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Old May 5th 06, 06:45 PM posted to uk.sci.weather
Jonathan Stott Jonathan Stott is offline
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First recorded activity by Weather-Banter: Oct 2003
Posts: 328
Default Definition of 'sunshine'

Chris Hogg wrote:
I have a Davis automatic weather station with solar radiation sensor.
The latter records in watts/m^2, and, quite reasonably, records levels
of solar radiation even on dull days. But it doesn't tell me the
traditional hours of sunshine, as such. Is there a threshold value of
w/m^2 that is generally accepted as being equivalent to actual
sunshine, either rule of thumb or scientific? Put another way, what's
the minimum strength of solar radiation in w/m^2 required to burn the
strip of paper in a glass sphere type of sunshine recorder?


A sunshine recorder and a solar radiation sensor are different
instruments. The solar radiation sensor on your Davis is measuring the
total solar radiation from the whole sky whereas a traditional sunshine
recorder only measures the light from the sun (as it's focused or tracked).

There are some interesting letters in the last couple of issues of the
COL bulletin - see http://www.met.rdg.ac.uk/~brugge/col.html

Jonathan
Canterbury