The World Builder - Wind

[RonHiler]

Hey all,

Sorry again for being quiet. I got a little wrapped up in my investigations of wind. Wind is a complex thing, and I have to make a decision on how realistic I want to model it.

In order to do that, we have to think about what modelling wind gets us. What does wind do, in world building terms? I think it does two things. One (and of lesser importance), it moves a bit of topsoil around. Not much, really, in comparison to what water will do, but a bit. So we'll do that (but no effect on the underlying bedrock).

Two, it moves water vapor around. This is the one that is important, I think. We'll add vapor to a tile based on water content and temperature, then move it based on wind speed and direction (and subsequently drop it as rainfall if it moves to an area of lower temperature and/or higher elevation).

So anyway, given that, I think we need only to model a fairly simplified version of wind. If you look at any global wind map, there are six major zones, three above the equator and three below (the whole thiing is caused by differing tempatures and something called the coriolis effect).

So, I think we'll just set up wind direction like this:

Zone 1 - North pole to ~60 degrees: South to Southwest
Zone 2 - 60 degrees to 30 degrees: North to Northeast
Zone 3 - 30 degrees to Equator: South to Southwest
Equator - Doldrums - no wind
Zone 4 - Equator to 30 degrees: North to Northwest
Zone 5 - 30 degrees to 60 degrees: South to Southeast
Zone 6: 30 degrees to South pole: North to Northwest

Not sure if I want to try to gradient between the zones, or if we can just use a sharp cutoff. As for windspeed, I'm not really sure of that either. Maybe it's not so important, we can just use direction and move water vapor one tile per iteration rather than trying to factor in speeds?

What makes wind complicated in the real world is the temperature differences between land masses and ocean. I don't know that we want to mess around with that (although as a result we will end up with somewhat unrealistic occurances of on-shore windflows rather than the much more common off-shore windflows).

Anyway, thoughts are welcome.

[Shane Christopher]

http://apod.nasa.gov/apod/image/0506/tornado_nguyen.jpg

ftw tbh ;)



On an on-topic note I think your idea is okay, so long as it rains more at higher altitudes and lower temps I'm happy. The different zones sound good too, some sort of gradient between them would be best though or else the effects might be a bit too different for tiles right beside eachother.

As for on shore winds etc I doubt we have to worry about that. This isn't a nasa simulator you want ;)

[Pix]

To be more specific, the prevailing winds aren't merely straight-line diagonals, they are bands of circular flow, alternating clockwise and counter-clockwise.

/yes, I have taken courses in college that discuss weather. :)

[RonHiler]

To be more specific, the prevailing winds aren't merely straight-line diagonals, they are bands of circular flow, alternating clockwise and counter-clockwise.

Yeah, we'll start them (for instance) going straight south then shift them to southwest as we move down the band. I just need to find an equation that will do that. Something sin-ish or cosin-ish will probably do the trick.


/yes, I have taken courses in college that discuss weather. :)
Awesome, be sure to catch anything I royally screw up then :) Do you have any thoughts on what ought to happen between the bands? Is there a sharp differentiation? Or is it a gradual shift?

[Pix]

Yeah, we'll start them (for instance) going straight south then shift them to southwest as we move down the band. I just need to find an equation that will do that. Something sin-ish or cosin-ish will probably do the trick.

Map a quarter-circle, maybe. Should be a good enough approximation.



Awesome, be sure to catch anything I royally screw up then :) Do you have any thoughts on what ought to happen between the bands? Is there a sharp differentiation? Or is it a gradual shift?

I'm not sure, actually, altho I think you wind up with general areas of low wind. Take a look at this: http://en.wikipedia.org/wiki/Horse_latitudes

[RonHiler]

Cool, thanks Pix. I was looking all over the place for an idea of what happened at the band junctures, and couldn't find anything anywhere. All they would tell me is what happened IN the bands. I knew about the doldrums, but not the horse lattitudes. So that's three of the five. Do you suppose the polar fronts are the same way? Probably so, huh?

[Pix]

Cool, thanks Pix. I was looking all over the place for an idea of what happened at the band junctures, and couldn't find anything anywhere. All they would tell me is what happened IN the bands. I knew about the doldrums, but not the horse lattitudes. So that's three of the five. Do you suppose the polar fronts are the same way? Probably so, huh?

http://en.wikipedia.org/wiki/Polar_front

[RonHiler]

Yeah, I saw that too. It doesn't say a whole lot about what happens there, wind-wise, though. I suppose it does *imply* there is no wind, so we'll go with that.

[Pix]

Yeah, I saw that too. It doesn't say a whole lot about what happens there, wind-wise, though. I suppose it does *imply* there is no wind, so we'll go with that.

No, it says what happens, just not clearly. A stationary front means that you have a more or less statically-positioned discontinuity in wind speed and/or direction. Furthermore, it says that cyclones can be formed, so you have winds moving in opposite directions on opposite sides of the front. Probably easiest way to simulate it (assuming for your purposes you will ignore cyclones/hurricanes/etc) is to act as if there's a wall that the wind can't cross, and (optionally) which causes most of the humidity to precipitate.