for the amateur meteorologists, question.

[john firth]

Maybe the last flight of the year, but memorable.

Atmosphere 10C, very unstable , with cloudbase 5000ft and tops above 10K; showers, wind W 15kt @ 1000ft.

climbed to 4000 (airspace limit) over the airfield ; flew upwind along a cloud street, holding 4000ft.
Street ended after 10 miles , then strong sink for 5 miles ending under a large cu.; at 1200 AGL
found zero sink but little more. Started circling but losing slowly, expecting to find real lift,
but probing found nothing better. Considered starting the engine, but that is admitting defeat too
early, with good fields below; and so I circled in smooth air and drifted, gaining 100 and losing it.
Clouds 4000 ft above drifted past.
Have faith! Unstable air has to get it together and accelerate; the fields drifted steadily
by underneath, in the weak October sunshine, interspersed with large woods, .
This went on for a long time, round and round, airfield unreachable even downwind.
( would I ever contemplate a 15 kt downwind landing? only as a life saver)
and so after 40 mins, still at about 1000 AGL, I see a dual lane highway, the airfield a mile beyond.
surprise! I can reach the airfield; after another couple of circles, I abandon the "thermal" and immediately hit 2 kts. End of suspense. I had drifted 14 miles at 1000ft in 50 mins doing 120 circles.

Now for the question: how does a parcel of air over 600ft diameter maintain a steady ascent
of 150 fpm for nearly an hour without either breaking away or dissipating. This was not a donut
as there was no central core. It must have been replenished from below.

Any similar experiences?

Have a well socially distanced winter!

John Firth (PIK 20E)

[John Foster]

On Monday, October 19, 2020 at 1:22:11 PM UTC-6, john firth wrote:
> Maybe the last flight of the year, but memorable.
>
> Atmosphere 10C, very unstable , with cloudbase 5000ft and tops above 10K; showers, wind W 15kt @ 1000ft.
>
> climbed to 4000 (airspace limit) over the airfield ; flew upwind along a cloud street, holding 4000ft.
> Street ended after 10 miles , then strong sink for 5 miles ending under a large cu.; at 1200 AGL
> found zero sink but little more. Started circling but losing slowly, expecting to find real lift,
> but probing found nothing better. Considered starting the engine, but that is admitting defeat too
> early, with good fields below; and so I circled in smooth air and drifted, gaining 100 and losing it.
> Clouds 4000 ft above drifted past.
> Have faith! Unstable air has to get it together and accelerate; the fields drifted steadily
> by underneath, in the weak October sunshine, interspersed with large woods, .
> This went on for a long time, round and round, airfield unreachable even downwind.
> ( would I ever contemplate a 15 kt downwind landing? only as a life saver)
> and so after 40 mins, still at about 1000 AGL, I see a dual lane highway, the airfield a mile beyond.
> surprise! I can reach the airfield; after another couple of circles, I abandon the "thermal" and immediately hit 2 kts. End of suspense. I had drifted 14 miles at 1000ft in 50 mins doing 120 circles.
>
> Now for the question: how does a parcel of air over 600ft diameter maintain a steady ascent
> of 150 fpm for nearly an hour without either breaking away or dissipating. This was not a donut
> as there was no central core. It must have been replenished from below.
>
> Any similar experiences?
>
> Have a well socially distanced winter!
>
> John Firth (PIK 20E)
Could it have been a line of convergence?

[Waveguru]

Or some kind of traveling wave?

Boggs

[2G]

