Residents in the city of Al Ain, United Arab Emirates, were left shocked and confused when they witnessed what they thought was a UFO in the sky. Near the border of Oman, people noticed a “whirlpool hole” in an otherwise heavily clouded sky, as if someone had punched a large hole above their heads.
Ebrahim Al Jarwan, who is an astronomer and meteorologist, was able to capture the strange phenomena on video and posted it to Twitter. This natural phenomena is known as a “hole punch cloud” or “fallstreak hole”. One user commented that it looked as though “God has thrown a stone into a lake”, while others wondered if it was made by a UFO. When a large circular patch of clear sky suddenly appears, surrounded by lots of clouds, it’s not surprising that some people believed that an unidentified flying object may have peaked through the clouds, therefore creating the hole.
Meteorologists, however, were quick to point out that it was a hole punch cloud that is normally created in mid-to-high level clouds and made from super-cooled water droplets (water that’s below 0 degrees Celsius but is not yet frozen) and they are actually caused by aircrafts, including commercial jet airliners, private jets, military jets, and turbo props.
As planes fly through the layer of clouds, the air expands and cools off as it passes over the propeller or wings of the aircraft. This sudden change in temperature causes the super-cooled water droplets to freeze, creating ice crystals which are then heavy enough to drop from the layer of clouds. That’s what causes the large hole to form. Andrew Heymsfield, who is from the National Center for Atmospheric Research, confirmed this by telling EarthSky, “The whole idea of jet aircraft making these features has to do with cooling of air over the wings that generates ice.”
Heymsfield’s team also found that when aircrafts create the large holes in the clouds, and after the droplets of water freeze to ice, they then turn into snow as they fall to the ground. Occasionally, within an hour of a hole punch cloud appearing, it can reach up to 30 miles wide because other water droplets beside the original ones begin to freeze. In fact, hole punch clouds can keep expanding for several hours after initially forming.
And while scientists know what hole punch clouds are and what causes them to appear, not everyone knows about them because they’re a rare occurrence. This is why so many people who haven’t seen them before often mistake them for UFOs.
from Mysterious Universe https://ift.tt/2Fx2HFn