Geostrophic winds cannot be exactly parallel to isobars
 

Lawrence D¹Oliveiro wrote:
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.

I know of no one who suggests that strongly accelerating
flow, such as your flow around a closed path, would be
geostrophic. Also, I'm not sure why you have assumed
that the pressure gradient would be the same initially
all around this low. If your initial conditions are not
physically realistic, I'm not surprised that your concluding
the flow is not physically possible.


Scott

Geostrophic winds cannot be exactly parallel to isobars
 

Now you have got me twisting in agony, the coriolis force is an
imagined force with the purpose of saving artillerist from complicated
math and learn school children basic meterological skills. Its real
name is _the coriolis effect_, an artifact caused by the conservation
of momentum(F=ma) and the earths rotation.

If you have to go ballistic on an imagined subject, try this one:
http://www.eoascientific.com/campus/...ew_interactive

Scott wrote in message . ..
Lawrence D¹Oliveiro wrote:
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.

Would a circular tube of fast flowing air located around the North
Pole, lets say 30 to 60 degrees north, also be impossible ?

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.

It cannot do work since it is imagined, the coriolis effect does
actually seem to speed up air moving northward, but it is really the
land surface slowing down and the air flowing relative frictionless
above groundlevel keeping its momentum .



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

I know of no one who suggests that strongly accelerating
flow, such as your flow around a closed path, would be
geostrophic. Also, I'm not sure why you have assumed
that the pressure gradient would be the same initially
all around this low. If your initial conditions are not
physically realistic, I'm not surprised that your concluding
the flow is not physically possible.


Scott

Geostrophic winds cannot be exactly parallel to isobars
 

"Scott" wrote in message
...
| Lawrence D¹Oliveiro wrote:
| 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.
|
| I know of no one who suggests that strongly accelerating
| flow, such as your flow around a closed path, would be
| geostrophic. Also, I'm not sure why you have assumed
| that the pressure gradient would be the same initially
| all around this low. If your initial conditions are not
| physically realistic, I'm not surprised that your concluding
| the flow is not physically possible.
|
|

There was a discussion about geostrophic flow on curved isobars a month or
two back on this very newsgroup (in June, thread "Wind Velocities"). The
curvature adds an extra term to the formula (the "cyclostrophic term")
representing the force required to accelerate the air and maintain it on the
curved path of the isobars.

It is possible for a balance to be set up between this cyclostrophic force
and the pressure gradient force alone, without regard to the coriolis force.
To all intents and purposes, this is what happens in a tornado, which it is
why it is possible to get an "anticyclonic" or "wrong way" tornado - the
coriolis force is insignificant on this scale (even though it may have an
effect on the scale of the cloud generating the tornado).

I would refer you back to that thread by the usual methods of reading old ng
postings.
--
- Yokel -
oo oo
OOO OOO
OO 0 OO
) ( I ) (
) ( /\ ) (

"Yokel" now posts via a spam-trap account.
Replace my alias with stevejudd to reply.

Geostrophic winds cannot be exactly parallel to isobars
 

Scott wrote in message . ..
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

Suppose 100% accurate analysis. Doesn't it look like the 552 low on
the westcoast get its horseshoe form because coriolis forces -acting
on northerly winds from the high- is causing a vacuum effect all along
the rockies, except straight west from the low where southwesterly
winds is piling up. The ageostrophic anomalies should therefore not be
any mystic at all with both piling up, windshear from the Rocky
Mountains and not unlikely some shear from a sharp turn in the
jetstream nearby.

No need to attack this particulary model/modeller you know, it contain
no traces of G.warming.;-).

Geostrophic winds cannot be exactly parallel to isobars
 

O18-C-O16 wrote:
Now you have got me twisting in agony, the coriolis force is an
imagined force with the purpose of saving artillerist from complicated
math and learn school children basic meterological skills. Its real

That's okay, the geostrophic wind is imaginary too :)

Scott

Geostrophic winds cannot be exactly parallel to isobars
 

O18-C-O16 wrote:
Scott wrote in message . ..

