[protonplayer]

Hi, is anyone able to tell me the relationship between solar radiation measurements and sunshine hrs. I've seen data where a sunnier location has less solar radiation than a cloudier location (but the sunnier location is closer to the equator). does not make sense. thanks, Jeremy

[Dave K]

protonplayer, on 26 November 2011 - 21:18, said:

Hi, is anyone able to tell me the relationship between solar radiation measurements and sunshine hrs. I've seen data where a sunnier location has less solar radiation than a cloudier location (but the sunnier location is closer to the equator). does not make sense. thanks, Jeremy

In general there is no easy direct relationship between solar radiation totals and sunshine hours. Solar radiation in w/m² is a measurement of energy flux and the only way to make a conversion to sunshine hours is by setting a threshold and taking the current reading to compare with the maximum possible for the date/time/latitude.

What is important to note is that bright white cloud on a sunny day causes a higher reading by reflecting solar radiation back to the ground which doesn't happen with a clear blue sky - this is called diffuse solar radiation as opposed to direct solar radiation which ignores the reflected element. So it is possible for a sunny day with lots of cumulus to give a diffuse reading of 1000 w/m² but for the next day with an apparently clear blue sky to read maybe 850 w/m² (and there may be a haze which is invisible to the naked eye). So I imagine in theory is that a location which is generally cloud free could have lower solar radiation average over a period of time to a location that is more prone to convective cloud even if sunshine hours are comparable.

If this isn't what you meant by your question could you give an example to show?