t feel this pressure because the air presses us from all directions. There are some facts about air pressure as-

§  Vertically, it is decreases with height. So air pressure is highest at sea level.

§  Horizontally the air pressure is influenced by the temperature of the air at a given place.  As the temperature increase air become warm and it will rise up and create low pressure. Low pressure is associated with cloudy skies and wet weather.

 

§  Due to low temperature, the air become cold, this is heavy so it creates high pressure. High pressure is associated with clear and sunny skies.

Ø The air always moves from high-pressure areas to low-pressure areas.

Ø Barometre is used to measures the atmospheric pressure.

v WIND

Ø The movement of air from high-pressure areas to the low-pressure area is called Wind. The strong wind is called as storm. A super cyclone hit Odisha coast on 29 Oct 1999 which affected 13 million people. The name of wind decided according to direction from which side it blow.

Ø TYPES OF WIND -Winds can be broadly divided into three types-

§  Permanent winds- The wind which blows constantly throughout the year in a particular direction is called as permanent winds. For example- Trade winds, Westerlies and Easterlies

§  Seasonal wind- These winds change their direction in different seasons. For example monsoons in India.

§  Local winds- The wind which blows in a particular area in specific time period is called as local wind. For example- Loo in Rajasthan, Chinook in USA.

v MOISTURE

Ø Water vapour present in the atmosphere is known as moisture. Water vapours are formed due to the evaporation from water bodies.

Ø Moisture in the air at any time is known as humidity.

Ø As the water vapour rises up it starts cooling. The water vapour condenses causing the formation of droplets of water (CLOUDS).

Ø When these droplets of water become too heavy to float in the air, they come down as precipitation.

Ø Precipitation is the falling of moisture in the form of rainfall, snow, fog, sleet and hailstones.

v RAINFALL

Ø The falling of precipitation in the form of liquid is called as rainfall. On the basis of mechanism, there are three types of rainfall:

§  The convectional rainfall

§  The orographic or relief rainfall

§  The cyclonic rainfall.

 

Ø IMPORTANCE OF RAINFALL

§  Rainfall is very important for the survival of plants and animals.

§  It brings fresh water to the earth’s surface.

§  If rainfall is less – water scacity and drought occur.

v IMPORTANT POINTS

Ø Moisture: Water vapour present in the atmosphere is known as moisture.

Ø Moisture means humidity. A humid day is one when the air is the full of water vapour. On a humid day, clothes take longer to dry and sweat from our body does not evaporate easily.

Ø Global warming: When the temperature of the earth’s atmosphere increases due to the increases in carbon dioxide, it is known as global warming.

 

Ø Cloud: It is a mass of water droplets.

Ø Thermometer: It is an instrument that measures temperature.

Ø Barometer: It measures atmospheric pressure.

Ø Rain gauge: It measures the amount of rainfall.

Ø Wind vane: It shows the direction of the wind.