"Brian Salt" wrote in message
k.co.uk...
In article ,
(Martin Rowley) wrote:

That is the method I felt would be used, but, as you say, the baseline
of
22 feet is not a useful distance.

.... I've now found a reference to the required minimum baseline: I
couldn't find it when I replied originally. To quote " by simultaneous
observations from the ends of a base line - the base line must be at
least 1/2 mile in length (hence the 'telephonic link') ....
This was only used when highly accurate upper wind finding was required
and now that I know where the airfield was (see below), and what it was
used for (mainly Fighter work) this can't be applicable to this
occasion.


I'm curious: *which* airfield in Devon are we talking about?
Harrowbeer Airfield, some 9 miles north of Plymouth.

.... thanks for that: I'm not sure if you are aware of the following site
(or you may be connected to it), but I found the history very
interesting in the context of your question.

http://www.bucklandmonachorum.org.uk...Harrowbeer.htm

It appears from this that the base was (for its short life) principally
a Fighter Command base. In this case, the Met Office would have in most
cases (always exceptions of course), be co-located with ATC. This was
standard Fighter Command practice ... see
http://www.controltowers.co.uk/Tower%20Designs.htm, because the MET
section had its sole role in the support of the airfield controller (low
cloud, fog, wind etc.) and so all the meteorology stuff was close-by.

In the other 'major' commands (e.g. Bomber, Coastal, Ferry & later
Transport), the Met Office tended to be apart from ATC (but not
necessarily a long way away, just enough to remove the instrument
enclosure etc.), and the pillars for theodolites etc., would not
necessarily be near/on the ATC/Watch Office. This was because the work
of the Office would be to brief aircrew, maintain links with duty
squadron/operations staff etc.


So what is the single theodolite method?

.... I think this has been answered elsewhere in this thread - for a
station as small as this, they wouldn't have had the need for high
accuracy of upper winds and this method (single) can give fair results -
Rodney and others have described it well: it does assume a constant rate
of ascent of the balloon, which for various reasons is not always true.


There is no mention of a Nephoscope is the information we have - and
it is
not mentioned on the plans of the watch office/control tower.

.... no, it probably wouldn't be mentioned as such in those plans- but it
was a long-shot anyway, and again I can't think they would have had the
requirement. Don't waste time on that. There might have been a comb
nephoscope??


Perhaps the need for 2 pillars was to use whichever would be better to
avoid the projection of the balloon filling room, which projects some
8
feet above the roof upon which the pillars are fixed. I can't imagine
that
the room for cause any obstruction, but maybe it was 'belt and
braces'!

.... this is much more likely. Perhaps the ATC/Watch Office was hurriedly
put up after the raids on Plymouth (as the airfield was built to a
standard Air Ministry design), and they then found the pillar was not
optimal. A second could have been built quickly. Or it may have always
been on the original plans - I have no knowledge of that: what I do know
is that if the low level winds were strong, the balloon once released
could go off quickly downwind at a low angle of elevation, such that
near obstructions would block the line of sight.


What would a balloon have be used for, given the technology available
in
1941-42? Determining cloud base, I suppose, as well as finding the
upper
winds?

.... balloons were often used (without theodolite) to measure the base of
low cloud - indeed, I would guess that this was the most often use of
such - smaller balloons than those used for the pilot balloon, with a
slightly slower rate of ascent - circa 400 ft/min, as opposed to 500 or
greater for pilot balloons. All you needed was the balloon, a stop watch
and the Mk1 eyeball to time when the balloon was lost into the base of
the cloud (or through the fog.)

.... as you are in Devon, you might consider making contact with the Met
Office archives (once they've settled down early in the New Year after
the move from Bracknell). They *may* still have the old Daily Registers
and other station information ... all MetOffices had to have plans of
where instruments etc., were. Inspection of the Registers (if still
extant) might show some useful information relating to use of
instrumentation.

See:- http://www.metoffice.gov.uk/corporat...ary/index.html

I have a couple of photographs here (in old publications of the time)
which show the operation of pilot balloon equipment - don't know how
well they would scan, but if you are interested, let me know and I'll
have a go sending them on.

all the best,


Martin.


--
FAQ & Glossary for uk.sci.weather at:-
http://homepage.ntlworld.com/booty.weather/uswfaqfr.htm