André Mermoud Posted September 12, 2013 Posted September 12, 2013 Commonly available meteo (climatic) data have usually some uncertainties, of different kinds, which may produce very significant differences between sources, or years in a same source. These may be:- The quality of the data recording, care of the operators, positioning, calibration and drift of the sensors, perturbations like shadings, dirt or snow on the sensors, etc. - The fact that many data sources are only available in Monthly values, involving a synthetic generation for getting hourly values, - For terrestrial measurements, the presence of a not negligible horizon,- For terrestrial measurements, the location difference (distance of measuring station),- For Satellite data, the quality of the models used for interpreting the data, which is in continuous improvement since 20 years, and the position of the satellite (if geostationnary), - The yearly variability, which may be supposed to have a gaussian distribution,- The evolution of the climate. In Europe, it seems that the irradiation has increased by as much as 5% or more since the beginning of the 21th century.See the differences in the PVGIS data between the old database and the more recent "Climate-SAF" database. Another example: in Geneva, for official measurements of the ISM, the 2003-2011 average is 10% above the 1980-2002 average ! (which is probably an extreme situation).
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