Influence of cloudy/clear-sky partitions and aerosols variabilities on surface solar irradiance measured in Lille, Northern France (2010-2022)
Résumé
The variability of solar radiation incident at the surface, vital for ecosystems and life, has also important implications for practical applications such as solarpower generation. Atmospheric conditions, especially clouds and aerosols largely influence the surface solar irradiance amount and evolution, as well as its repartition into direct and diffuse components. Here we analyze coincident daytime ground-based measurements of level 2.0 aerosol optical properties from AERONET photometer and of direct and diffuse horizontal surface irradiances from a set of pyrheliometer and pyranometer in operation at the ATOLL (Atmospheric Observations in LiLle) platform in north of France over the period 2010-2022. In order to isolate the radiative effect of aerosols from that of cloud, a separation between cloudy-sun, clear-sun with surrounding clouds and clear-sky moments is performed using two cloud detection algorithms at 1-min resolution. The measurements are further analyzed with the radiative transfer code SOLATRTDECO to simulate the spectrally integrated solar global horizontal irradiance (GHI) and its direct (BHI) and diffuse (DHI) components. Our analysis highlight that on average in ATOLL over the period 2010-2022, the proportion of clear-sky conditions is relatively low (11%), whereas clear-sun with clouds and cloudy sun situations represent 22% and 67%, respectively. These sky conditions highly influence measured GHI and their repartition into direct and diffuse components. The 2010-2022 mean of GHI is minimum in cloudy-sun situations (174 W/m2) and maximum for clear-sun with clouds situations (424 W/m2), with intermediate values in clear-sky conditions (375 W/m2). Seasonal variations (Figure 1) show that spring and summer, characterized by maximum monthly mean GHI values, are associated with lower influence of clouds but relatively high levels of AOD (aerosol optical depth) due to frequent continental polluted influence. Diffuse irradiances show highly variable monthly averaged contributions from less than 20% of GHI in clear-sky conditions (from May to August) to more than 90% during winter cloudy-sun situations. From 2010 to 2022, our measurements show significant upward trends in all-sky global GHI for both spring and summer seasons (around + 4 ± 2 W/m2/year), mainly driven by high rises in direct irradiances. Clear-sky global and direct irradiances also show upward trend in summer only. Moreover, over these 13 years, spring 2020 exhibited record values of both mean all-sky GHI (389 W/m2) and clear-sky frequency (34%). These variabilities and trends are further interpretated in terms of clear-sky/cloudy partitions and aerosols changes. Moreover, by combining our measurements with SOLARTDECO, the direct radiative effect of aerosols is calculated for clear-sky and clear-sun with clouds conditions in Lille.
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