[TowerTalk] Winds

[Roger (K8RI) on TT]

It's more than being above the trees. It is true for rolling , grassy hills.
Here in the flat-lands of Michigan's Saginaw Valley where the tallest 
buildings are at least 2 miles from the airport and not aligned with any 
runway, when landing on a windy day, you will find that "generally" the 
winds begin to diminish at 200-300 feet. More so the lower you get. At 
80 feet or so, the winds may become erratic in both direction and speed 
due to those ground based objects.
In over 20 years of flying I found the airport experience with winds to 
be pretty much the same at hundreds of airports.

Climbing my 100 ft 45G was a great way to experience the change in wind 
velocity.
My yard is 200 X 200' It is bounded by a row of homes on the S with 
woods on the W and N. with the tower about 100 feet from the woods on 
the N & W. Probably about 150 to 175 from the homes on the S.  East is 
open land except for the northern part of the front yard.
The wind is pretty much constant up to 30 feet. It then increases 
rapidly so it becomes fairly constant from 50 feet on up.
The full velocity seems to drop from the tops of the trees which is 80 
feet, give or take, down to about 50 feet just a 100 feet from the tree 
line.

This is just one location, but the experience applies to most locations 
in a relative sense.

73 Roger (K8RI)

On 5/16/2017 Tuesday 2:39 PM, Patrick Greenlee wrote:
> Most winds in general are horizontal with lower levels of the wind in 
> contact with the ground, trees, and other drag inducing objects which 
> slow the lower level wind through friction and turbulence. Slopes more 
> or less facing broadside to the oncoming wind can accelerate the wind 
> as more wind is passing through the same cross section.  Often a ridge 
> more or less at right angles to the wind will act similar to an 
> airplane wing where the wind over the top is accelerated and moves 
> faster than the air before feeling the effect of the ridge.
>
> Patrick        NJ5G
>
>
> On 5/16/2017 11:42 AM, Bill via TowerTalk wrote:
>> My place out in KH6 is an example of how much stronger the wind is up 
>> top.
>>
>> I live on a very steep slope facing the tradewinds, which normally 
>> blow at an average of 12-15 MPH.  When it is blowing this hard it is 
>> impossible to raise or lower antennas.  So any raising or lowering 
>> must be done at lower speed levels.
>>
>> Why, when the wind is only 5-6 MPH it is usually closer to 15 MPH at 
>> the top of a 90 foot tower.  It is amazing how at the base you feel 
>> almost no wind but it quickly picks up once you get about 20 feet or 
>> so.  I've had many 200 ft towers on the mainland but have never 
>> experienced such a big difference in surface and top of the tower 
>> speeds.
>>
>> Being on a steep upslope is the reason, I'm sure.
>>
>> 73  Bill KH7XS
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-- 

73

Roger (K8RI)


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