On Wednesday, May 29, 2019 at 2:51:21 PM UTC+1, wrote:
On Tuesday, May 28, 2019 at 7:22:38 PM UTC+1, Nick Gardner wrote:


As Graham has already stated our findings with regards to UV, the only
thing I can add is that it is thought that there is ozone depletion
above tropical maritime air masses. The mechanisms for this, I believe,
are poorly understood but someone (on this newsgroup) said that they
were aware of this when they were studying atmospheric sciences back in
the 1960s. It seems that this knowledge has been lost over the years.

Here in the SW we get some of the highest UV levels in northern Europe.
And, given a tropical air mass, throw in a bit of mist and a few clouds
and from mid-May to early August the UV can reach as high as the extreme
value of 10. On days like that I often do a scan of UV levels across the
rest of Europe and places as far south as Gibraltar and Cyprus can be
'wallowing' in levels around 7.

So stating that the UV levels are directly linked to elevation of the
sun is overtly simplistic and could be misleading.

--
Nick Gardner
Otter Valley, Devon
20 m amsl
http://www.ottervalleyweather.me.uk

I notice on the DEFRA site that on Saturday 25th, Stratospheric Ozone as measured at the only 2 English sites of Manchester and Reading, was nearly 2 SD below the long term mean.

Dick Lovett

That certainly ties in with the very high UV recording on that day. It would be interesting to check stratospheric ozone under a series warm sector ridge conditions. We are now entering one such phase so, as Nick said in his original post, we should see some very high readings (if the sun comes out!)

I am still of the opinion that very high humidity and vaguely sea misty conditions help increase levels even further, perhaps by reflection. On 3 or 4 occasions when UV was recorded on Scilly (St Martin's) I spotted it had hit 10, and each time there was sea fog in the vicinity. But, of course, they were also warm sector conditions.

Graham
Penzance