I've heard that dry ice, iodides have been used as seeding agents to induce rainfall. Is this technique really being used widely? What are the prerequisites for initiating seeding? Is it as bounteous as natural rainfall is?

  • User15523 you deserve a medal for being able to ask a question in this 'realm' and get personally written feedback instead of everyone else's research papers. And they were very respectful...amazing that weather control which we most certainly have the technology and hardware and money to TRY to pull off...and we are still seen as not having advanced since the Wright Brothers??? Sorry, sorry...hate to be the stick in the spokes...but someone has to...sigh. Did they answer your question adequately?? – stormy Nov 26 '15 at 22:59
  • Also interesting that these PILOTS that fly these recommissioned and refitted planes are hired based on their LACK of family, friends...totally shuttled around like they were possibly a problem of information leakage...not going to throw someone else's visuals to prove any of this. IF THEY ARE DOING THIS WEATHER CONTROL...and so far it is 50/50...we should KNOW about this expenditure, who is paying for this cloud seeding and what are the pollution potentials...really? Vapor trails that turn into clouds... – stormy Nov 26 '15 at 23:06
  • Haven't been thrown off yet...did anyone look up the patents that are in place and have been current since 1950's?? These crisscrossing persistent vapor trails make no sense in my universe and physics. Sorry, sorry, hate drama and bull...but this IS right in my face everyday and I am not at all educated by your answers... – stormy Nov 26 '15 at 23:10
up vote 4 down vote accepted

Cloud seeding has been attempted for well over a century, with mixed success. There is no doubt at all that, locally, rain can be increased by seeding the cloud base with such nucleating agents as dry ice or silver iodide smoke. There is a great deal of doubt as to whether there is any overall gain in rainfall - or is it just an expensive way of 'robbing Peter to pay Paul', of increasing rain in one location at the expense of rainfall further downwind. Is there any nett gain in regional rainfall? Probably not. Of course, there are many cases where locally increased rainfall may be worth the effort.

Not all cases of cloud seeding work. There are several requirements. First, the process involves vigorous convection within the cloud towers in order to loft the nucleating agent into a sufficiently super-cooled part of the cloud. If the cloud is too warm it won't work - which rules out many tropical applications. Second, the 'seed' has to be injected into the cloud base at about -10 to -20 deg C, which allows 'graupel' to form, i.e. a kind of granular ice that flash freezes onto snow or ice crystals direct from super-cooled water vapour. Third, the timing has to be right, just as the cumulus towers are beginning to form, usually in the early afternoon. Fourthy, the economics are very moot. Wikipedia ('Cloud Seeding') claims that the subject is no longer 'fringe science', which is true in that the physics have been studied seriously, but mostly untrue in the sense that it is now considered economically attractive. The great majority of studies have shown that cloud seeding is unreliable, expensive, and of dubious value, with other ways of delivering water (such as desalination) being a better bet.

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