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".