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uk.sci.weather (UK Weather) (uk.sci.weather) For the discussion of daily weather events, chiefly affecting the UK and adjacent parts of Europe, both past and predicted. The discussion is open to all, but contributions on a practical scientific level are encouraged. |
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On 23/04/2018 12:43, Keith Harris wrote:
So it is true what Ole said, and the algarithm seems correct based on the WMO definition of 120W/m2, which is very old... I'm not sure that the age of the definition has much to do with it (is it very old anyway?). Isn't the reality that sunshine hours is not actually a well-defined parameter and can't be because what you're trying to measure, ie the boundary between bright sun conditions and not, is subjective. It's a different kind of parameter to eg temperature or rainfall. So different measurement techniques inevitably give different answers and probably always will. The WMO definition is one approach and an appealing one because it defines a threshold which can be accurately measured with the right kit. But how well it parallels human feelings about what is bright sun, especially in hazy or dawn/dusk conditions, is endlessly debatable. I suppose an alternative definition could be built around just how sharp a shadow might be, given modern sensors and image analysis software. But even so, someone will still need to make the call about precisely where the cutoff is to be made. |
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