Atmosphere is a gaseous envelope that helps in control of temperature and acts as a shield against solar radiation.
Gravitational pull keeps the atmosphere attracted towards itself.
Its composition is the result of a very gradual change Which began with the origin of the Earth some 4.6 billion years ago.
Secondary atmosphere formed by the gases that were released through the process of degassing or vulcanism.
The Secondary atmosphere is composed of three main elements Water vapour, Carbon dioxide, Nitrogen.
Clouds formed due to the cooling of liquid water and water vapour.
Oxygen is the second most abundant gas in the atmosphere.

  1. Exosphere
  2. Ionosphere
  3. Mesosphere
  4. Stratosphere
  5. Troposphere
The lowermost part of the atmosphere is Troposphere in which we live.
It is 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 l6 km.
Above troposphere is the stratosphere which is primarily because of the presence of ozone.
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 transitional layer.
Above mesosphere lies the ionosphere,which has electrically conducting layers that help in radio communication.
Two important layers in Ionosphere are,
E Layer or Kennelly Heavyside layerthat reflects the medium radio waves,thus helping in short distance radio communication.
F Layer or Appleton layerthat 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.
It is the general term for the entire gaseous envelop surrounding the Earth, including the TROPOSPHERE and the STRATOSPHERE.
The composition of the atmosphere changes as we go higher from the earth's surface. Upto about a height of 50 km from the earth, the atmosphere is composed of:
  1. Nitrogen(N2) - 78.08
  2. Oxygen(O2) - 20.94
  3. Argpm(Ar) - 0.93
  4. Carbondioxide(CO2) - 0.03
  5. Neon(Ne) - 0.0018
  6. Ozone(O3) - 0.00006
Atmospheric Pressure
A litre of air weighs about 1.3g.At the sea level the air pressure is around 1033.6 g cm . This is referred to as one atmosphere.
The pressure exerted by the atmosphere is expressed in millibars.
The average pressure over the earth's surface at sea-level is 1013.25 mb.
Most of the atmospheric mass is concentrated in the lower layers:

  1. Below 5.6 km 50% of atmospheric mass
  2. Below 16 km 90% of atmospheric mass
  3. Below 32 km 99% of atmospheric mass
Vertical Distribution of Power
Air being a mixture of gases is highly compressible.
Its density is greatest at the lower layers, as a result the lower layers of the atmosphere have high pressure.
The higher layers are less compressed and hence, have low pressure.
Air pressure always decreases with increase in altitude.
Horizontal Distribution of Pressure
It is the distribution of atmospheric pressure across the latitudes.
The leading function of the general circulation of atmosphere is to redistribute heat and moisture across Earth's surface.
About Wind
Horizontal movement of the air is called wind and it flows from areas of high pressure to those of low pressure.
Winds are always named from the direction they blow; an east wind is one that blows from east to west and a southwest wind is one that blows from the south-west.
Wind Types
They are mainly of three types:
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.
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 regional language.
The word 'insolation' is an acronym for lNcoming SOLAr radiaTlON, which is received at the Earth's surface at the rate of 1.94 calories per square centimetre per minute.
Heat Budget
Temperature of Earth remains constant and it is 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.
Agriculture and urbanization have significantly changed the surface albedo and the capacity of the ground to absorb short-wave radiation and to emit long wave radiation.
Also, combustion of fuels has already altered the content of the atmosphere through the release of carbon dioxide and dust particles.
Jet Streams
In the mid-latitudes, high-speed winds are known as jet streams and it blows from west to east in the upper troposphere near the tropopause the interface between troposphere and stratosphere.
Jet streams play an important role in the possible formation steering or intensifying weather phenomena such as monsoons cyclones, anticyclones and other weather conditions.
About Clouds
A cloud is a mass of small water droplets or tiny ice crystals and its form when moist air rises and cools.
Heat from the sun turns water in the oceans, rivers, and moist soil, into water vapour and it expands as it rises and becomes cooler and it condenses into tiny water droplets forming clouds.
Types of Clouds
High Clouds:
  1. Cirrus-wispy shaped
  2. Cirrostratus-which produces a halo effect around the sun or moon
  3. Cirrocumulus- popularly known as the mackerel sky

Middle Clouds:
  1. Attostratus
  2. Altocumulus
Types of Clouds Cont..
Low Clouds:

  1. Stratus
  2. Nimbostratus-popularly called the rain clouds
  3. Stratocumulus

Clouds with vertical development:

  1. Cumulus is the familiar white woolpack cloud and it is the indication of bright brisk weather.
  2. Cumulonimbus - or the thunder clouds associated with heavy precipitation and thunderstorms.
On the basis of its origin, precipitation may be classified into three main types:
Convectional Precipitation is caused by convectional ascent of warm and humid air to great heights. Rains in the doldrums are of convectional nature and are also called the 4 o clock showers.
Orographic Precipitation occurs when warm and humid air strikes landform barriers such as mountain ranges and is forced to rise.The windward side of the mountain range gets more precipitation than the leeward side.
Cyclonic Precipitation is associated with a cyclonic circulation.
Acid Rain
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 convened to acids in the atmosphere.
Acid rain leaches crucial minerals like calcium and magnesium, which are essential for plant growth, from the soils.
Ozone Depletion
The ozone layer is found in the atmosphere between 20.50 km from the Earth's surface and it 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.
These chemicals are called Ozone Depleting Substances and include primarily the Chlorofluorocarbons (CFCs), Carbon Tetrachloride (CCI4,) and Hydro Chlorofluorocarbons (HCFCs).With less ozone in the atmosphere, more ultraviolet radiation reaches the Earth, leading to a higher damage to the earth.
Types of Wind
Winds are divided into three broad groups:
  1. Regular winds, e. g. trade winds and westerlies
  2. Periodical winds which blow seasonally, e. g. monsoons
  3. Variable winds, e. g. clones and other local winds.
Trade Winds
Trade winds are steady currents of air blowing towards the equator from the north -east and the south-east.
The trade winds blow towards the equator between 5° and 30° north and south latitude.
The westerlies are regular winds which blow outside the tropics in the temperate zone.
South of 40 degrees latitude the absence of any land mass enables these winds to gather force and thus they are known as the roaring forties.
The monsoons are seasonal winds which blow briefly over India, Sri Lanka, China and north-west Australia.
In summer, chiefly due to the high temperature over the earth's surface new the equator the air pressure is low, and winter droughts.
Other Types of Winds
Chinook is a hot dry wind on the east or leeward side of the Rocky Mountains (South America).Winds on the north of the Alps (Europe) are called Fohn.
Sirocco is a hot, moist wind which blows from the Sahara desert and moves eastwards across the Mediterranean sea.
Solano is a similar type of wind blowing from the Sahara towards the lberian Peninsula.
Harmattan is a hot, dry wind blowing outwards from the interior of West Africa.
Bora is a cold, dry wind blowing outwards from Hungary to the north of Italy.
Mistral is a very cold wind which blows down from the plateau of Central France.
Punas are cold dry winds blowing down towards the western side of the Andes.