On Wednesday, 27 May 2020 14:07:49 UTC+1, Graham Easterling wrote:

I have not seen any evidence UV levels are linked to high humidity. If UV levels are lower after a cold front it may be there is more cloud.

Nicholas
Meir Heath, Stoke-On-Trent 250 metres above sea level.

If you have not seen the evidence, you haven't looked. There is plenty of evidence that low level humidity & high level UV are linked.

If you don't believe it, I can only suggest you look at Camborne UV over a few summers, & compare it with the synoptic chart. That doesn't prove the exact mechanism (Freddie, any help here) but it proves the strong correlation.

Cloudless skies after the passage of a cold front give lower UV than before. UV is very low under cloud in mP air.

It really irritates may when observational evidence is dismissed as not evidence. The sea fog off the north Cornwall coast in't there because you haven't seen it?
. or you could just spend a moment using Google, I typed UV RH relationship & this came top of the list
" In this article, the ultraviolet radiation and relative humidity (RH) data from ground observations and a radiative transfer model were used to examine the influence of RH on ultraviolet radiation flux and aerosol direct radiative forcing under the clear-sky conditions. The results show that RH has a significant influence on ultraviolet radiation because of aerosol hygroscopicity. The relationship between attenuation rate and RH can be fitted logarithmically and all of the R2 of the 4 sets of samples are high, i.e. 0.87, 0.96, 0.9, and 0.9, respectively. When the RH is 60%, 70%, 80% and 90%, the mean aerosol direct radiative forcing in ultraviolet is −4.22W m−2, −4.5W m−2, −4.82W m−2 and −5.4W m−2, respectively. For the selected polluted air samples the growth factor for computing aerosol direct radiative forcing in the ultraviolet for the RH of 80% varies from 1.19 to 1.53, with an average of 1.31."

I agree that temperature is not linked to high UV levels. There is, of course, an association.

I have to confess I've been a bit of a beach bum. I can lie around all day in the clear sunny polar air, but a couple of hours surfing in shallow sea mist . . . (I'm talking about my younger days!)

There's loads of evidence of the link.

Graham
Penzance

I am not dismissing it as no evidence. I have not read the article but I have searched for it today. I have looked at the World Health Organization website and humidity is not mentioned as a factor with high UV levels so this made me think it was not. There are a lot of factors and all of them are not listed. There are also things that reflect UV levels that make them higher. One of these is water so the sea would affect them.

Nicholas
Meir Heath, Stoke-On-Trent 250 metres above sea level.