A question that someone here might be able to help with please:

Is it possible to get any idea of the likely pressure gradient
associated with wind over relatively short distances, eg 500-1000m - say
one end of a level field to the other?

Presumably there has to be some difference in pressure for the wind to
blow at all, but I'm guessing that even for a significant say 20kt wind
blowing directly along the length of the field then the difference over
1km might be relatively tiny, say 0.1mb?

On Wednesday, 17 June 2020 14:01:18 UTC+1, JGD wrote:
A question that someone here might be able to help with please:

Is it possible to get any idea of the likely pressure gradient
associated with wind over relatively short distances, eg 500-1000m - say
one end of a level field to the other?

Presumably there has to be some difference in pressure for the wind to
blow at all, but I'm guessing that even for a significant say 20kt wind
blowing directly along the length of the field then the difference over
1km might be relatively tiny, say 0.1mb?

Why do you want to know?

JGD wrote:

A question that someone here might be able to help with please:

Is it possible to get any idea of the likely pressure gradient
associated with wind over relatively short distances, eg 500-1000m -
say one end of a level field to the other?

Presumably there has to be some difference in pressure for the wind
to blow at all, but I'm guessing that even for a significant say 20kt
wind blowing directly along the length of the field then the
difference over 1km might be relatively tiny, say 0.1mb?

The wind is dependent on the broadscale pressure field. Over very small
distances the atmospheric pressure may be subject to small changes due
to the wind blowing over the relatively rough terrain (humps and
hollows, walls, trees etc) i.e. over very small distances the pressure
will fluctuate due to the wind rather than the other way round.

--
Norman Lynagh
Tideswell, Derbyshire
303m a.s.l.
https://peakdistrictweather.org
twitter: @TideswellWeathr

On 17/06/2020 16:47, Norman Lynagh wrote:
JGD wrote:

A question that someone here might be able to help with please:

Is it possible to get any idea of the likely pressure gradient
associated with wind over relatively short distances, eg 500-1000m -
say one end of a level field to the other?

Presumably there has to be some difference in pressure for the wind
to blow at all, but I'm guessing that even for a significant say 20kt
wind blowing directly along the length of the field then the
difference over 1km might be relatively tiny, say 0.1mb?

The wind is dependent on the broadscale pressure field. Over very small
distances the atmospheric pressure may be subject to small changes due
to the wind blowing over the relatively rough terrain (humps and
hollows, walls, trees etc) i.e. over very small distances the pressure
will fluctuate due to the wind rather than the other way round.


OK, thanks for the answer - much appreciated. But I'm less interested in
the mechanism than trying to get even a rough estimate of the likely
pressure gradient at small linear scale. Say there was a steady eg 20kt
10m wind blowing at sea then, is it possible to express the pressure
gradient as mb/km?

And BTW there is a point behind this seemingly idle question in a debate
about spacing of sensors for dynamic atmospheric pressure measurements.
But it would be really useful to have even a rough estimate of that
mb/km figure.

The best guess I can come up with is around 0.01mb/km for a sustained
20kt wind but it would be good for someone more expert than me to
confirm or to say rubbish!

On 17/06/2020 17:15, JGD wrote:
On 17/06/2020 16:47, Norman Lynagh wrote:
JGD wrote:

A question that someone here might be able to help with please:

Is it possible to get any idea of the likely pressure gradient
associated with wind over relatively short distances, eg 500-1000m -
say one end of a level field to the other?

Presumably there has to be some difference in pressure for the wind
to blow at all, but I'm guessing that even for a significant say 20kt
wind blowing directly along the length of the field then the
difference over 1km might be relatively tiny, say 0.1mb?

The wind is dependent on the broadscale pressure field. Over very small
distances the atmospheric pressure may be subject to small changes due
to the wind blowing over the relatively rough terrain (humps and
hollows, walls, trees etc) i.e. over very small distances the pressure
will fluctuate due to the wind rather than the other way round.


OK, thanks for the answer - much appreciated. But I'm less interested in
the mechanism than trying to get even a rough estimate of the likely
pressure gradient at small linear scale. Say there was a steady eg 20kt
10m wind blowing at sea then, is it possible to express the pressure
gradient as mb/km?

And BTW there is a point behind this seemingly idle question in a debate
about spacing of sensors for dynamic atmospheric pressure measurements.
But it would be really useful to have even a rough estimate of that
mb/km figure.

The best guess I can come up with is around 0.01mb/km for a sustained
20kt wind but it would be good for someone more expert than me to
confirm or to say rubbish!

I think you need to look up geostrophic wind and the scales which help
give wind speeds from isobar spacing. I think what you want will require
a lot of complicated maths. There's also the gradient wind. And remember
that the sea is rarely flat, so the friction effects Norman speaks of
will also happen there. It's a long time since I dabbled in such esoterica!

On Wednesday, 17 June 2020 17:41:20 UTC+1, Metman2012 wrote:
On 17/06/2020 17:15, JGD wrote:
On 17/06/2020 16:47, Norman Lynagh wrote:
JGD wrote:

A question that someone here might be able to help with please:

Is it possible to get any idea of the likely pressure gradient
associated with wind over relatively short distances, eg 500-1000m -
say one end of a level field to the other?

