EES 108 Class 08

# EES 108 Class 08 - Clouds,Fog,andRain EES108 Class#8...

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Clouds, Fog, and Rain EES 108 Class #8 Tuesday September 20 2011

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Test next week Covers everything through Chapter 5 Bring calculator, #2 pencils, eraser Test content: § Mostly about concepts, not math § Roughly half multiple-choice, half free-response  short-answer questions § All formulas, numbers will be provided Sample test will be posted later this week Optional review session  Monday 6:00-7:30 PM, this room
Water is much denser than air So why don’t clouds fall to the ground?

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Inside Clouds Terminal velocity § Bigger drops fall faster Time to evaporate § Smaller drops  evaporate faster Maximum fall distance § Distance =  Speed × Time § Bigger drops: Fall faster Last longer Fall much farther
Inside Clouds Cloud droplets: § 10–50 µm (0.02-0.05 mm) § Maximum fall distance  < LCL height Rain drops: § 1–4 mm § 100 times bigger across § Million times heavier § Maximum fall distance > LCL height

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More curvature =  Higher vapor pressure Faster evaporation
Small drops evaporate faster Very small droplets require  supersaturation  (RH >100%) compared to large drops Very small droplets will evaporate and disappear  even if RH > 100% Very important  for understanding clouds and rain

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1e-005 0.0001 0.001 0.01 0.1 1 10 0.0001 0.001 0.01 0.1 1 10 1e-006 0.0001 0.01 1 100 10000 1e+006 Terminal velocity (meter/sec) Fall distance (meter) Drop diameter (millimeter) Terminal velocity Fall distance Fall distance (~20 mph) (2 mph) (0.2 mph) (0.02 mph) (0.002 mph) Rain drop Cloud  Droplet
Types of clouds Layered: § High:  >6 km (20,000 ft) § Middle:

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## This note was uploaded on 12/15/2011 for the course EES 108 taught by Professor Giligan during the Spring '11 term at Vanderbilt.

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EES 108 Class 08 - Clouds,Fog,andRain EES108 Class#8...

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