Today and yesterday have seen quite high UV levels after what has been a
spring season of rather normal UV intensity.

The lack of tropical maritime air masses has probably been responsible.

The UV here today reached 8.6 despite quite cloudy and hazy conditions
with the sun always being partly obscured by haze or cloud. Yesterday's
hazy conditions saw the UV reach 8.0.

I suspect that now the CF has moved through this evening and we're in a
different air mass, the UV maximum tomorrow will be down to around 6.0
to 7.0.

Given the forecast for later this week, we may see an extremely high UV
level of +9.0 on Wednesday. Slip, slop, slap...oooerrrrr.

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

On Sunday, May 26, 2019 at 8:38:33 PM UTC+1, Nick Gardner wrote:
Today and yesterday have seen quite high UV levels after what has been a
spring season of rather normal UV intensity.

The lack of tropical maritime air masses has probably been responsible.

The UV here today reached 8.6 despite quite cloudy and hazy conditions
with the sun always being partly obscured by haze or cloud. Yesterday's
hazy conditions saw the UV reach 8.0.

I suspect that now the CF has moved through this evening and we're in a
different air mass, the UV maximum tomorrow will be down to around 6.0
to 7.0.

Given the forecast for later this week, we may see an extremely high UV
level of +9.0 on Wednesday. Slip, slop, slap...oooerrrrr.

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

Mainly cloudy at Camborne today, but yesterday was easily the highest UV of the year at Camborne, hitting 9.0. Needless to say, humid maritime air with sea fog patches as normal. A misty day out at Sennen

Shallow sea mist burns you as anybody who spends time on the water will have noticed.

Graham
Penzance

On Sunday, 26 May 2019 20:38:33 UTC+1, Nick Gardner wrote:
Today and yesterday have seen quite high UV levels after what has been a
spring season of rather normal UV intensity.

The lack of tropical maritime air masses has probably been responsible.

The UV here today reached 8.6 despite quite cloudy and hazy conditions
with the sun always being partly obscured by haze or cloud. Yesterday's
hazy conditions saw the UV reach 8.0.

I suspect that now the CF has moved through this evening and we're in a
different air mass, the UV maximum tomorrow will be down to around 6.0
to 7.0.

Given the forecast for later this week, we may see an extremely high UV
level of +9.0 on Wednesday. Slip, slop, slap...oooerrrrr.

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

UV levels are not related to temperature so they would not be lower because of a colder air mass and they would not be higher because of a warmer air mass. They relate to the position of the sun in the sky. At this time of year, it is at its highest point at 1 pm and this is when UV levels can be high.

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

On Monday, May 27, 2019 at 11:22:19 PM UTC+1, Nicholas Randall wrote:
On Sunday, 26 May 2019 20:38:33 UTC+1, Nick Gardner wrote:
Today and yesterday have seen quite high UV levels after what has been a
spring season of rather normal UV intensity.

The lack of tropical maritime air masses has probably been responsible.

The UV here today reached 8.6 despite quite cloudy and hazy conditions
with the sun always being partly obscured by haze or cloud. Yesterday's
hazy conditions saw the UV reach 8.0.

I suspect that now the CF has moved through this evening and we're in a
different air mass, the UV maximum tomorrow will be down to around 6.0
to 7.0.

Given the forecast for later this week, we may see an extremely high UV
level of +9.0 on Wednesday. Slip, slop, slap...oooerrrrr.

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

UV levels are not related to temperature so they would not be lower because of a colder air mass and they would not be higher because of a warmer air mass. They relate to the position of the sun in the sky. At this time of year, it is at its highest point at 1 pm and this is when UV levels can be high.

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

UV levels are not related to temperature, agreed. The height of the sun in the sky is by no means the only factor, air mass is important. Warm sector ridges are associated with very high UV levels. The reason for this is open to discussion, but it's indisputable. To people like Nick, who has a sunshine recorder it's blindingly obvious. For me, who keeps an eye on Camborne UV it's fairly dramatic.

