Tag Archives: clouds

Amazing CLoud Formations

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Kelvin-Helmoltz Clouds: Rolling Waves in the Sky (PHOTOS)
By: Chris Dolce
Published: August 15, 2013

Kelvin-Helmholtz breaking wave cloud over Laramie, Wyo. (NOAA/Brooks Martner)

Though it looks like someone painted the sky with breaking ocean waves in the collection of photos above, there’s a very good atmospheric explanation for what is really happening.

The rolling, wave-like cloud formations are called Kelvin-Helmoltz clouds. Sometimes they are also called billows. They are named for scientists Lord Kelvin and Hermann von Helmholtz, who discovered the process by which they form.

Severe Weather Expert Dr. Greg Forbes of The Weather Channel says, “They are the atmospheric equivalent of those great breaking waves that you sometimes see on the ocean.”

These breaking atmospheric waves occur in an environment with a large amount of vertical wind shear and stable air. Wind shear is a change in the speed and direction of winds as you go higher in the atmosphere.

In this case, winds at the top of the cloud layer are moving faster than the base of that same layer. This causes the top to crash downwards in a curling manner after it hits the stable layer above.

The rolling motion created by this type of wind shear also causes turbulence for aircraft.

However, the rolling clouds motions are often masked by a large amount of cloud cover. Other times, there are no clouds around to illustrate the wave pattern.

from:    http://www.wunderground.com/news/kelvin-helmholtz-billow-wave-clouds-20130815

The Sky is Falling?

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Shrinking Sky! Cloud Tops Dropping Closer to Earth, NASA Satellite Finds

Stephanie Pappas, LiveScience Senior Writer
Date: 22 February 2012 Time: 04:47 PM ET
Clouds in the sky at sunset.
The average height of clouds has dropped by about 1 percent in the last decade, new research finds.
CREDIT: Sebastian Kaulitzki, Shutterstock

The sky is falling… sort of. Over the last 10 years, the height of clouds has been shrinking, according to new research.

The time frame is short, but if future observations show that clouds are truly getting lower, it could have an important effect on global climate change. Clouds that are lower in the atmosphere would allow Earth to cool more efficiently, potentially offsetting some of the warming caused by greenhouse gases.

“We don’t know exactly what causes the cloud heights to lower,” study researcher Roger Davies of the University of Auckland in New Zealand said in a statement. “But it must be due to a change in the circulation patterns that give rise to cloud formation at high altitude.”

Clouds are a wildcard in understanding Earth’s climate. Ephemeral as they are, they’re difficult to track over time, and factors such as height and location make a big difference in whether clouds will slow the effects of global warming or exacerbate them. And no one fully understands how clouds will respond to a warming climate.

from:    http://www.livescience.com/18604-cloud-heights-declining.html

Tsunami Clouds in Alabama

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Giant Tsunami-Shape Clouds Roll Across Alabama Sky

Natalie Wolchover, Life’s Little Mysteries Staff Writer
Date: 19 December 2011 Time: 02:12 PM ET
Clouds along the horizon in Birmingham, Ala., on Friday (Dec. 16). Credit: ABC 33/40 in Birmingham
Clouds along the horizon in Birmingham, Ala., on Friday (Dec. 16).
CREDIT: ABC 33/40 in Birmingham

For a morning, the sky looked like a surfer’s dream: A series of huge breaking waves lined the horizon in Birmingham, Ala., on Friday (Dec. 16), their crests surging forward in slow motion. Amazed Alabamans took photos of the clouds and sent them to their local weather station, wondering, “What are these tsunamis in the sky?”

Experts say the clouds were pristine examples of “Kelvin-Helmholtz waves.” Whether seen in the sky or in the ocean, this type of turbulence always forms when a fast-moving layer of fluid slides on top of a slower, thicker layer, dragging its surface.

Water waves, for example, form when the layer of fluid above them (i.e., the air) is moving faster than the layer of fluid below (i.e., the water). When the difference between the wind and water speed increases to a certain point, the waves “break” — their crests lurch forward — and they take on the telltale Kelvin-Helmholtz shape. [Astonishing Video Shows a Face in the Clouds]

According to Chris Walcek, a meteorologist at the Atmospheric Sciences Research Center at the State University of New York, Albany, fast-moving air high in the sky can drag the top of slow-moving, thick clouds underneath it in much the same way.

“In the pictures [of the Birmingham sky] there is probably a cold layer of air near the ground where the wind speed is probably low. That is why there is a cloud or fog in that layer,” Walcek told Life’s Little Mysteries, a sister site to LiveScience. “Over this cloudy, cold, slow-moving layer is probably a warmer and faster-moving layer of air.”

Most of the time, the difference in wind speed and temperature between two layers of the atmosphere is small, and so the fast-moving air on top “simply slides smoothly over the slower-moving air like a hockey puck sliding along an ice surface,” Walcek said. At the other extreme, if the wind-speed difference is too large, the interface between the two layers breaks down into random turbulence.

Kelvin-Helmholtz waves form when the difference in the temperature and wind speed of the two layers hits a sweet spot. “What [these pictures] show is air between these two atmospheric layers that is just very close to that threshold for turbulence, and mixing to mix the two layers together,” he said.

from:    http://www.livescience.com/17545-giant-tsunami-shape-clouds-roll-alabama-sky.html