Cloud Formation and Images

8/8/2019 Cloud Formation and Images

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Cloud Formation

All clouds require 3 things

1. Water vapor

2. Cloud Condensation nuclei (CCN)

3. Cooling - heat transfer out of air parcelor work done by air molecules in parcel.

(1) Lifting – most clouds form when air is lifted.

a) Convergence – low press center – stratus

b) Mountains – lifting by terrain

c) Fronts – lifting over denser air.

d) Warm air relative to surroundings

i) Fires, volcanoes – cumulus

ii) 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



Cloud classification

Clouds are categorized by their (cloud base) height,appearance, and vertical development

– High Clouds - generally above 16,000 ft (>5 km) atmiddle 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



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; mackerelsky)

Cirrostratus (Cs)• Thin and sheet-like• Sun/moon clearly visible through them

• Halo common

• Often precede precipitation

Cirrus


sunrise/sunset

• Made of ice crystals

Cirrus (Ci)• Thin and wispy

• Move toward the east


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


Cirrocumulus




sunrise/sunset• Made of ice crystals

Cirrus (Ci)• Thin and wispy• Move toward the east


Cirrocumulus (Cc)• Less common than crirrus

• Small, rounded white puffs individually

or in long rows (fish scales; mackerelsky)

Cirrostratus (Cs)• Thin and sheet-like• Sun/moon clearly visible through them

• Halo common


Cirrostratus

Middle Clouds• Altostratus (As) – Gray, blue-gray

– Often covers entire sky

– No halo

– Sun or moon may showthrough dimly

• Usually no shadows

• Altocumulus – <1 km thick

– mostly water drops

– Gray, puffy – Differences from cirrocumulus

• Larger puffs

• More dark/light contrast

Altostratus (As)



Middle Clouds

• Altostratus – Gray, blue-gray

– Often covers entire sky

– Sun or moon may showthrough 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





Cumulus (Cu)• Puffy “cotton”

• Flat base, rounded top

• More space between cloud elements than stratocumulus

Vertically Developed Clouds

Cumulus Congestus

• Towering cumulus• Rain showers




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




Cloud type(Fog is just one type of cloud that touches ground)



Stc

Cb

Cu

Cu

Visible

Cb Ci

Cu

Infrared

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Cloud Formation and Images