A gust of wind - how does it actually work?

[CaptainPanic]

Within an ordinary gust of wind there can can be a certain wind speed. But the gust of wind itself (as a whole) moves forward at much lower speeds.

 

How does that work?

What puzzles me the most is that you have fast moving wind that moves into slower moving air in front of it. Where does it go? The air pressure isn't so different inside a wind gust that you can explain this by compression phenomena (I guess?).

 

The only thing I can come up with is that it works like a traffic jam (

to illustrate)? But in that video, you can see a compression, which we don't observe in a wind gust (or do we?)? My back-of-the-envelope calculations (mass balances) seem to fail.

 

Any thoughts?

[thinker_jeff]

I am not expert at all because it is too far from my field. Here is just some idea to share.

The air compression is a possible phenomena in a gust of wind. Human body is not very sensitive to such in short period. When you are jogging in a gym (no wind pretty much), the air pressure on your front is higher than its on your back. But you don't noticed that.

[J.C.MacSwell]

Within an ordinary gust of wind there can can be a certain wind speed. But the gust of wind itself (as a whole) moves forward at much lower speeds.

 

How does that work?

What puzzles me the most is that you have fast moving wind that moves into slower moving air in front of it. Where does it go? The air pressure isn't so different inside a wind gust that you can explain this by compression phenomena (I guess?).

 

The only thing I can come up with is that it works like a traffic jam (

to illustrate)? But in that video, you can see a compression, which we don't observe in a wind gust (or do we?)? My back-of-the-envelope calculations (mass balances) seem to fail.

 

Any thoughts?

 

 

 

Think 3D. The upper airflow is almost always higher velocity (and typically somewhat veered, clockwise, in the Northern hemisphere) compared to the lower airflow. In gusty conditions there is mixing of the two flows. The upper flow comes down creating a gust cell that fans out displacing the lower slower moving air. The cell and shear line between the two can move slower than the air in either flow and can in fact sometimes stay fairly stationary or even retreat, while still being "fed" from above and to windward and exiting upwards again and to leeward. So that is why the gust seems slower than the air in it. Sometimes they die out fairly quickly and sometimes they persist.

 

Often heating of the lower level air triggers the start of a gust, as it expands, becomes lighter, a pocket of air rises. The upper air fills in behind and begins the cycle.

 

But you are correct, there is very little compressibility, and the mass flows must balance.

Edited July 15, 2011 by J.C.MacSwell