Abstract
Abstract. The expedited near-real-time Level 1.5 Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) version 3 products were evaluated against data from the ground-based European Aerosol Research Lidar Network (EARLINET). The statistical framework and results of the three-year evaluation of 48 CALIOP overpasses with ground tracks within a 100 km distance from operating EARLINET stations are presented and include analysis for the following CALIOP classifications of aerosol type: dust, polluted dust, clean marine, clean continental, polluted continental, mixed and/or smoke/biomass burning. For the complete data set comprising both the planetary boundary layer (PBL) and the free troposphere (FT) data, the correlation coefficient (R) was 0.86. When the analysis was conducted separately for the PBL and FT, the correlation coefficients were R = 0.6 and R = 0.85, respectively. From analysis of selected specific cases, it was initially thought that the presence of FT layers, with high attenuated backscatter, led to poor agreement of the PBL backscatter profiles between the CALIOP and EARLINET and prompted a further analysis to filter out such cases; however, removal of these layers did not improve the agreement as R reduced marginally from R = 0.86 to R = 0.84 for the combined PBL and FT analysis, increased marginally from R = 0.6 up to R = 0.65 for the PBL on its own, and decreased marginally from R = 0.85 to R = 0.79 for the FT analysis on its own. This suggests considerable variability, across the data set, in the spatial distribution of the aerosol over spatial scales of 100 km or less around some EARLINET stations rather than influence from elevated FT layers. For specific aerosol types, the correlation coefficient between CALIOP backscatter profiles and the EARLINET data ranged from R = 0.37 for polluted continental aerosol in the PBL to R = 0.57 for dust in the FT.
Highlights
Aerosols have an impact on the global radiative budget directly via scattering and absorbing incoming and reflected solar radiation, and indirectly via the modification of cloud microphysical properties that lead to changes in cloud radiative properties along with cloud lifetimes (Haywood et al, 2003; Yu et al, 2006)
From analysis of selected specific cases, it was initially thought that the presence of free troposphere (FT) layers, with high attenuated backscatter, led to poor agreement of the planetary boundary layer (PBL) backscatter profiles between the CloudAerosol Lidar with Orthogonal Polarization (CALIOP) and EARLINET and prompted a further analysis to filter out such cases; removal of these layers did not improve the agreement as R reduced marginally from R = 0.86 to R = 0.84 for the combined PBL and FT analysis, increased marginally from R = 0.6 up to R = 0.65 for the PBL on its own, and decreased marginally from R = 0.85 to R = 0.79 for the FT analysis on its own
Over 3 years, 48 CALIOP overpasses occurred within a 100 km ground track offset distance from an operating EARLINET station, resulting in 7405 data points for the analysis presented here
Summary
Aerosols have an impact on the global radiative budget directly via scattering and absorbing incoming and reflected solar radiation, and indirectly via the modification of cloud microphysical properties that lead to changes in cloud radiative properties along with cloud lifetimes (Haywood et al, 2003; Yu et al, 2006). The European Centre for Medium-Range Weather Forecasts (ECMWF) is currently evaluating the potential use of an expedited CALIOP Level 1.5 data product (the total attenuated backscatter profile) for assimilation into their global forecasting model IFS-MOZART They found that the root mean square error (RMSE) of PM10 concentrations declined by 54 % when the lidar measurements were used in the assimilation This indicates the importance of evaluating the CALIOP Level 1.5 data by inter-comparing them with ground-based measurements. The inter-comparison of the 532 nm wavelength attenuated backscatter profiles between CALIOP and EARLINET reported here was performed for coincident daytime and night-time measurements
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