Re: The Weather

[Robert A Cohen <bbq@ESU.EDU>]

Out of the explanations given so far for the jet stream, I like John's the
best. It emphasizes two critical points:

1. sea-level pressure is assumed to be the same everywhere (or at least
sea-level differences are small compared to differences aloft), and

2. the jet is related to the differences in *column-averaged*
temperatures.

These two, when used with the ideal gas law (density related to
temperature) and the coriolis force, can be used to explain the jet
stream.

Still, this doesn't explain why TV meteorologists like to show the jet
stream.  Since the jet stream is related to horizontal differences in
temperatures, computer predictions of it can be used to:

1. get a picture of where cooling/warming will be expected, and

2. where the path of the storms are likely to be (since they will
typically be at the boundary between cold and warm air masses).

What bothers me about the TV treatment of the jet stream is that they
imply that the jet stream is like one continuous current of air.
Streamlines are not the same as trajectories.  Air in one part may (and
usually does) descend out of the jet stream before it gets to another
part.

----------------------------------------------------------
| Robert Cohen               Department of Physics       |
|                            East Stroudsburg University |
| bbq@esu.edu                East Stroudsburg, PA  18301 |
| http://www.esu.edu/~bbq/   (570) 422-3428              |
----------------------------------------------------------

On Mon, 15 May 2000, John Denker wrote:

> At 10:03 AM 5/15/00 -0400, Bob Sciamanda wrote:
> > What is the mechanism driving the jet stream?
>
> 1) I'm not entirely sure.
>
> 2) There is something called _thermal gradient wind_
>    http://www.monmouth.com/~jsd/how/htm/atmo.html#sec_thermal_gradient_wind
> which probably explains at least part of it.
>
> Cheers --- jsd