On 2003-01-21 21:18, blizzard wrote:
Very useful. The extent of the variation is surprising.
So the answer is to climb the nearest flag pole. Or maybe just add between say 30-40% to your reading?
On 2003-01-21 13:50, Peter_Frank wrote:
I made some graphs of the windgradient - that is how much the wind speed changes when going higher above the surface.
These are the standard wind gradients, meaning how they are if the weather is "normal", without wind shear or layer/temp. effects of any kind.
I've taken into account that the water surface gets more rough, when the wind picks up.
It is very evident, that a hand held anemometer can be very erroneous, because the wind speed changes so rapidly in "hand" height, especially in high winds.
And there is always some kind of shore effect, where the wind will be slowed down when reaching the shore (where you most likely are measuring).
If the anemometer is placed on a flagpole in 7-8 meters height, the readings will often be quite accurate, regardless of ground level errors.
The shore effect still exist - but is often very small in this height.
This is common knowledge to most of you, I know - but there are many who will find it useful.
Here is the graph, which is very interesting for ALL of us, I think:
If you want it in meter and m/s (European):
If you want it in feet and knots:
I've measured and checked these wind gradients on many weather stations and wind mill's here in Denmark, and it is often quite accurate - although there can be wind shear that makes it different - but not very often.
On 2003-01-21 20:48, aklbob wrote:
Very good! I often don't trust my wind meter, and often add 5 knots to its reading windspeed if it says it's 15, and I know I can use my X2-12, but if it's hitting 20 then I can't go out!!
It would be interesting to see a graph taking into account air temperature/power produced.. I was in Rarotonga once with the same windmeter, and it was reading 20 knots steady, and I could still put up my 11.8 Airblast and just hang on to it..
On 2003-01-22 12:07, Peter_Frank wrote:The height difference gives about 21% power difference, the "weather" pressure about 10%, the temperature about 10%, and the humidity about 3% - in this example which is a fictive and extreme case.
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