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Clouds and Classification (Principle of drop formation (Condensation…
Clouds and Classification
Principle of drop formation
Condensation process requires condensation nuclei
Super saturation is water vapour over 100% RH\
cloud with low bases hold more water that high cloud bases because temp is colder with height
ELR
less
than 1.5degree / 1000ft and saturated air is stable, cloud will be stratiform
ELR
greater
1.5degree / 1000ft and saturated air is unstable, cloud will be cumliform
Evaporation of cloud drops
Virga is evaporating and descending water
Cloud drops are very small compared to rain drops
Cloud Classification
vertical dimension
High cloud = from 5km and higher (17,000ft+)
Middle cloud = 2-5km (7-17,000ft)
Low cloud = below 2km (7,000ft)
High Cloud
Cirrostratus (CS) - sheeps wool appearance
Cirrocumulus (CC) - high winds aloftt
Cirrus (CI) - Indication of approaching bad weather
Middle Cloud
Altostratus
Approaching bad weather
Ice above freezing level
Light precipitation
Altocumulus
No preciptiitation
Low Cloud
Stratocumulus
Stratus
Cumulus
Bright white
thermal and orographic
Moderate turbulence
Cumulonimbus
Unstable air
Dense, heavy, an associated with Thunderstorms
Radius of 10-15kms
towering cumulus
No anvil like Cb
Nimbostratus
Extensive cloud
Poor visibily beneath
Heavy rain
Reporting of cloud
Few - 1-2 Oktas
Scattered (SCT) - 3-4 Oktas
Broken (BKN) - 5-7 Oktas
Overcast (OVC) - 8 Oktas
Clouds are simply suspended water in liquid or solid ice form
Main causes of cloud formation
Orographic rising
Air is blown towards mountains and forced to ascend
High moisture / unstable air = cumulus cloud with low base
Moist and stable air = stratiform cloud
Mechanical rising
Lifting due to small hills, buildings etc
Convective rising
Due to the earth surface heating, convection causes the air to rise
Dry and unstable air
Clouds consist of ice crystals