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Thermal spawning, ridge wind and weather configuration

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Re: Thermal spawning, ridge wind and weather configuration

Postby Thorsten » Mon May 17, 2021 6:32 pm

Thorsten, can blue thermals regularly be expected above cities/towns?


No, cities and towns are most likely to develop thermals, but whether a thermal is blue or with a cloud has nothing to do with terrain type.

Is ground type already taken into account and which types do develop thermals usually?


The more it heats up, the better thermals you get, watery ground (swamp, lake, ice) usually doesn't develop anything, rock and concrete work best. Local terrain elevations will be more likely to lead to a thermal than flat ground, and windward side of mountains works better than leeward.
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Re: Thermal spawning, ridge wind and weather configuration

Postby benih » Mon May 17, 2021 6:46 pm

Thank you!

Yay, today i had a very productive flight with the ASK21 together with another pilot nearby. others also joined sporadically, tough no radio contact.
Soaring was very nice, and i was able to effectively gain altitude in the nice developing cumulus clouds. In one instance i was very proud, i was able to climb 400 meter without dropping out of the core a single time :)

One question tough, i noticed that its really hard to climb above the mountain peaks. The clouds usually form at the peaks, and i spotted no clouds reaching higher....
What is the technique to go higher than 3000-something meters?
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Re: Thermal spawning, ridge wind and weather configuration

Postby Thorsten » Mon May 17, 2021 6:48 pm

One question tough, i noticed that its really hard to climb above the mountain peaks. The clouds usually form at the peaks, and i spotted no clouds reaching higher....
What is the technique to go higher than 3000-something meters?


In reality? Ridge or wave lift is the only thing that realistically gets you that high (a Cb cloud would, but it more likely gets you killed). In FG you need to use ridge lift, as I've never developed the wave code to the point that it was more than a demo.
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Re: Thermal spawning, ridge wind and weather configuration

Postby benih » Mon May 17, 2021 6:50 pm

Ah, thank you very much.
What did you stop from the wave code development?
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Re: Thermal spawning, ridge wind and weather configuration

Postby Thorsten » Mon May 17, 2021 6:57 pm

What did you stop from the wave code development?


Developing ALS mostly...
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Re: Thermal spawning, ridge wind and weather configuration

Postby benih » Mon May 17, 2021 7:02 pm

:)
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Re: Thermal spawning, ridge wind and weather configuration

Postby benih » Tue May 18, 2021 9:34 pm

I watched a video about thermals.
Getting the location of the thermals would enable a nice feature: birds (spawned ai circling upwards as indication seems to often be used)
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Re: Thermal spawning, ridge wind and weather configuration

Postby wkitty42 » Tue May 18, 2021 11:07 pm

funny! i was going to ask, the other day, about doing something like the birds in the draft to help fliers find the needed air...
"You get more air close to the ground," said Angalo. "I read that in a book. You get lots of air low down, and not much when you go up."
"Why not?" said Gurder.
"Dunno. It's frightened of heights, I guess."
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Re: Thermal spawning, ridge wind and weather configuration

Postby D-ECHO » Wed May 19, 2021 8:49 am

Speaking from my own experience, while there are sometimes birds that can be met in thermals, it's not so often (had it maybe once or twice a year) and you usually only see them for a short time when already in the thermal, simply as they're too small to be seen from further away (it's sometimes even difficult to spot other gliders while approaching a potential thermal). Having said that, thermals can usually be best found
a) if you're rather close to the ground by looking for their sources ( as described by Thorsten above )
b) if you're higher up by looking for cumulus clouds (if you're lucky), finding blue thermals higher up is one of the more difficult tasks, given that they are to some degree dissociated from their sources and you obviously don't see their caps. Fun fact: There are specially tinted glider pilot glasses that increase contrast in a way that sometimes make you able to see the updrafts
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Re: Thermal spawning, ridge wind and weather configuration

