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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
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
• 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.