"Nick Gardner" wrote...

As already been said, the UV intensity will generally be
proportional to how high the sun is in the sky, i.e., less
atmosphere (and ozone) for the light to travel through before
reaching the earth's surface.

Therefore, the greatest UV levels will generally occur, on a clear
day when the sun is at its highest elevation in the sky. There will
be no lag as you would expect with temperature.

Here is a link to a graph showing the UV index for today (8th) and
yesterday for Camborne in Cornwall, note the peak at around 1pm -
2pm.

http://www.btinternet.com/~nickgardn...ex08062008.jpg
________________

.... this graph shows a representation of the total global radiation
and UV radiation at an un-named spot:-


http://www.cpc.ncep.noaa.gov/product...s/diur_guv.gif

and is confirmed by the HPA site ...

http://www.hpa.org.uk/webw/HPAweb&HP...=1158934607746

These confirm the notes of others: the UV radiation should be
(ignoring effect of varying cloud cover), at a maximum around solar
noon (which does vary w.r.t. 'clock' noon).

If you are using 'Metcheck' then I note that their algorithms don't
seem to predict *any* UV radiation (despite forecast well broken cloud
cover), much before 10 o'clock local time, which at this time of the
year is unrealistic - particularly in Scotland: it may be lower than
midday, but it isn't going to be zero! Also, worryingly, the maxima
for a selection of sites I've just put in seem to coincide with the
day maximum temperature - to which it isn't connected as noted by
Nick.

Martin.


--
Martin Rowley
West Moors, East Dorset (UK): 17m (56ft) amsl
Lat: 50.82N Long: 01.88W
NGR: SU 082 023