Chapter14b - Lightning and Tornadoes Thunderstorms: brief...

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Lightning and Tornadoes
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Thunderstorms: brief review There are two basic types of thunderstorm cells:  ordinary cells  and  supercells . Ordinary cell thunderstorms tend to form where warm, humid air rises in a conditionally  unstable atmosphere and where vertical wind shear is weak. They are usually short-lived  and go through their life cycle of  growth  (cumulus stage),  maturity  (mature stage) and  decay  (dissipating stage) in less than an hour. They rarely produce severe weather. As wind shear increases (and the winds aloft become stronger) thunderstorms are more  likely to become  severe  and produce strong surface winds, large hail, heavy rain, and even  tornadoes.  The cells that comprise a  multicell thunderstorm  can be ordinary or supercell. A  squall line   is a long line of multicell thunderstorms that may form along a frontal boundary or out  ahead of it. A  Mesoscale Convective Complex  is  a large circular cluster of multicell  thunderstorms. Flooding : typically in the spring, when the snow is melting and the rivers are full.  Flash  floods : floods that rise rapidly with little or no advance warning. 
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Lightning What is it? An electrical discharge – a giant spark! Compare to: Plasma ball in the lobby outside
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Electricity 101 Particles may carry  positive  or  negative  charge. Opposite  charge particle s attract  each other Same  charge particles  repel  each other  Electrons  are negatively charged. They are very mobile. Nuclei  are positively charged. Molecules  are made up of nuclei and electrons. They have  no net charge.  Ions  are molecules which have  gained  or  lost  electrons: they can have a  negative  or a  positive  net charge. The motion of the charges results in  electrical current + + + -
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Charging a Thundercloud Raindrops, snow crystals and hail stones  collide inside the cloud. During these collisions  they may exchange electrons and ions.  The exact mechanism is not well understood, 
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This note was uploaded on 05/29/2011 for the course MET 1010 taught by Professor Matchev during the Spring '08 term at University of Florida.

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Chapter14b - Lightning and Tornadoes Thunderstorms: brief...

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