Characterizing Temporal Variability in Measurements of Surface Solar Radiation and its Dependence on Climate

The intrinsic temporal scales of the variability of the surface solar radiation are addressed by means of the empirical mode decomposition. High quality measurements of the solar radiation impinging on a horizontal plane at ground level, from different BSRN ground stations, are analysed. By first extracting all the embedded oscillations that share a common local time-scale, followed by Hilbert spectral analysis, the characteristic scales of variability, along with the fluctuations in the intensity of the pyranometric signal, are revealed. It is shown that data from stations with different local climates share some common features, most notably a high-frequency plateau of variability whose amplitude is found to be modulated by the seasonal cycle. The study has possible implications on the modelling and the forecast of the surface solar radiation, at different local time-scales.