Air



--> Our earth is surrounded by a huge blanket of air called atmosphere.

--> Carbon dioxide released in the atmosphere creates a green house effect by trapping the heat radiated from the earth. It is therefore called a greenhouse gas and without it the earth would have been too cold to live in. However, when its level in the atmosphere increases due to factory smoke or car fumes, the heat retained increases the temperature of the earth. This is called global warming.

--> When air is heated, it expands, becomes lighter and goes up. Cold air is denser and heavy. That is why it tends to sink down. When hot air rises, cold air from surrounding area rushes there to fill in the gap. That is how air circulation takes place.

--> Our atmosphere is divided into five layers starting from the earth’s surface. These are Troposphere, Stratosphere, Mesosphere, Thermosphere and Exosphere.

--> Troposphere: This layer is the most important layer of the atmosphere. Its average height is 13 km. The air we breathe exists here. Almost all the weather phenomena like rainfall, fog and hailstorm occur in this layer.

--> Stratosphere: Above the troposphere lies the stratosphere. It extends up to a height of 50 km. This layer is almost free from clouds and associated weather phenomenon, making conditions most ideal for flying aeroplanes. One important feature of stratosphere is that it contains a layer of ozone gas.

--> Mesosphere: This is the third layer of the atmosphere. It lies above the stratosphere. It extends up to the height of 80 km. Meteorites burn up in this layer on entering from the space.

--> i> Thermosphere: In thermosphere temperature rises very rapidly with increasing height. Ionosphere is a part of this layer. It extends between 80-400 km. This layer helps in radio transmission. In fact, radio waves transmitted from the earth are reflected back to the earth by this layer.

--> Exosphere: The upper most layer of the atmosphere is known as exosphere. This layer has very thin air. Light gases like helium and hydrogen float into the space from here.

--> You will be surprised to know that the earth receives only 1 in 2,000,000,000 parts of the sun’s energy.

--> The temperature you feel everyday is the temperataure of the atmosphere. The degree of hotness and coldness of the air is known as temperature.

--> Thermometer: Measures the temperature.

--> Barometre: Measures atmospheric pressure.

--> Rain Gauge: Measures the amount of rainfall.

--> Wind Vane: Shows the direction of the wind.

--> An important factor that influences the distribution of temperature is insolation. Insolation is the incoming solar energy intercepted by the earth.

--> The amount of insolation decreases from the equator towards the poles.Therefore, the temperature decreases in the same manner.

--> The standard unit of measuring temperature is degree Celsius. It was invented by Anders Celsius. On the Celsius scale the water freezes at 0°C and boils at 100°C.

--> As we go up the layers of atmosphere, the pressure falls rapidly. The air pressure is highest at sea level and decreases with height.

--> On the moon there is no air and hence no air pressure. Astronauts have to wear special protective space suits filled with air when they go to the moon. If they did not wear these space suits, the counter pressure exerted by the body of the astronauts would make the blood vessels burst. The astronauts would bleed.

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

--> The movement of air from high pressure area to low pressure areas is called wind.

--> A wind is named after the direction from which it blows, e.g. the wind blowing from the west is called westerly.

--> Winds can be broadly divided into three types. 1. Permanent winds – The trade winds, westerlies and easterlies are the permanent winds. These blow constantly throughout the year in a particular direction. 2. Seasonal winds – These winds change their direction in different seasons. For example monsoons in India. 3. Local winds – These blow only during a particular period of the day or year in a small area. For example, land and sea breeze.

--> Precipitation that comes down to the earth in liquid form is called rain.

--> there are three types of rainfall: the convectional rainfall, the orographic rainfall and the cyclonic rainfall.

--> Tick the correct answer.

(i) Which of the following gases protects us from harmful sun vays?
(a) Carbon dioxide
(b) Nitrogen
(c) Ozone

(ii) The most important layer of the atmosphere is
(a) Troposphere
(b) Thermosphere
(c) Mesosphere

(iii) Which of the following layers of the atmosphere is free from clouds?
(a) Troposphere
(b) Stratosphere
(c) Mesosphere

(iv) As we go up the layers of the atmosphere, the pressure
(a) Increases
(b) Decreases
(c) Remains the same

(v) When precipitation comes down to the earth in the liquid form, it is called
(a) Cloud
(b) Rain
(c) Snow

--> Match the following.

(i) Trade Winds              (a) Incoming solar energy
(ii) Loo              (b) Seasonal wind
(iii) Monsoon              (c) Horizontal movement of Air
(iv) Wind              (d) Layer of ozone gas
                         (e) Permanent wind
                         (f) Local wind