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Wheel in the sky wows local residents

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Inscrit le: 01 Sep 2006
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J'accepte La charte: Oui j'ai lu et pris connaissance de la charte, j'e l’accepte et je m’engage à la respécter

MessagePosté le: 22/12/2008 07:36:58    Sujet du message: Wheel in the sky wows local residents Répondre en citant

Wheel in the sky wows local residents

Published: Tuesday, December 16, 2008 at 3:00 p.m.
Last Modified: Tuesday, December 16, 2008 at 3:48 p.m.
HOUMA — Some people saw Jesus. Others blamed UFOs.

Sandra Ledet of Raceland sent this snapshot of the hole in the clouds she spotted Saturday from her home.

Harkening to the popular Journey song, a wheel in the sky appeared over Terrebonne and Lafourche parishes early Saturday morning, a seemingly perfect hole punched though the sheet of clouds blanketing the sky.

Locals who phoned and e-mailed the Daily Comet and The Courier this weekend about the strange cloud formation did agree on one thing: “It was the weirdest thing I’ve ever seen,” said Raceland resident Sandra Ledet, who shared some spectacular photos with the Daily Comet.

Shawn O’Neil, a meteorologist with the National Weather Service in Slidell, identified the phenomenon as a hole-punch cloud.

“They don’t occur all that often, and they are usually caused when an aircraft intersects altocumulus or cirrocumulus clouds,” he said.

Altocumulus are high-altitude clouds, usually white or gray in color, that occur in sheets or patches. Cirrocumulus also are high-altitude clouds made up of supercooled liquid water droplets and ice crystals.

An airplane passing through a mixed cloud layer while ascending or descending could disrupt the delicate coexistence between the ice crystals and the supercooled liquid water droplets, causing a hole to be punched in the sky like many residents saw Saturday, according to the National Weather Service.

Small-scale atmospheric movements, both up and down, caused by the jet stream, could cause a similar phenomenon.

Some seemed doubtful, when the phenomenon was explained to them, that something like a jet could cause the mystical “hole in the sky” they saw Saturday.

“My daughter called me and she said, ‘Mom, look at the sky,’ and I went back in, got my camera, and started snapping,” Ledet said. “It completely circled my house and then disappeared. It was too big, too round and too low to be caused by a jet.”

Annette Klingman of Houma said her husband called her and told her that there was a “strange thing outside,” and she should get her camera.

“I was in my pajamas, and I went outside and wondered what I was supposed to be looking for,” she said. “But then my son saw it, and it was so huge. It was awesome. It was beautiful. I’ve never seen anything like it.”

Nikki Buskey can be reached at 857-2205 or nicole.buskey@houmatoday.com.

RGB - Serenity is not freedom from the storm but peace within the storm (Native American Proverb)
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MessagePosté le: 22/12/2008 07:36:58    Sujet du message: Publicité

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MessagePosté le: 28/12/2008 08:05:28    Sujet du message: Hole Punch Cloud: the Uncloud Répondre en citant

Hole Punch Cloud: the Uncloud


A “Hole Punch” cloud is a non-technical name given to a cloud formed from an aircraft dissipation hole or trail. They are also called "Punch Hole" clouds. Rather than extending as a line, Hole Punch clouds appear as a circular or oval hole in a deck or thin layer of supercooled water clouds. They are not uncommon where jet flight paths intersect altocumulus or cirrocumulus layers. What is uncommon is when they form in a perfect circle that persists for a length of time to be widely observed.

On December 11, 2003 that’s exactly what happened along the central Gulf Coast. A remarkably circular and persistent Hole Punch cloud formed over Mobile, Alabama at lunchtime. Numerous curious people photographed it. The event was so much a topic of conversation that it was the top local news story of the day.

At wkrg.com in the Weather Education section you'll find a Hole Punch article with background and pictures. Also check the website of the Mobile office of the National Weather Service for an extensive article with links to the synoptic charts of the day. The University of Wisconsin MODIS images give a space perspective both medium and close.

Hole punch clouds are not new. They've been seen around the world and more pictures are on the website for Project Atmosphere Australia.

Download a large image of this hole punch cloud for personal use only.

Source here

some pictures Hole Punch Cloud





What Happened ? - During the early afternoon of Wednesday, 11 December 2003, a strange and unusual cloud formation occurred over the Mobile, Alabama area. The name..."Hole Punch Clouds".

Has it happened before ? Yes. A quick internet search quickly reveals a few strikingly similar past photos that were taken in south Florida, the Carolinas and even Australia and Canada. Therefore one can conclude that the phenomena has happened before, but on a relatively infrequent basis.

