July 3rd Very High UV on Scilly

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July 3rd Very High UV on Scilly

Postby Graham Easterling » 2014 Jul 03, 15:44

9.9 on Martin's Scilly! http://www.weatherlink.com/user/taperki ... &headers=1 This is the highest reading since it topped 10 on 8th July 2008, when it also reached 9.6 at the MetO Camborne site.

We are now basically in a humid warm sector ridge, which is always the situation with the highest readings.

Any other very high readings today?

Attached Sunset pic from Sennen Cove 22:00 on 2nd . A pretty end to a glorious day.
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140702-2200.jpg
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Graham

Penzance Weather Station
Grid Ref:
SW464231 - Post Code: TR18 4TP
19m AMSL - Aspect SSE
In a SE - NW orientated valley

23 Years of Penzance Weather Records : http://penzanceweather.atspace.com/weather.html
Graham Easterling
 
Posts: 316
Joined: 2011 Nov 30, 20:29
Location: Penzance, Cornwall

Re: July 3rd Very High UV on Scilly

Postby Nick Gardner » 2014 Jul 03, 18:52

Graham Easterling wrote:Any other very high readings today?


Graham, the UV was 8.4 here which is high but 9.9 is rather remarkable.

What was interesting is that I recorded a UV of 8.4 with a cloudless, crystal clear, deep blue sky with excellent visibility. That is very unusual when normally I would record 7.0 to 7.5 but no more.

Fair weather cloud adds around 10% to 15% to the solar radiation values (The highest values (+1100 W/m²) always occurr when there is cloud near the sun). Today the solar radiation fitted the cloudless sky conditions with a maximum of 974 W/m². The UV follows a similar pattern and my highest UV values (my joint record of 9.0 last Saturday occurred with plenty of cloud in the sky) never occur under cloudless conditions. I suspect (and my observations have shown) that given a bit of cloud I would have recorded +9.0 UV Index today and broken my record.

The UV does seem higher this year than last year.
Near Newton Poppleford, Sidmouth - Devon
50:41N 3:17 W; 20 metres AMSL; Station Grade B-BAAA37
http://www.ottervalley.co.uk
Nick Gardner
 
Posts: 429
Joined: 2012 Jan 27, 17:25
Location: Rural riverside valley location near the village of Newton Poppleford and 2 km from the sea.

Re: July 3rd Very High UV on Scilly

Postby Graham Easterling » 2014 Jul 03, 19:29

Fair weather cloud adds around 10% to 15% to the solar radiation values (The highest values (+1100 W/m²) always occurr when there is cloud near the sun). Today the solar radiation fitted the cloudless sky conditions with a maximum of 974 W/m². The UV follows a similar pattern and my highest UV values (my joint record of 9.0 last Saturday occurred with plenty of cloud in the sky) never occur under cloudless conditions. I suspect (and my observations have shown) that given a bit of cloud I would have recorded +9.0 UV Index today and broken my record.


Nick, on Scilly there was broken thin Sc at the time of the high reading, also visibility had declined to < 10km at the time of the peak reading, so it fits with everything you say.
Graham

Penzance Weather Station
Grid Ref:
SW464231 - Post Code: TR18 4TP
19m AMSL - Aspect SSE
In a SE - NW orientated valley

23 Years of Penzance Weather Records : http://penzanceweather.atspace.com/weather.html
Graham Easterling
 
Posts: 316
Joined: 2011 Nov 30, 20:29
Location: Penzance, Cornwall

Re: July 3rd Very High UV on Scilly

Postby John Wilson » 2014 Jul 06, 17:46

Would someone please explain the uv index to a very amateur observer with antiquated instrumentation?
regards to all
John
John Wilson
COL station id44018
John Wilson
 
Posts: 23
Joined: 2012 Apr 09, 21:28
Location: Arnold, Nottinghamshire, just off Mapperley Plains. 115m. amsl

Re: July 3rd Very High UV on Scilly

Postby Nick Gardner » 2014 Jul 06, 18:56

John Wilson wrote:Would someone please explain the uv index to a very amateur observer with antiquated instrumentation?


