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difference in the strength of cold/dry vs warm/humid wind

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edt
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Re: difference in the strength of cold/dry vs warm/humid win

Postby edt » Thu Jan 17, 2013 4:59 pm

Bille wrote:I Really notice that difference whenever i go from Mohave
to the coast in San Diego !

A 25 in the Dry Mohave desert, isn't anywhere Near as strong
as that coastal air with the same wind strength. I remember Mohave
being about 640ft above sea level, so it isn't really an altitude thing.

Bille


640 feet means about 1027mbar so it's about 1% less powerful than sea level wind purely from altitude. The dry air is about 0.05% more powerful than the moist coastal air. With a 20F difference in temperature that's about 1.5% less powerful warm air.

We can feel the dry air very easily so we like to think it affects the kite but it's everything else that's more important.

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Re: difference in the strength of cold/dry vs warm/humid win

Postby Bille » Thu Jan 17, 2013 5:34 pm

edt wrote:...

We can feel the dry air very easily so we like to think it affects the kite but it's everything else that's more important.


So it's mostly physiological then ?

One thing for Sure though , the SD crowd gets a Good laugh when
i show up with my Full wetsuit in the middle of summer !
i like it best when it's a hundred deg + & the water is Way warm .

Bille

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Re: difference in the strength of cold/dry vs warm/humid win

Postby TheJoe » Thu Jan 17, 2013 5:41 pm

Like someone else said currents play a large role in power or perceived power. Strong currents can make or break a location. Here in the Houston area Galveston East beach is the main surf spot the problem with it is the strong current that is created from the jetty and shipping channel. Current will normally be with wind so as a personal rule I won't even attempt to kite there unless the forecast is over 20kts.

All so we get lots of pressure bubbles that pushes the wind up higher than our kites. This is because the island really is just a sand bar and until the bay gets hot the wind is really light on the beach. Usually 10kts lighter.

One last thing I will bring up is changing wind directions. Not only will the wind lull and gust it can shift direction. If it is real shifty and changing its angle a lot you could find your self going down wind even though you feel powered. This is really hard to notice and get in sync with. Just the other day I was out and about to pack up when I figured out that it was just shifting. Changed up my tacks with the wind and found myself shooting upwind even though the wind was light and I only really had enough to power to stay upwind with the tide going out.

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Re: difference in the strength of cold/dry vs warm/humid win

Postby Dr Makani » Thu Jan 17, 2013 6:19 pm

http://www.gribble.org/cycling/air_density.html

for dummies: hot, high and wet = bad

If you are interested how much, then you should calculate your rho (lbs/cuf or kg/kuM) and multiply it with your kite size. Playing with some numbers shows you exactly how your kite (and its pull) is affected by temp, altitude and dew point.

peace

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Re: difference in the strength of cold/dry vs warm/humid win

Postby edt » Thu Jan 17, 2013 7:24 pm

Bille wrote:So it's mostly physiological then ?


Bille


oh no. The difference you feel is quite real. The problem is that we can feel moisture in the air very easily but we find it very difficult to tell when we are up or down 800 feet in altitude. So we think it's the dry air when it really is the altitude. Or maybe it will be a dry day and the wind gradient is very even, so it's 15mph on the ground and 15mph 20 meters up in the air, but on a moist day the wind gradient might be 15mph on the ground and 25mph 20 meters up in the air. So we think it's the dry air but it's really the wind gradient / altitude / temperature / current etc.

But the difference is definitely real.

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Re: difference in the strength of cold/dry vs warm/humid win

Postby shawn13 » Thu Jan 17, 2013 7:38 pm

Does anyone have a Temp X Windspeed = Force chart for this? Because that would come in handy...

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Re: difference in the strength of cold/dry vs warm/humid win

Postby edt » Thu Jan 17, 2013 7:50 pm

shawn13 wrote:Does anyone have a Temp X Windspeed = Force chart for this? Because that would come in handy...


pressure is proportional to temperature measured in K. 20c (68F) is 293K. So going from 20c to 10C (50F) is 10/293 about 3% stronger wind. You dont really need a chart just be able to do division.

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Re: difference in the strength of cold/dry vs warm/humid win

Postby Peter_Frank » Thu Jan 17, 2013 8:38 pm

Would just point to a 10 year old thread: http://www.kiteforum.com/viewtopic.php?f=1&t=5159

The image links were "old" (meaning, our national phone company has closed these sites), but I've replaced with new worlking pictures/links today 8)

If anyone find a "dead" link from me anywhere, any posting - please let me know, as I have all the data, and can easily be replaced.

Dont know if it can be used - but the very same topic :thumb:

Another thread, similar: http://www.kiteforum.com/viewtopic.php?f=1&t=2312432

:D Peter

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Re: difference in the strength of cold/dry vs warm/humid win

Postby shawn13 » Thu Jan 17, 2013 9:37 pm

I was actually looking for something like this:

http://localkitespots.com/boost.htm

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Re: difference in the strength of cold/dry vs warm/humid win

Postby Peter_Frank » Thu Jan 17, 2013 9:46 pm

shawn13 wrote:I was actually looking for something like this:

http://localkitespots.com/boost.htm


Exactly - thats why I linked to this (the very same) :thumb:

But if easier, a direct link:

Image

:D PF


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