Author Topic: Solar Radiation Question...  (Read 4396 times)

jg

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Solar Radiation Question...
« on: October 01, 2012, 08:31:35 PM »
Today was much sunnier than yesterday, but the Solar Radiation "Gauge" only shows 782.  The weather almanac shows that today had nearly an hour more sunlight than yesterday.  Does that make sense?

http://www.jgweather.info/RoslynWeather/index.html

WCDev

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Re: Solar Radiation Question...
« Reply #1 on: October 01, 2012, 10:20:36 PM »
When calculating sunshine hours, WeatherCat simulates a Campell-Stokes sunshine recorder. This is basically a strip of paper behind a glass globe facing towards the sun. The glass globe concentrates the suns rays on the paper which then burns if the solar radiation is strong enough (more details at   http://en.wikipedia.org/wiki/Campbell?Stokes_recorder).

So it isn't really the strength of the solar radiation, but just a question of is the sun strong enough to burn the paper; either it's burnt or it isn't (we then add up the length of the burn for any given day to get the number of hours).

How accurate is it? I have a real one about three miles away from me, which is used to calibrate WC's simulation. The largest discrepancy I've seen is about an hour.

jg

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Re: Solar Radiation Question...
« Reply #2 on: October 02, 2012, 04:40:45 AM »
Does Solar Radiation have anything to do with UV?  It seems impossible that there were 100 less units today than the day before as there was more sun today, less clouds, etc.

WCDev

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Re: Solar Radiation Question...
« Reply #3 on: October 02, 2012, 06:58:53 PM »
All WeatherCat does with solar and UV  is record the data - all I can think of is possible high cloud cutting down the radiation hitting the sensor.

jg

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Re: Solar Radiation Question...
« Reply #4 on: October 02, 2012, 07:01:03 PM »
Thanks.  The ET data is very interesting and has great uses in landscaping/agricultural field.

elagache

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Measurements related but not the same. (Re: Solar Radiation Question...)
« Reply #5 on: October 02, 2012, 08:01:39 PM »
Howdy JG, Stu, and WeatherCat fans,

Today was much sunnier than yesterday, but the Solar Radiation "Gauge" only shows 782.  The weather almanac shows that today had nearly an hour more sunlight than yesterday.  Does that make sense?

The solar radiation "gauge" is actually a measure of the power of the photons striking the sensor.  It is measured in Watts/m2.  So that measurement is how much power is available say for a solar panel to convert into electricity.  It is not the same as say how warm the sun feels or other things you might associate with the sun's effect on your body or the land.

Does Solar Radiation have anything to do with UV?  It seems impossible that there were 100 less units today than the day before as there was more sun today, less clouds, etc.

This isn't the same as either solar radiation or things like the sun's warmth.  It is measure of the photons in the Ultra-Violet specifically.  Ultra-Violet light can be effected by atmospheric conditions that aren't immediately viable.  So for example water vapor could absorb UV but not appear in the sky as clouds.  Alternatively a day with less total solar radiation would have a stronger UV effect because the air is particularly transparent.   That's why Davis provides two sensors.  You can't reliably predict one value from the other.

Cheers, Edouard  [cheers1]

jg

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Re: Measurements related but not the same. (Re: Solar Radiation Question...)
« Reply #6 on: October 02, 2012, 08:07:06 PM »
Howdy JG, Stu, and WeatherCat fans,

Today was much sunnier than yesterday, but the Solar Radiation "Gauge" only shows 782.  The weather almanac shows that today had nearly an hour more sunlight than yesterday.  Does that make sense?

The solar radiation "gauge" is actually a measure of the power of the photons striking the sensor.  It is measured in Watts/m2.  So that measurement is how much power is available say for a solar panel to convert into electricity.  It is not the same as say how warm the sun feels or other things you might associate with the sun's effect on your body or the land.

Does Solar Radiation have anything to do with UV?  It seems impossible that there were 100 less units today than the day before as there was more sun today, less clouds, etc.

This isn't the same as either solar radiation or things like the sun's warmth.  It is measure of the photons in the Ultra-Violet specifically.  Ultra-Violet light can be effected by atmospheric conditions that aren't immediately viable.  So for example water vapor could absorb UV but not appear in the sky as clouds.  Alternatively a day with less total solar radiation would have a stronger UV effect because the air is particularly transparent.   That's why Davis provides two sensors.  You can't reliably predict one value from the other.

Cheers, Edouard  [cheers1]

Wow, thanks.  My father in law is a helioseismologist who also spends a lot of time on climate "change" - I know a big focus of his work is evaluating the clouds "up high" which we can't see but apparently have more of an effect on temperature than all the other factors combined.  For what its worth, his research/science does not fall into  the anthropogenic global warming camp.  I guess I should have him explain this stuff to me, but then I may get lost quite fast.