I have noticed over the last week since i transfered a digital thermometer
probe into the middle of my large evergreed hedge that it is doing a very
good job of being a Stevenson Screen (I am comparing its results to that of
my screen).

It would lead me to suggest that in non-screen situations a large evergreen
hedge (over 8 feet) may be a good alternative. I wonder what you think?

brian
aberfeldy

More snow for Ben Lawers today

On Thu, 29 Apr 2004 16:38:45 +0100, "Brian Blair" wrote:

I have noticed over the last week since i transfered a digital thermometer
probe into the middle of my large evergreed hedge that it is doing a very
good job of being a Stevenson Screen (I am comparing its results to that of
my screen).

It would lead me to suggest that in non-screen situations a large evergreen
hedge (over 8 feet) may be a good alternative. I wonder what you think?

I use something similar, with my Oregon sensor head located in a deciduous
hedge. The lack of leaves in the winter is not a problem as the sun is then too
low to shine on the hedge.

I make sure the business end of the head unit is pointed away from the sun.
Like you I have noticed that the reading from the hedge-mounted device does not
differ significantly from one mounted in a home-made "Stevenson screen"

Still, sunny days may well cause a slight over-reading, but remember that leaves
have evolved to absorb solar energy and convert it to chemical energy with
possibly a slight cooling effect due to evapo-transpiration. I'm convinced that
as a result they do not rise in temperature much in direct sunlight, so in that
respect they are probably as good as a white-painted Stevenson screen.

JPG



brian
aberfeldy

More snow for Ben Lawers today

"Brian Blair" wrote in message
newsk9kc.663$7n5.54@newsfe1-win...
I have noticed over the last week since i transfered a digital thermometer
probe into the middle of my large evergreed hedge that it is doing a very
good job of being a Stevenson Screen (I am comparing its results to that
of
my screen).

It would lead me to suggest that in non-screen situations a large
evergreen
hedge (over 8 feet) may be a good alternative. I wonder what you think?

brian
aberfeldy

More snow for Ben Lawers today



I tried this, my daytime temps were fine but I found that overnight on clear
nights the temperature remained a couple of degrees higher than the
thermometer in my shade. Presumably due to radiation being hindred by the
leaves of the hedge.

This is fine advice if you have a hedge. I make do with a Russian vine (nasty,
fast growing deciduous thing that would climb right over the house without
weekly clipping). However, it provides nicely ventilated shade for my sensor
which is inside a white painted flower pot. If anything, my setup overdoes the
shade (10th August 'only' 36.9 C) and I am sure that if I had a screen in the
middle of my very sheltered back garden it would read oddly high, and would
probably give the some of the highest maxima in the country.

Julian
Julian Mayes, West Molesey, Surrey.
temps resulting from my odd exposure can be seen at
www.roehampton.ac.uk/weather
(and yes they do need to be updated!).

JPG wrote:
On Thu, 29 Apr 2004 16:38:45 +0100, "Brian Blair"
wrote:

I have noticed over the last week since i transfered a digital
thermometer probe into the middle of my large evergreed hedge that
it is doing a very
good job of being a Stevenson Screen (I am comparing its results to
that of
my screen).

It would lead me to suggest that in non-screen situations a large
evergreen hedge (over 8 feet) may be a good alternative. I wonder
what you think?

I use something similar, with my Oregon sensor head located in a
deciduous hedge. The lack of leaves in the winter is not a problem
as the sun is then too low to shine on the hedge.

I make sure the business end of the head unit is pointed away from
the sun. Like you I have noticed that the reading from the
hedge-mounted device does not differ significantly from one mounted
in a home-made "Stevenson screen"

Still, sunny days may well cause a slight over-reading, but remember
that leaves have evolved to absorb solar energy and convert it to
chemical energy with possibly a slight cooling effect due to
evapo-transpiration. I'm convinced that as a result they do not rise
in temperature much in direct sunlight, so in that respect they are
probably as good as a white-painted Stevenson screen.

There are a couple of IR photos on my website taken with a Ricoh
badged Philips ESP-80 and a full daylight blocking IR filter. White
areas show most IR emission/reflection.

--
Graham W http://www.gcw.org.uk/ PGM-FI page updated, Graphics Tutorial
WIMBORNE http://www.wessex-astro-society.freeserve.co.uk/ Wessex
Dorset UK Astro Society's Web pages, Info, Meeting Dates, Sites & Maps
Change 'news' to 'sewn' in my Reply address to avoid my spam filter.

