Author Topic: Anemometer Height Adjustments  (Read 425 times)

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Offline Bohaiboy

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Anemometer Height Adjustments
« on: January 15, 2022, 03:39:56 PM »
I know an anemometer is supposed to be mounted at 30 ft.  For me its not practical.  I know during hurricane season, a lot of offshore rigs report some very high winds because they are some 150 ft plus above the water.  I have seen some information suggesting there is a multiplier that gets the winds down to a 30 ft level, but is there a multiplier to go from 10 ft to 30 ft as to take the ground's friction out of the equation.  I recently had a gust to 46 at the 10 ft elevation and assume the real wind was closer to 50 but maybe even higher.  Located in the Hill Country of Texas about 60miles NW of San Antonio  TIA

Offline PaulMy

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Re: Anemometer Height Adjustments
« Reply #1 on: January 15, 2022, 04:04:18 PM »
I have seen some published tables for various anemometer heights but the only thing I can quickly find is https://cumulus.hosiene.co.uk/viewtopic.php?p=10465#p10465


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Offline mcrossley

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Re: Anemometer Height Adjustments
« Reply #2 on: January 15, 2022, 04:21:59 PM »
In the Cumulus Wiki we have... https://cumuluswiki.org/a/Wind_measurement
Mark

Offline sky_watcher

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Re: Anemometer Height Adjustments
« Reply #3 on: January 15, 2022, 04:33:28 PM »
I know an anemometer is supposed to be mounted at 30 ft.  For me its not practical.  I know during hurricane season, a lot of offshore rigs report some very high winds because they are some 150 ft plus above the water.  I have seen some information suggesting there is a multiplier that gets the winds down to a 30 ft level, but is there a multiplier to go from 10 ft to 30 ft as to take the ground's friction out of the equation.  I recently had a gust to 46 at the 10 ft elevation and assume the real wind was closer to 50 but maybe even higher.  Located in the Hill Country of Texas about 60miles NW of San Antonio  TIA
I think the effects of ground friction would be relatively easy, if we lived on the surface of a billiard ball - it can be handled with an equation like a barometer height correction.  However, if you have significant obstructions in the area such as trees, building or significant topographical features getting a consistently accurate correction is probably unlikely.

When I tried this by doing comparisons with the local airport, I found the speed difference and the speed difference variability varied with direction and the speed of the wind,  but did not appear to have a significant pattern that would allow a sound adjustment. While the speed was (mostly) always lower, the variability appeared to decrease with increasing wind speed, but we don't have frequent enough high winds to make any comparisons significant as it also varies with wind direction. Light winds are much more common, but appear to be much more affected by local eddies and a waste of time trying to analyse.

Hopefully you may have better luck working out your situation.
“The more a man knows, the more willing he is to learn. The less a man knows, the more positive he is that he knows everything...” ― Robert G. Ingersoll

Offline Mattk

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Re: Anemometer Height Adjustments
« Reply #4 on: January 15, 2022, 05:42:22 PM »
So many dynamic variables, way too much inconsistency to have any meaning. 

Offline Bashy

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Re: Anemometer Height Adjustments
« Reply #5 on: January 15, 2022, 11:09:59 PM »
From what i gather, the 10m (33ft) isn't really about ground friction (or is it?), i was always under the impression that its more about obstacles. Not all official anemometers are at 33ft, that I've seen anyway.
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Bashy

Offline CW2274

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Re: Anemometer Height Adjustments
« Reply #6 on: January 15, 2022, 11:48:15 PM »
In the States, all official data is gathered from ASOS and AWOS which are exclusively located at airports, so obviously terrain is not a consideration. The ten meters is an "average" height of control surfaces on most air-carrier aircraft.

Offline mcrossley

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Re: Anemometer Height Adjustments
« Reply #7 on: January 16, 2022, 08:42:33 AM »
So many dynamic variables, way too much inconsistency to have any meaning.

Agreed, unless you are in a open field location, factors other than the slowing of the boundary layer are much more likely to be dominant.
Mark

Offline Bashy

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Re: Anemometer Height Adjustments
« Reply #8 on: January 16, 2022, 08:47:30 AM »
So many dynamic variables, way too much inconsistency to have any meaning.

Agreed, unless you are in a open field location, factors other than the slowing of the boundary layer are much more likely to be dominant.

What is the boundary layer, Google was no help when I asked the other day...
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Bashy

Offline CW2274

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Re: Anemometer Height Adjustments
« Reply #9 on: January 16, 2022, 04:15:05 PM »
So many dynamic variables, way too much inconsistency to have any meaning.

Agreed, unless you are in a open field location, factors other than the slowing of the boundary layer are much more likely to be dominant.

What is the boundary layer, Google was no help when I asked the other day...
It's the atmosphere from ground level to approximately 10,000' MSL, or H7 in the meteorological world.

Offline Bashy

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Re: Anemometer Height Adjustments
« Reply #10 on: January 16, 2022, 05:39:46 PM »
What is the boundary layer, Google was no help when I asked the other day...

It's the atmosphere from ground level to approximately 10,000' MSL, or H7 in the meteorological world.

Thank you, hopefully, it will help in the future, i use wxcharts and they mention it on the Sky cover Meteogram graphs.
Its like this, Sky cover %, High cloud, Mid cloud, Low cloud and Boundary layer, looks like its all in %$, see image...

A quick follow up, to me, i would have thought low cloud is ground level up to around 6,500ft and above 6,500ft to 23,000ft would be mid cloud, so I'm a bit puzzled as to the boundary layer now. why isn't that classed as Low cloud? or is it because it goes up into the mid layer part way and serves some other purpose? Thanks again, its nice to know what I'm actually looking at now :)
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Bashy

Offline CW2274

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Re: Anemometer Height Adjustments
« Reply #11 on: January 16, 2022, 05:48:51 PM »
The BL (boundary layer) per definition has nothing to do with clouds. The BL can dictate what kind of clouds you may or may not get, but is strictly used to indicate the lowest "slice" of the atmosphere.

Offline Bashy

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Re: Anemometer Height Adjustments
« Reply #12 on: January 16, 2022, 06:02:28 PM »
Thank you, so what can i glean from seeing the percentage of the BL on that graph, please?
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Bashy

Offline CW2274

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Re: Anemometer Height Adjustments
« Reply #13 on: January 16, 2022, 06:04:49 PM »
I have absolutely no idea. Never saw that kind of chart before.

Offline Bashy

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Re: Anemometer Height Adjustments
« Reply #14 on: January 16, 2022, 06:08:06 PM »
I have absolutely no idea. Never saw that kind of chart before.


 :lol:  me too, lol the chart is on http://wxcharts.com on the right is the meteogram selection (top), then choose 5 or 10 days and the cloud graph is at the bottom
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Bashy

Offline CW2274

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Re: Anemometer Height Adjustments
« Reply #15 on: January 16, 2022, 06:12:27 PM »
I stared at it for a couple of minutes and it started to give me a headache, so I grabbed an adult beverage.  UU

Offline Bashy

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Re: Anemometer Height Adjustments
« Reply #16 on: January 16, 2022, 06:12:58 PM »
I stared at it for a couple of minutes and it started to give me a headache, so I grabbed an adult beverage.  UU

Ha ha, as ya do.... :)
Kind regards
Bashy