CLOUDS AND PRECIPITATION DSV(2).pptx.pdf

Weather

1. CLOUDS AND PRECIPITATION

3. WATER CYCLE

4. WATER CYCLE

5. CLOUDS
“A visible aggregate of minute droplets of water or particles of ice
or a mixture of both floating in the free air”

6. CLOUD FORMATION
Air parcel expands as it rises and this expansion or
work, causes the temperature of the air parcel to
decrease
At some point saturation occurs beyond which the
extra water vapour settles down as dew
To settle down as water droplet it requires a surface

7. Principle of Condensation
Water vapour condenses on Aerosols
Aerosols enable the water vapour present in the
atmosphere to condense
Particles on which condensation takes place are
called Condensation Nuclei
CONDENSATION NUCLEI

8. CONDENSATION NUCLEI
NUCLEI
HYDROSCOPIC HYDROPHOBIC

9. CONDENSATION NUCLEI
Name Size
Aitken nuclei Radius less than 0.1 Micron
Large Nuclei Radius between 0.1 and 1.0 Micron

Giant Nuclei Radius more than 1.0 Micron

10. STABILITY

11. v
STATE OF EQUILIBRIUM

12. ADIABATIC PROCESS
Although the air parcel can expand and contract
freely, it does not break apart, but remains as a
single unit
Neither external air nor heat can mix with the air
inside the parcel
Air pressure surrounding the parcel lowers as it
is lifted up
The lower pressure outside allows the air
molecules inside to push the parcel walls
outward, expanding the parcel
Figure : Difference between Isothermal and
Adiabatic process

13. ADIABATIC PROCESS
Because there is no other energy source, the air molecules
inside must use some of their own energy to expand the
parcel resulting a drop in temperature
If the parcel is lowered to the surface, higher pressure
squeezes (compresses) the parcel back into its original
(smaller) volume
A rising parcel of air expands and cools, while a sinking
parcel is compressed and warms
If a parcel of air expands or compresses, with no interchange
of heat with its surroundings, this process is called an
adiabatic process
Figure : Adiabatic expansion and
compression

14. LAPSE RATE
Rate of change of temperature with height is Lapse Rate
Positive Lapse Rate : Temperature decreases with height
Negative Lapse Rate : Temperature increases with height
Isothermal Layer : Temperature doesn’t change with height

15. ENVIRONMENTAL LAPSE RATE (ELR)
The rate at which the air temperature surrounding us would
be changing if we were to climb upwards into the
atmosphere is known as Environmental Lapse Rate (ELR)
Radiosonde is an instrument used to find the vertical
temperature profile of the atmosphere and gives the ELR
ELR is the prevailing lapse rate which an air parcel will
actually follow at a given time and place
Figure : Environmental Lapse Rate

16. v
DRY ADIABATIC LAPSE RATE (DALR)
The rate of adiabatic cooling or warming for unsaturated air
(RH less than 100 percent) remains constant
The rate of change of temperature of unsaturated parcel is
known as Dry Adiabatic Lapse Rate (DALR)
This rate of heating or cooling is about 10°C for every 1000
m of change in elevation (5.5°F per 1000 ft)
Figure : Dry Adiabatic Lapse Rate

17. v
SATURATED ADIABATIC LAPSE RATE (DALR)
The rate at which rising or sinking saturated air changes
temperature is the Saturated Adiabatic Lapse Rate (SALR)
or Moist Adiabatic Lapse Rate
SALR is not constant, but varies greatly with temperature
and, hence, with moisture content
An average of 6°C per 1000 m (3.3°F per 1000 ft) is used as
a standard value
Figure : Moist Adiabatic Lapse Rate

18. v
ATMOSPHERIC EQUILIBRIUM
Stable Atmosphere - If the rising air is colder than its environment, it will be more dense
(heavier) and tend to sink back to its original level.
Unstable Atmosphere - If the rising air is warmer and, therefore, less dense (lighter)
than the surrounding air, it will continue to rise until it reaches the same temperature as
its environment
Neutral Atmosphere - If rising or sinking air cools or warms at the same rate as the air
around it. At each level, it would have the same temperature and density as the
surrounding air

19. v
STABILITY CRITERIA
ELR < SALR or ELR < DALR Absolute Stability
ELR = SALR or ELR = DALR Neutral Stability
ELR > SALR or ELR > DALR Absolute Instability
DALR > ELR > SALR Conditional Instability

20. v
TRIGGERING MECHANISMS
1. Convection 2. Topography
3. Convergence 4. Fronts

21. v
CONDITIONS FOR CONDENSATION
Moisture
Condensation Nuclei
Saturation

22. v
CLASSIFICATION OF CLOUDS – NOMENCLATURE
French Naturalist Lamarck (1744 – 1829) proposed the first system for
classifying clouds in 1802
Luke Howard, an English naturalist, developed a cloud classification
system that found general acceptance
Howard system classified clouds in to four basic forms as they appear to
a ground observer

23. CLOUD GROWTH
Collision and Coalescence Bergeron Process

24. SerLatin RootTranslation Example
(a) Cumulus Heap Fair Weather
Cumulus
(b) Stratus Layer Altostratus
(c) Cirrus Curl of hair Cirrus
(d) Nimbus Rain Cumulonimbus
CLASSIFICATION OF CLOUDS – NOMENCLATURE

