In article ,
"R. Martin" wrote:

Lawrence D¹Oliveiro wrote:

In article ,
Scott wrote:

Lawrence D¹Oliveiro wrote:

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.

And at what heights were the wind directions determined--ground level?
So the isoheights don't correspond to the wind directions on that chart
at all, and any parallelism between the two is really accidental.

Lawrence D¹Oliveiro wrote:
In article ,
"R. Martin" wrote:


Lawrence D¹Oliveiro wrote:

In article ,
Scott wrote:


Lawrence D¹Oliveiro wrote:


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.


And at what heights were the wind directions determined--ground level?
So the isoheights don't correspond to the wind directions on that chart
at all, and any parallelism between the two is really accidental.

What ARE you talking about?

The heights of the wind at 500mb are the height of the 500mb
surface, which varies between 5000 and 6000 geopotential meters,
approximately.

Wind barbs will be parallel to the height contours on an
isobaric surface or, equivalently, isobaric contours on
a height surface if the flow is geostrophic. Geostrophic
flow is unaccelerated. For straight, slowly-varying,
frictionless flow at 500 mb, that's not a bad approximation.

Scott

Lawrence D¹Oliveiro wrote:

In article ,
"R. Martin" wrote:

Lawrence D¹Oliveiro wrote:

In article ,
Scott wrote:

Lawrence D¹Oliveiro wrote:

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.

And at what heights were the wind directions determined--ground level?
So the isoheights don't correspond to the wind directions on that chart
at all, and any parallelism between the two is really accidental.

You clearly don't know what you're talking about. I suggest you
take a course or two in meteorology. If you have, I suggest you
demand your money back, since you received very poor instruction.

Cheers,
Russell
--
All too often the study of data requires care.

Lawrence D¹Oliveiro wrote:

In article ,
"R. Martin" wrote:

Lawrence D¹Oliveiro wrote:

In article ,
Scott wrote:

Lawrence D¹Oliveiro wrote:

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.

And at what heights were the wind directions determined--ground level?
So the isoheights don't correspond to the wind directions on that chart
at all, and any parallelism between the two is really accidental.

P.S. I'm going offline for a while, so consider my previous comment
my last on the topic since I won't be able to argue with you even if
I wanted to waste my time.

Cheers,
Russell
--
All too often the study of data requires care.

On Sat, 21 Aug 2004 22:44:54 +1200,
Lawrence D¹Oliveiro , in
wrote:

+ I thought the definition
+ http://ww2010.atmos.uiuc.edu/(Gl)/ww...hret=/guides/m
+ tr/fw/fric.rxml was that the Coriolis force was in balance with the
+ pressure gradient force. Which I took to mean, that component of the
+ pressure gradient force perpendicular to the direction of the wind.
+
+ As long as the drag is nonzero, there must be a component of the
+ pressure gradient force in the direction of the motion of the wind, to
+ offset the drag. So the wind can never be exactly parallel to the
+ isobars.

You're gonna make me drag out Holton? that's gonna cost you.

The geostrophic wind is a *mathematical* solution to the horizontal
equation of motion given a certain set of assumptions. That does not
mean that it provides all possible solutions (it doesn't), but "As
discussed in Section 2.4.1, the geostrophic wind is generally a good
approximation to the actual wind in extratropical synoptic-scle
disturbances."

Particularly once you get above the boundary layer, where drag is for
the most part negligible.

Reference:

Holton, James R., An Introduction to Dynamic Meteorology, Third
Edition, 1992, ISBN 0-12-354355-X. See Chapter 3.

James
--
Consulting Minister for Consultants, DNRC
I can please only one person per day. Today is not your day. Tomorrow
isn't looking good, either.
I am BOFH. Resistance is futile. Your network will be assimilated.

On Mon, 23 Aug 2004 23:56:43 GMT,
R. Martin , in
wrote:

+ 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.

After rereading Holton's chapter 3, I remember why I like an isobaric
coordinate system...if you think our friend would quibble over
the geostrophic wind, I'm sure he'd have a cow if we had to play with
value of density...

James
--
Consulting Minister for Consultants, DNRC
I can please only one person per day. Today is not your day. Tomorrow
isn't looking good, either.
I am BOFH. Resistance is futile. Your network will be assimilated.

