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Weather is the state of temperature,
pressure, winds, humidity,
precipitation etc. at a given place and
time.
It is often confused with the term
‘climate”
Atmospheric
temperature
Atmospheric
pressure
Moisture
Wind
1. ATMOSPHERIC TEMPERATURE
The main source of heat on the earth
is the Sun. The heat and light
received by the Sun is called
Solar radiation.

A very small amount of solar
radiation reaches the earth surface.
This is called Insolation.



The earth absorbs maximum solar radiation during
the day.
At night, it is radiated back to the atmosphere.
This is called terrestrial radiation.
It becomes
lighter and
rises up.
The air over the earth
surface gets heated
due to its contact with
the surface.
Thus,
different
layers of
atmosphere
are heated.
The amount of insolation
received on the earth
surface is not the same.
It goes on decreasing
from the equator to the
poles.
The earth is thus, divided into
three heat zones.
The instrument to measure
temperature is called thermometer.
It has two scales• 1. Fahrenheit (melting point of ice is 32 degree and
boiling point of water is 212 degree)
• 2. Celsius (melting point of ice is 0 degree
• boiling point is 100 degree)

The atmosphere exerts its weight as pressure on
the earth’s surface. This is called Atmospheric
Pressure.

The weight of air column is maximum at the mean
sea level.

I
It is measured with an instrument
called Barometer.
The normal atmospheric pressure at
sea level is 76 cm of the mercury
column in the barometer.
Millibar(mb) is the unit to measure
atmospheric pressure.
It
decrease
s with
increase
in
altitude.
It
decrease
s with
increase
in
moisture
in air.
Earth’s
rotation
changes
the
Atmosphe
ric
pressure.
It decreases
with increase in
temperature.
1. Equatorial low pressure belt
2. Northern Sub Tropical high pressure belt
3. Northern Sub Polar low pressure belt
4. Northern Polar High pressure belt.
5. Southern Sub Tropical high pressure belt.
6. Southern Sub Polar low pressure belt.
7. Southern Polar high pressure belt.
Horizontal moving air is called wind.
It moves from a high pressure region to
a low pressure region.
It is named after the direction from
where it blows.
the right in the
Northern
Hemisphere
the left in the
Southern
Hemisphere
The speed of the
wind is measured
by an Anemometre.
The direction of wind
is found by a Wind
Vane
Planetary winds
• Also called as permanent winds
• Mainly originate due to presence of permanent
pressure belts.
• Examples –Trade winds,Westerlies and Polar winds
Periodic winds
• These blow in definite direction during a particular
time of the day or year
• Mainly originate due to differential heating of the
earth surface or local difference of atmospheric
pressure.
• Examples-Monsoon winds, Land and Sea breeze.
Local winds
• These blow over a small area and for a short Period
• Mainly derive local names.
• Examples-Loo, Chinook,Harmattan.
4.MOISTURE
Amount of water present in atmosphere is called
Moisture.
It is present in all three forms i.e. solid, liquid and
gaseous
Moisture in air varies from place to place.
There is more moisture in air
in the summer season.
The amount of
moisture decreases
with height above
the sea level.
The air in
equatorial regions
has maximum
moisture.
The amount of
moisture in the air is
about zero at the
poles in winters.
Condensation
Evaporation
Precipitation
Rising of water
from the earth to
the atmosphere in
form of water
vapour is called
Evaporation.
It takes place at all
times at all places.
It increases on a hot
and windy day.
When the air rises up in the atmosphere, it becomes
cool and water vapour changes into tiny droplets.
This is called Condensation.
It takes place around dust particles in the air.
Clouds
Forms of
condensation
Fog
Dew
Cumulus
Cirrus
Clouds are
water drops
condensed
around dust
particles
Stratus
When clouds
get saturated
with water
vapour they
fall on earth.
This is called
Precipitation.
Rain
Drizzle
Snow
Hailstones