thermal wave

[firsys]

Yesterday, close to my home field, after I had given up( 2500 ft cloudbase)
I noticed lennie like clouds lining up across the light NW wind.

I have flown thermal wave often in the past, but nothing in the last ten years.
Missed this one but probably too weak to use.

These systems can difficult to get into but extensive and rewarding if you can do it.

Has anyone any idea of the met conditions for development of T.W?

Here are a couple:

Weak convection in the lower layer with light winds.

An upper wind of 15+ kts above an inversion, rising with height.

But there must be something else or I would see this more frequently.

John Firth
Ottawa

[krasw]

On Sunday, 23 July 2017 20:45:38 UTC+3, firsys wrote:
> Yesterday, close to my home field, after I had given up( 2500 ft cloudbase)
> I noticed lennie like clouds lining up across the light NW wind.
>
> I have flown thermal wave often in the past, but nothing in the last ten years.
> Missed this one but probably too weak to use.
>
> These systems can difficult to get into but extensive and rewarding if you can do it.
>
> Has anyone any idea of the met conditions for development of T.W?
>
> Here are a couple:
>
> Weak convection in the lower layer with light winds.
>
> An upper wind of 15+ kts above an inversion, rising with height.
>
> But there must be something else or I would see this more frequently.
>
> John Firth
> Ottawa

They are pretty common everywhere in flatlands but obviously hard to spot as wave is almost always above cloudbase level and often weak. Wave occurs in stable atmosphere, so inversion above convective layer is common, preferable with strong wind shear. Approaching fronts usually create wave patterns..

[Duster[_2_]]

Pileus clouds are cap-like clouds that can be used to identify thermal wave.. Good convection apparently acts like orographic barrier, wind shear hits it, forced up and moisture condences. Climb is on windward side of cumulus, from my limited experience. The Pileus often don't last very long, though the lift may still be there.

https://www.youtube.com/watch?v=mGM7kJQr0RA

https://www.youtube.com/watch?v=3eHKYWMvmWE

[Dave Nadler]

Hi John! Sure...

On Sunday, July 23, 2017 at 1:45:38 PM UTC-4, firsys wrote:
> Yesterday, close to my home field, after I had given up( 2500 ft cloudbase)
> I noticed lennie like clouds lining up across the light NW wind.
>
> I have flown thermal wave often in the past, but nothing in the last
> ten years. Missed this one but probably too weak to use.
>
> These systems can difficult to get into but extensive and rewarding
> if you can do it.
>
> Has anyone any idea of the met conditions for development of T.W?
> Here are a couple:
>
> Weak convection in the lower layer with light winds.

No, doesn't have to be weak.

> An upper wind of 15+ kts above an inversion, rising with height.

More important is a change in direction at the top and above
the convective layer.

> But there must be something else or I would see this more frequently.

It is actually very common, but much easier to see from above.
In eastern North America, especially near frontal passages (because of wind
rotation). I've flown in thermal wave often in New England and also flat terrain
in Florida, Texas, South Carolina, a few Australian sites, etc.
See for example: http://www.ssa.org/Contests?show=blog&id=4169
https://www.onlinecontest.org/olc-2.0/gliding/flightinfo.html?flightId=-1131309345

Fun stuff!
Best Regards, Dave

[firsys]

On Sunday, July 23, 2017 at 1:45:38 PM UTC-4, firsys wrote:
> Yesterday, close to my home field, after I had given up( 2500 ft cloudbase)
> I noticed lennie like clouds lining up across the light NW wind.
>
> I have flown thermal wave often in the past, but nothing in the last ten years.
> Missed this one but probably too weak to use.
>
> These systems can difficult to get into but extensive and rewarding if you can do it.
>
> Has anyone any idea of the met conditions for development of T.W?
>
> Here are a couple:
>
> Weak convection in the lower layer with light winds.
>
> An upper wind of 15+ kts above an inversion, rising with height.
>
> But there must be something else or I would see this more frequently.
>
> John Firth
> Ottawa

PS In the last ten years or so, here in E Ontario, it has not been common, or even frequent as it was in the 70s and 80s; I have been looking to fly any day since 2008 and think I would have noticed.
(BTW I published a paper in the OSTIV journal reporting a flight to 16000
ft after a low level struggle in weak convection; I think it was presented at the 1978 meeting at Chateauroux)

[Martin Gregorie[_5_]]

On Sun, 23 Jul 2017 12:15:03 -0700, Duster wrote:

