On Thursday, 16 July 2015 12:52:43 UTC+1, Ken Cook wrote:
Hi, All,

MetO installed a Campbell Stokes sunshine recorder at the Copley Site on 1st July.
The electronic R&D recorder is set at its most sensitive and will not go any lower, as that was the best setting under weak sun. As it is on the 10 metre anemometer pole it records an extra hour of sun from 04Z-05Z which the Campbell Stokes, on a screen stand, does not capture. The rest of the day has no shade for either instrument.
To my surprise, as I thought the electronic would be more sensitive, during partly cloudy conditions, the C/S records more sun than the electronic, so much so that the C/S is currently running upwards of 10% higher for the month so far.

I am sure MetO Quality Control will put me right if I am reading the trace incorrectly when they look at the cards and visit the site. I have read the Observer's Handbook time and again and am sure I'm doing it right. It does seem very subjective, however!

Anyway, the half-way figures for Copley for July 2015, up to 09Z 16th:
Mean max 19.7C Mean min 10.0C Mean 14.9C(+0.2C)
Rain 54.3mm(76%)
Wind WSW 7.4KT(-0.2KT)
Sun(E) 94.3hr(59%)
Sun(C/S) 102.5hr

This morning's ob 09Z-09Z Max 18.4C min 5.5C grass -0.1C rain nil sun 15th 10.6hr(8.9hr electronic)

Ken
Copley
Teesdale
http://www.kencook.magix.net/
----------------------------------------------------------------------------
Hi Ken,
The Campbell Stokes can give an overburn of the card in partly sunny conditions.
Something to do with reflection from the cloud as I understand.

It is a bit of a can of worms comparing it with the electronic recorder in my experience.
Campbell Stokes is only meant to record bright sunshine. There is a threshold set on the electronic recorder (200 W per sq m ?). I seem to remember there were particular discrepancies early and late in the day, which led to different sunshine totals.

Len
Wembury, SW Devon

--------------------------------------------------------------------------