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Lecture 11

ATMO 201 Lecture Notes - Lecture 11: Cloud Condensation Nuclei, Cloud Top, Cumulonimbus Cloud

Atmospheric Sciences
Course Code
ATMO 201
Timothy Logan

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Lecture 11
Tuesday, February 28, 2017
3:55 PM
Precipitation process
Precipitation - falling hydrometeors from nimbus type clouds that can be
either liquid or frozen
o What are those "nimbus" types again? (Cumulonimbus, nimbostratus)
Not all clouds produce precipitation
o Why???
Clouds on steroids
o Enhanced precipitation or "Invigoration Effect"
Clouds on a diet
o Diminished precipitation or "suppression effect"
o Their rain can't survive long enough to make it to the ground
All cloud droplets must first start as nuclei (starts as condensation nucleus,
then typical cloud droplet, then a typical raindrop)
Recall condensation nuclei (submicron size)
CN becomes CCN (cloud condensation nuclei)
Precipitation process is slow and difficult
o 1 million cloud droplets to make 1 rain drop
Two types:
o Warm rain process
Cloud environment more or less remains at temperatures above
Cloud top is close to or a little above freezing
o Cold rain process (has ice)
Cloud environment is mixed phase (ice and water)
Contribution from ice particles
Snow can make it rain (snow is responsible for the rain)
Warm Rain Process
Collision and coalescence (C+C)
Difficult for cloud droplets to grow (stop it)
o Evaporate (if less than 20 um in diameter)
o Re-condense (other CN receive "evaporated" water)
o Collide with and shatter one another
o Collide and stick (coalesce) then fall out of the cloud
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