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Penrith Snow

Cheap Clever Method of Recording Sunshine Hours

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I was talking to a fellow weather geek recently and moaning about how difficult it is to record sunshine hours as equipment is very expensive and very few weather stations come with a sunshine sensor.

He then told me how he records sunshine for free! Basically he brought a spare temperature sensor for his weather station (which is able to record 4 separate temperature units) and put it in an upside down jam jar.

When it was cloudy the jar thermometer was only a degree or two above the screen one but as soon as the sun comes out the temperature rockets to over 10c more than that in screen even during the winter.

This data is then recorded on a computer as a graph and the amount of sunshine is thus recorded by the temperature difference between the jar and screen! Small difference means it was cloudy, big difference meant it was sunny.

Ingenious or what, he reckons his sunshine 'readings' are within 10% of those at a nearby MetO station.

Can anyone see an obvious downside to this apart from the thermometer possibly melting during a heat wave Lol.

Andy

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It seems like potentially a good idea to get a rough measurement of the amount of sunshine. Wouldn't the sensor take a while to cool down if the sun goes in though, meaning you may find it takes a while to register any cloud cover?

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I think this method would be reasonably accurate on days with continuous, or long spells, of sunshine but would be subject to significant error on days with sunny intervals and brief periods of cloud, or days with very short sunny intervals.

On the former the temperature in the jar wouldn't fall significantly before there was another interval of sunshine and on the latter it wouldn't have time to heat up before it was cloudy again.

Also, on days with spells of weak sunshine through a veil of As, particularly in spring, summer and early autumn, the jar would heat up almost as much as in bright sunshine and would therefore give the impression of continuous bright sunshine.

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Yes, some good points, the jar would need to ventilate quickly to get rid of solar heat but I might try the idea and try to refine it.

But why do so few weather stations record sunshine? Is it really that difficult?

Andy

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Yes, some good points, the jar would need to ventilate quickly to get rid of solar heat but I might try the idea and try to refine it.

But why do so few weather stations record sunshine? Is it really that difficult?

Andy

I suppose there are two limiting factors. Firstly very few integrated automatic stations come with a sunshine recorder so it would mean buying a stand alone recorder for about £200.

Secondly, to get any meaningful readings you need an exposure with as few obstructions to direct sunlight as possible which normally means mounting the recorder on the house roof, or a tall mast, or both.( probably the reason most automatic stations don't have a sunshine recorder as they're mounted on a short mast designed to be fixed to the ground)

It's quite a lot of effort and expense unless you're really keen to have sunshine records.

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I run an Oregon Scientific WMR 200 and have had 3 UV sensors that also record sunshine hours, they are probably the worst sensors I have had the misfortune to own.

They usually cease to work after 12 - 18 months at a £40 a throw I'm not going to replace it again.

I may well try the temperature sensor in a jar, as described by Brian Hamilton author of weather display.

He recommends painting the base of the jar black, so it becomes a black body and gives full instruction as to how to set it up within weather display.

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