Measuring sunshine accuracy across Europe

Q Is it possible that places with a lower latitude and shorter day such as Schleswig yesterday for example can report higher sunshine values than stations further north such as Kinloss on the same equally sunny day?

A I suppose it might depend on the exposure of the sunshine sensor and it’s sensitivity. Yesterday it was sunny across the north of Scotland from Dawn till dusk and completely cloudless locally and Kinloss reported 13.7 hours of sunshine or 93.8% of the theoretical maximum for 57° 38′ 34.79″ N, on a day that’s 14 hours and 40 minutes long. Meanwhile in Schleswig they reported 13.8 hours of sunshine or 96.4% of the theoretical maximum for 54° 31′ 26.152″ N 9° 33′ 47.617″ E, on a day that’s 14 hours and 26 minutes long. So how come on a completely sunny day with very clear air and with 14 minutes less daylight could Schleswig report ~10 minutes more sun? There are a couple of possible answers to that, the exposure of their sensor is better or one of the sensors, and I reckon the one at Schleswig, needs recalibrating or it’s just more sensitive. I don’t know what the rules are regarding what constitutes bright sunshine in these new fangled sensors in AWS these days, but I reckon that 95% of possible might be a reasonable maximum value.

I won’t even go into why places such as Kraljevo, a city in Serbia, can report an impossible 14.2 hours of sunshine for yesterday which is 104.6% of the theoretical maximum. All I will say is that the WMO has it’s work cut out if it want’s to standardise climate observations in Europe if this kind of practice goes on. It reminds me of the story of a climate observer for one of the resorts on the south coast who was adept at using a lit cigarette to extend the trace on a sunshine card!

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