Lecture 13-15 Atmospheric Instability

47 deriving the energy l 5x108 500 million kg or

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Unformatted text preview: ice even at - 20°C l༆  - 40°C is 100% ice crystals l༆  Rain (snow) forms in two ways: 38 Rain - FormaAon l༆  Rain (snow) forms in two ways: 1. Collision and Coalescence l༆  Drops simply hit each other and increase in size as it falls through the cloud Note: taller the cloud, bigger the potenAal drops l༆  Takes place in warm clouds l༆  2. Ice Crystal (Bergeron) Process l༆  Either a pure cold cloud or a mixed ice/droplet cloud l༆  Droplets accrete (build) onto a crystal e.g. from condensaAon nucleii due to difference in saturaAon vapour pressure (less over the ice surface) Graupels (ice pellets) form l༆  l༆  l༆  These smash into eachother and coalesce into…..snow flakes Also locaAon for charge carrying…. 39 40 Heavy Winds l༆  Falling rain pulls air down with it and you get downdrajs l༆  Major concerns for pilots (not to menAon the hail/rain/ice) l༆  Also known as wind shear (formaAon of hurricanes – later) 41 Hail l༆  Now our ice pellet is in the cloud (the start of the hailstone) l༆  Will accrete super- cooled droplets that then freeze on contact as it’s below freezing / delta between the SVP ice/water l༆  Will melt as it falls through warmer air but if it gets big enough it can make it to the surface l༆  Golf ball sized hail needs >5- 10 mins to form. Can only happen if updrajs (the rising air/turbulent air) causes hail to return higher into the cloud 42 l༆  hkp://www.youtube.com/watch?v=wZr8jXo1Uso 43 Tornado 44 45 l༆  hkp://www.youtube.com/watch?v=d9MyV3fGP4M l༆  hkp://www.youtube.com/watch?v=XT7CtF5ljxY&feature=fvsr 46 Power at the Source l༆  Not...
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