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<br />the cloud which forms is <br />a cumulo-nimbus. These <br />are the tall columns of <br />cloud often with an anvil <br />shaped top. <br /> <br />Clouds <br /> <br />HAIL CANNON HANDBOOK <br /> <br />AS the warm air expands, <br />it gets colder - even <br />though it is colder, it <br />is still warmer than the <br />air it is rising through, <br />so it keeps rising. <br /> <br />,...;.;..,,~;,~7._:';;~;.', ':::::.,'.': ,:;:::~ <br /> <br />time it takes to get from <br />melting to boiling. Now <br />that is the reverse of <br />freezing, but the heat <br />you put in to melt it, <br />hils to be taken out to <br />freeze it. <br /> <br />Despite what you learnt <br />Clouds form when the in school physics, the Back to our droplet; it <br />moisture in the air jOins water doesn't always cannot freeze right <br />into drops instead of freeze at OOC. through quickly, so it <br />being vapour. This can be freezes from the outside <br />deceptive, but there is a Actually any droplet or i~!~_t~~~~~tE~._~i.t___ <br />- - - - - - - -dTIrerenceoetween -steam - -ra-rger aoes -free-ze,bli't - - -keeps bumping into more <br />and vapour - if you watch water vapour will only nearly frozen drops, it <br />a vigorously boiling freeze near this will form an outside <br />kettle you should find temperature if it has frozen shell with liquid <br />that steam appears a something to freeze onto. water inside, and it will <br />small distance from the A dust particle, or a only freeze right through <br />outlet. In between there tiny salt crystal from when the loss of heat is <br />is a clear space where the sea are the most faster than the gain. <br />the vapour leaves the common "somethings". In <br />kettle, before it clean air, the <br />condenses into steam. temperature may have to <br />drop to -300e or lower <br />before the vapour <br />freezes. <br /> <br />Water vapour can be <br />present in different <br />amounts in the air. When <br />air is holding all the <br />vapour it can, the <br />humidity is 100%. As the <br />temperatu~e changes the <br />amount of water the air <br />can hold changes. As the <br />air cools it can hold <br />less water, and if there <br />is anything which it can <br />condense onto it will do <br />so, <br /> <br />Hail <br /> <br />When the right conditions <br />occur in a cloud, there <br />is an upward wind of warm <br />air which is light enough <br />to rise rapidly. AS this <br />wind rises, the air <br />around is thinner, which <br />allows the warm air to <br />expand. <br /> <br />The point of this is that <br />the "warm" air may rise <br />to a very great height <br />before it condenses, or <br />freezes. when the droplet <br />does form, its weight <br />makes it start to fall, <br />and as it falls it bumps <br />into other lighter <br />droplets (which fall <br />slower), and it becomes <br />heavier. <br /> <br />If the temperature is <br />cool enough, this droplet <br />begins to freeze, but -- <br />then it has to" lose a lot <br />of heat. The most obvious <br />demonstration of this is <br />probably to note how when <br />you try to melt ice, it <br />stays frozen for a long <br />time, compared with the <br /> <br />MIKE EGGERS LTD. Nelson, New Zealand <br /> <br />During this semi-solid <br />period a comparatively <br />small disturbance can <br />destroy the forming <br />hailstone, this is where <br />a small action <br />(cavitation due to the <br />ultrasonic pulses) can <br />have a big effect (the <br />destruction of the <br />fragile hailstone). <br /> <br />Experience <br /> <br />A review of the results <br />of cannons used in the <br />Nelson area suggests that <br />some makes of cannon work <br />and others do not. <br /> <br />The variable way that <br />hail occurs means one has <br />to be cautious about the <br />reliability of the <br />evidence, but serious <br />crop damage on either <br />side of a cannon of one <br />type in an area covered <br />by different makes of <br /> <br />Page 3 <br />