Clouds Flashcards
What are clouds?
The presence of water droplets/ice crystals suspended in the atmosphere l.
Clouds impede visibility, how?
They scatter the light.
What does the amount of light that passes through cloud depend upon?
1) concentration of water droplets
2) the thickness of the layer
How do clouds form?
When water vapour condenses in the atmosphere.
Name the 3 ways in which water droplets are cooled below their dew point.
1) Adiabatically
2) Mixing Air; temperature drop
3) Evaporation/ condensation causing heat loss.
What are convection currents?
Happens when the surface of the earth absorbs radiation from the sun at differing rates. Localised heating occurs.
When this occurs convection currents are set up, carrying warm less dense air upwards.
What are the two classifications if cloud?
Cumuliform; or
Stratiform
The formation of cloud depends upon
The lifting process involved; and
Stability of air
Cumuliform clouds are characterised by marked vertical development. Caused by localised heating at the surface or lines produced by frontal activity or orographic ascent
True
The strong advection currents within the cumuliform clouds can reach speeds in excess of?
100mph
CBs are firmed in unstable air and grows rapidly until it reaches warm air or the tropopause. Creatingbthe anvil top.
True
How are stratified clouds produced?
Moist air is carried upwards by turbulence, cooled and condenses.
These clouds spread horizontally
List the high clouds
Cirrus (Ci)
Cirro-cumulus (CC)
Cirro-stratus (CS)
How high are the high clouds?
20,000ft and above
List the medium clouds
Alto-cumulus (Ac)
Alto-stratus (As)
Numbing-stratus (Ns)
How high are the medium clouds?
7,000-20,000ft
Nimbo-stratus (Ns) can form lower than 7,000ft. True or False?
True.
List the low clouds
Stratocumulus (Sc)
Stratus (St)
Cumulus (Cu)
Cumulonimbus (Cb)
What height do low clouds firm at?
Below 7,000ft
What is cloud base?
The height of the base of any cloud above AD elevation
What is cloud ceiling?
The vertical distance from the AD elevation to the lowest part of any cloud visibility from the AD which is sufficient to obscure more than one half of the sky’s visibility
How are cloud bases assessed at Aerodromes?
By electronic cloud base recorder. Laser beams sent and reflected to give accurate distance.
Ok weather reports cloud height is referred to?
Above AD elevation
Few =
1-2 OKTA
SCT=
3-4 OKTA
BKN =
5-7 OKTA
OVC=
8 OKTA
List the two ways in which cloud is dispersed
1) Evaporation = mixes with drier air increasing relative humidity, water droplets change to water vapour.
2) Precipitation = Air is cooled and releases water and may cause relative humidity to fall below 100%