Saturday it was sunny at Camborne around 13:00, visibility was M to G with patchy low cloud, hazy conditions, sea fog patches nearby and fairly weak shadows. UV hit 9. Yesterday also sunny around the same time, VG visibility, deeper colours, lower humidity, sharper shadows, UV 7. Under a hot, dirty continental air mass, it would be even lower.

I've had discussions with people like Martin Rowley in the past, and researched it. The generally accepted explanation seems to be that it's associated with upper atmospheric conditions under warm sector ridges. However, I'm of the view that the low level near 100% humidity also has a role to play.

I think anyone who spends any time on the water when there are sea mist patches on a warm summer's day, knows how quickly you get burnt. It's an issue for me with a bald head. People like Norman L have also commented on it on USW.

If in doubt, I suggest you check Camborne UV levels from late May to the end of July over 2 or 3 years, then compare the very high readings with the synoptic chart. I suspect NIck G has records you could also compare. Also records from Scilly http://www.scillyman.co.uk/WeatherStation.html (if he kept them). The association is striking.

Graham
Penzance

On Tuesday, May 28, 2019 at 9:09:19 AM UTC+1, Graham Easterling wrote:
On Monday, May 27, 2019 at 11:22:19 PM UTC+1, Nicholas Randall wrote:
On Sunday, 26 May 2019 20:38:33 UTC+1, Nick Gardner wrote:
Today and yesterday have seen quite high UV levels after what has been a
spring season of rather normal UV intensity.

The lack of tropical maritime air masses has probably been responsible.

The UV here today reached 8.6 despite quite cloudy and hazy conditions
with the sun always being partly obscured by haze or cloud. Yesterday's
hazy conditions saw the UV reach 8.0.

I suspect that now the CF has moved through this evening and we're in a
different air mass, the UV maximum tomorrow will be down to around 6.0
to 7.0.

Given the forecast for later this week, we may see an extremely high UV
level of +9.0 on Wednesday. Slip, slop, slap...oooerrrrr.

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

UV levels are not related to temperature so they would not be lower because of a colder air mass and they would not be higher because of a warmer air mass. They relate to the position of the sun in the sky. At this time of year, it is at its highest point at 1 pm and this is when UV levels can be high.

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

UV levels are not related to temperature, agreed. The height of the sun in the sky is by no means the only factor, air mass is important. Warm sector ridges are associated with very high UV levels. The reason for this is open to discussion, but it's indisputable. To people like Nick, who has a sunshine recorder it's blindingly obvious. For me, who keeps an eye on Camborne UV it's fairly dramatic.

Saturday it was sunny at Camborne around 13:00, visibility was M to G with patchy low cloud, hazy conditions, sea fog patches nearby and fairly weak shadows. UV hit 9. Yesterday also sunny around the same time, VG visibility, deeper colours, lower humidity, sharper shadows, UV 7. Under a hot, dirty continental air mass, it would be even lower.

I've had discussions with people like Martin Rowley in the past, and researched it. The generally accepted explanation seems to be that it's associated with upper atmospheric conditions under warm sector ridges. However, I'm of the view that the low level near 100% humidity also has a role to play..

I think anyone who spends any time on the water when there are sea mist patches on a warm summer's day, knows how quickly you get burnt. It's an issue for me with a bald head. People like Norman L have also commented on it on USW.

If in doubt, I suggest you check Camborne UV levels from late May to the end of July over 2 or 3 years, then compare the very high readings with the synoptic chart. I suspect NIck G has records you could also compare. Also records from Scilly http://www.scillyman.co.uk/WeatherStation.html (if he kept them). The association is striking.

