On Apr 6, 6:26*am, "Col" wrote:
wrote in message

...

* * * *Unfortunately, Dave, the sun will raise the screen temperature
above the true air temperature whether there are gaps in it or not. *I
notice this when the sun goes behind a tree in next door's garden.
You could rotate the screen so that the door faces north. *Bit of a
palaver.

..................

So what is the 'true air temperature', how can it be measured?
I thought that an official screen had to be placed in open ground
in direct sunlight.
--
Col

Bolton, Lancashire
160m asl

It does, but it still reads high when the sun is out, the
amount depending on the wind speed. Forced ventilation of all screens
with an internal fan would be an answer, or a moveable parasol say
twenty feet in the air that shaded only the screen. Then you'd have
the huge problem of incompatibility with previous records. Screen
temperatures in sunlight are always high, sometimes by nearly 4 deg -
it's a fault of the system.

Tudor Hughes, Warlingham, Surrey.