Depicting the regime of different aerosol types in NAMEE (North Africa - Middle East - Europe) based on CALIOP-CALIPSO retrievals

The aerosol-induced perturbations of the Earth-Atmosphere system radiation budget are determined by the load and the nature of the suspended particles. Therefore, it is crucial to identify accurately various aerosol types characterized by different optical properties, which regulate aerosol-radiation interactions. The discrimination among aerosol species can be sufficiently achieved from ground-based observations in contrast to those derived by satellite sensors subjected to several limitations. In the case of CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation) and the CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) aerosol product, such deficiencies are attributed either to the erroneous classification of the detected aerosol layers or to the incorrect modelling of aerosol microphysics for particular aerosol subtypes.

In the present study, we are developing and demonstrating a simplified aerosol classification scheme capable of identifying dust, marine, clean continental, smoke and urban/smoke particles. For its development, we are relying on quality-assured CALIOP-CALIPSO vertically resolved retrievals (Level 2, Version 4.20) of the backscatter coefficient and the linear particle depolarization extracted from the LIVAS (LIdar climatology of Vertical Aerosol Structure for space-based lidar simulation studies) database. In addition, simulated relative humidity (RH) profiles from MERRA-2 (Modern-Era Retrospective analysis for Research and Applications version 2) as well as the land cover type from the IGBP (International Geosphere–Biosphere Programme) dataset are jointly processed. Moreover, we are applying a discrimination technique suitable for decoupling the individual components of dust-marine and dust-smoke-urban categories, assuming external aerosol mixtures. Finally, for each defined aerosol type we are setting a representative lidar ratio (LR), derived via an extensive literature review of studies utilizing ground-based measurements, required for the derivation of the extinction coefficient at 532nm. Our algorithm is implemented within the NAMEE (North Africa – Middle East – Europe) domain, hosting a variety of aerosol species of natural and anthropogenic origin, and it is applied over a 14-year period (2007-2020).

At the first step of the analysis we are evaluating the columnar aerosol optical depth (AOD), derived from our new classification algorithm, against the corresponding measurements from the ground-based AERONET stations situated within NAMEE as well as versus quality-assured spaceborne (MODIS-Aqua) retrievals. In order to justify the added-value of our approach, we are comparing the assessment results against those obtained from the corresponding evaluation of the raw CALIOP-CALIPSO retrievals using the default and upgraded LRs. After final adjustments in our classification scheme, the aerosol type dependent backscatter and extinction coefficient profiles are gridded at 1° x 1° spatial resolution and on a monthly basis for presenting a 4D climatology within the NAMEE domain. Finally, for each aerosol category we are defining the optical properties required as inputs in a radiative transfer model for estimating the aerosol-induced direct radiative effects within the Earth-Atmosphere system.           

Acknowledgements: Authors acknowledge support by the Hellenic Foundation for Research and Innovation (H.F.R.I.) under the “2nd Call for H.F.R.I. Research Projects to support Post-Doctoral Researchers” (Project Acronym:  ATLANTAS, Project number:  544).