Re: [Phys-l] Coriolis effect puzzlement

[John Denker <jsd@av8n.com>]

On 12/01/2011 03:08 PM, I wrote:

> 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.