Clouds

Cloud formation Large mass of air rises, cools to dew point Condensation (or deposition) occurs on condensation nuclei salt, dust, soil, pollutants

elevation at which air becomes saturated is lifting condensation level (flat base of clouds)

A cloud is a mass of suspended water, supercooled water and/or ice particles. particles 20-50 micrometers Water is supercooled : liquid below freezing

< -40oC (-40°F): all ice crystals < -20oC: predominantly ice crystals -12o to -20o C: mixture of ice and supercooled water > -12oC (10°F): all water

Cloud classification (according to shape and altitude) Shape Classes: Flat: stratiform Globular: cumuliform

Altitude Families: High Cloud (cirro-): ice crystal clouds > 6000 m (20,000 ft.) CIRRUS, CIRROSTRATUS, CIRROCUMULUS

cirrus

cirrus

Cirrostratus (halo around sun or moon)

cirrostratus

cirrocumulus

Altitude Classes: Middle Cloud (alto-) 3000 – 6000 m (10,000 - 20,000 ft.) ALTOSTRATUS, ALTOCUMULUS

altostratus

altostratus

altostratus

altocumulus

altocumulus

altocumulus

altocumulus

Altitude Classes: Low Cloud (stratus) <3000 m (10,000 ft) STRATUS, NIMBOSTRATUS, STRATOCUMULUS

stratus

stratus

stratus

nimbostratus

stratocumulus

stratocumulus

stratocumulus

Altitude Classes: Vertically developed clouds (CUMULONIMBUS)

Vertically Developed Clouds: cumulonimbus

cumulonimbus

cumulonimbus

cumulonimbus

mammatus

lenticular Strong wind flow over rugged terrain often stacked

Cumulonimbus pileus

Cumulus fractus (small, ragged)

Cumulus humilis (smaller vertical extent)

Altocumulus translucidus

Altostratus translucidus

Altocumulus undulatus

contrails

contrails