On Monday, October 19, 2020 at 1:30:41 PM UTC-7, John Foster wrote:
> On Monday, October 19, 2020 at 1:22:11 PM UTC-6, john firth wrote:
> > Maybe the last flight of the year, but memorable.
> >
> > Atmosphere 10C, very unstable , with cloudbase 5000ft and tops above 10K; showers, wind W 15kt @ 1000ft.
> >
> > climbed to 4000 (airspace limit) over the airfield ; flew upwind along a cloud street, holding 4000ft.
> > Street ended after 10 miles , then strong sink for 5 miles ending under a large cu.; at 1200 AGL
> > found zero sink but little more. Started circling but losing slowly, expecting to find real lift,
> > but probing found nothing better. Considered starting the engine, but that is admitting defeat too
> > early, with good fields below; and so I circled in smooth air and drifted, gaining 100 and losing it.
> > Clouds 4000 ft above drifted past.
> > Have faith! Unstable air has to get it together and accelerate; the fields drifted steadily
> > by underneath, in the weak October sunshine, interspersed with large woods, .
> > This went on for a long time, round and round, airfield unreachable even downwind.
> > ( would I ever contemplate a 15 kt downwind landing? only as a life saver)
> > and so after 40 mins, still at about 1000 AGL, I see a dual lane highway, the airfield a mile beyond.
> > surprise! I can reach the airfield; after another couple of circles, I abandon the "thermal" and immediately hit 2 kts. End of suspense. I had drifted 14 miles at 1000ft in 50 mins doing 120 circles.
> >
> > Now for the question: how does a parcel of air over 600ft diameter maintain a steady ascent
> > of 150 fpm for nearly an hour without either breaking away or dissipating. This was not a donut
> > as there was no central core. It must have been replenished from below.
> >
> > Any similar experiences?
> >
> > Have a well socially distanced winter!
> >
> > John Firth (PIK 20E)
> Could it have been a line of convergence?

https://chessintheair.com/convergence/

[Martin Gregorie[_6_]]

On Mon, 19 Oct 2020 12:22:08 -0700, john firth wrote:

> Maybe the last flight of the year, but memorable.
>
> Atmosphere 10C, very unstable , with cloudbase 5000ft and tops above
> 10K; showers, wind W 15kt @ 1000ft.
>
> climbed to 4000 (airspace limit) over the airfield ; flew upwind along
> a cloud street, holding 4000ft. Street ended after 10 miles , then
> strong sink for 5 miles ending under a large cu.; at 1200 AGL found zero
> sink but little more. Started circling but losing slowly, expecting to
> find real lift,
> but probing found nothing better. Considered starting the engine, but
> that is admitting defeat too early, with good fields below; and so I
> circled in smooth air and drifted, gaining 100 and losing it. Clouds
> 4000 ft above drifted past.
> Have faith! Unstable air has to get it together and accelerate; the
> fields drifted steadily by underneath, in the weak October sunshine,
> interspersed with large woods, .
> This went on for a long time, round and round, airfield unreachable
> even downwind.
> ( would I ever contemplate a 15 kt downwind landing? only as a life
> saver)
> and so after 40 mins, still at about 1000 AGL, I see a dual lane
> highway, the airfield a mile beyond.
> surprise! I can reach the airfield; after another couple of circles, I
> abandon the "thermal" and immediately hit 2 kts. End of suspense. I
> had drifted 14 miles at 1000ft in 50 mins doing 120 circles.
>
> Now for the question: how does a parcel of air over 600ft diameter
> maintain a steady ascent of 150 fpm for nearly an hour without either
> breaking away or dissipating. This was not a donut as there was no
> central core. It must have been replenished from below.
>
> Any similar experiences?
>
Yep, but not recently.

This was definitely convergence over the front of sea-air incursion. A
winch launch at Gransden Lodge, 10 miles west of Cambridge UK, put me in
zero sink with a cloud line, which turned out to be a convergence line,
running N-S along the road about 1 km to the east. I cruised over to it
with no height loss, turned north along it cruising at 50 kts and
climbing slowly but steadily to cloud base at 3500/4000 ft. It ended
around 5miles/8km I glided out to the motel on the A1 at Peterborough and
back to the cloud line for the loss of around 1500ft, drove back along it
to GRL and landed. That was my first XC in my 201 Libelle - a 100km out
and return in almost exactly an hour.

I haven't seen convergences like that in the last few years, but they
used to be frequent enough not to be unusual in Eastern UK and were
almost always in calm, high pressure conditions when an E or NE breeze
brought sea in from the North Sea.


