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HarryO

Roll Clouds

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Hi there

Was flying in the simulator on a typically nice cumulo cloud morning as depicted by CumulusX/ASE/REX2. The CumulusX simulation will allow cumulo clouds to form into bands or lines of cumulus clouds in certain situations and that phenomonen was particular strong that morning. It got me thinking....

I was flying the glider parallel along a distinct band of cumulo that had formed a line allowing me to make some decent progress in distance at no cost. The glider's altitude was greater than the cloud base flying adjacent to the clouds themselves. Fly too close and you hit the turbulent sink. Fly into the cloud line and you get turbulence and cannot see left from right. But if you fly parallel to the cumulo line just outside of the turbulence area ahead of the line, you hit an area of very slight and smooth lift where the glider's normal ~1.7ft/sec sink rate is cancelled out. I do not know why the simulation does this, but try it for yourself and see.huh.gif The experience truly felt something like what it must be to fly ahead of a line of rolling clouds!

The interesting bit is that the shape of the CumulusX clouds when they sit in a line almost look like a roll cloud already! (see attached image). If the simulation already creates a line of subtle lift parallel to the band of clouds, all that has to happen in CumulusX unsure.gif to make the band of cumulo "roll", is to put the clouds closer together so that there are no gaps unsure.gif, then spawn new cumulo objects ahead of the band and delete the old cumulus objects at the rear of the band unsure.gif, and the cloud line would essentially appear to "roll" forward in a line unsure.gif. I realise that the degree of the updraft ahead of the cloud would be wrong relative to reality, and also the downdraft at the rear of the line would be wrong too, but it's an idea anyway. rolleyes.gif

Here in Aus we have the amazing Morning Glory Phenomenon (see attached). I'd say this phenomenon could be implemented in CumulusX but I totally appreciate that it is not as easy as I think, that it takes a lot more time than I think, and that it will possibly never be simulated because the phenomenon is too rare in the real world to bother to simulate.

Whatever. Thought I would throw my two cents worth in.

Cheers

Harry

post-31745-074911300 1293583709_thumb.jp

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Hi Harry,

what you probably have observed is the "AirTexture" feature in CumulusX!, which you can find in the manual on page 11. This is a pattern of more or less ondulated bands of weak lift and sink. The thermals concentrate on the areas with lift, thus forming streets of clouds, mostly visible in areas with negligible roughness and around wind speed of 10-15 kn. These bands are oriented in parallel to the prevailing wind direction. Actually they move along, but as they are in parallel to the wind direction, the sideway movement is a bit arbitrary.

The Morning Glory Phenomenon (I heard already about it and saw pictures), however, seems to me a sort of wave effect. As I understood, the rolling clouds are perpendicular to the wind direction and may indicate underlaying rotors, which are covered by a laminar wave flow.

Indeed, I'm concentrating on wave lift in mountains right now, but I regret that I cannot make much hope for a reasonable algorithm for this special kind of waves, which are (afaik) a pure product of wind gradient and atmospheric stratification.

best regards,

Peter

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Indeed, I'm concentrating on wave lift in mountains right now, but I regret that I cannot make much hope for a reasonable algorithm for this special kind of waves, which are (afaik) a pure product of wind gradient and atmospheric stratification.

Thanks anyway and best wishes for the new year 2011 Peter and fingers crossed that you can achieve a wave lift algorithm this year! Here is a link to the Canberra Gliding Club who fly the real thing!

http://www.canberrag...waveFlying.html

Cheers

Harry

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