Atmosphere : The blanket of air that covers the Earth is known as the atmosphere.
The atmosphere goes up to about 1000 km from the surface of the Earth. 99% of the total mass of the atmosphere is contained within 32 km. The atmosphere gases are held by the gravitational pull of the Earth.
Composition of the Atmosphere
Atmosphere contains 78% of nitrogen and 21% of oxygen. The remaining 1% of air is made up of a number of gases like Argon, CO2 etc.
Carbon dioxide : The percentage of CO2 is small but it is an important constituent of air because it has the ability to absorb heat and thus keep the atmosphere warm.
Water vapour : Water vapour is an important component of the atmosphere. It effects the weather.
Role of Water Vapour
1. Water vapour is the source of clouds and precipitation.
2. Water vapour, has the ability to absorb heat energy.
3. When water changes from one state to another, it absorbs or releases energy.
Dust particles : The atmosphere also has dust particles on which clouds are formed. The amount of dust varies from place to place.
Role of Dust
1. Dust intercepts and reflect incoming isolation.
2. On dust particles water vapour may condense. This function is basic to the formation of clouds and fog.
3. Dust in the atmosphere exhibits the red and orange colours of sunlight at sunrise and sunset.
Layers of the Atmosphere
Atmosphere has 5 distinct layers :
1. Troposphere : Troposphere is the first layer of the atmosphere.
(i) It extends to a height of 18 km at the Equator and 8 km at the poles.
(ii) In this layer, temperature decreases with height. This is due to the fact that the density of air decreases with height and so the heat absorbed is less.
(iii) Most of the water vapour are contained in this layer, therefore clouds form in this layer. All weather changes takes place in the troposphere.
(iv) Tropopause is the height at which the temperature stops decreasing. Here the temperature may be as low as–58OC.
2. Stratosphere : The second layer of the atmosphere is called stratosphere.
(i) The tropopause is about 50 km above the surface of the Earth.
(ii) Ozone in this layer absorbs ultra violet radiations of the sun, hence the temperature slowly increases to 4OC.
(iii) This layer does not have any clouds and free from weather changes.
(iv) At about 50 km the temperature begins to fall again. This marks the end of the stratosphere which is called the stratopause.
3. Mesosphere : Mesosphere lies above the stratosphere.
(i) The mesosphere goes up to a height of 80 km.
(ii) Here the temperature decreases again, going to – 90OC. The mesosphere has the lowest temperatures in the atmosphere.
(iii) Mesopause is the end of this layer.
4. Thermosphere : Above mesosphere lies the thermosphere.
(i) This layer goes up to a height of about 90 km.
(ii) In this layer temperatures rises upto 1480OC and rise in temperature is due to the fact that the gas molecules in this layer absorb the X-rays and the short wave ultraviolet radiation of the Sun.
High temperature and radiations break-up the gas molecules into positively and negatively charged particles.
(iii) The electrically charged gas particles of the thermosphere reflect radio waves. This layer is mainly called as the ionosphere. The long distance communications are possible because of this layer.
(iv) The thermosphere also protects earth from meteors and obsolete satellites, because the high temperatures burn up nearly all the debris coming towards the earth.
5. Exosphere : Above thermosphere lies exosphere. This layer lies above the thermosphere.
(i) It goes beyond the thermosphere upto 960 km. Gradually it merges with interplanetary space.
(ii) The temperatures in exosphere ranges from about 300OC to1650OC.
(iii) This layer contains only traces of gases like oxygen, nitrogen, argon and helium.
Effects of the Atmosphere
(i) Atmosphere acts as a shield for the earth from sun’s radiation. It also acts as a shield for ultra-violet radiations.
(ii) The CO2 and water vapour in lower atmosphere absorb the heat radiated from earth’s surface. This is called ‘Green house’ effect.
(iii) The heating up of earth’s surface causes rain, hail and snow.
(iv) All forms of life on earth has an affect of different seasons.
How the Sun produces Heat and Light
Sun is made up of hydrogen and helium in the 3 : 1 ratio. The core of the sun which is extremely hot acts as a fusion reactor and by fusion reactions it converts hydrogen into helium. The fusion process releases tremendous amount of energy as heat and light. Solar radiations are the primary source of heat and light for the earth.
Insolation : The incoming energy from the sun intercepted by earth is called insolation.
Terrestrial Radiation : Solar energy absorbed by the earth’s surface and radiated out into space is known as terrestrial radiation.
Effects of Land and Sea Contrasts
1. During the night and winter oceans are warmer.
2. During the day and in summer land is warmer than oceans.
3. The difference between land and ocean temperature is greater in winter.
4. The difference between land and ocean temperature is greater in the Northern Hemisphere.
5. Sea coasts have less difference between the highest and lowest temperature.
6. The interior of the continents have greater difference between the highest and the lowest temperature.
7. Land and sea temperature difference are responsible for the monsoon winds.
Temperature Graphs and Maps
Graph : The temperature of a place can be shown by a graph. Line graphs and bar graphs are often used to represent climatic data.
Time is marked on X-axis and temperature in OC or rainfall in millimetres is makred on the y-axis according to their respective scales.
Map : A map is generally used to show the temperatures of a region.
Life exists on the surface of the earth as well as to great heights of the atmosphere.
Shopping Cart