Wind and Thermals

[Singing Bridge]

I've done some study of the formula's and physics behind mechanical, as well as thermal, turbulence. The particular bluff I am hunting, on an average day, clearly has mechanical turbulence as the overriding factor that creates the air movement up the leeward side of the bluff. But there are days where I believe it is secondary to thermal turbulence. On its own, away from excessive friction created from mountainous or rough terrain, Thermal turbulence has a similar impact on surface wind as mechanical turbulence does. It also has an impact on aviation at higher altitudes than mechanical turbulence.

With mechanical turbulence, if your variables remain constant- wind direction and speed, flowing over a constant mass (my bluff I'm hunting), the turbulence generated should also be constant... and yet on slow wind or calm wind days, I find the air rising up the leeward side to be quite variable. It really picks up and blows hard up this big bluff on the downwind side from about midmorning through midafternoon on slow wind speed days. I believe the thermals rising have a major impact in this situation and add a lot to the "less than normal" mechanical turbulence generated. The "eddies" created by the slow wind speed almost seem to be overwhelmed by the strength of the thermal activity.

In essence, it appears to be a combination of the thermal activity coinciding with the mechanical turbulence. I believe that the assumption that mechanical turbulence in hill country is the only factor creating this movement is in error- the thermals do exist and have an impact and it is rather strong in this particular situation of light and variable wind. While it is possible that this particular hunting spot is unique, it is not probable.

[Autumn Ninja]

Please dont get mad at me like some do on this site...this is the real type of hunting stuff I like talking about. The rest bores me to death.

I've done some study of the formula's and physics behind mechanical, as well as thermal, turbulence.

Good deal, so what is your take on this fluke off thermal flow?

On its own, away from excessive friction created from mountainous or rough terrain, Thermal turbulence has a similar impact on surface wind as mechanical turbulence does.

Exactly!! Key word, away from.

It also has an impact on aviation at higher altitudes than mechanical turbulence.

Of course it dose, mechanical turbulence only happens when the wind passes over, under or around a solid object. kinda irrelevant, unless your flying around in the rocks. BUT if you dig into the physics of the matter...aviation...the only reason that plan can fly is mechanical turbulence, shape of wing, shape of prop and wind speed.

The area I hunt only has elevation changes of 3 to 4 hundred feet, so thermals play very little roll, the wind dictates the flow.

[Autumn Ninja]

Sorry I put this in two parts...my wife wanted on the PC, lol.

With mechanical turbulence, if your variables remain constant.

IF and WHEN are very BIG words when talking about wind speed and direction.

In essence, it appears to be a combination of the thermal activity coinciding with the mechanical turbulence.

The domino effect,,,,a little goes a long way with (and only with) a starter...that keeps it in motion.

I believe that the assumption that mechanical turbulence in hill country is the only factor creating this movement is in error- the thermals do exist and have an impact and it is rather strong in this particular situation of light and variable wind.

Did I say that thermals didnt exist? I'm not going back through this thread...so if I did Im sorry, I was wrong they do exist.

While it is possible that this particular hunting spot is unique, it is not probable.

I do agree with this.

[JoeRE]

I've done some study of the formula's and physics behind mechanical, as well as thermal, turbulence. The particular bluff I am hunting, on an average day, clearly has mechanical turbulence as the overriding factor that creates the air movement up the leeward side of the bluff. But there are days where I believe it is secondary to thermal turbulence. On its own, away from excessive friction created from mountainous or rough terrain, Thermal turbulence has a similar impact on surface wind as mechanical turbulence does. It also has an impact on aviation at higher altitudes than mechanical turbulence.

With mechanical turbulence, if your variables remain constant- wind direction and speed, flowing over a constant mass (my bluff I'm hunting), the turbulence generated should also be constant... and yet on slow wind or calm wind days, I find the air rising up the leeward side to be quite variable. It really picks up and blows hard up this big bluff on the downwind side from about midmorning through midafternoon on slow wind speed days. I believe the thermals rising have a major impact in this situation and add a lot to the "less than normal" mechanical turbulence generated. The "eddies" created by the slow wind speed almost seem to be overwhelmed by the strength of the thermal activity.

In essence, it appears to be a combination of the thermal activity coinciding with the mechanical turbulence. I believe that the assumption that mechanical turbulence in hill country is the only factor creating this movement is in error- the thermals do exist and have an impact and it is rather strong in this particular situation of light and variable wind. While it is possible that this particular hunting spot is unique, it is not probable.

Very well put sir. Those are the complex variables that dictate air flow on a micro level (on a scale relevant to a hunter) in a nutshell!

[SaddleMaster]

After reading through this thread I went looking for some more info. I came across a really cool book called Fire Weather that's available as a .pdf download. It's for forest firefighters but has a lot of good info for hill country deer hunters. It has a couple of chapters dedicated to the wind. It was written in 1970 and I guess it was scanned in, so you'll come across a misspelled word or two.

You can download the whole book or individual chapters.
http://www.firemodels.org/index.php/behaveplus-introduction/behaveplus-publications#Fire%20weather


The http://www.firemodels.org site also has a wind simulator called WindNinja that can be downloaded. But it says that it doesn't handle the leeward side of hills correctly so I haven't bothered trying it out yet.

[cbay]

After reading through this thread I went looking for some more info. I came across a really cool book called Fire Weather that's available as a .pdf download. It's for forest firefighters but has a lot of good info for hill country deer hunters. It has a couple of chapters dedicated to the wind. It was written in 1970 and I guess it was scanned in, so you'll come across a misspelled word or two.

You can download the whole book or individual chapters.
http://www.firemodels.org/index.php/behaveplus-introduction/behaveplus-publications#Fire%20weather


The http://www.firemodels.org site also has a wind simulator called WindNinja that can be downloaded. But it says that it doesn't handle the leeward side of hills correctly so I haven't bothered trying it out yet.

Thanks for the link (WindNinja). I had previously been on firemodels but never saw the wind model. Very interesting. Played around with it enough to get some good use out of it. Not as far as the tunnel, but it can really provide insight on how the wind and thermals travel the topography. Naturally it showed the bedding areas as having thermal arrows pointing to them from all directions.