Assessing Inversion Products Differences in co-Located SKYNET and AERONET Sites

Continuous observations at high spatial and temporal resolutions over the globe are necessary to characterise the high variability of atmospheric aerosol in space and time. At the global scale, two of the most widely used photometer networks for aerosol studies, operating since the end of 90’s, are SKYNET (Nakajima et al., 2020) and AERONET (AErosol ROboc NETwork; Holben et al., 1998). Both the networks provide, in near real time, day and night columnar aerosol optical and physical properties, with open access from their respective websites. The official instruments are robotic multichannel radiometers produced by PREDE and CIMEL, respectively. Both instruments measure solar (and lunar for some of them) direct irradiance and the angular distribution of sky diffuse radiation. Over the last decades, both  networks have been supported by space agencies, as they represent essential tools for Fiducial Reference Measurements  for  satellite aerosol retrievals (e.g. Sentinel-3, TROPOMI, EarthCare). However, recent comparisons of the respective aerosol retrievals (e.g., Khatri et al., 2016; Nakajima et al., 2020; Kudo et al., 2021) revealed discrepancies in some products. This study aims to analyse common long-term datasets from both the  SKYNET and AERONET instruments, at selected sites where the two instruments operate co-located: downtown Rome and Rome-Tor Vergata (Italy), Valencia (Spain), Lindenberg (Germany) and Chiba (Japan). All inversion products from simultaneous co-located measurements will be compared, and potential discrepancies will be investigated. In particular,  we will focus on Single Scattering Albedo, complex Refractive Index, Asymmetry Factor, volume Size Distribution, Depolarization and Lidar Ratios, precipitable water vapour content and diurnal and nocturnal (where available) Aerosol Optical Depths (AOD). For all  products, a statistical analysis of the differences will be carried out across different AOD classes using both AERONET Level 1.5 and 2.0  and SKYNET Level 2 datasets.  The influence of meteorological parameters (e.g.  relative humidity, wind direction and intensity, and ambient temperature) will also be evaluated. Finally, the climatology of some aerosol products from both networks will be compared.