Articles with tag: "clouds"

1. Water Drops

   The size of water drops in clouds

   The water that causes most aircraft in-flight icing is small drops in clouds. Average drop sizes are typically 10 to 50 "Micrometers" (μm) in diameter (for comparison, a human hair is about 50 to 100 micrometers in diameter).

   
   Typical drop sizes, approximately proportional. Public domain image by Donald Cook.

   In a particular cloud, not all water drops are the same size. The "Langmuir Drop Size Distributions" describe an idealized approximation of how the drop sizes vary in a cloud about an average or median drop size. It has seven bins, each with a representative drop size and fraction of the total water content in the cloud.

   
   from "Aircraft Icing Handbook", DOT/FAA/CT-88/8-1 apps.dtic.mil

   The impingement of water drops on aircraft surfaces

   Calculating the amount of water that hits or impinges on the surface of an airplane as it flies …

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2. Supercooled Clouds

   "If the [ice] crystal is exceedingly small, rather than growing, it may melt."

   SUPERCOOLED CLOUDS ¹

   Summary

   Several aspect of icing clouds physics are discussed.

   Key Points

   1. Supercooling and nucleation rates are key to the formation of icing clouds.
   2. Vapor pressure differences of liquid water and ice play a role.
   3. Tips are given for recognizing supercooled clouds.
   4. Types of icing clouds are discussed.

   Discussion

   This includes a theoretical understanding of the physics of icing clouds, but also practical tips, such as how to identify supercooled icing clouds in flight.

   While this is not a long lecture (11 pages), I left out of this review for brevity items such as the artificial seeding of clouds, which is only tangentially related to aircraft icing, although I will briefly discuss that here.

   Wikipedia summarizes about the author and presenter Bernard Vonnegut:

   Bernard Vonnegut (August 29, 1914 – April 25, 1997) was an American atmospheric …

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