Re: [Phys-l] Coriolis effect puzzlement

["John Clement" <clement@hal-pc.org>]

While the water going down the drain is affected by the geometry and goes
either way, hurricanes always go in the same direction.  Living in an area
where they will happen, I have never seen one go in the "wrong" direction.
I suspect the Coriolis effect comes in as the hurricane forms, and then once
it is strong, a Coriolis explanation is not needed.  And on the equator I
would presume the dust devils would go either way.  Perhaps hurricanes do
not form as readily on the equator because of lack of the Coriolis effect?
Does anyone know about this?

And what about the rising hot air.  Does it go in the opposite direction
from the air at ground level?  That would produce severe wind shear which
might be part of the reason why tornadoes are spawned.

Incidentally although Europeans claims to not have tornadoes, that is not
true.  I remember an etching in an encyclopedia showing water spouts off the
shore of Greece.  Ok, Greece is far from France, but still in Europe.  And I
had a friend whose mother went through what was probably a tornado in
Yugoslavia.

John M. Clement
Houston, TX

> > Why do you think figure 12 explains the Coriolis effect at 
> > all?  Because wikipedia said so?
>
> Along those lines:  They have dust devils in Kenya, right on the
> equator.
>
> Do you really want to explain the spin of such things in terms
> of the Coriolis effect?
>
> =========
>
> The main thing that is going on is the balance between (a) the 
> pressure gradient and (b) the curvature of the flow.
>
> If you have an air mass that is not spinning, and establish
> low pressure in the middle, the air will fall into the low,
> and that will be the end of the story.
>
> If the air mass has some initial spin, as it falls inward the
> rate of spin will increase, just like the proverbial ice skater
> pulling in her arms.  At some point the spin will just balance
> the pressure gradient, and from then on the situation will be
> stable (except for small corrections due to friction et cetera).
>
> There are four or five ways of analyzing the details, some of
> which involve Coriolis and some of which don't.  One thing is
> for sure:  near the equator the Coriolis part of the story is
> zero.  The initial rotation (if any) of the air mass will be 
> due to local accidents.