At what atmospheric level did this occur ? -A regional sounding (meteorological instrumentation that shows how temperature and moisture vary with height) taken near Valparaiso, Florida reveals a cloud layer between approximately 25,000 and 27,000 feet. The cloud layer was likely a few thousand feet lower according to a sounding taken further west over Slidell Louisiana near the time of sunset (not shown). Meteorologists refer to clouds at this level as 'cirro-form' clouds. Generically, these are termed 'high clouds.' However, the white puffy-like texture in the cloud deck that surrounds the "hole" possesses traits of both cirroform and cumulo-form clouds (which form at much lower altitudes). Cirroform clouds with a cumulus-like appearance are termed 'cirrocumulus' clouds.

What was the weather pattern that day ? - Although a large scale high pressure system was building in at the surface with northerly winds in progress, the "hole punch clouds" occurred at a much higher level in the atmosphere. Just above the cloud layer and at about 32,000 feet above ground level, the high level winds were blowing was from west to east over much of the US Deep South. The clouds were aligned along this rapidly flowing stream of air, known as the jet stream.

How does the hole occur in the clouds ? - The puffy clouds were likely composed of ice crystals and very small super-cooled liquid water droplets. Studies have shown that very small supercooled liquid water droplets can exist well below freezing (as low as -40 degrees (C, or Centrigrade) ). The temperature in the cloud layer was around -24 deg (C) at the time of occurrence. Sometimes...when ice and the supercooled liquid droplets coexist within a cloud...a process occurs whereby ice crystals grow at the expense of the droplets. If the mixed cloud is agitated...the supercooled droplets freeze instantaneously. It is understood through microphysical arguments that water vapor must evaporate from the surrounding supercooled droplets and flow towards the ice crystals. This would start a cycle whereby newly formed ice crystals cause the surrounding droplet to evaporate...resulting in a circular form void of clouds with a mass of crystals in the center. Many photos taken that day seem to represent this process.

What caused the disturbance to begin ? One possible explanation is a jet plane. Visible satellite imagery that day suggested several "hole punch" clouds over both southern Mississippi and Alabama. These coincided with jet contrails. Click here and you will see a photo of "hole punch" clouds taken in Australia with an airplane contrail nearby. An airplane passing through the mixed cloud layer while ascending or descending would likely disrupt the delicate coexistence between the ice crystals and the supercooled liquid water droplets. A second possible explanation is that small scale atmospheric vertical motions (both up and down) related to the jet stream brought ice crystals downward into the moist cloud layer, thus effectively 'setting off' the cyclic process described above.

One thing is for sure... Without an ability to directly measure these small scale vertical motions and the quantities of temperature and moisture directly within and adjacent to the actual clouds, we can only speculate on what caused this common but relatively infrequent awesome phenomena to occur !...

source here

Depending on where you were, it may have been hard to tell that the clouds in the middle of the hole were falling lower than the other clouds. For this phenomenon to occur you only need to do one thing- increase the relative humidity fast. There are several ways to do this.
An easy way to artificially raise the humidity is to fly a jet plane through the cloud. As the engines burn fuel, they release water vapor to increase the relative humidity. Ice crystals that are already in the air will pull as much of the vapor as possible and then grow larger, and heavier, to fall. This is one of the reasons we see condensation trails behind jets that fly high. Jet engines also release tiny particles that serve as a base for ice crystals to form on.
Other ways that relative humidity is raised naturally is when waves in the atmosphere cause the air to rise and sink, just like water waves near a beach. Rising air cools and that can cause the relative humidity to rise and produce precipitation. Even if the air sinks, it's possible that ice crystals may fall into a region of high moisture that is not frozen and immediately form big crystals.

Take a look at this high resolution satellite image of the central Gulf Coast. It shows natural clouds, condensation trails, and several areas where likely, a jet passed through the clouds and caused the clouds to precipitate in its wake. Here's a closer picture centered on southern Mississippi. Click on either picture for the original image.

The process is pretty simple but there are details. For example, It's possible to have water droplets when the temperature is way below freezing. We called them supercooled. It's also possible for the relative humidity to be over 100%
Pictures below are from NASA Terra satellite on January 29, 2007

An even closer view in Texas south of the Red River. You can also see ripples in the clouds. Some of the holes are up to 10 miles across.


source here  


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MessagePosté le: 20/06/2018 09:09:44    Sujet du message: Wheel in the sky wows local residents

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