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(Sample Material) IAS Online Coaching : India & World Geography - "Atmosphere"

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Our planet is enveloped by a keep blanket of gases extending several kilometers above its surface.
Like the lithosphere and hydrosphere, the atmosphere too is an integral part of a gigantic system i.e. earth.
When compared with the radius of our planet, the atmosphere appears to be only a very thin layer of gases.
However, because of the force of gravity, it is inseparable from the Earth.

Atmosphere contains life-giving gases, like oxygen for man and animal, and carbon dioxide for plants.

It also acts like a greenhouse and thus keeps the Earth warmer than it would otherwise be.
The atmosphere, thus, acts like a blanket.
It regulates the heat balance of the Earth and also protects us from the harmful ultraviolet radiation of the sun.
The atmosphere serves as a storehouse for water vapour, which leads to precipitation and hence facilitates the hydrological cycles.

The atmosphere has a layered structure, because of density stratification as a result of which lighter gases move up and denser ones settle down.
The lowermost part of the atmosphere in which we live, and which is the theatre for which we live, and which is the theatre for almost all the weather phenomena is known as the troposphere.
Troposphere literally means the region of ‘mixing’ and has been derived from the Greek word ‘tropos’, meaning mixing or turbulence.
The height of the troposphere at the poles is about 8 km, while at the equator it is about 16 km. This is because there is greater heating at the equator.
Above troposphere is the stratosphere, which is important primarily because of the presence of zone.
This layer of calm and clear air is preferred for high-speed jet flights because of the absence of air pockets.
Also, the near absence of water vapour in this layer prevents the formation of clouds, thus providing pilots with better visibility.
Above stratosphere is mesosphere, which is more of a transitional layer.

Nitrogen             78.0%
Oxygen               21.0%
Argan                 0.93%
Carbon Dioxide 0.03%
Neon                  0.0018%

In traces-Water vapour, Dust particles, Hellum, Ozone, Krypton, Xenon, Methane

Above mesosphere lies the ionosphere, which has electrically conducting layers that help in radio communication.
There are two important layers in the ionosphere viz. E Layer of Kennelly Heavy side layer that reflects the medium radio waves, thus helping in short distance radio communication and F Layer or Appleton layer that reflects the short radio waves and helps in long distance radio communication.
The outermost layer of the Earth’s atmosphere is known as the exosphere. It is so highly rarified a region that its boundary is not clear.

Insolation

The word ‘insolation’ is an acronym for Incoming solar radiation, which is received at the Earth’s surface at the rate of 1.94 calories per square centimeter per minute.
Interstingly, the solar radiation falling on the Earth’s surface in one day would equal all the world’s industrial and domestic energy requirements for the next 100 years based on current rates of consumption.

Energy transfers in the atmosphere take place in three ways: radiation, conduction and convection.
The vast amount of energy coming to and leaving the Earth is through radiation.
This, from the sun, is in the form of short waves.
Radiation from the Earth is called terrestrial radiation and it is in the form of long waves. The atmosphere is heated more by terrestrial radiation than the incoming solar radiation and this also explains why the atmosphere is heated from the ground up instead of vice versa, specially in the troposphere.

Heat Budget

The average temperature of Earth remains rather constant. It has been possible because of the balance between the amount of incoming solar radiation and the amount of terrestrial radiation returned to space.
This balance of incoming and outgoing radiation has been termed Earth’s heat budget.

Latitudinal Heat Balance

At latitudes below 40 degrees, more solar radiation is received than is lost to space by Earth.
The opposite is true for higher latitude where more heat is lost than received.
Although Earth as a whole maintains a balance between the incoming and outgoing radiation, its ratio is not uniform all over the Earth.
The atmosphere and the oceans act as giant thermal engine that transfers heat from the tropics towards the poles.
In this heat transfer, the air masses, winds and ocean currents play crucial rote.
Most of the heat transfer takes place across the mid-latitudes hence; much of the stormy weather is associated with this region.
Thus, the transfer of surplus energy from the lower latitudes to the deficit energy zone of the higher latitudes maintains an overall balance over the Earth’s surface.

Inversion of Temperature

Occasionally the temperature in the lower layers of the air increases instead of decreasing with elevation.
It occurs particularly on cold winter night, when the sky is clear, the air is very dry, and there is no wind.
These conditions permit quick radiation of heat from the earth’s surface as well as from the lower layers of the atmosphere.
The upper air which loses its heat less rapidly remains comparatively warm.
Thus, there is reversal in the vertical distribution of temperature, which is known as the inversion of temperature.
This phenomenon is specially observed in the intermontane valleys.

Temperature Anomaly

Temperature varies even along the same parallel of latitude, land and water contrasts, prevailing winds and ocean currents.
The difference between the mean temperature of any place and the mean temperature of its parallel is called the temperature anomaly or thermal anomaly.
The anomaly is said to be negative when the temperature at a place is less than the expected temperature of the latitude.
The anomaly is positive when the temperature at a place is more than the expected temperature of the latitude.

Atmosphere Pressure

Air is an extremely compressible gas, and as result, atmospheric pressure varies considerably with height.
Since the pressure will vary according to the weight of the air above it, the lowest layers of air are densest.
The modern metric unit of pressure measurement is the millibar (mb), one millibar being equal to the pressure necessary to support 0.75 mm of the mercury column.
The mean sea level pressure of the atmosphere is 1013.2 mb.

I. Below5.6 km: 50% of atmospheric mass
II. Below16 km: 90% of atmospheric mass
III. Below32 km: 99% of atmospheric mass

The origin of pressure

Air has weight and it therefore exerts pressure, called atmospheric pressure, on the earth’s surface.
The pressure is not the same for all regions, nor is it always the same for any one region all the time.
Atmospheric pressure is affected by altitude, by temperature, and by earth rotation.