Graham
Penzance

And the UV index graphs for any day at Camborne and 13 other places can be viewed at
https://uk-air.defra.gov.uk/data/uv-index-graphs

Len
Wembury

On 27/05/2019 23:22, Nicholas Randall wrote:
UV levels are not related to temperature so they would not be lower because of a colder air mass and they would not be higher because of a warmer air mass. They relate to the position of the sun in the sky. At this time of year, it is at its highest point at 1 pm and this is when UV levels can be high.

Thanks for this. If only it was that simple (as the Met Office seems to
think so).

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

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

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

Graham Easterling wrote:

On Monday, May 27, 2019 at 11:22:19 PM UTC+1, Nicholas Randall wrote:
On Sunday, 26 May 2019 20:38:33 UTC+1, Nick Gardner wrote:
Today and yesterday have seen quite high UV levels after what has
been a spring season of rather normal UV intensity.

The lack of tropical maritime air masses has probably been
responsible.

The UV here today reached 8.6 despite quite cloudy and hazy
conditions with the sun always being partly obscured by haze or
cloud. Yesterday's hazy conditions saw the UV reach 8.0.

I suspect that now the CF has moved through this evening and
we're in a different air mass, the UV maximum tomorrow will be
down to around 6.0 to 7.0.

Given the forecast for later this week, we may see an extremely
high UV level of +9.0 on Wednesday. Slip, slop, slap...oooerrrrr.

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

UV levels are not related to temperature so they would not be lower
because of a colder air mass and they would not be higher because
of a warmer air mass. They relate to the position of the sun in the
sky. At this time of year, it is at its highest point at 1 pm and
this is when UV levels can be high.

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

UV levels are not related to temperature, agreed. The height of the
sun in the sky is by no means the only factor, air mass is important.
Warm sector ridges are associated with very high UV levels. The
reason for this is open to discussion, but it's indisputable. To
people like Nick, who has a sunshine recorder it's blindingly
obvious. For me, who keeps an eye on Camborne UV it's fairly dramatic.

Saturday it was sunny at Camborne around 13:00, visibility was M to G
with patchy low cloud, hazy conditions, sea fog patches nearby and
fairly weak shadows. UV hit 9. Yesterday also sunny around the same
time, VG visibility, deeper colours, lower humidity, sharper shadows,
UV 7. Under a hot, dirty continental air mass, it would be even lower.

I've had discussions with people like Martin Rowley in the past, and
researched it. The generally accepted explanation seems to be that
it's associated with upper atmospheric conditions under warm sector
ridges. However, I'm of the view that the low level near 100%
humidity also has a role to play.

I think anyone who spends any time on the water when there are sea
mist patches on a warm summer's day, knows how quickly you get burnt.
It's an issue for me with a bald head. People like Norman L have also
commented on it on USW.



Graham
Penzance


Indeed. With my fair skin I burn most easily in misty conditions. More
so than in bright sunshine,


--
Norman
(currently re-charging my Scottish accent!)

On Tuesday, 28 May 2019 19:22:38 UTC+1, Nick Gardner wrote:
On 27/05/2019 23:22, Nicholas Randall wrote:
UV levels are not related to temperature so they would not be lower because of a colder air mass and they would not be higher because of a warmer air mass. They relate to the position of the sun in the sky. At this time of year, it is at its highest point at 1 pm and this is when UV levels can be high.

Thanks for this. If only it was that simple (as the Met Office seems to
think so).

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 am aware that there are other factors that affect UV levels but I only stated one. Others are latitude, altitude and ozone. Lower ozone values lead to higher UV levels and higher ozone values lead to lower UV levels. With latitude, the lower the location is, the higher the UV levels are. With altitude, at the top of a mountain UV levels are higher because the air is thinner and cleaner. Another factor that affect UV levels is reflection which I have seen Graham mention today. Most surfaces reflect UV levels but some do more than others. Water does reflect UV and that has been mentioned here. I do not think high humidity or mist cause high UV levels. When Graham mentions sea mist, I think it would be the water causing them to be high through reflection.

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