I see that the old UV Index scale of 0-10+ seems to have been replaced
by a newer 1-11 scale in May this year. But I'm struggling to find a
reference as to exactly how the old scale maps to the new one. (There
are limitless Google links on how to interpret the new scale in terms
of sunburn protection but little about the exact relationship between
old and new scales.) I've seen a suggestion that the mid-scale values
(eg 3-6) are in fact little changed, which seems a little odd.

Does anyone have any info or links that might give more detail on old
vs new.

TIA
John Dann
www.weatherstations.co.uk

On Wed, 28 Jul 2004 14:22:38 +0100, John Dann wrote:

I see that the old UV Index scale of 0-10+ seems to have been replaced
by a newer 1-11 scale in May this year. But I'm struggling to find a
reference as to exactly how the old scale maps to the new one. (There
are limitless Google links on how to interpret the new scale in terms
of sunburn protection but little about the exact relationship between
old and new scales.) I've seen a suggestion that the mid-scale values
(eg 3-6) are in fact little changed, which seems a little odd.

Does anyone have any info or links that might give more detail on old
vs new.

TIA
John Dann
www.weatherstations.co.uk


Not really answering your question but, coincidentally, I was reading a recent
"New Scientist" that had a relevant article.

See:

http://www.newscientist.com/news/news.jsp?id=ns99996184


Warning of bigger burn for sunbathers


10:00 24 July 04

Exclusive from New Scientist Print Edition.

People outdoors are exposed to higher levels of harmful ultraviolet rays than
previously thought, according to a three-year study.

The present estimate of UV exposure, the UV index, is based on measuring how
much radiation hits a horizontal surface. But this often underestimates how much
UV hits a vertical surface when the sun is low in the sky, says Peter Hoeppe, a
biometeorologist at Geo Risk Research in Munich, Germany.


UV warning

His team has developed a new way of estimating UV exposure that it hopes is more
accurate. The researchers measured the UV radiation hitting 27 surfaces inclined
at different angles at three different locations in Germany.

Using data from three years' worth of readings taken every two minutes, Hoeppe's
team constructed a three-dimensional model of the human body showing accurate UV
exposure in different solar conditions and body postures.

Their model also takes into account UV reflected off nearby surfaces. It
predicts that even at midday, parts of the body will receive higher doses of UV
than the UV index estimates (see graphic). And in some circumstances a person
standing would receive more UV than if lying down. "In many cases dermatologists
are underestimating the amount of UV exposure," he says.


Midday sun


Snow can reflect as much as 60 per cent of UV, says Hoeppe, which means that
skiers are at a greater risk of skin cancer than previously thought.


Mike Clark at the National Radiological Protection Board, which is responsible
for measuring and disseminating the UK's UV index to weather services, says the
major risk is still from sunbathing in a horizontal position in the midday sun.

"When the sun is low in the sky, people are less likely to be sunbathing,
especially while standing up," he points out.

Sara Hiom of Cancer Research UK's SunSmart campaign says there is a danger of
overcomplicating the message. The bottom line, she says, is cover up.

Journal reference: International Journal of Biometeorology (DOI:
10.1007/s00484-004-0211-9)

On Wed, 28 Jul 2004 15:04:44 +0100, JPG wrote:

Not really answering your question but, coincidentally, I was reading a recent
"New Scientist" that had a relevant article.

Yes, interesting - thanks.

Also just realised that the difference between old and new scales may
be something as simple as the fact that the UV Index values seem to
have become integer only. (Though the NRPB/Met Office online graphs
are still plotting all the intermediate values - did Chilton really
peak at 7 today??) So maybe all the old decimal values are simply
rounded up to the next integer (presumably on the basis of being on
the safe side when it comes to sunburn risk). Still seems odd to have
an index of 1 in the middle of the night though.

John Dann
www.weatherstations.co.uk

"John Dann" wrote in message
...

Also just realised that the difference between old and new scales may
be something as simple as the fact that the UV Index values seem to
have become integer only. (Though the NRPB/Met Office online graphs
are still plotting all the intermediate values - did Chilton really
peak at 7 today??) So maybe all the old decimal values are simply
rounded up to the next integer (presumably on the basis of being on
the safe side when it comes to sunburn risk). Still seems odd to have
an index of 1 in the middle of the night though.

Must be all that reflected moonlight!

Col
--
Bolton, Lancashire.
160m asl.
http://www.reddwarfer.btinternet.co.uk

I've never quite understood the point of this UV scale. It is only
useful if it varies significantly from day to day, given the same solar
altitude and a cloud-free sky. Does it? It always seems to have the same
value - about 6 - whatever that means. They may as well say "look, it's
midsummer; if you lie out in the sun too long you'll get burnt". Just as if
you go out in the rain you'll get wet and if you drive there will be puddles
and spray. Weather forecasters should not need to waste their time pointing
out what should be common sense. Are we becoming so infantilised that we need
to be told these things?

Tudor Hughes, Warlingham, Surrey.

On 29 Jul 2004 00:19:32 GMT, (TudorHgh) wrote:

I've never quite understood the point of this UV scale.

I think there are two separate questions. First, do you want to
measure the intensity of solar UV radiation at all, bearing in mind
that it will obviously vary with the degree of overcast and presumably
the ozone concentration above the area of measurement. Second, if
yes, which scale do you use?

As to the first, it's probably agreed that UV intensity is not a
primary weather parameter although still having some bearing on human
wellbeing, much as visible solar radiation does. But in practice it's
often measured by the same instrumentation package as other weather
variables and so its discussion probably belongs as much with
meteorology as any other discipline.

As to the scale, yes I'd rather see a simple intensity scale used,
but the UV Index does correlate with intensity at specific wavelengths
(albeit in a weighted fashion) and so it does essentially give the
same information as an intensity scale but not using the units you
might prefer to see. But using the UV Index scale is difficult to
avoid in practice when instrument makers use it, as does the
UKMO/NRPB.

John Dann
www.weatherstations.co.uk