25. Broadly divided into three families according to the average
height and development
Ser Type Height in ft
(a) High Above 20,000
(b) Medium 6,000 – 20,000
(c) Low Up to 6500
Prefix "cirr-", as in cirrus clouds are located at high levels
Prefix "alto-", as in altostratus, are found at middle levels
CLASSIFICATION OF CLOUDS – NOMENCLATURE

26. CLASSIFICATION OF CLOUDS – NOMENCLATURE

27. Form above 20,000 feet (6,000
meters)
Composed of ice crystals
(temperatures are so cold at such
high elevations)
Thin and white in appearance, but
can appear in a magnificent array of
colours when the sun is low on the
horizon
Cirrus
Cirrostratus
Cirrocumulus
HIGH-LEVEL CLOUDS

28. Appear between 6,500 to 20,000 feet
(2,000 to 6,000 meters)
Composed primarily of water droplets
Can also be composed of ice crystals
when temperatures are cold enough
Altocumulus
Altostratus
MID-LEVEL CLOUDS

29. Cloud base generally lie below 6,500 feet (2,000 meters)
Mostly composed of water droplets
When temperatures are cold enough, these clouds may also contain ice
particles and snow
LOW-LEVEL CLOUDS

30. Nimbostratus
Stratocumulus Fair weather Cumulus Towering Cumulus
LOW-LEVEL CLOUDS
Stratocumulus
Stratus
Cumulonimbus
Stratocumulus

31. CLOUDS

32. SPECIAL TYPE OF CLOUDS
Lenticular Clouds (Lens shaped clouds seen at times near mountain tops
or on the leeward side of the mountains)
Line Squall Clouds (roll clouds of dark color in the shape of an arc, slightly
ahead of a long line of cumulonimbus clouds. Their approach indicates
impending severe weather)
Rotor Clouds (roll type of clouds, which sometimes form on the leeward
side of a mountain in a zone of severe turbulence)

33. SPECIAL TYPE OF CLOUDS
Lenticular
clouds
Rotor
clouds

34. SPECIAL TYPE OF CLOUDS
Squal
l

35. SUPPLEMENTARY FEATURES OF CLOUDS
Mamma. Also known as "mammatus". Hanging bulges on
the undersurface of a cloud. Usually beneath a Cb cloud
Virga. Trails of precipitation from the base of cloud, not
reaching the surface
Tuba. Funnel shaped column from the base of cloud
associated with a tornado

36. SUPPLEMENTARY FEATURES OF CLOUDS
Mammatu
s
Virg
a

37. SUPPLEMENTARY FEATURES OF CLOUDS
Tuba

38. PRECIPITATION

39. v
CONDITIONS FOR CONDENSATION
Moisture
Condensation Nuclei
Saturation

40. Any form of water particles, liquid or solid that fall from sky and reach the
ground
Can be long lasting and steady, or may fall as brief and intense shower
Removes water vapour from the atmosphere
PRECIPITATION

41. CLOUD DROPLET

42. CURVATURE AND SOLUTE EFFECT

43. Saturated vapour pressure of a convex surface is more than that of
plane surface
Thus, a drop will not develop if its radius is small
Beyond a radius of 2 micron, the curvature effect disappears
Solute and curvature effects are important ones at the beginning of
the process
CURVATURE AND SOLUTE EFFECT

44. Presence of water in the troposphere
Decrease in pressure of mixture of dry air and water vapour in the upper
troposphere and decrease in relative humidity
Condensation of water droplets
‘Condensation nuclei’ and their presence is essential for the initiation of
condensation
Rate of condensation depends on factors like availability of water vapour, the
rate of removal of latent heat, size and hygroscopic nature of condensation
nuclei
PRINCIPLE OF PRECIPITATION

45. Aitken nuclei need considerable super saturation to become active during the
condensation process due to their small size
Large nuclei will be first to claim the available water by virtue of their larger size
Large nuclei are more in number than the giant nuclei too
SIZE OF CLOUD DROPLET

46. Large nuclei take part actively in cloud formation
Cloud droplets compete for the available water vapour
If concentration of condensation nuclei is more, the number of cloud droplets will
be more, but size would be small
Condensation begins on larger and more active nuclei and grow to full size
droplets, when humidity is 100%
SIZE OF CLOUD DROPLET

47. Factors that affect the growth of cloud
droplets are nature of nuclei, surface
tension of droplets, the rate of
dissipation of released latent heat to
the surrounding air and its temperature
Precipitation mechanism
SIZE OF CLOUD DROPLET

48. Primarily explain the occurrence of
precipitation in clouds which do not reach
0
0
C i.e. from relatively warm clouds
Wake capture
Direct capture
THE COALESCENCE MECHANISM
(CAPTURE PROCESS)

49. Explains the precipitation from the clouds which
reach above 0 deg C isotherm
Deposition
GROWTH OF ICE CRYSTALS AND
BERGERON PROCESS

50. GROWTH OF DROPLETS

51. TYPES OF PRECIPITATION
DRIZZLE : DROPLET SIZE < 0.5 mm RAIN : DROPLET SIZE > 0.5 mm

52. TYPES OF PRECIPITATION
SHOWER SNOW

53. TYPES OF PRECIPITATION

54. TYPES OF PRECIPITATION
RIME