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Aug 24, 2015, 09:40 AM
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on thermals and stranger things


i have been an enthusiast about flying on thermals, since my days of free flight, and now more with sailplanes, radio and vario at my hand am having the time of my life.
i have been compiling data on the subject, and as i said, with the aid of the vario am learning still more about them.
as far as i knew, thermals form from the ground and rise to the condensation level and become clouds. their shape could be bubbles or a column.
but now am getting some updrafts that look like waves that run along, like some clouds that are lines that run parallel.
has any1 experienced this?
is there any link about this?
Last edited by phil alvirez; Aug 26, 2015 at 04:51 AM.
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Aug 24, 2015, 10:02 AM
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Two possibilities: a thermal cloud street or a lee wave. Check these links for starters:

http://www.brockmann-consult.de/Clou...escription.htm

https://en.wikipedia.org/wiki/Lee_wave

https://www.faa.gov/regulations_poli...a/gfh_ch10.pdf
Aug 24, 2015, 10:18 AM
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no ridge


great links. thank you very much.
1 thing that intrigues me is that in the 3rd link, the waves are generated only at ridges, but here the place is flat beyond the horizon.
there is a lake not too far from where the wind blows, but that is all that may affect the air in any way.
any idea if this may be the reason?
or any other idea?
thanks again for the great and fast response.
Aug 24, 2015, 10:35 AM
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Quote:
Originally Posted by phil alvirez
...there is a lake not too far from where the wind blows, but that is all that may affect the air in any way.
any idea if this may be the reason?
Could be, is there any bank and/or treeline or something on the shore that could trigger an upwards motion? If so, the wind will push each subsequent "bounce" of the wave a little higher until the energy dissipates to much. I highly doubt that this kind of small-scale wave could rise high enough to form clouds, but it is perfectly usable for rc gliders once you manage to find it.

In your case I'm guessing that the convection street is more probable explanation.
Aug 24, 2015, 11:59 AM
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there are no trees on sight from that direction, neither the shoreline is close. the fact is that this happens on clear sky, or with a few clouds around, but not aligned with the area where the thermals are, so i catch that wave only if i hear to the vario and follow it by the beeps. that is what allows me to measure it up. otherwise is invisible.
never heard of something like this.
Aug 24, 2015, 05:15 PM
windyhill

thermal waves


Sig 100 thermals in cross pattern, 9 mph winds (5 min 13 sec)


I do these all the time, If you have a canyon, they come right up the center and you can serf them really high if the wind is not blowing to hard.

enlarge the video so you can see it better.
Last edited by desertdog1; Aug 24, 2015 at 05:20 PM.
Aug 24, 2015, 05:46 PM
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rdeis's Avatar
Quote:
Originally Posted by phil alvirez
the waves are generated only at ridges,
Waves can propagate far beyond the ridge or treeline that caused the first one. A wind shear can also create a rotor that looks like wave lift.
Aug 24, 2015, 06:40 PM
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Phil
I'll bet that the lake you're talking about has a hand in thermal generation. The difference in temperature between the land and the water generates a non-uniformity in the rising air. Free flight contests in an area with asphalt parking lots and athletic fields can count on thermals when the sun warms up.
Aug 24, 2015, 08:29 PM
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Thanks Jkettu. I enjoyed reading the inputs you provided.

I use to fly free flight. Switching to RC glider sure takes some getting use to the difference in thermals. Generally I use to except the thermal to be in the direction of the wind feeding the thermal. I have often found the lift behind the thermal if I am at any altitude.

I have only once found what I call wave lift down low. Up high at times it seems the lift is either everywhere or no where.

Art
Aug 25, 2015, 05:21 AM
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wind shear


Quote:
Originally Posted by rdeis
Waves can propagate far beyond the ridge or treeline that caused the first one. A wind shear can also create a rotor that looks like wave lift.
what i said was: 1 thing that intrigues me is that in the 3rd link, the waves are generated only at ridges, but here the place is flat beyond the horizon.

and about the wind shear, could you please tell us more or bring a link?
thanks
Aug 25, 2015, 05:30 AM
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waves


Quote:
Originally Posted by DuPageJoe
Phil
I'll bet that the lake you're talking about has a hand in thermal generation. The difference in temperature between the land and the water generates a non-uniformity in the rising air. Free flight contests in an area with asphalt parking lots and athletic fields can count on thermals when the sun warms up.
what you say about the lake makes sense. thanks for the input.
but then again, i never experienced anything like this. perhaps because i never flew at a place not too far from a lake, and the wind blowing from it.
and about the asphalt, that is another story: those are surface thermals, that is, that go up.
but the 1s am finding are in a horizontal line, like waves: those are the 1s am trying to learn about.
Aug 25, 2015, 06:08 AM
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conversion street


Quote:
Originally Posted by jkettu
Could be, is there any bank and/or treeline or something on the shore that could trigger an upwards motion? If so, the wind will push each subsequent "bounce" of the wave a little higher until the energy dissipates to much. I highly doubt that this kind of small-scale wave could rise high enough to form clouds, but it is perfectly usable for rc gliders once you manage to find it.

In your case I'm guessing that the convection street is more probable explanation.
agree. just to confirm that, i got this at google:
http://rammb.cira.colostate.edu/wmov...lStr/index.htm
Aug 25, 2015, 08:20 AM
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Phil
Glad to help.
I'm thinking that any circulation and rising air can be detached from the ground by a little wind that's fairly steady. I lost a P-30 free flight plane last year that way. A buddy with a bigger plane was searching 25 miles down wind for his until he found it that day.
Aug 25, 2015, 02:49 PM
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no clouds


when i have encountered these waves, the sky is clear: no clouds.

so seems that there is no need to have clouds for this to happen.
it is a completely different phenomenom from thermals.
Last edited by phil alvirez; Aug 25, 2015 at 03:25 PM.
Aug 25, 2015, 06:37 PM
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Thread OP

conclusions


from all that i have learned, thanks to you guys, the ways for a plane to stay up there are by thermals or street waves, these by consequence of the shape of the surrounding terrain. these waves could form from a cliff, or wind from a nearby lake, as is in my case.
the lake is about 5 km (3 mi) so it well may be so.
i was familiar with thermals, but the waves i have learned of recently, as i said, thanks to you folks.
so, thanks for the input.
if there is something to add, please feel free to do so.
regards


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