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

Stratus

Cumulus

Cirrus

Cirrostratus

Cirrostratus

Cirrocumulus

Altostratus (and cirrus, higher)

Altostratus

Altocumulus

Stratocumulus

Nimbostratus

Cumulonimbus

Mammatus clouds

Three kinds of fog Radiation fog Advection fog Evaporation fog Evaporation fog on the Kentucky River

Inland radiation fog

California; advection fog

Coastal California advection fog

Maine evaporation fog

Evaporation fog

Virga

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 The air reaches saturation and some of the resulting droplets will come in contact with freezing nuclei (assuming they have reached the activation temperature). We will now have a combination of ice crystals and supercooled water droplets. From the perspective of the supercooled droplets, the air is in equilibrium at saturation, but from the perspective of the ice crystals, the air is supersaturated. Therefore, water vapor will sublimate on the ice crystals. Since the amount of water vapor in the air has decreased, and from the perspective of the supercooled water droplet, the air is subsaturated, the supercooled water will evaporate until the air once again reaches saturation. The process then continues. In short summary, the ice crystal grows through sublimation at the expense of the supercooled water droplet.

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.

Jan 2013

Albedo greater in polluted atmosphere More albedo in polluted air Albedo greater in polluted atmosphere Clouds last longer in polluted atmosphere