Clouds

1
Clouds
2
The Recipe

• Clouds need three things to form
• Moisture
• Cooling air to its Dew Point (condensation)
• Condensation Nuclei (dust, smoke)

3
How do we get to the Dew Point

• The easiest way to bring an air masses
  temperature to its dew point is to move air to a
  higher altitude

Cool
As the moist air rises its temperature decreases
and the water vapour begins to condense
Moist Air
Warm
4

• The drier air is the farther it has to climb to
  reach its dew point
• At higher altitudes the temperatures are much
  colder and below freezing

Dry Air
Moist Air
5

• Moist air has more water vapour and will become
  saturated at a warmer temperature
• As a result clouds will form at lower altitudes
  out of water droplets

Moist Air
6

• When the Dew point is below freezing this means
  that when the water vapour condense it will
  actually freeze into ice crystals
• This usually happens at very high altitudes in
  dry conditions

Moist Air
7
Cloud types

• Clouds can be classified in three different ways
• Shape
• Altitude
• Is there precipitation?

8
Cloud Shape

• Cumulus
• Puffy
• Stratus
• Shapeless
• fog
• Cirrus
• Dry conditions
• Ice crystals

9
Cloud Height

• Up to 2000 m
• Just use cloud shape name
• 2000 6000 m
• Use prefix alto with the shape
• 6000 m and above
• Use prefix cirro- or suffix -cirrus with
  cloud shape
• Example altostratus or cirrostratus

10
Precipitation

• Precipitation
• Use prefix nimbo- or suffix nimbus with the
  shape
• Example - cumulonimbus

11
Precipitation

• The average drop is just 0.02 mm across in a
  cloud (too small to fall)
• By the time it hits the ground the average drop
  is 2 mm across
• So how does it grow?

12
Growing by Coalesce

• As the raindrop falls in the cloud it collides
  with other drops and begins to grow
• Wind will continue to circulate the drop until it
  becomes to heavy and falls to the ground as
  precipitation