CLOUDS HOW DO CLOUDS FORM Condensation or deposition

CLOUDS

HOW DO CLOUDS FORM? § Condensation or deposition of water above Earth’s surface creates clouds. § Clouds develop in air masses that become saturated (relative humidity = 100%).

Condensation Can Form: 1. 2. 3. 4. Fog Clouds Frost Dew

Fog § When water vapor condenses on nuclei and a large # of these droplets for a mass § Minor condensation § Four Types

Radiation Fog § Outgoing radiation of Earth creates a cold ground § Air directly above surface cools to dew point = condensation

Advection Fog § Movement of warm moist air over a colder surface § Warm air is cooled = condensation § Can be persistent § “sea fog”

Upslope fog § A warm breeze ascends a mountain and cools to the dew point = condensation

Smog § Many condensation nuclei present § Can occur before dew point

WHAT CAUSES CLOUDS TO DEVELOP? § Saturation depends on: – Relative humidity of the air – Degree of cooling (has to reach dew point) – Condensation nuclei

WHAT CAUSES CLOUDS TO DEVELOP? § OROGRAPHIC UPLIFT – air forced to rise because of elevated land (mountains). § CONVENTIONAL UPLIFT – due to heating of the Earth’s surface. § CONVERGENCE OR FRONTAL LIFTING – results from the collision of air masses that have different temperature and moisture characteristics.

3 Ways Air Rises to Form Clouds Text and Photographs © 2002 Peter J. & Shirley F. Robinson

Cloud Classification § Height – Strato = Low clouds – have bases below 6, 500 ft. – Alto = Middle clouds – have bases between 6, 500 ft. and 20, 000 ft. – Cirro = High clouds – have bases above 20, 000 ft. § Shape – – – Cirrus – feather-like Stratus – horizontal, layered, gray Cumulus – vertical (heaped), “cauliflower”, unstable § Multi-level clouds – vertically thick, spanning multiple layers (nimbostratus, cumulonimbus) § Orographic clouds – distinct clouds that form via interaction between wind and mountainous terrain

High Clouds Cirrus Cirrocumulus Cirrostratus

Cirrus clouds

Cirrus Clouds

Wavy Cirrocumulus

Cirrostratus

Middle Clouds Altocumulus Altostratus

Altocumulus

Altocumulus at Sunset

Altostratus

Low Clouds Cumulus Stratocumulus Stratus Fog

Cumulus clouds over the Atlantic Ocean

Stratocumulus

Stratus Clouds

More stratus clouds

Stratus clouds: a view from above

Multi-Layer Clouds Stratonimbus Cumulonimbus

Anvil Formation

Cumulonimbus (Thunderhead)

Orographic Clouds Cap clouds Lenticular clouds

Is this a UFO?

Are these clouds?

YES! Another type of cloud can be formed from the vapor contained in the exhaust of a jet engine of an airplane when they are flying at high enough altitudes where cold temperatures cause the vapor to turn into ice crystals like cirrus clouds. These clouds are called contrails (short for "condensation trails") and look like lines in the sky.