Lawrence DčOliveiro wrote:
In article ,
Scott wrote:
Lawrence DčOliveiro wrote:
In article ,
"Yokel" wrote:
In the absence of ground friction, (which applies very nearly in the free
atmosphere a kilometre or two up or more), the geostrophic wind is a very
close approximation, providing the systems are not moving too quickly or are
developing/decaying rapidly. These circumstances also produce effects not
included in the geostrophic wind calculation.
Another thing to keep in mind is that the Coriolis force increases with
latitude. This means that, even in the complete absence of drag, the
wind cannot follow a closed path (which is what an isobar is), as that
would cause a pressure build-up at some point, which would stop the wind
flowing.
Thus, even neglecting drag, the idea of winds flowing parallel to
isobars is still unrealistic.
I guess someone oughta tell the 500-mb flow that, then 
You have some empirical evidence contradicting my claim?
If you're talking *exactly* parallel to the isobars at all times, no.
But the 500 mb winds do flow generally approximately parallel to the
isobars, to within a good enough approximation for many purposes,
especially in areas of respectable gradients. A look at a couple of
500 mb synoptic charts will show that. For instance see
http://www.hpc.ncep.noaa.gov/dailywx..._20040101.html .
Note that the contours are isoheights of the 500 mb surface, not
isobars, but it makes no difference to Scott's point. If you want
to dig out a meteorology text from the 1940s or 1950s, when they
still used isobars on a constant height surface, be my guest.
Cheers,
Russell
--
All too often the study of data requires care.