Bernard Burton wrote..........

Another example of excessively high screen maximum
in calm sunny conditions.

Wokingham, Berkshire, UK.

Same here in Southcote in calm sunny conditions.
Also exposure of sensor comes into play. Situated in enclosed rear garden,
with other houses in vicinity.

Last two days..........

14th +10.0
15th +10.6

Cold overnight, with Min -3.1 and Grass Min -5.0.
Temperature has risen steadily and now reads +4.2 at 1100.

Eric Belton

On Nov 16, 11:01 am, "Eric Belton" wrote:
Bernard Burton wrote..........

Another example of excessively high screen maximum
in calm sunny conditions.

Wokingham, Berkshire, UK.

Same here in Southcote in calm sunny conditions.
Also exposure of sensor comes into play. Situated in enclosed rear garden,
with other houses in vicinity.

Last two days..........

14th +10.0
15th +10.6

Cold overnight, with Min -3.1 and Grass Min -5.0.
Temperature has risen steadily and now reads +4.2 at 1100.

Eric Belton

I think the problem here is not so much the exposure of
the whole site but sunshine on the screen at a low altitude, combined
with calm conditions, of course. The problem seems to less in summer,
ironically, the reason probably being that is very rarely calm on hot
summer days owing to differential heating on a small mesoscale and
strong convection in the lower layers. I have occasionally observed
differences of nearly 4 degC in winter between screen reading and a
psychrometer whirled in the shade. Too bad, that's the system; all
you can do is keep the screen as white and clean as possible.

Tudor Hughes, Warlingham, Surrey, 556 ft.

On 16 Nov, 15:21, Tudor Hughes wrote:
On Nov 16, 11:01 am, "Eric Belton" wrote:



Bernard Burton wrote..........

Another example of excessively high screen maximum
in calm sunny conditions.

Wokingham, Berkshire, UK.

Same here in Southcote in calm sunny conditions.
Also exposure of sensor comes into play. Situated in enclosed rear garden,
with other houses in vicinity.

Last two days..........

14th +10.0
15th +10.6

Cold overnight, with Min -3.1 and Grass Min -5.0.
Temperature has risen steadily and now reads +4.2 at 1100.

Eric Belton

I think the problem here is not so much the exposure of
the whole site but sunshine on the screen at a low altitude, combined
with calm conditions, of course. The problem seems to less in summer,
ironically, the reason probably being that is very rarely calm on hot
summer days owing to differential heating on a small mesoscale and
strong convection in the lower layers. I have occasionally observed
differences of nearly 4 degC in winter between screen reading and a
psychrometer whirled in the shade. Too bad, that's the system; all
you can do is keep the screen as white and clean as possible.

Tudor Hughes, Warlingham, Surrey, 556 ft.

Has anyone ever done comparison experiments with a screen painted
silver?

Or maybe just the south facing side?

wrote in message
...
On 16 Nov, 15:21, Tudor Hughes wrote:
On Nov 16, 11:01 am, "Eric Belton" wrote:



Bernard Burton wrote..........

Another example of excessively high screen maximum
in calm sunny conditions.

Wokingham, Berkshire, UK.

Same here in Southcote in calm sunny conditions.
Also exposure of sensor comes into play. Situated in enclosed rear
garden,
with other houses in vicinity.

Last two days..........

14th +10.0
15th +10.6

Cold overnight, with Min -3.1 and Grass Min -5.0.
Temperature has risen steadily and now reads +4.2 at 1100.

Eric Belton

I think the problem here is not so much the exposure of
the whole site but sunshine on the screen at a low altitude, combined
with calm conditions, of course. The problem seems to less in summer,
ironically, the reason probably being that is very rarely calm on hot
summer days owing to differential heating on a small mesoscale and
strong convection in the lower layers. I have occasionally observed
differences of nearly 4 degC in winter between screen reading and a
psychrometer whirled in the shade. Too bad, that's the system; all
you can do is keep the screen as white and clean as possible.

Tudor Hughes, Warlingham, Surrey, 556 ft.

Has anyone ever done comparison experiments with a screen painted
silver?

Or maybe just the south facing side?
-------------------------
This is a thorny old topic that seems to crop up quite a bit. Ron Button and
myself have had some fun mounting a small solar powered fan in our
enclosures to keep the air moving.. The beauty of it is it only trips on
when the solar panel is exposed to strong sunshine. The downside is it's
non-standard and you might get lower values than a perfectly placed
Stevenson's screen. I've also added a piece of foam polystyrene to the
underside of the roof and the, South facing side but have a large amount of
ventilation elsewhere. It has definitely improved my readings compared to
other more professional nearby sites.

Dave, S.Essex, 5.4C