watervole | I hate Coriolis Force

When a perfectly self-respecting wind blows north, it gets deflected eastwards (it's all due to the Earth's rotation and the fact that the area it is coming from is rotating faster than the area it is going to).

Thus, winds in the northern hemisphere blow clockwise round areas of high pressure and anti-clockwise around areas of low pressure.

Now, an area of low pressure is cyclonic and an area of high pressure is referred to as an anti-cyclone.

In nothern hemisphere, the wind blows clockwise round anti-cyclones and in the southern hemisphere, the wind blows anti-clockwise round anti-cyclones (because Coriolis force is operating in the other direction).

Is your brain hurting yet? (It's all the different 'antis' that do it to me.)

And I confess to not understanding at all why winds in the northern hemisphere that are blowing west-east are still deflected to the right. (I think I understood this once about 26 years ago when I struggled with it for a day or two with a friend, but the short OU course I'm doing now is too basic to cover that particular bit and in any case I'm not sure if I could cope with the explanation or not.)

Anyone think they can explain it?

Flat | Top-Level Comments Only

Anyone think they can explain it?

It's all because of the trees waving their branches about. So says Belgarath in the Belgariad.

(in Magician's Gambit, if I remember correctly, in his tower in the Vale, right at the point when he switches from being Mister Wolf to being Belgarath, which I always thought was a fantastic piece of subliminally indicating the viewpoint character's change of perspective.)

I'm guessing here, but I suspect it might be that the air tries to move toward the place where it would be travelling at the same speed as the land. ie if the wind is going West-East faster than the land is, it will try to move toward the equator where the land is moving faster. Or if it's going East-West, then it's not going as fast as the land it's passing over, and it'll try to move toward the nearest pole, where the land is moving more slowly.

Or that might be complete rubbish. I can't seem to find anything on the net that supports the idea that West-East winds are deflected South. What do East-West winds do according to your OU text?

THe short version is that all winds in the northern hemisphere are deflected to the right and all southern hemisphere winds are deflected to the left.

Any answer that involves the words 'wants' or 'tries to' is disqualified on the grounds that air masses are not sentient. (You can get simplified analogies that way, but they're very limited and can't prove anything)

Yep, I would phrase it differently under exam conditions :)

Wind blowing west to east in northern hemisphere is naturally deflected outwards, at right angles to the earth's axis, by rotation.

But the two-dimensional mapping of this onto the earth's surface varies with latitude (because being perpendicular the the earth's axis is not the same as a line from the surface to the centre). At the equator, there is no horizontal component of this at all. The farther north you go, the more the perpendicular-to-the-earth's axis atrts to look like the horizontal.

It's all an artifact of the problem of "horizontal" not relly being in a straight line, because we are all rotating...

The WikiPedia article is helpful.

I'm not sure I understand your explanation, and I don't think the Wikipedia article explains the effect of Coriolis force on Easterly or Westerly moving objects either (I've read it several times, along with everything else I can find with Google).

I've found another article which does explain it in a fair amount of detail without getting heavily into vector mathematics though: Getting Around the Coriolis Force (http://www.physics.ohio-state.edu/~dvandom/Edu/newcor.html) from Ohio State University.

Here's my new explanation: an object moving faster than the rotation of the Earth (ie Westerly) wants to move straight "up" (away from the axis), but it can't because it's restrained by gravity, so it does the next best thing and moves toward the equator, which is further from the axis of rotation. An object moving slower than the rotation of the Earth (ie. Easterly) tries to move "down" (toward the axis), but it can't because it's restrained by the ground, so it does the next best thing and moves toward the nearest pole. One way to understand why the air wants to move "up" or "down" (relative to the axis of rotation) if you speed it up or slow it down relative to the Earth's rotation, is to think of air particles as being like trillions of orbiting satellites, except the thing holding them up against gravity is air pressure rather than centripetal force. If you increase the orbital velocity of a satellite, it climbs into a higher orbit, and if you decrease its velocity, it falls into a lower one.

That is a better article. I think I've just about got it. The vector components just about make sense.

I must admit, I was thinking of satellite orbits when I was originally puzzling with this, but couldn't find a mechanism to work between the two.

Okay, I can see what you're saying here. I can see a southward component (as the Earth is a sphere) on a perpendicular deflection of a W-E wind. The effect would be greater as one moves northwards.

However, what about the E-W wind? That's deflected northwards.

and I've worked out now how I can explain the movement as a consequence of Newton's First Law, in the same way in all directions.

[I was struggling before because the way we explain the rightward deflection of the wind when blowing north or south completely breaks down if you try to use it to explain the rightward deflection of the wind blowing east or west—it turns out that's because it's a bad way of explaining it]

Now I just need to be in the same room as the person I'm explaining it to, with a pencil and some scrap paper :-)

I managed to break the movement components down to vectors, first perpendicular to the EArth's axis of rotation, then perpendicular to the EArth's surface. That seemed to fix the W-E, E-W problem. N-S I find easier visually as the wind is aiming for a place that has moved on, so to speak.

I hate Coriolis Force

Piffle

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I've been thinking about it

Re: I've been thinking about it