On 2013-05-08 13:54:41 +0000, Weatherlawyer said:

Why does the metric for 30 inches mean about 1016 millibars?
I was looking at a tape measure for the first time in (an interesting
career????) and noticed that 1016 millimeters is 40 inches. Is it time
I bought a new tape?

I can't say I have ever noticed that 760 mm appears at the centre of
even the worst storms on the charts I use.

Whilst I am on the subject how high is thickness calculated for 500
(is it) DAM.

I think that you may be confusing many separate subjects here.

The usual usage of the word thickness is for the height difference
between two atmospheric levels, such as the 1000mb and 500mb.

Cold air will be denser than warm, and therefore the difference in
height between the two pressure levels will be less. It is much easier
to attach a pressure sensor to a balloon which can be filled with a
precise amount of gas so that it rises through the atmosphere at a
steady rate. By this method the time taken to reach various pressure
levels, 850mb, 700mb, etc. can be read from a stopwatch, and the
heights of those levels calculated. Subtract one height from another,
and you have the 'thickness'.

On May 9, 10:13*am, yttiw wrote:
On 2013-05-08 13:54:41 +0000, Weatherlawyer said:

Why does the metric for 30 inches mean about 1016 millibars?
I was looking at a tape measure for the first time in (an interesting
career????) and noticed that 1016 millimeters is 40 inches. Is it time
I bought a new tape?

I can't say I have ever noticed that 760 mm appears at the centre of
even the worst storms on the charts I use.

Whilst I am on the subject how high is thickness calculated for 500
(is it) DAM.

I think that you may be confusing many separate subjects here.

The usual usage of the word thickness is for the height difference
between two atmospheric levels, such as the 1000mb and 500mb.

Cold air will be denser than warm, and therefore the difference in
height between the two pressure levels will be less. It is much easier
to attach a pressure sensor to a balloon which can be filled with a
precise amount of gas so that it rises through the atmosphere at a
steady rate. By this method the time taken to reach various pressure
levels, 850mb, 700mb, etc. can be read from a stopwatch, and the
heights of those levels calculated. Subtract one height from another,
and you have the 'thickness'.

That sounds dafter than the discrepancy I am struggling with. Why
would the balloon rise at a standard rate in a logarithmic
environment?

Hell, whilst we are on the subject, how do they measure the altitude
of weather balloons?
Is there a little man on board looking at the barometer as it rises?
Strewth!

What confused the hell out of me is that in English we can measure
1016 in inches to get near 30 inches as dam is to eh.. were we
talk...ah..

But you can't convert 30 inches into metric to get the right answer
for some reason. That bloody Napoleon! The little napoleon!!

On 2013-05-09 15:03:49 +0000, Weatherlawyer said:

On May 9, 10:13*am, yttiw wrote:
On 2013-05-08 13:54:41 +0000, Weatherlawyer said:

Why does the metric for 30 inches mean about 1016 millibars?
I was looking at a tape measure for the first time in (an interesting
career????) and noticed that 1016 millimeters is 40 inches. Is it time
I bought a new tape?

I can't say I have ever noticed that 760 mm appears at the centre of
even the worst storms on the charts I use.

Whilst I am on the subject how high is thickness calculated for 500
(is it) DAM.

I think that you may be confusing many separate subjects here.

The usual usage of the word thickness is for the height difference
between two atmospheric levels, such as the 1000mb and 500mb.

Cold air will be denser than warm, and therefore the difference in
height between the two pressure levels will be less. It is much easier
to attach a pressure sensor to a balloon which can be filled with a
precise amount of gas so that it rises through the atmosphere at a
steady rate. By this method the time taken to reach various pressure
levels, 850mb, 700mb, etc. can be read from a stopwatch, and the
heights of those levels calculated. Subtract one height from another,
and you have the 'thickness'.

That sounds dafter than the discrepancy I am struggling with. Why
would the balloon rise at a standard rate in a logarithmic
environment?

Hell, whilst we are on the subject, how do they measure the altitude
of weather balloons?
Is there a little man on board looking at the barometer as it rises?
Strewth!


Presumably the pressure reading is transmitted to someone on the ground.

Technology does seem to have moved on from a couple of Georgian
'aviators' standing in a tethered hot air balloon shouting out readings
to their assistants down below.

"yttiw" wrote in message
news:2013050910130752063-cuddles@britpostcom...

I think that you may be confusing many separate subjects here.

The usual usage of the word thickness is for the height difference between
two atmospheric levels, such as the 1000mb and 500mb.

Cold air will be denser than warm, and therefore the difference in height
between the two pressure levels will be less. It is much easier to attach
a pressure sensor to a balloon which can be filled with a precise amount
of gas so that it rises through the atmosphere at a steady rate. By this
method the time taken to reach various pressure levels, 850mb, 700mb, etc.
can be read from a stopwatch, and the heights of those levels calculated.
Subtract one height from another, and you have the 'thickness'.

Well, you could use that method, but the result would be subject to
considerable error. It is possible to cause a balloon to ascend at an
approximately fixed rate, though already with a certain margin or error. But
it has to be recognised that the 'fixed rate' of ascent is through an
assumed benign medium which is neither ascending or descending itself. This
is almost never the case in the atmosphere, where waves and eddies are
embedded on a multitude of scales. Thus the possibility of obtaining
anything other than an approximate thickness is vanishingly small.



--
Bernard Burton

Wokingham Berkshire.

Weather data and satellite images at:
http://www.woksat.info/wwp.html

On May 9, 8:17*pm, "Bernard Burton" wrote:
"yttiw" wrote in message

news:2013050910130752063-cuddles@britpostcom...



I think that you may be confusing many separate subjects here.

