Join the conversation about Contrails can and should form readily in clean, cold, and dry air. Normal clouds, on the other hand, require higher moisture levels and a particulate, or aerosol base, from which to develop. The radical transformation of our sky is a direct result of aircraft activity, now forces us to address an entirely new set of conditions. Aircraft are now repeatedly dispersing materials into the upper atmosphere at flight altitude, roughly from 35,000 to 40,000 feet. These materials expand rather than evaporate and they usually transform into an unsightful haze that over the recent years has decreased our general visibility down to ground levels. One of the remarkable facts is that this commonly now occurs at various low levels of relative humidity, on the order of 30 to 40 percent, instead of the 70 percent or greater that is associated with cloud formation. And so we know now that these are not clouds in any conventional sense, they are indeed a unique and artificial creation that now crosses new thresholds in the atmospheric and geophysical sciences.
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