Flashcards in lol short term memory let's go Deck (18):
What is the recipe for precipitation?
Unsaturated air rises and cools by adiabatic expansion, reaching saturation.
Presence of cloud condensation nuclei (CCN, such as aerosol) allow for condensation, leading to formation of tiny droplets.
Droplets grow by additional condensation
For rain to occur, what must happen
Velocity > water
Warm Clouds: Collision-Coalescence
Growth in warm clouds (T>0°C) – mostly in the tropics and warm season in midlatitudes
• Two droplets collide and coalesce (i.e., merge)
• Promoted by large collector drops, which have high
• More efficient in clouds with large distribution of droplet sizes and strong updrafts
At top of cold/cool clouds:
it's glaciated- there's ice and vapor -> not much growth!
What happens at T<0 Cels
Mixed ice and supercooled water droplets (all three phases co-exist)
1. Bergeron process
What happens at T>0 Cels
liquid droplets and vapor (Same as warm cloud: collision-coalescence)
What is the bergeron process?
• Saturation vapor pressure of ice is less than that of supercooled water
• Water vapor is satured over supercooled water, but supersatured over ice
• Ice crystals grow rapidly at the expense of supercooled droplets (via net deposition and net evaportaion)
What is riming?
(liquid water freezes onto ice crystals)
(ice crystals collide and merge via thin coating of liquid water)
What limits the growth of ice particles by the Bergeron process?
The amount of supercooled water in the cloud & The time an ice particle remains in the cloud
Describe snow crystals
Snow crystals: single crystals
• Shapes of ice crystals (crystal habits) depend on temperature and degree of supersaturation (for ice)
Snowflakes: aggregates of snow crystals
Warmer clouds: snowflakes formed by riming which forms dense “wet” snowpack (snowball fights)
Colder clouds: snowflakes formed by aggregation which forms less dense powdery snowpack (skiing)
Lake Effect Snow:
develops as the warm lake waters evaporate into cold air
predominant in tropics
Most middle-latitude precipitin starts out as snow, then melts to rain.
Rimed ice crystal
concentric layers of ice built around graupel- wet growth results in solid ice