[Ref Understanding Weather & Climate, Books a la Carte Edition (6th Edition) #ISBN-13: 978-0321773227 #ISBN-10: 0321773225 CH 5 Atmospheric Moisture, CH 6 Cloud Development and Forms, Pilot’s Handbook of Aeronautical Knowledge, FAA-H-8083-25B Page 12-15]
Clouds are visible indicators of water content and are often indicative of future weather.
Three (3) basic criteria for clouds to form
- adequate water vapor
- condensation nuclei
- method by which the air can be cooled
Formation and Dissipation of Cloud Droplets
At about 50m or so above the LCL, all the condensation nuclei in the air will have attracted water (occupied), and further uplift leads only to the growth of existing water droplets – no new droplets form, instead, the existing droplets grow larger only.
The condensation products (clouds) may not be evaporated during descent – the atmosphere loses moisture by precipitation of rain and snow.
4 mechanisms lift air so that condensation and cloud formation can occur:
- Orographic lifting
- Frontal lifting
- Convergence – due pressure difference
- Localized convection – due heating
3 main types of clouds and lists of Classification of clouds
Cloud type is determined according to the height of their bases:
- low clouds (surface to 6,500 feet AGL)
- middle clouds (6,500 to 20,000 feet AGL)
- high clouds (>20,000 feet AGL)
Specific cloud types could have a list of classification – according to the outward appearance and cloud composition:
- Cumulus – heaped or piled clouds
- Stratus – formed in layers
- Cirrus – ringlets, fibrous clouds, also high level clouds above 20,000 feet
- Castellanus – common base with separate vertical development, castle-like
- Lenticularus – lens-haped, formed over mountains in strong winds
- Nimbus – rain-bearing clouds
- Fracto – ragged or broken
- Alto – middle level clouds existing at 5000 to 20000 feet
In general, clouds with extensive vertical development are cumulus clouds that build vertically into Towering cumulus (TCU) or Cumulonimbus clouds (CB). These types of cloud indicate areas of instability in the atmosphere.
Besides, to pilots, the CB is known as either an air mass or ororaphic thunderstorm.
Should the CB form in a continuous line, we call that “squall lines”
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