UV Index is a linear scale originally devised in Canada in 1992 and now adopted around the world by many organisations. It used to go from 1 to 10 with 10 being the maximum likely to be encountered in Canada but as it is being used elsewhere UV Index can often go well into the teens for tropical and mountain environments and areas where the ozone is thin.

There is a wealth of information on Wikipedia about the UV Index:
http://en.wikipedia.org/wiki/Ultraviolet_index

Well worth a read.
Near Newton Poppleford, Sidmouth - Devon
50:41N 3:17 W; 20 metres AMSL; Station Grade B-BAAA37
http://www.ottervalley.co.uk
Nick Gardner
 
Posts: 429
Joined: 2012 Jan 27, 17:25
Location: Rural riverside valley location near the village of Newton Poppleford and 2 km from the sea.

Re: July 3rd Very High UV on Scilly

Postby John Wilson » 2014 Jul 07, 08:25

Thank you Nick. The Wikipedia stuff is very interesting, but how do you (and Graham, and others) actually measure the UV index? Is it calculated from solar radiation measurements? What instrument do you use?
Kind regards
John
John Wilson
COL station id44018
John Wilson
 
Posts: 23
Joined: 2012 Apr 09, 21:28
Location: Arnold, Nottinghamshire, just off Mapperley Plains. 115m. amsl

Re: July 3rd Very High UV on Scilly

Postby Nick Gardner » 2014 Jul 07, 18:41

John Wilson wrote:Thank you Nick. The Wikipedia stuff is very interesting, but how do you (and Graham, and others) actually measure the UV index? Is it calculated from solar radiation measurements? What instrument do you use?


John, I use a Davis VP2+ weather station. It comes with solar and UV sensors (as well as the usual temperature, humidity, pressure, rainfall and wind speed/direction). The UV sensor detects UV light intensity at wavelengths of 290 to 390 nanometres. This spectral response is closely matched to the Erythema Action Spectrum as defined by McKinlay & Diffey (1987) and internationally recognised as the wavelengths most likely to cause sunburn.

The VP2 gives UV readings in two scales: MEDs (Minimum Erythermal Dose) and UV Index.

The current UV Index is displayed in the same way as temperature or humidity, i.e., in real-time but also stores readings in 15 minute interval data sets (this recording interval can be set to 1, 2, 5, 10 etc minutes but I use 15) and a daily high and the time that occurred.
Near Newton Poppleford, Sidmouth - Devon
50:41N 3:17 W; 20 metres AMSL; Station Grade B-BAAA37
http://www.ottervalley.co.uk
Nick Gardner
 
Posts: 429
Joined: 2012 Jan 27, 17:25
Location: Rural riverside valley location near the village of Newton Poppleford and 2 km from the sea.

Re: July 3rd Very High UV on Scilly

Postby Nick Gardner » 2014 Jul 10, 19:10

The very high UV continues with 9.0 today (10th July) at 13:18. The Scilly Isles reported a UV Index of 10.5 today.

The UV this summer so far year has been consistently higher than for the summer last year. The following data shows just how much higher.

Maximum UV Index: July 2013; July 2014
1st 6.7; 8.4
2nd 2.7; 7.9
3rd 6.6; 8.4
4th 7.1; 8.9
5th 6.8; 7.6
6th 6.8; 8.2
7th 6.3; 6.9
8th 6.8; 8.1
9th 7.0; 8.5
10th 7.1; 9.0

Either my UV sensor has gone awry or is the ozone thinner this year?
Near Newton Poppleford, Sidmouth - Devon
50:41N 3:17 W; 20 metres AMSL; Station Grade B-BAAA37
http://www.ottervalley.co.uk
Nick Gardner
 
Posts: 429
Joined: 2012 Jan 27, 17:25
Location: Rural riverside valley location near the village of Newton Poppleford and 2 km from the sea.


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