Composition
* The atmosphere is a layer of gases that envelopes the earth.
* The atmosphere protects us from the harmful rays of the sun and provides us the air we breathe.
* It regulates the earth’s temperature and makes life possible.
* While nitrogen and oxygen make up the bulk of the atmosphere, it also has carbon dioxide, argon, helium, ozone, hydrogen, water vapour and other components.
* Nitrogen is an essential constituent of all living organisms.
* Plants get nitrogen through nitrogen – fixing bacteria that covert nitrogen from the air into water – soluble compounds.
* The content of oxygen and carbon dioxide in the air remains constant due to the exchange of gases through the processes of photosynthesis and respiration.
* The balance of oxygen gets disturbed mainly due to deforestation.
Structure
Our atmosphere is divided into five different layers.
* Troposphere
* Stratosphere
* Mesosphere
* Thermosphere
* Exosphere
* All weather phenomena, like rainfall, fog and hailstorm occurs in the troposphere.
* Aeroplanes, weather balloons and commercial aircraft use the stratosphere to fly.
* The presence of the ozone layer is the most important feature of the stratosphere to fly.
* Meteorites that entre the earth’s atmosphere burn up in the mesosphere.
* The mesopause lies between the mesosphere and the thermosphere and is the coldest place in the earth’s atmosphere with a temperature of – 100 degress centigrade. The International Space Station lies in this layer.
* The ionosphere enables radio transmission.
* The exosphere is the upper limit of our atmosphere.
Weather and Climate
* Weather is the day – to – day condition of the atmosphere.
* Temperature is the degree of hotness or coldness of the air.
* Isolation is the measure of solar energy received on the surface of the earth in a given time. The pressure exerted by the weight of air on the earth’s surface is defined as air pressure.
* The movement of air from a high – pressure area to a low – pressure area is known as wind.
Winds are classified into three types:
* Permanent Winds
* Seasonal Winds
* Local Winds
Humidity and Rainfall
* The presence of moisture in the air is called humidity or absolute humidity.
* The process by which water vapour becomes liquid water or snow is called condensation.
Clouds are classified on the basis of their shape and height:
* Cirrus clouds
* Cumulus clouds
* Stratus clouds
Precipitation is the process in which condensed water vapour falls to the earth’s surface.
Three main types of rainfall are:
* Conventional rainfall
* Frontal or cyclonic rainfall
* Relief or orographic rainfall
Cyclone
* A cyclone is associated with circulatory winds in the lower parts of the atmosphere.
* A cyclone has low pressure at the centre and is surrounded by high pressure all around.
* A cyclone blows towards the centre at a high speed and is destructive in nature.
* A super cyclone occurred in Orissa on October 29, 1999, causing large – scale destruction of life and property.
Natural Resources – Biogeochemical Cycle
* The continual cycle of water between the land, the ocean and the atmosphere is called the water cycle.
* The interaction of biotic and a biotic components between the biological and geological world is called biogeochemical cycle.
* In the carbon cycle, green plants use carbon dioxide from the atmosphere for photosynthesis and finally release it during respiration.
* The sequence in which nitrogen in the atmosphere is passed into the soil and life – forms, and then released back into the atmosphere, is called the nitrogen cycle.
* The Greenhouse effect keeps the Earth Warm to sustain life.
* The ozone layer blocks the harmful ultraviolet rays from reaching the Earth.
The Mechanism of Monsoon
* The climate in India is strongly influenced by monsoon winds. The word monsoon refers to the season in which the wind system reverses completely.
* They are experienced in the tropical area roughly between 20°N and 20°S.
* Due to the atmospheric conditions encountered on the way, the monsoon winds are not steady, but are pulsating in nature.
* The winter monsoon is experienced in the states of Tamil Nadu, Kerala and Andhra Pradesh in the first week of January.
* The sudden increase in the rainfall that continues for several days is called the ‘burst of the monsoon.
* The monsoon arrives at the southern tip of the Indian Peninsula generally by the first week of June.
* By early September, the monsoon starts to withdraw or retreat, which is a more gradual process.
* By mid – October, it withdraws completely from the northern half of the peninsula.
* The winter monsoon is experienced in the states of Tamil Nadu, Kerala and Andhra Pradesh in the first week of January.