Adjustment of the Angstrom-Prescott equation from Campbell-Stokes and Kipp-Zonen sunshine measures at different timescales in Spain

Resumen

The sunshine-based Ångström–Prescott model and the temperature-based is widely used in the scientific literature, and, in general, it is accepted that the sunshine-based methods are more accurate. Sunshine duration is registered in many climatological stations, and it is highly correlated with solar radiation. However, in many applications of the Ångström–Prescott equation, no attention is payed to the sensor used for recording sunshine duration. In Spain, the Campbell-Stokes sensors are being replaced by Kipp and Zonen sensors. This study assessed the Ångström–Prescott goodness-of-fit and adjusted coefficients for Campbell-Stokes and Kipp and Zonen daily records at 10 stations in Spain. The analysis considered three different temporary windows, namely global, seasonal and monthly scales based. The results show differences in the sunshine hours measured by the two instruments, mainly because the Campbell-Stokes recorder is prone to over-burning. The Kipp and Zonen sensors can be considered as suitable as the Campbell-Stokes sensor, and provides a significant reduction in the statistical errors. The results also highlight the importance calibrating the Ångström–Prescott equation using seasonal and monthly coefficients, instead of using a unique pair of values. Further, the equation performance shows a clear seasonal pattern, with a higher accuracy during the summer.