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


Suppose 100% accurate analysis. Doesn't it look like the 552 low on
the westcoast get its horseshoe form because coriolis forces -acting
on northerly winds from the high- is causing a vacuum effect all along
the rockies, except straight west from the low where southwesterly
winds is piling up. The ageostrophic anomalies should therefore not be
any mystic at all with both piling up, windshear from the Rocky
Mountains and not unlikely some shear from a sharp turn in the
jetstream nearby.

No need to attack this particulary model/modeller you know, it contain
no traces of G.warming.;-).

Well, I look at the isoheights around that 522 low off the
west coast and see different jets moving around it.
Propagating jets = very strong accelerations = very
non-geostrophic flow. So the 522 low has a horseshoe
shape because there are jets, which are related to
the horizontal temperature gradients at levels below
500, among other things.

I find your discussion a little confusing, though, so
maybe I'm missing your meaning. How can an ageostropic
anomaly be mystic, for example?

Scott

Geostrophic winds cannot be exactly parallel to isobars
 

On Fri, 27 Aug 2004 10:49:27 -0500,
Scott , in
wrote:
+ O18-C-O16 wrote:
+ Now you have got me twisting in agony, the coriolis force is an
+ imagined force with the purpose of saving artillerist from complicated
+ math and learn school children basic meterological skills. Its real
+
+ That's okay, the geostrophic wind is imaginary too :)

Heh. I've had baby meteorologists try to tell me the thermal wind is
real, too...

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.

Geostrophic winds cannot be exactly parallel to isobars
 

I R A Darth Aggie wrote:

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.

Agreed.

BTW, damned shame Jim Holton passed away.

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

Geostrophic winds cannot be exactly parallel to isobars
 

Scott wrote in message . ..
O18-C-O16 wrote:
Scott wrote in message . ..

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


Suppose 100% accurate analysis. Doesn't it look like the 552 low on
the westcoast get its horseshoe form because coriolis forces -acting
on northerly winds from the high- is causing a vacuum effect all along
the rockies, except straight west from the low where southwesterly
winds is piling up. The ageostrophic anomalies should therefore not be
any mystic at all with both piling up, windshear from the Rocky
Mountains and not unlikely some shear from a sharp turn in the
jetstream nearby.

No need to attack this particulary model/modeller you know, it contain
no traces of G.warming.;-).

Well, I look at the isoheights around that 522 low off the
west coast and see different jets moving around it.
Propagating jets = very strong accelerations = very
non-geostrophic flow. So the 522 low has a horseshoe
shape because there are jets, which are related to
the horizontal temperature gradients at levels below
500, among other things.

I find your discussion a little confusing, though, so
maybe I'm missing your meaning. How can an ageostropic
anomaly be mystic, for example?

Scott

I don't know, but maybe Lawrence found to arrows indicating wind
blowing uphill(from low to high) and slowing down. He might have
conceived this inconsistent with the following statement because he
did not notice the initially at rest criteria and read, Wind blows
because air move from high to low pressure, instead: "An air parcel
initially at rest will move from high pressure to low pressure because
of the pressure gradient force (PGF)"
http://ww2010.atmos.uiuc.edu/(Gl)/gu...r/fw/geos.rxml

Shortening detailed and logical child/student misinterpretation proof
textbook definitions into short easy to remember lines with intuitive
appeal, often cause misperception of phenomena outside personal
experience.

....Individuals who remember such definitions AND that has the skill to
use them logical AND sufficient long span attention to avoid random
mistakes AND the motivation/will to actually do so, is a rare
species...

Geostrophic winds cannot be exactly parallel to isobars
 

On Fri, 27 Aug 2004 23:13:54 GMT,
R. Martin , in
wrote:

+ BTW, damned shame Jim Holton passed away.

I had not heard that. That is indeed a sad news.

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.