cloud - soest · cloud classification clouds are categorized by their (cloud base) height,...
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Cloud FormationAll clouds require 3 things
1. Water vapor2. Cloud Condensation nuclei (CCN)3. Cooling - heat transfer out of air parcel
or work done by air molecules in parcel.
(1) Lifting – most clouds form when air is lifted.a) Convergence – low press center – stratusb) Mountains – lifting by terrainc) Fronts – lifting over denser air.d) Warm air relative to surroundings
i) Fires, volcanoes – cumulusii) Latent heat
(2) Mixing – seeing your breath on cold day
(3) Contact – with cold surface: advection fog
(4) Radiation – fog in winter mornings
Mechanisms for Cooling the Air
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Cloud classificationClouds are categorized by their (cloud base) height, appearance, and vertical development– High Clouds - generally above 16,000 ft (>5 km) at
middle latitudes and up to the tropopause• Main types - Cirrus, Cirrostratus, Cirrocumulus
– Middle Clouds – 7,000-23,000 feet (2-7 km)• Main types – Altostratus, Altocumulus
– Low Clouds - below 6,500 ft (2 km)• Main types – Stratus, stratocumulus,
nimbostratus– Vertically developed clouds (via convection)
• Main types – Cumulus, Cumulonimbus
Cellular structure in a top viewRayleigh-Benard convection
Cellular structure of stratocumulus clouds over the NE Pacific (9/14/06)
10o
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High Clouds• White in day; read/orange/yellow at
sunrise/sunset• Made of ice crystals
Cirrus (Ci)• Thin and wispy• Move toward the east• Indicate fair weather
Cirrocumulus (Cc)• Less common than crirrus• Small, rounded white puffs individually
or in long rows (fish scales; mackerel sky)
Cirrostratus (Cs)• Thin and sheet-like• Sun/moon clearly visible through them• Halo common• Often precede precipitation
Cirrus
High Clouds• White in day; read/orange/yellow at
sunrise/sunset• Made of ice crystals
Cirrus (Ci)• Thin and wispy• Move toward the east• Indicate fair weather
Cirrocumulus (Cc)• Less common than crirrus• Small, rounded white puffs individually
or in long rows (fish scales; mackerel sky)
Cirrostratus (Cs)• Thin and sheet-like• Sun/moon clearly visible through them• Halo common• Often precede precipitation
Cirrocumulus
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High Clouds• White in day; read/orange/yellow at
sunrise/sunset• Made of ice crystals
Cirrus (Ci)• Thin and wispy• Move toward the east• Indicate fair weather
Cirrocumulus (Cc)• Less common than crirrus• Small, rounded white puffs individually
or in long rows (fish scales; mackerel sky)
Cirrostratus (Cs)• Thin and sheet-like• Sun/moon clearly visible through them• Halo common• Often precede precipitation
Cirrostratus
Middle Clouds• Altostratus (As)
– Gray, blue-gray– Often covers entire sky– No halo– Sun or moon may show
through dimly• Usually no shadows
• Altocumulus– <1 km thick– mostly water drops– Gray, puffy– Differences from cirrocumulus
• Larger puffs• More dark/light contrast
Altostratus (As)
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Middle Clouds• Altostratus
– Gray, blue-gray– Often covers entire sky– Sun or moon may show
through dimly• Usually no shadows
• Altocumulus (Ac)– <1 km thick– mostly water drops– Gray, puffy– Differences from cirrocumulus
• Larger puffs• More dark/light contrast
Altocumulus (Ac)
Low CloudsStratus (St)• Uniform, gray• Resembles fog that does not reach the ground• Usually no precipitation, but light mist/drizzle possible
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Stratocumulus (Sc)• Low lumpy clouds• Breaks (usually) between cloud elements• Lower base and larger elements than altostratus
Low Clouds
Nimbostratus (Ns)• Dark gray• Continuous light to moderate rain or snow• Evaporating rain below can form fractus
Low Clouds
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Cumulus (Cu)• Puffy “cotton”• Flat base, rounded top• More space between cloud elements than stratocumulus
Vertically Developed Clouds
Cumulus Congestus• Towering cumulus• Rain showers
Vertically Developed Clouds
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Cumulonimbus (Cb)• Thunderstorm cloud• Very tall, often reaching tropopause, often with anvils• Individual or grouped• Violent vertical motion that may exceed 50 knots• Large energy release from water vapor condensation
Vertically Developed Clouds
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Cloud type (Fog is just one type of cloud that touches ground)
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Stc
Cb
Cu
Cu
Visible
Cb Ci
Cu
Infrared