Postby MariuszXC » Wed May 19, 2021 9:07 am

@benih: In real life a very good area for easy thermal flying is a south border of Alps. There is a large area of flat land and southerly exposed slopes, which together create a very nice mix of ridge and thermal lift. Expect strong windshear at approx 3000m though, where local area weather meets the regional wind (usualy northerly, while local breeze is from the south). Try the ridge between Bassano del Grappa (NW of Venezia) and Vittorio Veneto (N of Venezia). The neighbouring valley to the north (between Belluno and Feltre) is also very nice :)

@wkitty42: had this happen in real life in my earlier days of paragliding. I was trying to locate a core and did not have much luck, staying mostly in 'turbulent zeroes'. A hunting bird flew to me, did a half circle, like saying 'follow me' and when I did, led me to a nice wide thermal core. We did a couple of turns together, like wing to wing and then he flew away. One of the best memories of my life.

@Thorsten: Thank you for implementing this.

@D-ECHO: seems we were typing in parallel
- I found the glasses to be snake oil (iow they did not work for me), but some pilots swore by them. Go figure...
- Looking for Cumulus clouds needs a small clarifiction. What one should look for are _developing_ clouds, those are being fed by an active thermal. Once Cu cloud is developed there may be some residual inertial lift at the base, but 'the train is gone'.
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Re: Thermal spawning, ridge wind and weather configuration

Postby D-ECHO » Wed May 19, 2021 9:33 am

Good point about looking for the clouds! Found the best lift under clouds that were merely a "real cloud" when I started circling but became a full-blown Cu once at the top :D

I have never tried these glasses myself, it may well be they're not reall helping anything :D
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Re: Thermal spawning, ridge wind and weather configuration

Postby benih » Wed May 19, 2021 10:45 am

Are you talking about that fuzzy small baby-cumuli clouds?
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Re: Thermal spawning, ridge wind and weather configuration

Postby Thorsten » Wed May 19, 2021 11:14 am

Are you talking about that fuzzy small baby-cumuli clouds?


In reality they might be promising. In FG they're not so much. At one point we had code for complete cloud life cycles that would form and decay thermals, but it was expensive to run, frustrating to fly and didn't make the transition to a general cloud-generating interface.
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Re: Thermal spawning, ridge wind and weather configuration

Postby MariuszXC » Wed May 19, 2021 11:27 am

Yes. The beginning of Cu cloud formation is a signal that it has an active feed (thermal).

On a thermal day the sequence of events is:
- sun heats the surface,
- air near surface gets heated, but it is viscous and 'clings' to the surface,
- once it is heated enough it will overcome the viscosity and start to rise, usually at some favourable point (picture an uneven ceiling and water dropping from it),
- rising air will form a column and gain momentum, at the same time cold air will flow downwards to replace the rising warm air,
- while rising, warm air will cool (I believe it is adiabatic cooling, but stand to be corrected),
- once cool enough, condensation will start to appear(*), and Cu cloud will start to form. This is the first visible sign of an active thermal (ok, earlier changes in wind direction can be observed, e.g. on a grassy field),
- in the meantime the supply of warm air will stop and the thermal detaches from the surface,
- Cu continues to form(**), using the kinetic energy of the column of air and the energy released by water condensation.

(*) that is, unless the upper air is really dry. In such case, moisture will just dissolve without forming a cloud.
(**) usually stopped by inversion layer. If the inversion layer is weak, there is a chance of further development into Cb.
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Re: Thermal spawning, ridge wind and weather configuration

Postby Johan G » Wed May 19, 2021 1:14 pm

MariuszXC wrote in Wed May 19, 2021 9:07 am:I was trying to locate a core and did not have much luck, staying mostly in 'turbulent zeroes'. A hunting bird flew to me, did a half circle, like saying 'follow me' and when I did, led me to a nice wide thermal core. We did a couple of turns together, like wing to wing and then he flew away. One of the best memories of my life.

I can imagine. :D
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