Clouds

• Identify cloud types from photos

• Recognize and define prefixes and suffixes for cloud types

• Describe different fog types

• Associate general weather conditions with cloud types

Clouds

Cloud Appreciation Society

Three kinds of fog

• Radiation fog

• Advection fog

• Evaporation fog

Evaporation fog on the Kentucky River

Precipitation

• Explain the collision coalescence process and the Bergeron process

• Describe how aerosols and dust act as condesation nuclei or freezing nuclei

• Explain how supersaturated atmospheric conditions develop

• Describe how air pollution impacts cloud formation and precipitation

• Explain the logic behind cloud seeding

• Collision coalescence process– Water droplets collide

and increase in size until large enough for gravity to pull them out of the cloud

– Occurs in tropics and warmer midlatitudes

– Precip leaves cloud as liquid water

• Collision coalescence process requires presence of condensation nuclei– In clean air, RH must

equal 120% for condensation to occur

– Air would be considered supersaturated with water vapor

– Presence of condensation nuclei allows condensation at 100% humidity

http://www.youtube.com/watch?v=E8AvfXar9zs

• Bergeron process of precipitation formation– Also requires “dirty”

atmosphere– Supercooled water (-40

degrees C) crystallizes upon contact with freezing nuclei

• Bergeron process– Ice crystals form around

freezing nuclei and grow through deposition

– Precipitation leaves cloud as ice crystal

– Occurs in midlatitudes to poles

Precipitation under Bergeron conditions

• Rain – ice crystal melts and liquid water reaches surface

• Sleet – warm layer melts ice but refreezes as “pellet”. Winter phenomena.

• Snow – ice crystal falls to ground intact

• Freezing rain – supercooled liquid water freezes at surface

• Hail – summertime thunderstorm phenomena.

Albedo greater in polluted

atmosphere

Clouds last longer in polluted

atmosphere