Transcript What are clouds?

Clouds
D. Blanck
Water, Energy and Temperature
 Gas - water
vapor (invisible)
 Liquid - water
droplets (visible)
 Solid - ice
crystals, hail,
snow
What are clouds?
Clouds are formed of tiny droplets of water or
ice. (~20 microns in diameter)
Necessary ingredients for cloud formation:
1. Humidity
2. Rising, expanding, cooling air
• Adiabatic expansion/cooling
3. Condensation nuclei
How is air cooled?
 Contact with a cold surface such as
over land in winter.
 Convection: uplift over warm ground.
 Orographic: air rising over mountains.
 Frontal: a mass of warm air meeting
and rising over a mass of cold air.
What happens when air is cooled?
 Relative humidity increases.
 Dew point is reached (100% relative
humidity).
 Water vapor (invisible) condenses to
form water droplets (visible).
 Sometimes the water vapor may change
straight into solid state: called
sublimation.
Cloud shapes
Clouds can be classified by their shape and height
Flat clouds
eg Stratus (St)
Fluffy clouds
eg Cumulus (Cu)
Wispy clouds
eg Cirrus (Ci)
Cloud heights
Clouds can also be classified by height of cloudbase
Low level (below 2000m)
eg stratus
Middle level - alto
(2,000 to 6, 000m)
eg alto-cumulus
High level - cirro (above
6,000m)
eg cirrus
Cloud Diagram
Specific Cloud Examples
Cirrus
Whispy, fibrous, feathery.
Calm clear day.
Made up of ice crystals
Predict approaching storms
Cirrostratus
“tangled web”
Halo effect
Cirrocumulus
Tiny balls of cotton,
Also called a “mackerel sky,” fish scales.
Altocumulus
Great flock of sheep
Altostratus
Sun shines through, frosted glass
Stratocumulus
Twisted cotton
Stratus-Nimbostratus
Formless, blanket like cloud
Nimbus = RAIN
Some clouds develop vertically
Cumulus
Fluffy, cottonball appearance
Generally fair weather clouds
Cumulus Congestus or
Towering Cumulus
Cumulonimbus
Storm clouds.
Currents of rising air meet tropopause
Anvil head appearance.
Thunder and lightning
Other clouds
Lenticular cloud
“UFO” shape
Scud cloud
Ragged stratus cloud usually
associated with Cumulonimbus.
Fog
A cloud at ground level
Noctilucent clouds
Spot the cloud!
Low and flat …..
Stratus
Spot the cloud!
Middle level,
fluffy …..
Alto -Cumulus
Spot the cloud!
High level,
wispy …..
Cirrus
Spot the cloud!
Rain bearing,
storm clouds …..
Cumulo-Nimbus
World cloud patterns
Can you explain the major world cloud belts?
Clouds in Forecasting