Analysis of cloud effects on long-term global and diffuse photosynthetically active radiation at a Mediterranean site

This study addresses the analysis of cloud effects on photosynthetically active radiation (PAR, 400–700 nm) for global (PAR Global ) and its diffuse component Diffuse ). To this aim, a 11-year database measured PAR modeled Difuse recorded in Mediterranean site was analyzed, both clear-sky all-sky scenarios. mean values entire period were estimated (200 ± 50) Wm −2 (240 all- scenarios, respectively, while obtained (59 6) all-skies (51 5) clear-skies. monthly averages show typical annual pattern driven by course solar position presents similar but less marked pattern. The observed seasonal behavior explained terms cover, frequency, liquid ice content Higher variability during spring detected due to more complex features season. Cloud Radiative Effect (CRE) showed negative associated with decrease (−36 14) positive corresponding an increase (+7 . A clear found CRE higher autumn, lower summer winter. Additionally, PAR-to-Total ratio fraction (k evaluated under different sky conditions. Monthly steady around 0.44 any dependence clearness index t nor total cover (TCC) found. However, k seemed TCC, taking 0.45 0.28 For conditions colder months. secondary maximum value revealing important effect Saharan dust intrusions region. Finally, well-defined logistic relationship between , leading estimate from irradiance measurements. • Seasonal related features. vs. leads irradiance.