> Does FlightGear currently "support" cloud turbulence? You know, like  
> when you go through a cumulus cloud, there's /a lot/ of turbulence?  
> Well, IIRC, FlightGear doesn't support have any.

Yes, it does - it's part of modelling thermals in Advanced Weather. There's a 
checkbox on the detailed options tab of Advanced Weather to start that 

> My guess is that the size/density of the cloud will have to be
> calculated for the turbulence to be even close of realistic.

Well, yes :-)

The model starts by noting the time of day and the latitude to get an idea of 
the overall likelihood to produce Cu clouds, then samples the terrain to prefer 
spots which might develop convection (ridges, elevations, concrete 
surfaces,...) over those which might not (open water, ice,...) - so you can see 
Cu development lining the coast, but not extending to the sea, or see it heavy 
in the mountains and weak in the valleys.

That gets modulated with the overall instability of the convective layer (which 
is a user-selectable parameter) and the amount of available water vapour (which 
is part of the overall weather situation assessment of the system) - the first 
parameter determines the strength of the convection, along with the assessment 
of terrain and daytime done before, the second modulates the size of the cloud 
being generated given convection of a certain strength.

Dependent on conditions, the system generates large thermals with weak updrafts 
and rather modest turbulence correlated with smooth clouds or very small 
thermals with strong updrafts and hefty turbulence correlated with ragged 
clouds shooting up quite a bit beyond the lowest inversion layer - so even 
looking at the clouds can give you a reasonable idea what strength of updraft 
and what magnitude of turbulence to expect. Especially in the afternoon, 
there's also the possibility of overdevelopment, leading to Cb formation and 
rain (and ultimately even thunderstorms). Cloud placement altitude depends on 
the underlying terrain - terrain obstacles tend to push clouds somewhat up.

Thermals are slanted, wasp-waisted pillars of lift with a 3-d 
position-differential lift function, surrounded by regions of turbulence. In 
principle there is support coded for simulating the full life-cycle of thermals 
and convective clouds, continually re-generating and decaying them  - but 
that's currently off due to performance concerns.

The whole convective system is benchmarked by my real-life experiences in 
flying gliders, and I have to say it reproduces the challenges rather well - 
I've flown quite a few cross country tours with the ASK-13, and finding 
suitable thermals and climbing them is just as in real life - sometimes a joy, 
sometimes a frustrating battle, sometimes there's just nothing which can 
provide enough lift. 

So, I'm guessing as far as realistic modelling of convective clouds and 
associated phenomena is concerned, FG is pretty high up - I'm not aware of any 
other simulation going through that amount of detail... :-)


* Thorsten

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