GEOG 3610 Lecture Notes - Lecture 4: Weather Front, Hadley Cell, Atmospheric Circulation
28 Mar 2018
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Document Summary
Growth in warm clouds (e. g. over tropics): collision-coalescence process. Growth in cool and cold clouds (e. g. over portion of mid-latitude): bergeron- For ice to form, some water molecules must align in correct crystal structure. High probability of this happening by chance in puddle or ice cube with zillions of molecules. Reduced probability in a very small quantity of water with far fewer molecules. Cloud droplet molecules need help getting aligned: cloud droplet is 1-millionth of a raindrop, helpers are called (cid:498)ice-forming nuclei(cid:499) Not enough water molecules for droplets to freeze. Saturation vapour pressure over ice is lower than over super-cooled water. Freezing of cloud droplets requires an ice-forming nucleas (in). Clay particles are closest match in the atmosphere. Natural in start activity about -9c, but few area active at first, so a few ice crystals in a sea of water droplets in -10c to -20c region. This is good for growing for growing big ice crystals.
