AOSC200Lect8

AOSC200Lect8 - AOSC 200 Lesson 8 Precipitation Growth in...

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Unformatted text preview: AOSC 200 Lesson 8 Precipitation Growth in Warm Clouds • Cloud droplets are typically 10 microns in size. small raindrops are typically 1000 microns (one million droplets) • How does one go from one to the other? • Simplest explanation is that the droplet grows by condensation of water vapor on its surface. But this would take several days. • One way for raindrops to form is by a processes known as collision- coalescence. • This process requires lots of droplets - high absolute humidity - seen only in the tropics. Collision-Coalescence • Also known as a warm cloud process because it mainly occurs in the tropics. • As the cloud droplet is formed it is pulled down by gravity but then is moved upward by the rising air within the cloud. Hence within a cloud one has droplets moving in all directions and they can collide and form larger droplets by coalescing. • Once a drop grows to a size when the force of gravity exceeds the uplift from the rising air, the drop moves downward through the cloud picking up other droplets as it falls. Collision Coalescence Fig. 4-31, p. 114 Collision- coalescence process Precipitation Growth in Cold Clouds • Outside of the tropics there are just not enough cloud droplets to form rain drops by...
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This note was uploaded on 01/30/2012 for the course AOSC 200 taught by Professor Hudson during the Fall '08 term at Maryland.

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AOSC200Lect8 - AOSC 200 Lesson 8 Precipitation Growth in...

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