Atmospheric Composition: Gases, moisture and dust particles are the major constituents of our atmosphere that blanket our earth. It is the gravitational attraction of the earth that holds the atmosphere close to the earth.
Atmospheric Gases: Familiarize the major gases in the atmosphere and their proportionate volume by observing the given table.
Almost all the gases in our
atmosphere support the sustenance of life directly or indirectly. Observe the
pictures given. You can notice the importance of gases such as
oxygen, carbon dioxide and nitrogen in the existence of life forms.
- Plants make use of Carbon dioxide for photosynthesis.
- Man and other organisms make use of oxygen for respiration.
- Plants make use of nitrogen for their growth through nitrogen
fixation.
Water molecules are a major constituent in the lower parts of the atmosphere. As you know, water reaches the atmosphere through evaporation and causes cloud formation and rain. There is spatial and temporal variation in the amount of water present in the atmosphere. Look at the factors influencing the amount of water in the atmosphere.
·
Rate of evaporation will be high at places experiencing higher
temperature. So the water content in such places will be high.
·
The amount of water will be high in the atmosphere close to the
surface water sources such as oceans, rivers and other water bodies.
Troposphere
- This layer extends up to about 90 Km from the
surface of the earth and lies close to the earth.
- The height of the troposphere is more in the
equatorial regions because of strong convection here. (about 18 Km)
- Almost all the weather and climatic phenomena such
as cloud formation, rain, snow, wind, thunder and lightning etc. take place in
this layer.
- In the troposphere the temperature decreases at a
uniform rate of 1°Celcius for every 165 metres of altitude. This is called
Normal Lapse Rate.
- The zone of transition above the troposphere is
called tropopause.
Stratosphere
- Extends up to a height of about 50 Km from the
earth and lies above the tropopause.
- In the lower parts of the stratosphere there is no
change in temperature with altitude. This zone is called isothermal zone.
Beyond this there is increase in temperature with altitude.
- Ozone layer which forms part of this layer absorbs
the harmful ultra violet rays from the sun and prevents it from reaching the
earth.
- Allows the free movement of jet aircrafts through
clear atmospheric conditions and absence of air gutters.
- The zone of transition above the stratosphere is
called stratopause.
Mesosphere
- Extends from about 50 to 80 Km altitude from the earth.
- Temperature decreases with altitude and the lowest temperature
of the atmosphere is felt at the mesopause. ( -80°C to -100°C)
- The meteors on reaching the mesosphere gets burnt out
due to friction.
- The zone of transition above the mesosphere is
called mesopause.
Transition zones: Transition zones are the parts of the atmosphere separating the major atmospheric layers. Tropopause, stratopause and mesopause are the respective transition zones between troposphere, stratosphere, mesosphere and thermosphere.
Thermosphere
- Extends from about 80 to 600 Km altitude.
- There is considerable increase in temperature with
altitude.
- The lower part of the thermosphere is known as
ionosphere.
- Ionosphere helps in the transmission of radio
waves.
Ionosphere:
- At an altitude of about 80 to 400 Km in the atmosphere
the intense solar rays such as Ultra violet, X-rays etc. react with gaseous molecules
to form ions. This process is called ionization and this part of the atmosphere
is called ionosphere. Ions conduct electricity.
- As the radio waves are electromagnetic waves this layer is made use for long distance radio transmission.