> Pileus clouds are cap-like clouds that can be used to identify thermal
> wave. Good convection apparently acts like orographic barrier, wind
> shear hits it, forced up and moisture condences. Climb is on windward
> side of cumulus, from my limited experience. The Pileus often don't last
> very long, though the lift may still be there.
>
> https://www.youtube.com/watch?v=mGM7kJQr0RA
>
> https://www.youtube.com/watch?v=3eHKYWMvmWE

I didn't know the name until now, but I remember some years ago coming
off the Channel car ferry at Calais and heading for Hungary. This took us
through Lille and across Belgium into Germany at Aachen. All the way
across Belgium there were really good-looking Cu with Pileus caps on the
northerly slopes of most of them with bright sun on the ground and a
decent northerly blow, so good, unstable, thermally lower atmosphere. I
remember thinking that this would have a been a great day to have taken
an early launch in southern England to cross the Channel and see how far
into France or Germany you could get.

The trick seems to be to leave the English coast high enough to get to
France with enough height move away from the coast and into the first
thermal region. Still, you may get lucky on the way. I remember reading
that Philip Wills was lucky enough to drift most of the way across in
what sounds like some sort of self-recycling lift bubble before leaving
as it decayed and finally landing at St.Omer, 30km from the coast, as the
day died.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

[[email protected]]

On Sunday, July 23, 2017 at 1:45:38 PM UTC-4, firsys wrote:
> Yesterday, close to my home field, after I had given up( 2500 ft cloudbase)
> I noticed lennie like clouds lining up across the light NW wind.
>
> I have flown thermal wave often in the past, but nothing in the last ten years.
> Missed this one but probably too weak to use.
>
> These systems can difficult to get into but extensive and rewarding if you can do it.
>
> Has anyone any idea of the met conditions for development of T.W?
>
> Here are a couple:
>
> Weak convection in the lower layer with light winds.
>
> An upper wind of 15+ kts above an inversion, rising with height.
>
> But there must be something else or I would see this more frequently.
>
> John Firth
> Ottawa

Back in the early 80's my friend Bennie Flowers and I flew a Florida wave on three different occasions. The wave took us well offshore south of Miami and we could have easily landed in the Bahamas. There was an article written for Soaring Magazine which depicted photos of the clouds. Since that time I have seem that same type cloud formation only a couple of times. As I recall the cloud base was about 2500 feet and we flew between the row of clouds and started going up like a homesick angel. Wish I could find those same conditions again. Bob

[[email protected]]

One needs to differentiate between thermal waves and ridge lift induced by thermals.

Real thermal waves are actually quite rare, at least here in the German flat lands. They require a significant wind-shear in direction and strength above the inversion layer. Cloud-streets lining-up 90° to the actual wind direction below inversion are an indicator of such thermal waves. These are real waves that bring you way above the convection layer. There were reports of altitudes >4000m AGL (cloud base at <2000m).

Climbing in front of a Cu like in front of a ridge happens quite often. All it needs is a wind increase above the condensation level. The lift in most cases is not very strong and brings you a few hundred metres above cloud base level. I had one occasion earlier this year that brought me to the Cu-top, some 800m above cloud base.

[Dan Marotta]

On 7/24/2017 5:25 AM, wrote:
>
> Back in the early 80's my friend Bennie Flowers and I flew a Florida wave on three different occasions. The wave took us well offshore south of Miami and we could have easily landed in the Bahamas. There was an article written for Soaring Magazine which depicted photos of the clouds. Since that time I have seem that same type cloud formation only a couple of times. As I recall the cloud base was about 2500 feet and we flew between the row of clouds and started going up like a homesick angel. Wish I could find those same conditions again. Bob
Wow! That would have been some retrieve!! Or maybe you could do a
ground launch behind a para-sail boat. Even pay to have him drag you to
within gliding distance of home.
--
Dan, 5J

[danlj]

On Sunday, July 23, 2017 at 12:45:38 PM UTC-5, firsys wrote:
> Yesterday, close to my home field, after I had given up( 2500 ft cloudbase)
> I noticed lennie like clouds lining up across the light NW wind.
>
> Has anyone any idea of the met conditions for development of T.W?
>
> John Firth
> Ottawa

Here's the link to the talk I gave at OSTIV in January...
http://www.danlj.org/~danlj/Soaring/SoaringRx/2016-11-20_OSTIV-convective-wave-over-plains.pdf
Dan Johnson

[Duster[_2_]]

Very useful article to the question, thanks for posting. Now, can you write one on "anti-gravity waves"?