A Roll Cloud Over Uruguay (2010 Jan 05)

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A Roll Cloud Over Uruguay (2010 Jan 05)

Post by APOD Robot » Tue Jan 05, 2010 4:55 am

Image A Roll Cloud Over Uruguay

Explanation: What kind of cloud is this? A roll cloud. These rare long clouds may form near advancing cold fronts. In particular, a downdraft from an advancing storm front can cause moist warm air to rise, cool below its dew point, and so form a cloud. When this happens uniformly along an extended front, a roll cloud may form. Roll clouds may actually have air circulating along the long horizontal axis of the cloud. A roll cloud is not thought to be able to morph into a tornado. Unlike a similar shelf cloud, a roll cloud, a type of Arcus cloud, is completely detached from their parent cumulonimbus cloud. Pictured above, a roll cloud extends far into the distance in 2009 January above Las Olas Beach in Maldonado, Uruguay.

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Re: A Roll Cloud Over Uruguay (2010 Jan 05)

Post by PHN » Tue Jan 05, 2010 1:54 pm

A baby roll cloud in Illinois: http://www.wunderground.com/wximage/myp ... sen#select
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Re: A Roll Cloud Over Uruguay (2010 Jan 05)

Post by Xiro » Tue Jan 05, 2010 2:15 pm

This looks alot like a morning glory cloud that was posted a few months back. What is the difference between the two?
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Re: A Roll Cloud Over Uruguay (2010 Jan 05)

Post by neufer » Tue Jan 05, 2010 3:20 pm

Xiro wrote:This looks alot like a morning glory cloud that was posted a few months back. What is the difference between the two?
Morning Glories have a bigger roll to play:
http://www.greenhorsesociety.com/Clouds/Glory.htm wrote:
<<Morning Glories appear as one or more roll cloud formations extending from horizon to horizon, sometimes more than 1000 km in length. The base of roll clouds can be 150 to 300 m above the ground or sea surface, and the cloud itself may have a depth of 600 to 1300 m. Morning Glory clouds seldom produce measurable precipitation, but are almost always accompanied by short-lived, often intense, surface wind squall. They are reported to travel at speeds of about 40 km/hr, occasionally over 60 km/hr.

A Morning Glory is a cloud formed by a solitary wave in the lower atmosphere. It is thought that solitary waves develop in the presence of a temperature inversion and are generated by disturbances such as thunderstorm activity or the collision of opposing ocean breeze fronts. A temperature inversion is a situation in which there is a cold layer of air close to the ground, with a warmer layer on top, creating a "lid" over the cooler surface air. This layer of surface air is highly stable and enables the solitary wave to propagate without being damped, and to travel long distances. Thus the layer acts as a "wave guide". >>
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Re: A Roll Cloud Over Uruguay (2010 Jan 05)

Post by Xiong » Tue Jan 05, 2010 11:07 pm

I could have sworn this same pic was shown a few weeks ago.

Perhaps when I have a bit more time I'll see if I can find it.
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Re: A Roll Cloud Over Uruguay (2010 Jan 05)

Post by geckzilla » Tue Jan 05, 2010 11:54 pm

Roll clouds seem to be one of the editors' favorite non-astronomy topics. There are several of them in the archives. Chances are you are thinking of one of them.
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Re: A Roll Cloud Over Uruguay (2010 Jan 05)

Post by bystander » Tue Jan 05, 2010 11:55 pm

Image APOD: 2009 August 24 - Morning Glory Clouds Over Australia
Image APOD: 2008 January 22 - Shelf Cloud Over Saskatchewan
Image APOD: 2006 January 17 - A Roll Cloud Over Missouri

only references I could find in APOD search
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Re: A Roll Cloud Over Uruguay (2010 Jan 05)

Post by The Code » Wed Jan 06, 2010 12:04 am

geckzilla wrote:Roll clouds seem to be one of the editors' favorite non-astronomy topics.


The sea has tidal forces, and so does the earth. Sun and Moon.

Why would the atmosphere be any different?
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Re: A Roll Cloud Over Uruguay (2010 Jan 05)

Post by geckzilla » Wed Jan 06, 2010 12:06 am

Mark, the sun and the moon's gravity also affect me in some way, but I don't consider myself to be of astronomical interest. ;)
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Re: A Roll Cloud Over Uruguay (2010 Jan 05)

Post by Chris Peterson » Wed Jan 06, 2010 12:51 am

mark swain wrote:The sea has tidal forces, and so does the earth. Sun and Moon. Why would the atmosphere be any different?
It is well known that tidal forces are responsible for some movement of the atmosphere. These clouds don't have anything to do with tides, however.
Chris

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Re: A Roll Cloud Over Uruguay (2010 Jan 05)

Post by The Code » Wed Jan 06, 2010 2:42 am

prove it!

Show me why they don,t. Tidal forces move the air, and heavy clouds, why would I be wrong. What else would make these clouds?
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Re: A Roll Cloud Over Uruguay (2010 Jan 05)

Post by bystander » Wed Jan 06, 2010 3:30 am

mark swain wrote:Show me why they don,t. Tidal forces move the air, and heavy clouds, why would I be wrong. What else would make these clouds?
How about you prove why you would be right? Anybody proposing a new idea (can't really cal it a theory, not well formed enough) should expect to have to prove why their concept is viable. Don't ask others to prove you wrong if you can't prove you are right.
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Re: A Roll Cloud Over Uruguay (2010 Jan 05)

Post by Chris Peterson » Wed Jan 06, 2010 5:00 am

mark swain wrote:Show me why they don,t. Tidal forces move the air, and heavy clouds, why would I be wrong. What else would make these clouds?
You don't seem to understand tidal forces. They aren't the same thing as gravitational forces. They don't act stronger on more massive objects. Tides are differential forces. Lunar and solar tides distort the entire atmosphere, they don't exert any kind of local forces. There are much simpler explanations for cloud formation. These roll clouds certainly appear to be convective structures of some kind, which suggests that they are caused by heat transport mechanisms, of which there are many types.
Chris

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Re: A Roll Cloud Over Uruguay (2010 Jan 05)

Post by DavidLeodis » Wed Jan 06, 2010 12:30 pm

Great image. I've never seen a roll cloud, but they look awesome in images such as this one. :)
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