--
Martin | martin at
Gregorie | gregorie dot org

[john firth]

On Monday, October 19, 2020 at 11:41:14 PM UTC-2, Martin Gregorie wrote:
> On Mon, 19 Oct 2020 12:22:08 -0700, john firth wrote:
>
> > Maybe the last flight of the year, but memorable.
> >
> > Atmosphere 10C, very unstable , with cloudbase 5000ft and tops above
> > 10K; showers, wind W 15kt @ 1000ft.
> >
> > climbed to 4000 (airspace limit) over the airfield ; flew upwind along
> > a cloud street, holding 4000ft. Street ended after 10 miles , then
> > strong sink for 5 miles ending under a large cu.; at 1200 AGL found zero
> > sink but little more. Started circling but losing slowly, expecting to
> > find real lift,
> > but probing found nothing better. Considered starting the engine, but
> > that is admitting defeat too early, with good fields below; and so I
> > circled in smooth air and drifted, gaining 100 and losing it. Clouds
> > 4000 ft above drifted past.
> > Have faith! Unstable air has to get it together and accelerate; the
> > fields drifted steadily by underneath, in the weak October sunshine,
> > interspersed with large woods, .
> > This went on for a long time, round and round, airfield unreachable
> > even downwind.
> > ( would I ever contemplate a 15 kt downwind landing? only as a life
> > saver)
> > and so after 40 mins, still at about 1000 AGL, I see a dual lane
> > highway, the airfield a mile beyond.
> > surprise! I can reach the airfield; after another couple of circles, I
> > abandon the "thermal" and immediately hit 2 kts. End of suspense. I
> > had drifted 14 miles at 1000ft in 50 mins doing 120 circles.
> >
> > Now for the question: how does a parcel of air over 600ft diameter
> > maintain a steady ascent of 150 fpm for nearly an hour without either
> > breaking away or dissipating. This was not a donut as there was no
> > central core. It must have been replenished from below.
> >
> > Any similar experiences?
> >
> Yep, but not recently.
>
> This was definitely convergence over the front of sea-air incursion. A
> winch launch at Gransden Lodge, 10 miles west of Cambridge UK, put me in
> zero sink with a cloud line, which turned out to be a convergence line,
> running N-S along the road about 1 km to the east. I cruised over to it
> with no height loss, turned north along it cruising at 50 kts and
> climbing slowly but steadily to cloud base at 3500/4000 ft. It ended
> around 5miles/8km I glided out to the motel on the A1 at Peterborough and
> back to the cloud line for the loss of around 1500ft, drove back along it
> to GRL and landed. That was my first XC in my 201 Libelle - a 100km out
> and return in almost exactly an hour.
>
> I haven't seen convergences like that in the last few years, but they
> used to be frequent enough not to be unusual in Eastern UK and were
> almost always in calm, high pressure conditions when an E or NE breeze
> brought sea in from the North Sea.
>
>
> --
> Martin | martin at
> Gregorie | gregorie dot org

I am afraid none of these ideas fit the observations; I am familiar with convergence
lines ( this was not a line) both as a lake effect and locally, terrain differential.
waves are not stable in a unstable atmosphere nor is the flat , slightly ridged terrain
condusive to wave generation.
The puzzle is that this bubble did not coalesce with a convective cloud passing overhead.

John F

[WaltWX[_2_]]

John,

Likely the answer is some kind of weak linear region of lift or convergence.. The atmospheric boundary layer if one could look down it often has lift lines parallel to the wind... or the lines look like like a "mesh" pattern. These may not be referenced necessarily to terrain or ground features.

Walt Rogers WX

[Waveguru]

Waves aren't always generated by hills or mountains, sometimes the air bounces off of another air mass.

Boggs

[[email protected]]

Basically, we don't understand meteorological conditions on the micro-micro level, as in the anomalies that happen for whatever reason in a tiny area. Of course, the "tiny" area is much smaller than can be predicted from satellite imagery, atmospheric analysis of airmass movement and surface disturbances. Essentially it all boils down to just flying in it and making some guesses about what is happening. The best competition pilots generally have many hours and good memories, enough so that they can recognize conditions they have experienced in the past and make assumptions and decisions based on prior knowledge.

For the rest of us, we are essentially clueless until someone with more data can provide a reasonable explanation. And even then, there is a good chance they are blowing smoke. Remember that it was less than 100 years ago (1933) that mountain wave formation was observed and explored by Wolf Hirth and Hans Deutschmann.

