Integrated Guidance Programme of General Studies for IAS
Subject - India & World Geography
Chapter : Atmosphere
Importance of Atmosphere
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.
Structure of the Atmosphere
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.
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.
Above stratosphere is mesosphere, which is more of a
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
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
Heating and Cooling of the Atmosphere
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.
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.
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.
- 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
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.
- 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.
- 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.
- Prevailing or Planetary winds blow throughout the year
from one latitude to the other in response to the
latitudinal differences in air pressure, for example, the
trade winds and the westerly winds.
- Westerlies of the southern hemisphere are stronger and
more constant in direction than those of the northern
hemisphere because of the vast expanse of water.
- They are developed between 40º and 65º south latitudes.
These latitudes are hence often called Roaring Forties,
Furious Fifties and Shrieking Sixties dreaded terms for
- Periodic winds reverse their direction periodically with
season. For example, monsoons, land and sea breeze and
mountain and valley breeze.
- Local winds flow in comparatively small area and have
special characteristics. A lot of them are found in the
Mediterranean lands and their nomenclature derived from the
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A cloud is a mass of small water
droplets or tiny ice crystals.
Clouds form when moist air rises and
Heat from the sun turns, water in the
oceans, rivers and moist soil, into water vapour.
The water vapour expands as it rises
and becomes cooler.
Cool are cannot hold asmuchmoisture
as warm air and soon reaches a saturation point.
The water vapour condenses into tiny
water droplets forming clouds.
Their form, shape, height and
movements tell us a great deal about the sky conditions
and the likely weather.
Clouds are classified according to
their appearance, form and height. There are four
A High clouds 6000 to 12000 m
B Middle clouds 2100 to 6000 m
C Low clouds below 2100 m
D Clouds of great 1500 to 9000 m
The different types of cloud are
given Latin names which are all combinations of the
1.Cirrus means looking like a feather, it is used to
describe the very high clouds.
2.Cumulus means looking like a heap. It is used to
describe clouds which have flat bases and rounded tops.
There are patches of blue sky between the clouds.
3. Stratus means lying in level sheets. It is used for
4. Nimbus means rain cloud.
5. Alto means high.
- At interval of some 3 to 8 years there occurs a
remarkable disturbance of ocean and atmosphere.
- It begins in the eastern Pacific Ocean and spreads
its effects widely over the globe for more than a year’s
- It bring with it unseasonal weather patterns with
abnormalities in the form of droughts. Heavy rain falls,
severe spells of heat and cold, or a high incidence of
- This occurrence is referred to as EL NINO, meaning
the ‘Christ Child’ in Spanish since this phenomenon
occurs each year around Christmas time.
- With the onset of El Nino, upwelling ceases, the
cool water is replaced by warm water from the west, and
the plankton and their anchoveta predators disappear.
- Vast numbers of birds that feed on the anchoveta die
- The El Nino (EN) condition influences climates on
the two sides of the tropical Pacific Ocean.
Global Warming & Climate
Global warming refers to an average
increase in the Earth’s temperature, which in turn, causes
changes in climate. A warmer Earth may lead to changes in
rainfall patterns, a rise in sea level, and a wide range of
impacts on plants, wildlife, and humans. When scientists
talk about the issue of climate change, their concern is
about global warming caused by human activities.
The Impact of Climate Change
It has been conclusively proved that
climate change is attributable to human intervention.
Carbon dioxide, emitted mainly by the burning of fossil
fuels, and the emission of methane, nitrous oxide, CFC’s
and other greenhouse gases thickens the blanket of
greenhouse gases over the earth’s atmosphere, upsetting
the natural flow of energy from the sun.
Deforestation accelerates global
warming by reducing the absorption of carbon dioxide in
Based on current emission levels, it
is estimated that the global temperature will rise by
between 1ºC and 3.5ºC by the year 2100; that even after
emission levels are stabilized, climate change will
continue to occur for hundreds of years
The Greenhouse Effect is the result of the atmosphere’s
absorption of long-wave radiation emitted by Earth.
Among the atmospheric constituents, carbon dioxide
absorbs the largest proportion of that radiation.
Thus, when the carbon dioxide content of air changes, a
corresponding increase or decrease in the greenhouse effect occurs.
The ozone layer is found in the
atmosphere between 20-50 Km from the Earth’s surface.
The ozone layer is a region of
concentration of the allotrope of an oxygen molecule
known as ozone (O3), which is produced by the action of
solar radiation on ordinary oxygen atoms.
It filters sunlight and prevents the
harmful ultraviolet radiation from reaching the Earth’s
surface by absorbing most of the ultraviolet radiation.
If these ultraviolet rays were to
reach the Earth’s surface in full intensity, all exposed
bacteria would be destroyed and animal tissues damaged
It is the precipitation charged with
an excessive amount of acid droplets formed when oxides
of Sulphur and Nitrogen, released by the burning of
hydrocarbons, are converted to acids in the atmosphere.
Acid rain leaches crucial minerals
like calcium and magnesium, which are essential for
plant growth, from the soils. A related problem is the
continued leaching of heavy metals and other substances,
providing a persistent source of toxicity to surrounding
vegetation and aquatic life.
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