Funny Pics of Driving Crazy in Circles
"It really is like breaking waves," Chuang said. "A wave breaks when the water on top moves so much faster than the water below that it kind of piles up on itself."
Images: Above: UCAR/NCAR. Below: 1) Mila Zincova/Wikimedia commons. 2) UCAR/NCAR
This spectacular photo of the eruption of Sarychev Volcano in the Kuril Islands, northeast of Japan on June 12 shows an interesting example of a pileus cloud. The ash plume appears to have a smooth white cap on it as it breaks through the cloud cover above.
This type of cloud is caused by strong, relatively fast upward motion. Situations where this occurs include quickly growing thunderheads, volcanic eruptions and even nuclear explosions. In each case, something pushes warm, moist air upward quickly.
"You can see them very commonly above thunderstorms storms, and that's because the air is moving so rapidly up there that the air flow gets perturbed above it," Breed said. "And as soon as it cools enough for a cloud to form, you get these cloud caps."
Chuang says pileus clouds look similar to the smooth caps sometimes seen on top of cumulus clouds, which are actually ice caps.
"If you have very strong convection, pushing quickly and very high, it forms more of an ice cloud because it is high enough for the crystals to freeze," Chuang said. "It's nothing more mysterious than things freezing."
Image: NASA
We became aware of noctilucent clouds here at Wired Science in July when the strange glowing clouds began appearing over the United States and Europe, much farther south than they were normally seen.
These "night shining" clouds are formed by ice at the boundary of Earth's atmosphere and space, 50 miles high. They shine because they are so high they remain lit by the sun even after it has gone below the horizon. It's not clear why these clouds have migrated down from the poles, or why more of them are appearing in the polar regions, too, and shining more brightly.
Nobody knows for sure, but most of the answers seem to point to human-caused global atmospheric change.
The clouds form at temperatures around minus-230 degrees Fahrenheit, when dust blowing up from below or falling into the atmosphere from space provides surfaces for water vapor to condense on and freeze. Right now, during the northern hemisphere's summer, the atmosphere is heating up and expanding. At the outside edge of the atmosphere, that actually means that it's getting colder because it's pushed farther out into space.
"The prevailing theory and most plausible explanation is that CO2 buildup, at 50 miles above the surface, would cause the temperature decrease," said James Russell, an atmospheric scientist at Hampton University and the principal investigator of an ongoing NASA satellite mission to study the clouds. He cautioned, however, that temperature observations remain inconclusive.
But the truth could be far more complex, and there are many other theories about these clouds.
Images: Above: Mike Hollingshead, Extreme Instability. Below: NCAR/UCAR
Morning Glory clouds are a specific and more unusual type of roll clouds, which are more common, and not usually as long.
Roll clouds typically occur in the lower atmosphere ahead of a storm front. Warm updrafts in the storm front push cold air up, which then flows down along the sides of the updraft. The cold downdraft then bounces back up a bit setting up a wave-like structure in front of the storm.
On the upswing, the cold air forms a cloud. Evaporation of the cloud causes a downdraft on the edges that erodes the cloud, forming a roll. If the wave continues, a series of roll clouds, called a street, can form.
Image: Above: Flickr/jonnyr1. Below: Flickr/tlindenbaum.
See Also:
- Mysterious Tubular Clouds Defy Explanation
- Mysterious, Glowing Clouds Appear Across America's Night Skies
- Erupting Volcanoes on Earth as Seen From Space
Source: https://www.wired.com/2009/09/clouds/
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