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It is easy to observe that on a windy day, the wind does not blow for several hours at constant speed, then gradually subside. Instead, on a time scale of seconds or tens of seconds, there are stronger gusts of wind followed by lulls.

Presumably this is an effect of turbulence. If so, is this turbulence due to the complicated geometry around me - buildings, trees, hills, etc.? If we removed these features and had wind blowing over a flat ocean surface or a flat plain for hundreds of miles, would we still observe the wind to blow in the same sorts of gusts, or should I expect a more steady flow?

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7 Answers 7

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I believe you're exactly right: it's the complexity of hills, buildings, trees, asphalt, water, etc that make surface winds complicated. As you go higher in the atmosphere, these surface effects disappear and the winds become much more steady. You can see this in the winds aloft forecasts issued by the FAA for use in aviation:

http://aviationweather.gov/adds/winds/

In the upper left there is a drop-down box allowing you to select altitudes from the surface (SFC) to 48,000 feet (FL480). As you go up in altitude, the relatively chaotic surface winds blend into a much smoother (and faster!) flow.

I assume the effect is similar at sea, given the simpler boundary conditions.

(I admit this does not directly address your question of, "how variable are the winds at sea"? I too am curious to hear an authoritive answer.)

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Strangely enough Nasa thinks that winds gust stronger over the oceans than over land.

Wind tends to blow stronger over the ocean than over land. The ocean presents a smooth surface over which wind can glide without interruption, while hills, mountains, and forests tend to slow or channel wind over land.

This map is interesting.

I have watched gusts sweeping over calm seas , where one can predict the arrival of wind from the observed disturbance in the distance. So both land and ocean have changing winds, but which is stronger in producing gusts, as defined rigorously, is not obvious.

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I think it depneds upon your definition of gustiness. Is it the max speed of the wind at a given point? Or is it some measure of the shortterm dispersion in time resolved windspeed at a given point. The ratio of say the 5th and 95th percentile instantaneous windspeed might be a good example of the later sort of gustiness. Stronger winds at some point do not necessarily imply stronger gustiness (using the second definition). –  Omega Centauri Apr 20 '11 at 18:47

anecdotally from my sailing experience around a coast, and the conventional sailing knowledge:

A wind that has travelled over the sea to get there is more even that one that has come off off the land.

P.S. The statement above: "Wind tends to blow stronger over the ocean than over land" does not imply that it is more gusty

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Even if the surface is perfectly smooth, you'll still get boundary layer turbulence.

But yes, winds coming off the ocean do tend to be more laminar.

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Do not you think that the various pieces of land and sea can warm up faster or slower and so the air over them does change temperature, and consequently, areas with different pressures are formed. The water is warming up faster than land in the morning, and therefore there is higher pressure over water than over land, and wind is blowing from sea to the land - this is morning breeze. Similarly, rocks and soil will warm up at different rates. Maybe this local differences in air pressure trigger gusts. And gusts are some kind of disturbances which can have an influence on wind speed.

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The answer is that gusts form over the ocean, too. However local geography also contribute to gusting and general instability. Here's a good explanation of how gusts work.

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Your link does not work, you may want to fix it? –  Bernhard Jul 25 '12 at 7:33

I think wind Gust stronger over land due to funnelling through valleys ect. But the wind blows stronger on a constant basis at sea

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