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HarryO

Wave lift

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Hi there

Thought I might just add some real life examples of mountain wave lift in case it is of interest long term for CumulusX. Check out this fascinating and awe inspiring official forecast for the potential for mountain wave conditions at the mighty ridge of the Sangre De Cristo Mountains (Spanish Peaks) in Colorado USA. Here is a quote:

AREA FORECAST DISCUSSION

NATIONAL WEATHER SERVICE PUEBLO CO

945 PM MDT WED JUN 16 2010

AVIATION...

VFR CIGS AND VIS EXPECTED TO CONTINUE THROUGH THU. MAIN AVN CONCERN

WILL BE MTN WAVE ACTIVITY OVER THE ERN SLOPES OF THE

SANGRES...WETS...AND RAMPARTS FROM 06Z TONIGHT THROUGH THU MORNING.

WINDS WILL BECOME GUSTY FROM THE W TO SW IN THE AFTERNOON OVER ALL

THREE TAF SITES...WITH GUSTS UP TO 40 MPH EXPECTED. 44

Here is the actual link:

http://forecast.weather.gov/product.php?site=NWS&issuedby=PUB&product=AFD&format=CI&version=4&glossary=1

Now, how would a glider pilot feel about getting up at dawn to try for a mountain wave!? I am not sure if I would pass out or just go into a cold sweat!

Cheers

post-31745-127684545138_thumb.jpg

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It's worth mentioning that it's straightforwardly possible to create a simulated wave lift bar using the FSX mission capability (basically plant a ridgelift object up in the air somewhere). Creating soaring missions is kind of a niche hobby though and hand-placement of lift has become extremely rare now that CumulusX does the best job for thermals and ridge lift. Only a couple of us ever created missions using the FSX thermal and ridgelift mission objects except for the original Aces/Microsoft Soaring missions included with deluxe (ah, ancient history - up to Austrian Soaring 4 on my page here).

Ideally the lift bar would have a lenticular cloud by it giving you a clue where the rising air was but I have no idea how you'd achieve that without resorting to custom cloud scenery which is even more of a niche hobby...

As with thermals and ridgelift, life gets easy if some clever bloke creates a utility that automatically places wave lift in all the right places, appropriate to the terrain and weather conditions, but there aren't many Peter Luerkens. While we have a technique of computing *ridge* lift in real time by sampling terrain relatively close to the user aircraft, the calculation of wave lift requires a potentially much larger area of terrain to be analysed, probably requiring a pre-compute stage.

Interesting technical problem though. My suspicion is we could create an image map of the USA where each pixel represents wave lift for a given wind direction. I.e. you start with something a bit like this:

usa_toporelief_1968_l.jpg

and mangle it so colours (i.e. pixel values) represent wave lift in NW wind (so you'd need 16 maps for all wind directions). The FSX module would look up wave values in real time as the user flies. Question is how detailed the 'image map' should be - this one is 1024x670 (also 3644x2384) - for max performance you need the data to be compact and there's always the temptation to use gigabytes of elevation data in real time but I don't think that is actually necessary...

B21

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Wow nice idea B21. A once off computation that produces these wave lift maps for all the regions of the world that becomes a look up table in the simulation. The beauty of this is that we are not talking real life, and so such a once off computation of wave lift areas does not have to be painstakingly accurate, just a reasonably good guess. As the glider flies over a slope and the rate of increase of the terrain goes beyond a limit and the ridge lift goes beyond a limit as well, the wave lift algorithm would fire up and look up the appropriate map data for the prevailing wind and then lay down bands of ridge lift in the look up table region scaled according to actual wind conditions. Although the use of precomputed data reduces the CPU load substantially, even if this caused a once off "glitch" in the simulation as the level of CPU calculation goes through the roof momentarily, it would not be such a bad thing because wave lift conditions are pretty rare and the wave lift algorithm would be mostly completely dormant. It would be worth an initial slight hesitation to be able to soar to really high altitudes.

A lot more work than I make out here!!! I humbly apologise for my ignorance. If nothing else, I wonder if anyone has ever attempted to produce wave lift maps for North America for all 16 wind directions. I for one would be eager to take a look! It would be fun to see where the possible wave lift areas are, as well as to have a n algorithm that can actually guess it.

Cheers

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