The usual usage of the word thickness is for the height difference between
two atmospheric levels, such as the 1000mb and 500mb.

Cold air will be denser than warm, and therefore the difference in height
between the two pressure levels will be less. It is much easier to attach
a pressure sensor to a balloon which can be filled with a precise amount
of gas so that it rises through the atmosphere at a steady rate. By this
method the time taken to reach various pressure levels, 850mb, 700mb, etc.
can be read from a stopwatch, and the heights of those levels calculated.
Subtract one height from another, and you have the 'thickness'.

Well, you could use that method, but the result would be subject to
considerable error. It is possible to cause a balloon to ascend at an
approximately fixed rate, though already with a certain margin or error. But
it has to be recognised that the 'fixed rate' of ascent is through an
assumed benign medium which is neither ascending or descending itself. This
is almost never the case in the atmosphere, where waves and eddies are
embedded on a multitude of scales.

The possibility of obtaining anything other than an approximate thickness is vanishingly small.

Wow another eye opener.

Yes ou are quite right I was mixing up terms with that millibars and
millimeters. In all the years I have been trying to understand the
weather it never occurred to me to check.

What surprises me is that in all the years I have had a tape measure
in my hand, it never occurred to me to compare 1016 millimeters with
30 inches.

But I was reading an old theory about the weather based on the
author's undestanding of the subject in the 1850's and came across the
argument that an increase in the air pressure of 4 inches or whatever
from very low to very high is means an increase in the air columns of
several miles out to infinity (whatever that is.)

Yet apparently that is all taken care of by the time 500 millibar
levels are concerned. All very pointless to deliberate now, 160 years
later but it was a topic of material interest to Georgian aeronauts
"standing in a tethered" hydrogen "balloon shouting out readings to
their assistants down below."

Or even writing to them from several miles away.
Whatever the case was.

On 2013-05-10 13:45:18 +0000, Weatherlawyer said:

On May 9, 8:17*pm, "Bernard Burton" wrote:
"yttiw" wrote in message

news:2013050910130752063-cuddles@britpostcom...



I think that you may be confusing many separate subjects here.

The usual usage of the word thickness is for the height difference between
two atmospheric levels, such as the 1000mb and 500mb.

Cold air will be denser than warm, and therefore the difference in height
between the two pressure levels will be less. It is much easier to attach
a pressure sensor to a balloon which can be filled with a precise amount
of gas so that it rises through the atmosphere at a steady rate. By this
method the time taken to reach various pressure levels, 850mb, 700mb, etc.
can be read from a stopwatch, and the heights of those levels calculated.
Subtract one height from another, and you have the 'thickness'.

Well, you could use that method, but the result would be subject to
considerable error. It is possible to cause a balloon to ascend at an
approximately fixed rate, though already with a certain margin or error. But
it has to be recognised that the 'fixed rate' of ascent is through an
assumed benign medium which is neither ascending or descending itself. This
is almost never the case in the atmosphere, where waves and eddies are
embedded on a multitude of scales.

The possibility of obtaining anything other than an approximate
thickness is vanishingly small.

Wow another eye opener.

Yes ou are quite right I was mixing up terms with that millibars and
millimeters. In all the years I have been trying to understand the
weather it never occurred to me to check.

What surprises me is that in all the years I have had a tape measure
in my hand, it never occurred to me to compare 1016 millimeters with
30 inches.

But I was reading an old theory about the weather based on the
author's undestanding of the subject in the 1850's and came across the
argument that an increase in the air pressure of 4 inches or whatever
from very low to very high is means an increase in the air columns of
several miles out to infinity (whatever that is.)

Yet apparently that is all taken care of by the time 500 millibar
levels are concerned. All very pointless to deliberate now, 160 years
later but it was a topic of material interest to Georgian aeronauts
"standing in a tethered" hydrogen "balloon shouting out readings to
their assistants down below."

Or even writing to them from several miles away.
Whatever the case was.

On the subject of several miles away, what about a weather balloon
launched from Cornwall on a day with a strong westerly wind?

The resulting readings can be plotted on a tephigram labelled Camborne
03808, but by the time the balloon has reached the 300mb level it might
be vertically above Bognor.

And yet we are supposed to say "bugger Bognor, we will still call it
the Camborne ascent".

On the subject of several miles away, what about a weather balloon
launched from Cornwall on a day with a strong westerly wind?

The resulting readings can be plotted on a tephigram labelled Camborne
03808, but by the time the balloon has reached the 300mb level it might be
vertically above Bognor.

And yet we are supposed to say "bugger Bognor, we will still call it the
Camborne ascent".

That will soon change. The TEMP code's days are numbered now, as it will
soon be superseded by a binary BUFR code form. This new code form has
"levels" like a TEMP message, but each level has latitude and longitude
data - so the concept of assigning all the data at the various levels to the
location of the launch will not exist. That should help with model
analysis/assimilation cycle and, consequently, accuracy of model
predictions.
--
Freddie
Bayston Hill
Shropshire
102m AMSL
http://www.hosiene.co.uk/weather/
https://twitter.com/#!/BaystonHillWx for hourly reports

On 08/05/2013 14:54, Weatherlawyer wrote:
Why does the metric for 30 inches mean about 1016 millibars?

I presume you mean here 30" Hg is 762mmHg or 1016millibars

A standard atmosphere is 760mmHg = 1013.25mb
A quirk of the units of measure only makes these numbers match.

One pascal is basically an annoying factor of ~10^5 too small!

I was looking at a tape measure for the first time in (an interesting
career????) and noticed that 1016 millimeters is 40 inches. Is it time
I bought a new tape?

No. 40 x 25.4 is also 1016mm. But unless you are very heavily into
arcane numerology it is of no significance whatsoever.

--
Regards,
Martin Brown