ATOC 1050 Lecture Notes - Lecture 9: Satellite Imagery, Cumulonimbus Cloud, Hail
14 Feb 2017
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Document Summary
Raindrops are much larger than cloud droplets. Two processes that cause cloud droplets to grow into rain droplets: collision-coalescence process. Clouds made entirely of liquid droplets must contain some droplets that are larger than. This occurs when giant condensation nuclei are present when hygroscopic particles (sea ice) exist. Large droplets will start to fall through the cloud and collide with smaller, slower droplets (coalesce). This causes the droplet to increase in size. They then fall more rapidly, colliding with more droplets, etc. The longer a droplet remains in the cloud, the larger it can grow. Involves ice-crystal growth and depends on the coexistence of liquid cloud droplets and ice crystals (occurs mostly in the mid-latitudes) The cloud droplets do no freeze at 0 degrees celsius. Pure water suspended in the air does not freeze until about -40 degrees celsius. Water that remains in the liquid state below 0 degrees celsius is known as supercooled.
