Humidity refers to the amount of water vapor in the air. It is measured by relative humidity and dew point temperature. Condensation occurs when warm, moist air rises and cools, causing water vapor to condense into liquid water droplets. The main types of precipitation are rain, snow, sleet, hail, and drizzle, which occur via different meteorological processes like convection, orographic lifting, and frontal lifting. Thunderstorms occur when upward motion within clouds causes water droplets to collide and become electrified.

1.  Humidity is a measure of the quantity of
water vapour in the air
 Humidity is nothing but water vapour
present in the atmosphere
 It refers to the water in the gas form in the
atmosphere
• It is measured in either relative terms
(relative humidity) or absolute terms (dew
point temperature).
Atmospheric Humidity

2. Condensation
• Condensation is the phase change of water from
its gaseous form (water vapour) into liquid
water.
• Condensation generally occurs in the
atmosphere when warm air rises it expands and
cools below its saturation point. Then its
capacity to hold water vapour more than its
holding capacity also reduces. As a result, the
water vapour available in the air parcel will
condense on the aerosols (dust particles) to form
cloud droplets.

3. Source:
1. The water from different water bodies like ocean, sea, river,
lake and soil moisture is gets evaporated. Also the water
transpired and subsequently evaporated from the plants.
2. Solar energy brings about evaporation by supplying
necessary energy. Besides the evaporation, convection,
diffusion and wind also supply water vapour to the
atmosphere.
3. The percentage of water vapour in the atmosphere is highly
variable and changes according to season, land and sea
presence .
4. Water vapour decreases with height & most of the
atmosphere moisture content exist below 500 mb at 5574
meter heightt.
Atmospheric Humidity

4.  Humidity mainly depends on air temperature. The changes of
moisture between the surface and the atmosphere determined
the humidity.
How the moisture move to atmosphere:
 The flux of water vapour is upward.
 The evaporative loss is maximum/strongest during the day and
often continuous at a reduced rate throughout the night.
 Combination of high temperature and high RH adversely affect
all life (human, animal and plant) as the humidity declines, the
vapour pressure gradient between leaf surface and surrounding
air increases and consequently rate of evaporative cooling rises
through higher heat loss.

5. Different terms of Humidity:
 The temperature of the environment is closely
associated with the amount of water vapour present.
Water vapour in the air condenses & takes different
forms like rain, snow, hail, sleet etc.
 Therefore humidity is an imp weather element and it is
expressed in different terms.
1. Partial vapour pressure:
• When water vapour make mixes with other gases of
atmosphere, it exerts pressure in all the directions
as that of other gases.
• It is the part of atmosphere pressure due to water
vapour is known as partial vapour pressure. So it is
the combination of water vapour and gases that the
total atmosphere pressure.

6. • Total pressure Pw = PO2 + PCO2 +PN2 +PH2O
• The pressure exerted by actual air (dry air) is
known as actual vapour pressure.

7. 2. Dew point temperature
• It is defined as the temperature at which the actual
mass of water vapour present in certain volume of
air is just able to saturate it and the invisible water
vapour begins to condense into the visible form like
small water droplets.
• This is the temperature at which dew appears.
• Usually 50C is considered as dew point
temperature.

8. 3. Saturated water vapour
At a given temperature, air holds certain
amount of vapour which is given by the
vapour pressure at that temperature.
When air contains all the moisture that it
can hold to maximum limit is called
saturated air otherwise it is unsaturated.

9. 4. Relative humidity (RH)
Actual qty of water vapour/given vol. of air
RH = ----------------------------------------------------------------------- X 100
Max qty of water vap that air can hold by the same vol of air
SVP at dew point
= ---------------------------------- X 100 SVP= sat. vap pressure
SVP at air (room) temp.
• Relative humidity is given always per cent. The RH represents the
amount of water vapour actually present in the air, compare with the
maximum amount the air can hold at a given temperature.
• It tells simply the relative content and indicates the degree of
saturation of air at a given temperature with water vapour.
• The RH of saturated air is 100%.
Ex: RH is 80% means 20% moisture is required to saturate the
atmosphere.

10. 5. Absolute humidity (AH): (Actual Humidity)
 It is defined as actual quantity by water vapour
present in the given volume of air.
 It is measured in g/m3 or lbs/ft3 or in terms of partial
pressure of water vapour in air in mb or mm.
Wt. of water vapour
AH = ----------------------------------- X 100
Vol. of air

11. 6. Specific humidity
 It is ratio of mass of water vapour actually present in the air
to a unit mass of air including the water vapour (Dry air +
moisture).
 It is expressed as grams of water vapour per kg of moist air
mass.
 It is measured in g/kg i.e g of water vapour per kg of air.
Mass of water vapour (MW)
q = --------------------------------------- X 100
Mass of air (dry air + moisture)

12. 7. Mixing ratio
 It is the mass of water vapour measured in grams of
mixing which 1 g. of dry air.
Mass of water (MW)
MR = --------------------------------
Mass of 1 g. of air
 It is differs from specific humidity, it is related to only
air instead of to the total dry air + vapour in case of
specific humidity.
 Instruments used to measure humidity are called
Hygrometer.

