How the west was filtered.

The Canadian weather and environmental services are very good. I suppose they need to be on the ball for the sake of all those helpless baby seal clubbers.

Still, they do have good web-sites when they get back. If they get back. …

Originally posted by Meteorological Service of Canada:

Whenever the wind encounters an obstacle, it tends to shift to the left, and to strengthen. This is true in the case of islands, capes and points.

When the wind is with you, it's always tempting to go along with it and sail around an island to the left. Just be careful to check your charts to make sure you won't find any unpleasant surprises in the form of shoals.

There won't be much wind to the right of the obstacle. In the lee of the island, you may run into turbulence for quite a while, but you can avoid it by staying very close to the shore.

The rules:
High above the earth's surface, the wind blows freely. Over the ocean, friction between the water and the wind slows it down slightly and deflects it to the left.

The braking and deflection effects are stronger over the land, since there is greater friction between the land and the wind.

Buys Ballots Law. Invented for wind directions and adapted to all field dynamics:

In the Northern Hemisphere, with your back to the wind, the low pressure area will be on your left.

Originally posted by Wikipedia:

Wind travels counterclockwise around low pressure zones in the Northern Hemisphere. It is approximately true in the higher latitudes of the Northern Hemisphere, and is reversed in the Southern Hemisphere. The angle between the pressure gradient force and wind is nowhere near a right angle in low latitudes

Now for the graphics:

This image is similar to an earlier on in the same album. It shows how winds tend to eddy and thus slow down. It does not explain the full story though.

Air will diffuse pretty quickly and you'd think the pressure in an area of mixing and forcing would increase. So why does it drop?This one is interesting as it shows that winds can filter out of each other as well as force mix.

But again. It does not show how.

Wind seems to form level layers that do not intermix.
So how does a jet-stream affect the weather? One would think that according to the laws of gasses they'd mix or corom off each other or both.

But low pressure areas tend to avoid high pressure areas rather than be attracted to them. And the same is true of the reverse.

Which tend to make the filtering of gasses over storm clouds a science in itself. But at least the angles involved get a nice picture across of how pressure systems separate over land and gather over seas.

Or not, as the case may be.


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