I read somewhere that the sun at its midday peak is 10 times more
intense (in terms of harmful UV rays) than three hours before or
after. As someone interested in protecting myself from dangerous sun
exposure, I?d like to know what the distribution of sun intensity
throughout day and season is? A good answer should be expressed in
terms of percentage of the peak. That is, if zero is absolute
protection from sun (e.g., inside a sun-proof chamber underground),
and the most extreme value time and season is set to 100, how does the
sun intensity vary?

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Request for Question Clarification by pafalafa-ga on 13 Feb 2005 17:59 PST

Typical variation in UV intensity -- the part of sunlight that causes
sunburn -- can be seen here:


http://www.cpc.ncep.noaa.gov/products/stratosphere/uv_index/gif_files/diur_guv.gif



The blue line represents UV radiation, and peaks at a value of 275 at
noon.  Three hours earlier or later, the values are about 125, so the
intensity -- while considerably less -- can hardly be said to be ten
times more intense at noon.

Similar graphs are available for seasonal variations for different
locations throughout the US.  Would these meet your needs?  And if so,
what part of the country (assuming you're in the US!) would best suit
you.

Thanks,

pafalafa-ga

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Request for Question Clarification by pafalafa-ga on 13 Feb 2005 18:00 PST

The link above is the DAILY variation, as I should have made clear originally.

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Clarification of Question by mharoks-ga on 13 Feb 2005 19:30 PST

Thanks for the comments, pafalafa and sqylogin!
These appear to be a good start, but a little more is needed to
address my question. The chart identified by pafalafa does a nice job
of showing the variation in intensity during a single day (and the
information it contains could easily be converted into a 0-100 scale
by the researcher). However, I'll also want to compare this
information across seasons. Thus, for example, I'd want to know what
the intensity would be in the middle of winter (on a 100-point scale).
Thus, for example, if the worst day in summer at midday is 100, I want
to know not only what the value would be at various hours on that day
(values every hour or two would be ideal), but also for different
months (preferably every 2-3 months, if not monthly). I would have
thought that this distribution was fairly similar across days and
different locations (though, obviously, the amount of UV exposure will
vary by location), but perhaps that is not true. The researcher can
give the data for the state of Minnesota, although ideally I'd like to
know if the variation really changes by state/country (e.g., wouldn't
the same distribution hold for New Zealand?). Information about how
this varies due to different levels of cloud cover will earn a bonus.
Thanks a lot!
mharoks

This information is more generalized than what you would have, but it
may still be of interest, regardless:
http://66.102.7.104/search?q=cache:ZTs2NEdh-YcJ:www.pueblo.gsa.gov/cic_text/health/sun_uv/sun-uv-you.htm+uv+radiation+intensity+day+distribution&hl=en

Here's a study of solar intensity, but in terms of months instead of hours.
http://almashriq.hiof.no/lebanon/600/610/614/solar-water/idrc/10-19.html