Trying to explain atmospheric phenomena requires lots of data, gathered a few bits at a time, and needs to be experienced by as many observers as possible to build even a little bit of understanding.

We used to say in hang gliding, "If we could see air, we'd probably quit flying!"

[krasw]

On Thursday, 22 October 2020 at 03:41:13 UTC+3, Waveguru wrote:
> Waves aren't always generated by hills or mountains, sometimes the air bounces off of another air mass.
>
> Boggs

Waves form in stable layer, convection in neutral layer. Hard to imagine you could connect with wave 1000ft agl and same time have cu clouds passing above.

[[email protected]]

Le jeudi 22 octobre 2020 Ã* 08:33:03 UTC+2, krasw a écritÂ*:
> On Thursday, 22 October 2020 at 03:41:13 UTC+3, Waveguru wrote:
> > Waves aren't always generated by hills or mountains, sometimes the air bounces off of another air mass.
> >
> > Boggs
> Waves form in stable layer, convection in neutral layer. Hard to imagine you could connect with wave 1000ft agl and same time have cu clouds passing above.

My dear friends,
The answers to most of your questions (or doubts) are printed in the book “Dancing With the Wind�, for sale in the on-line shops (Cumulus-Soaring, Wings & Wheels, www.topfly.aero).
Including a lot of historical data regarding US pilots and others.
All the best, take care!

[[email protected]]

On Monday, October 19, 2020 at 3:22:11 PM UTC-4, john firth wrote:
> Maybe the last flight of the year, but memorable.
>
> Atmosphere 10C, very unstable , with cloudbase 5000ft and tops above 10K; showers, wind W 15kt @ 1000ft.
>
> climbed to 4000 (airspace limit) over the airfield ; flew upwind along a cloud street, holding 4000ft.
> Street ended after 10 miles , then strong sink for 5 miles ending under a large cu.; at 1200 AGL
> found zero sink but little more. Started circling but losing slowly, expecting to find real lift,
> but probing found nothing better. Considered starting the engine, but that is admitting defeat too
> early, with good fields below; and so I circled in smooth air and drifted, gaining 100 and losing it.
> Clouds 4000 ft above drifted past.
> Have faith! Unstable air has to get it together and accelerate; the fields drifted steadily
> by underneath, in the weak October sunshine, interspersed with large woods, .
> This went on for a long time, round and round, airfield unreachable even downwind.
> ( would I ever contemplate a 15 kt downwind landing? only as a life saver)
> and so after 40 mins, still at about 1000 AGL, I see a dual lane highway, the airfield a mile beyond.
> surprise! I can reach the airfield; after another couple of circles, I abandon the "thermal" and immediately hit 2 kts. End of suspense. I had drifted 14 miles at 1000ft in 50 mins doing 120 circles.
>
> Now for the question: how does a parcel of air over 600ft diameter maintain a steady ascent
> of 150 fpm for nearly an hour without either breaking away or dissipating.. This was not a donut
> as there was no central core. It must have been replenished from below.
>
> Any similar experiences?
>
> Have a well socially distanced winter!
>
> John Firth (PIK 20E)
John, the unusual pattern of what we called flatland wave has been experienced a few times here in Florida. In 1983 Bennie Flowers and myself flew at least two of these occurrences during a few weeks span. I was able to gather some good information on the weather conditions for one particular flight which included satellite photographs. Our late friend Harry Senn assisted in gathering and analyzing the information. On one particular flight Bennie and I rode this wave to about 25 miles offshore on the East Atlantic coastline, we could have easily made the Bimini. May1983, Soaring magazine, Catching A Florida Wave.
The lift started below the cloudbase and we flew between these strange lines or rows of clouds that looked like a long loaf of bread with about two or three miles between each cloud, as I recall the cloudbases were only about 3K AGL and we rode the wave to well over 10K AGL. Bob

[Tango Whisky]

I had that one over Norther Germany (whis is as flat as flat can be). Cloud streets with base at 1200 m and tops at 1800 m. Wave lift started just under the base in front (upwind) of the cloud, and I managed to go over the tops.
You need a wind shift of 30° or so at cloud base level, with the air becoming stable (and the convective layer to be significantly unstable so that the thermals are pushed far into the stable layer above).