Lawrence D¹Oliveiro wrote in message ...
In article ,
"R. Martin" wrote:

Lawrence D¹Oliveiro wrote:

In article ,
Scott wrote:

Lawrence D¹Oliveiro wrote:

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.

And at what heights were the wind directions determined--ground level?
So the isoheights don't correspond to the wind directions on that chart
at all, and any parallelism between the two is really accidental.

900 or 850 mb maybe, lacking professional meterological education I
can't tell you what approach that is most common or useful. What I can
tell you is after reading this thread, I get the impression that you
are caught in a not pariculary useful vorticy generated by the small
differences between idealized models(tools used in understanding,
theaching and prediction) and real observations. Or perhaps 'trolling'
to create an entertaining thread on the subject.

Either way, you might benefit from first using the idealized modells
to grasp the big picture and then go back and try to
understand/improve the models you used. It is for instance less
tempting to go back and improve something you have used a lot of time
and effort on.

Imagine that one way to get the big picture is to find ground level
winds, 850 mb heights/winds, 500 mb heights/winds and 300 mb
heights/winds analysis maps for a tropical cyclone.

Assume - from the coriolis effect and bernoulli equation(If your not
familiar with the bernoulli equation, google it) - that the 850 mb
heights/winds below the convective cloud cover will have a relative
large ageostrophic component towards the center and thus get stronger
untill the centrifugal forces annihilates the agestrophic
component(the eye).

- And that the 300 or 200 mb heights/winds will have a agestrophic
component away from the center and slow down as they blow outwards.


*Don't think this type of trolling is especially bad or deceitful,
more like talking about the weather to a pretty female TV
meterologist(or weather man if being a woman).

In article ,
"R. Martin" wrote:

You clearly don't know what you're talking about.

And yet if you look carefully at the chart you mentioned
http://www.hpc.ncep.noaa.gov/dailywx..._20040101.html , you
can see a few wind vectors pointing _away_ from the low.

Do you understand why that's not physically possible?

In article ,
I wrote:

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.

Let me explain this a bit further. Assume you have a wind flowing around
a closed path with zero drag and air viscosity. Due to the Coriolis
force, this flow will be anticlockwise in the northern hemisphere, and
clockwise in the southern hemisphere. Or to put it another way, the half
flowing east-to-west is closer to the respective pole than the half
flowing west-to-east.

But closer to the pole, the Coriolis force is stronger. That means that
the half of the wind flowing closer to the pole must be moving on
average faster than that half further from the pole, otherwise the
deflection in direction caused by the Coriolis force would mean their
paths would not join up.

But if the east-to-west part is flowing faster, then there must be a
buildup of pressure at the western side of the path, and a corresponding
reduction in pressure at the eastern side. These changes in pressure
represent transfers between the kinetic energy of the wind and the
potential energy of the atmospheric pressure. But the Coriolis force
cannot perform such transfers of energy--it can do no work, since it
always acts perpendicular to the direction of motion. Therefore any such
pressure buildup would stop the wind from flowing.

Therefore the closed-path wind motion is not physically possible.

Lawrence D¹Oliveiro wrote:
In article ,
"R. Martin" wrote:


You clearly don't know what you're talking about.


And yet if you look carefully at the chart you mentioned
http://www.hpc.ncep.noaa.gov/dailywx..._20040101.html , you
can see a few wind vectors pointing _away_ from the low.

Do you understand why that's not physically possible?

Well, I carefully looked, and saw nothing unusual.

I think it's important, when looking at an analysis like
that to ask yourself: what is the scale of the analysis,
and what is the scale of the observations? The 500-mb
chart you've linked to is obviously a synoptic-scale
analysis, and I'll suggest it's first guess field is
derived from a model, which model results may or may
not jibe with reality near the radiosonde observations.
Depending on how the analysis is constructed, those
observations at variance with the model forecast may
or may not be considered by the analysis, and for that
reason you may have wind vectors that appear not to
follow the flow -- of course, the analysis is just
wrong, or the wind vector is significantly ageostrophic
(which means the wind vectors are accelerating). Or both!

Scott