Presumably there has to be some difference in pressure for the wind
to blow at all, but I'm guessing that even for a significant say 20kt
wind blowing directly along the length of the field then the
difference over 1km might be relatively tiny, say 0.1mb?

The wind is dependent on the broadscale pressure field. Over very small
distances the atmospheric pressure may be subject to small changes due
to the wind blowing over the relatively rough terrain (humps and
hollows, walls, trees etc) i.e. over very small distances the pressure
will fluctuate due to the wind rather than the other way round.


OK, thanks for the answer - much appreciated. But I'm less interested in
the mechanism than trying to get even a rough estimate of the likely
pressure gradient at small linear scale. Say there was a steady eg 20kt
10m wind blowing at sea then, is it possible to express the pressure
gradient as mb/km?

And BTW there is a point behind this seemingly idle question in a debate
about spacing of sensors for dynamic atmospheric pressure measurements.
But it would be really useful to have even a rough estimate of that
mb/km figure.

The best guess I can come up with is around 0.01mb/km for a sustained
20kt wind but it would be good for someone more expert than me to
confirm or to say rubbish!

I think you need to look up geostrophic wind and the scales which help
give wind speeds from isobar spacing. I think what you want will require
a lot of complicated maths. There's also the gradient wind. And remember
that the sea is rarely flat, so the friction effects Norman speaks of
will also happen there. It's a long time since I dabbled in such esoterica!

As Metman2012 says, it would be good to read up on geostrophic wind scales - that will give you some insight into the complexities. For a given isobaric spacing (and ignoring the effects of rough terrain) there would be a range of possible values owing to isobaric curvature and the presence (or lack of) vertical motion.

--
Freddie
Dorrington
Shropshire
115m AMSL
http://www.hosiene.co.uk/weather/
Stats for the month so far: https://www.hosiene.co.uk/weather/st...cs/latest.xlsx

On Wednesday, 17 June 2020 17:15:46 UTC+1, JGD wrote:
On 17/06/2020 16:47, Norman Lynagh wrote:
JGD wrote:

A question that someone here might be able to help with please:

Is it possible to get any idea of the likely pressure gradient
associated with wind over relatively short distances, eg 500-1000m -
say one end of a level field to the other?

Presumably there has to be some difference in pressure for the wind
to blow at all, but I'm guessing that even for a significant say 20kt
wind blowing directly along the length of the field then the
difference over 1km might be relatively tiny, say 0.1mb?

The wind is dependent on the broadscale pressure field. Over very small
distances the atmospheric pressure may be subject to small changes due
to the wind blowing over the relatively rough terrain (humps and
hollows, walls, trees etc) i.e. over very small distances the pressure
will fluctuate due to the wind rather than the other way round.


OK, thanks for the answer - much appreciated. But I'm less interested in
the mechanism than trying to get even a rough estimate of the likely
pressure gradient at small linear scale. Say there was a steady eg 20kt
10m wind blowing at sea then, is it possible to express the pressure
gradient as mb/km?

And BTW there is a point behind this seemingly idle question in a debate
about spacing of sensors for dynamic atmospheric pressure measurements.
But it would be really useful to have even a rough estimate of that
mb/km figure.

The best guess I can come up with is around 0.01mb/km for a sustained
20kt wind but it would be good for someone more expert than me to
confirm or to say rubbish!

Your figure is certainly of the right order - possibly a little low. It would be practically impossible to measure such a small quantity over a short distance and the result would be very unreliable because of short-period pressure fluctuations due to turbulent flow around various obstructions. Also, height differences may overwhelm any horizontal pressure changes. 0.02 mb corresponds to a height difference of about 16 cm.

The whole thing only works because of its huge scale in relation to the size of local disturbing influences so it is really rather inappropriate to try and measure pressure differences over small distances.

Tudor Hughes

Tudor, thanks for that - it's the kind of order of magnitude intimation
I was looking for.

It was really to counter a notion that hyperlocal (elevation-corrected)
pressure monitoring from multiple pressure sensors in a local array
might have any value but just needed some sort of o-o-m figure to make
the point.

On Thursday, 18 June 2020 11:15:16 UTC+1, JGD wrote:
Tudor, thanks for that - it's the kind of order of magnitude intimation
I was looking for.

It was really to counter a notion that hyperlocal (elevation-corrected)
pressure monitoring from multiple pressure sensors in a local array
might have any value but just needed some sort of o-o-m figure to make
the point.

Once mo Why do you want to know?
Is it a problem you wish to apply to a wind generation plant or what?

The phenomenon can be heard quite easily at any wind farm and data across a broad enough scale is likely well documented.If you want to do your own on a field in any park you can set up something similar with the kind of windmills sold at funfairs at sea-sides all over the country and couple it with video with any suitable phone

On Wednesday, 17 June 2020 14:01:18 UTC+1, JGD wrote:
A question that someone here might be able to help with please:

Is it possible to get any idea of the likely pressure gradient
associated with wind over relatively short distances, eg 500-1000m - say
one end of a level field to the other?

Presumably there has to be some difference in pressure for the wind to
blow at all, but I'm guessing that even for a significant say 20kt wind
blowing directly along the length of the field then the difference over
1km might be relatively tiny, say 0.1mb?

https://groups.google.com/forum/?hl=en-GB#!searchin/uk.sci.weather/JGD$20%7Csort:date

Why have all your posts been deleted?