In an interesting article in Science Daily researchers have discovered that mysterious clouds are created when turboprop and turbojet airplanes climb or descend through mid-level clouds under certain conditions. Apparently as air is cooled behind propellers or over the wings of jet aircraft water droplets freeze and descend towards the Earth's surface. This seeding process apparently leaves behind some odd-shaped holes or channels in the clouds. When the atmospheric temperature is below 5 degrees Fahrenheit (-15 degrees Celsius) these holes in the clouds are created as seen in the photograph on the right. According to Andrew Heymsfield, a scientist with the National Center for Atmospheric Research "Any time aircraft fly through these specific conditions, they are altering the clouds in a way that can result in enhanced precipitation nearby, just by flying an airplane through these clouds, you could produce as much precipitation as with seeding materials along the same path in the cloud." Following is an excerpt from this article: "But scientists had not previously observed snow as it fell to the ground as a result of aircraft until Heymsfield and his colleagues happened to fly through some falling snow west of Denver International Airport with an array of instruments. While the research team did not notice anything unusual at the time of their 2007 flight, a subsequent review of data from a ground-based radar in the area revealed an unusual echo, indicating that the band of precipitation had evolved quickly and was unusually shaped. "It became apparent that the echo had evolved in a unique way, but I had no satisfactory explanation," says Patrick Kennedy, a Colorado State University radar engineer who spotted the unusual readings and helped write the study.