precipitation,ppt,forms of precipitation

2. Group Members
Zohaib Hassan
B-15077
Muhammad Zohair
B-15086
Mubasher Rasheed
B-15107
A.Saeed Sajid
B-15576

4. Definition
All types of moisture reaching the surface of earth from
atmosphere.
Precipitation is the basic input to the hydrology
 Factors determining
precipitation or the amount
of atmospheric moisture
over a region
 Climate
 Geography
 Ocean surfaces is the chief
source of moisture for
precipitation
.

6. Forms of precipitation

7. Rain
Rain is the most common type of
precipitation in our atmosphere. Rain is
when liquid droplets fall to the surface of
the Earth.
There are two different forms of rain,
either in the form of
showers
drizzles
Showers are heavy, large drops of rain
and usually only last a period of time.
Drizzles however usually last longer and
are made up of smaller droplets of
water.
Rain can either be formed as ice crystals
melt or it can be smaller water droplets.
Light
I = 2.5mm/hr
Moderate
I = 2.8-7.6mm/hr
Heavy
I > 7.6 mm/hr

8. Snow
 Snow is the second most common precipitation in
the North East.
 Snow forms when water vapor turns directly into
ice without ever passing through a liquid state.
This happens as water condenses around an ice
crystal.
Density of freshly fallen
snow varies between 125500mm of snow required to
equal 25mm of liquid water
Average density
gravity) = 0.1
(specific

9. Hail
 Hail is created when moisture and wind are together. Inside the
cumulonimbus clouds ice crystals form, and begin to fall towards
the surface of Earth. When this starts to happen wind gusts start
to pick up the ice crystals pushing them up high into the clouds. As
they start to fall down again they continue to grow in size. A wind
gust might catch the hail stone again which will push it back up
into the cloud. This whole process gets repeated several times
before the hail stone becomes so big that it is too heavy for the
wind to carry so it must fall towards Earth.
Shapes of hail particles
1.Spherical
2.Conical
3.Irregular
Diameter range 5 to 125 mm
Specific gravity = 0.8
Average density (specific gravity) = 0.1

10. Fog
 There is really no different between fog and the
clouds that are high in the sky. In simple terms fog
is; a cloud that has formed near the surface of the
Earth.
 There are four main types of fog,
 radiation fog
 advection fog
 upslope fog
 evaporation fog

11. Dew
 The small drops of water which can be found on cool
surfaces like grass in the morning.
 This is the result of atmospheric vapor condensing on
the surface in the colder night air.
 Dew Point is the temperature in which condensation
starts to take place or when dew is created.

12. Mist / Drizzle
Mist is a bunch of small droplets of water which are in the
air. This occurs with cold air when it is above a warm
surface, for example water.
Fog and mist are very similar, the only difference is their
visibility.
If you cannot see 1 kilometer or less you know you're dealing with
fog.
You can see visuals through mist and it is more haze looking than
a thicker substance.
Diameter range between 0.1
and 0.5 mm/hr

13. Glaze
 Glaze is the ice coating, generally clear and
smooth, formed on exposed surfaces by the
freezing of super cooled water deposited by
rain or drizzle.
Specific gravity may be as high as 0.8-0.9

14. Sleet
Sleet consists of transparent, globular, solid
grains of ice formed by the freezing of raindrops
or freezing of largely melted ice crystals falling
through a layer of sub freezing air near the earth’s
surface.

16. Measurement of Precipitation
 1. Amount of precipitation
 2. Intensity of precipitation
 3. Duration of precipitation
 4. Arial extent of precipitation

17. Measurement Methods
Measurement of precipitation (Rain and Snow)
can be done by various devices. These measuring
devices and techniques are;
Rain Gauges
Snow Gauges
Radars
Satellites
Scratching of snow packs
Water equivalent in snow packs

18. RAIN GAGES
 Rain gages are most commonly used for the
measurement of precipitation, both in terms of
rain fall and snow.

19. Types of rain gages
 There are two main types of rain gages which
are used to measure the precipitation. These
are;
 1. Non recording rain gages
 2. Recording rain gages

20. Non recording rain gauges
 It is a rain gage which does not provide the
distribution of amount of precipitation in a day. It
simply gives the amount of precipitation after 24
hours (daily precipitation).

21. Recording rain gauges
 These rain gauges are also called integrating rain
gauges since they record cumulative rainfall. In
addition to the total amount of rainfall at a
station, it gives the times of onset and cessation
of rains (thereby gives the duration of rainfall
events)

22. Types of recording Rain
gauges
 There are three main types of recording rain
gauges
 1. Float type rain gages
 2. Tipping bucket type rain gages
 3. Weighing type rain gages

23. 1. Tipping bucket gauges
 A tipping bucket rain gauge is used for
measurement of rainfall. It measures the rainfall
with a least count of 1 mm and gives out one
electrical pulse for every millimeter of rainfall

24. 2. Weighing type gauges
It consists of a storage bin, which is weighed to record the
mass. It weighs rain or snow which falls into a bucket, set on
a platform with a spring or lever balance. The increasing
weight of the bucket and its contents are recorded on a
chart. The record shows accumulation of precipitation.

25. 3. Float recording gauges
 The rise of float with increasing catch of rainfall is recorded. Some
gauges must be emptied manually while others are emptied
automatically using self starting siphons. In most gauges oil or
mercury is the float and is placed in the receiver, but in some cases the
receiver rests on a bath of oil or mercury and the float measures the
rise of oil or mercury displaced by the increasing weight of the receiver
as the rainfall catch freezes. Float may get damaged by rainfall catch
freezer