Le jeudi 22 octobre 2020 Ã* 13:50:12 UTC+2, a écritÂ*:

> John, the unusual pattern of what we called flatland wave has been experienced a few times here in Florida. In 1983 Bennie Flowers and myself flew at least two of these occurrences during a few weeks span. I was able to gather some good information on the weather conditions for one particular flight which included satellite photographs. Our late friend Harry Senn assisted in gathering and analyzing the information. On one particular flight Bennie and I rode this wave to about 25 miles offshore on the East Atlantic coastline, we could have easily made the Bimini. May1983, Soaring magazine, Catching A Florida Wave.
> The lift started below the cloudbase and we flew between these strange lines or rows of clouds that looked like a long loaf of bread with about two or three miles between each cloud, as I recall the cloudbases were only about 3K AGL and we rode the wave to well over 10K AGL. Bob

[Martin Gregorie[_6_]]

On Thu, 22 Oct 2020 07:09:32 -0700, Tango Whisky wrote:

> I had that one over Norther Germany (whis is as flat as flat can be).
> Cloud streets with base at 1200 m and tops at 1800 m. Wave lift started
> just under the base in front (upwind) of the cloud, and I managed to go
> over the tops.
> You need a wind shift of 30° or so at cloud base level, with the air
> becoming stable (and the convective layer to be significantly unstable
> so that the thermals are pushed far into the stable layer above).
>
I've seen that too, in Cambridgeshire, UK directly over our airfield, but
the bases were lower - only 1200-1400 ft with a fairly brisk breeze,
blowing. The first time I saw it, the streets had short branches almost
at right angles to the street. It was possible to slope soar 150-200 ft
up the front of a branch. The second time there were no branches but
there was lift enough to climb up and over the street and then glide down
on the other side. I don't recall there being sink on the way down and
don't remember whether there was a crosswind under the street, which was
more or less circular in cross section.


--
--
Martin | martin at
Gregorie | gregorie dot org

[john firth]

On Thursday, October 22, 2020 at 12:31:35 PM UTC-2, Martin Gregorie wrote:
> On Thu, 22 Oct 2020 07:09:32 -0700, Tango Whisky wrote:
>
> > I had that one over Norther Germany (whis is as flat as flat can be).
> > Cloud streets with base at 1200 m and tops at 1800 m. Wave lift started
> > just under the base in front (upwind) of the cloud, and I managed to go
> > over the tops.
> > You need a wind shift of 30° or so at cloud base level, with the air
> > becoming stable (and the convective layer to be significantly unstable
> > so that the thermals are pushed far into the stable layer above).
> >
> I've seen that too, in Cambridgeshire, UK directly over our airfield, but
> the bases were lower - only 1200-1400 ft with a fairly brisk breeze,
> blowing. The first time I saw it, the streets had short branches almost
> at right angles to the street. It was possible to slope soar 150-200 ft
> up the front of a branch. The second time there were no branches but
> there was lift enough to climb up and over the street and then glide down
> on the other side. I don't recall there being sink on the way down and
> don't remember whether there was a crosswind under the street, which was
> more or less circular in cross section.
>
>
> --
> --
> Martin | martin at
> Gregorie | gregorie dot org


The comments are interesting but a convergence zone usually takes surface air up to the inversion;
I am familiar with flatland ( thermal) wave and have used it numerous times..

I was too quick to dismiss the donut vortex ring model. Vortices can be stable entities.
If the core was more than 600 ft dia., the donut could be over 1000 ft across; some energy
has to be supplied to keep it circulating.
This could come from the surface wind pushing the vortex; slightly unstable air is then picked up
at the downwind side and ascends in the core ; it spills out at the sides and rear and descends.
This could be quite smooth flow as indeed it was. It would explain why exploring all four quadrants
only showed sink. (ie not wave).
a drifting vortex ring might act as a mechanical trigger for local patches of "buoyant but sticky"
surface air (a.k.a. super adiabatic) to join the ring and keep it sustained. (thanks Dave Frank)