13. Precipitation

14. Precipitation
• Precipitation refers to the transfer
of water from the atmosphere to
the surface of the Earth, in the
form of rains, ice crystals, snows
and hails.

15. Types of Rainfall
1.Conventional Rainfall
2. Orographic Rainfall or Relief rainfall
3. Cyclonic Rainfall or Frontal rainfall

16. 1. Conventional Rainfall
 Common in tropical countries or high temperature areas.
 Due to heating, the air near the ground – hot and starts upward
movement (Convection).
 Lapse rate : DALR Dry Adiabatic Lapse Rate 9.8 0C/km
 Air becomes saturated and attain humidity 100% at which dew
point is reached where condensation starts.
 This height is called at SALR – Saturated Adiabatic Lapse Rate 4
0C/km
 Here first cloud is formed – “Conventional rain “

17. Conventional rainfall

19. 2. Orographic type or Relief rainfall
 When the moist air coming from sea/ocean that encounter the
mountains/relief barrier.
 It cant move horizontally to cross the mountain.
 Air rises upwards, it cools down and clouds are formed and
condensation starts giving precipitation.
 It Rains heavily in the wind ward side of the mountain region.
 After crossing the mountains the air descends to leeward side of
mountain. – has low moisture content and warmer.
 Rain shadow region – gives fewer rains.
 Ex: Mumbai (windward side), Pune (Leeward side).

20. Orographic or relief rains

22. 3.Cyclonic Rainfall or Frontal rainfall
 It is produced when opposite air currents (warm and cold) meets
 Vertical lifting of air mass takes place. – Condensation,
precipitatiom.
 When warm air mass meets cold air mass, the colder air being
denser tends to push below the warm and light air & replace it.
 The boundary zone along which air masses meet – Fronts
 The settled cold air pushes warm air vertically & results convection
 When warm air mixes with cold air mass, the temp. of warm air
falls down, saturation takes place and precipitation.
 Such mechanisms are responsible for cyclone formation
 Rains received from cyclone are called “Cyclonic rains”.

23. Cyclonic or frontal rains……

24. Process of THUNDER STORMS

25. Process Thunder storms
 In the formation of thunder storms the cumulonimbus clouds are
produced by the upward motion of the humid air.
 Condensation of water vapour and formation of many rain drops.
 In the strong upward motion of the air, these water drops are broken
up and electrified positively. The air with its –Ve charge.
 Large quantity of +Ve and –Ve charges accumulates in different
regions and the electric force are increases until lighting flash ..
 The process repeated and temp. created enormous about
50,000 0F (27,7600C).
 Air gets suddenly expanded and molecule atoms dissociated with a
large noise which is known as thunder.

26. Forms of Precipitation
• The usual forms of precipitation are
1. rain
2. drizzle
3. snow
4. sleet
5. hail

27. Rain, drizzle -
Occurring during the monsoon &
summer seasons
Snow, sleet -
Occurring during the winter season.
Hail, shower -
Occurring during the summer season
due to high intensity of rainfall

29. 1. Rain
Rain is the precipitation of liquid water
particles in the form of drops 0.5mm diameter
or smaller to widely scattered drops.
When the precipitation process is very active,
the lower air is moist and clouds are very deep,
then the rainfall will be in the form of heavy
down pour.

30. 2. Drizzle
Fairly form of precipitation having fine or
very small droplets (<0.5 mm diameter)
which are carried away by the light winds.
The drizzle falls from low laying nimbo-
stratus clouds, if the drop of drizzle
completely evaporates before it reaching the
ground is called mist.

31. 3. Snow
It is the precipitation of solid water in the
form of white and opaque grains of ice.
In water when the temp is below the
freezing point in the whole atmosphere, ice
crystals falls from the alto- stratus clouds.

32. 4. Sleet
 It is the precipitation in the form of mixture of
rain + snow (both form of liquid + solid).
 It consists of small pallets of transparent ice
of 5 or <5 mm diameter.
 It is referred to as frozen rain, when air
falling to the earth passing through a layer of
cold air & freezes in very low temperature.
 It is not commonly seen in India except the
ranges of north & north-east during winter
season.

33. 5. Hail
It is a precipitation of small pieces of ice which
a diameter up to 50 mm or more.
 The rainfall associated with the hail stones are
called as Hail storms.
The highest hail recorded was 152 mm
weighing 766g at Canoas, USA on 3rd Sept.
1970.
 In India during the month of March, April &
May receiving this type of hail storms.
 The thunderstorms of cumulo-nimbus clouds
are most dreaded and destructive from of
precipitation.

34. 6. Shower
It is the precipitation lasting for short time
with relatively clear intervals.
Usually it occurs from the passing / moving
clouds.