I think a lot of us with back garden stations have a similar problems.
I have to move my Davis sensors to a north facing wall for the summer
months which gives accurate maximums. However, for my COL summaries I
still adjust the minimum temperatures from a max/min which is located
in a box 1m above the grass. I also have a possible location in a
hedge, but it is also under a tree which again could affect the
minimums through the months when the tree is full of leaves. Unless
you have the space, one has to always make compromises.

Keith (Southend)

http://www.southendweather.net

(JJCMayes1) wrote in message ...
This is fine advice if you have a hedge. I make do with a Russian vine (nasty,
fast growing deciduous thing that would climb right over the house without
weekly clipping). However, it provides nicely ventilated shade for my sensor
which is inside a white painted flower pot. If anything, my setup overdoes the
shade (10th August 'only' 36.9 C) and I am sure that if I had a screen in the
middle of my very sheltered back garden it would read oddly high, and would
probably give the some of the highest maxima in the country.

Julian
Julian Mayes, West Molesey, Surrey.
temps resulting from my odd exposure can be seen at
www.roehampton.ac.uk/weather
(and yes they do need to be updated!).

On Thu, 29 Apr 2004 22:19:06 +0100, "Graham W"
wrote:

JPG wrote:
On Thu, 29 Apr 2004 16:38:45 +0100, "Brian Blair"
wrote:

I have noticed over the last week since i transfered a digital
thermometer probe into the middle of my large evergreed hedge that
it is doing a very
good job of being a Stevenson Screen (I am comparing its results to
that of
my screen).

It would lead me to suggest that in non-screen situations a large
evergreen hedge (over 8 feet) may be a good alternative. I wonder
what you think?

I use something similar, with my Oregon sensor head located in a
deciduous hedge. The lack of leaves in the winter is not a problem
as the sun is then too low to shine on the hedge.

I make sure the business end of the head unit is pointed away from
the sun. Like you I have noticed that the reading from the
hedge-mounted device does not differ significantly from one mounted
in a home-made "Stevenson screen"

Still, sunny days may well cause a slight over-reading, but remember
that leaves have evolved to absorb solar energy and convert it to
chemical energy with possibly a slight cooling effect due to
evapo-transpiration. I'm convinced that as a result they do not rise
in temperature much in direct sunlight, so in that respect they are
probably as good as a white-painted Stevenson screen.

There are a couple of IR photos on my website taken with a Ricoh
badged Philips ESP-80 and a full daylight blocking IR filter. White
areas show most IR emission/reflection.

It's noticeable how green vegetation shows up white, almost as white as the
(visible) white siding of the houses.

JPG

On 30 Apr 2004 02:59:56 -0700, (Keith
Southend 2) wrote:

I think a lot of us with back garden stations have a similar problems.
I have to move my Davis sensors to a north facing wall for the summer
months which gives accurate maximums. However, for my COL summaries I
still adjust the minimum temperatures from a max/min which is located
in a box 1m above the grass. I also have a possible location in a
hedge, but it is also under a tree which again could affect the
minimums through the months when the tree is full of leaves. Unless
you have the space, one has to always make compromises.

If you use too good a location (meaning one that gives the truest air
temperature) it can be hard to make comparisons with other local
stations that use a wooden Stevenson screen. These do, of course, tend
to produce max/mins that are too extreme, in clear conditions with
light winds.

I often use "North wall" locations for the measurement of outside air
temperatures (i.e. well away from the actual wall but in its shade).
No matter what additional type of screen I use, in calm-ish clear
conditions (only), official stations in the area will report max/mins
up to 2 deg C more extreme than mine. I know I will never break any
local temperature records for max/mins because the wooden Stevensons
will always beat me. Grrr!

I reckon that too good a hedge location would suffer from the same
"problem".

--
Dave
Fareham

"Dave Ludlow" wrote in message
I often use "North wall" locations for the measurement of outside air
temperatures (i.e. well away from the actual wall but in its shade).
No matter what additional type of screen I use, in calm-ish clear
conditions (only), official stations in the area will report max/mins
up to 2 deg C more extreme than mine. I know I will never break any
local temperature records for max/mins because the wooden Stevensons
will always beat me. Grrr!

I reckon that too good a hedge location would suffer from the same
"problem".

--
Dave
Fareham

yeh, thats true, on 'that' day 10th August 2003 last year here in Bedford my
shade thermometer on a north wall managed 'just' 34.5C while the screen hit
the dizzy heights of 36.0C. See it on many occasions.

, think a lot of us with back garden stations have a similar problems.-Keith
After landscaping operations are finished here the time will come to install some instruments.But
the site is appalling-surrounded by houses,trees and fences,not even a decent hedge-I think almost
not worth spending on decent kit.
Is there anywhere -book,website-that offers specific advice on such poor locations?

--
regards,
david
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