Its often said that tropical/trade winds have less power than equivalent speed sea breezes. What would be a reasonable estimate of the power produced by a 20knt trade wind in terms of knts of a WA seabreeze....... 20knts trade wind = ? knts WA seabreeze. Thanks in advance.
Hey Snalberski, I was idly wondering the same thing as I was tooling around on my 9m in Mauritius riding SE trades this afternoon. So, seeing as you asked I did my best to calculate it, and the answer seems to be not as much as you would think.
Using yesterday’s data for Mauritius and Perth, air pressures are pretty close at 1021 and 1022 hPa, high temps are 16 and 25 respectively, giving air densities of 1.230kg/m and 1.196kg/m (using a simplified formula for dry air). When calculating loads from wind, the nerd engineer types use ‘velocity pressure’ which is the kinetic energy per unit volume of air flow. It is probably a good basis for comparing your two scenarios as it is how much energy the wind will exert on a structure. There is obviously other factors with kiting being an aerodynamic activity, but I’ll leave that to others if they have strong feelings on what I’ve worked out.
So velocity pressure = ½ x density x velocity squared. So we can see that the wind speed itself dominates over the density effect. But if we plug that all into excel, it turns out as: Perth yesterday, velocity pressure = 65.25 N/m2, Mauritius yesterday, velocity pressure = 63.45 N/m2, or a 2.75% difference.
So your 20 knot kite session in Perth yesterday would ‘feel’ power-wise, like 20.57 knots compared with my session in Mauritius (this has to be the most long-winded gloat ever). Taking Perth’s lowest pressure and temperature and comparing with Mauritius’ highest pressure and temperature gives a slightly more exciting 21.4 knots. So, for you in Perth the effect is pretty marginal – but as the temperature drops to zero, it comes close to ten percent.
I’m totally bored of this now and it’s beer o’clock here, so I’ll leave other people to riff further on this!
Jack
Select to expand quoteharry potter said..
More to do with temperature .... Cold air is denser and packs more punch.
^^ the tldr; version of my post! 
Select to expand quotesnalberski said..
Its often said that tropical/trade winds have less power than equivalent speed sea breezes. What would be a reasonable estimate of the power produced by a 20knt trade wind in terms of knts of a WA seabreeze....... 20knts trade wind = ? knts WA seabreeze. Thanks in advance.
For conversion to WA seabreeze:
Multiply tradewind speed by factor of 0.9 (cause nine is a magic number)
Surely 20knots in light air is exactly the same as 20 knots of dense air because the wind meter takes into account speed as well as density in coming up with its reading. So the 20 knots in light air might be travelling a bit faster but because its less dense will have less effect on the rotors but 20 knot measurement is still 20knots.
Exactly 20Kts is 20Kts? the condition of the airflow is a product of the environment which has no effect on the speed of the mass. define a trade wind? as apposed to a sea breeze. there two separate enteritis
Air compresses! The denser it is to begin with the less it'll compress when harnessed by your kite. Meaning more "punch"
Select to expand quoteNickT said..
Air compresses! The denser it is to begin with the less it'll compress when harnessed by your kite. Meaning more "punch"
The wind blows because of differences in air pressure from one location to another. Wind blows from areas of high pressure toward areas of low pressure. If the high pressure area is very close to the low pressure area, or if the pressure difference is very great, the wind can blow very fast.
wind speed is a direct relation to pressure high to low yeah? convergent as apposed to divergent ( air in a convergent state increases in mass because of compression temperature drops and velocity slows until the flow becomes divergent then velocity increases pressure decreases = wind speed increases and pressure drops ( Pascals 3rd law)
Trade wind: a wind blowing steadily towards the equator from the north-east in the northern hemisphere or the south-east in the southern hemisphere, especially at sea. Two belts of trade winds encircle the earth, blowing from the tropical high-pressure belts to the low-pressure zone at the equator.
Sea Breeze.
a breeze blowing towards the land from the sea, especially during the day owing to the relative warmth of the land.
its like making the statement:
100kph on dirt road is slower than 100kph on bitumen because the dirt has a higher friction coefficient.? as a stupid example?
Yes, 20 knots is 20 knots - the difference is the pressure exerted, which is related to the density of the fluid (the air).
As a simple example, if you were in a boat doing 20 knots with no other wind, you'd feel 20 knots of air on your face. But if you were to put your head in the water you would feel a lot more force because the water is significantly denser than the air. Even though the velocity of the fluid is the same.
Disclaimer - the author recommends that you do not attempt to put your head in the water while travelling at 20 knots in a boat.
remember to achieve (x) the factor of Mass required at a higher density is more than the factor of Mass required at a lower density to achieve the same work
so a low density environment requires less energy spent to achieve (x) Which i think is what your getting at? it doesn't make it stronger it just means less energy is required to achieve the same work. remembering wind flows from High to Low systems too
Trade winds obviously also come from the sea, assuming you're on the windward side of the island.
A true Seabreeze is started by hot air rising on the land, causing localised low pressure, filled by cooler air from the sea. When fully developed it is a huge vertical rotation of air. Hot air rising over land, headed out to sea up high as it cools, dropping over the cooler sea and blowing onto the land. Thus the wind does tend to be colder temperature (denser) than a normal pressure gradient wind blowing from the sea.
Wish I could stand on a beach with a trade wind right now. The only question would be should I pump up the 6 or the 9.
Your physics seem sound Jack Forbes
fly a zephyr in 20kts @ cable beach broome
fly a zephyr in 20kts @ sandy bay exmouth
then tell me theres no difference
20 knots at Cable beach Doctor? You must have been there on the one day of the year?
Apparently there is a difference but only by a factor of 0.9.
Not sure if wind at Cable beach is technically Trade wind.
