Comment on amt-2023-59

Abstract

<strong class="journal-contentHeaderColor">Abstract.</strong> For the observation of the global three-dimensional distribution of aerosol composition and the evaluation of shortwave direct radiative forcing (SDRF) by aerosols, we developed a retrieval algorithm that uses observation data of the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) onboard the Cloud Aerosol Lidar Infrared Pathfinder Satellite Observations (CALIPSO) satellite, and the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard Aqua. The CALIOP-MODIS retrieval optimizes the aerosol composition to both the CALIOP and MODIS observations in the daytime. Aerosols were assumed to be composed of four aerosol components: water-soluble particles (WS), light-absorbing particles (LA), dust (DS), and sea salt (SS). The outputs of the CALIOP-MODIS retrieval are the vertical profiles of the extinction coefficient (EC), single-scattering albedo (SSA), and asymmetry factor (AF) of total aerosols, and the ECs of WS, LA, DS, and SS. Daytime observations of CALIOP and MODIS in 2010 were analysed by the CALIOP-MODIS retrieval. The global means of the aerosol optical depth (AOD) at 532 nm were 0.147 &plusmn; 0.148 for total aerosols (WS+LA+DS+SS), 0.072 &plusmn; 0.085 for WS, 0.027 &plusmn; 0.035 for LA, 0.025 &plusmn; 0.054 for DS, and 0.023 &plusmn; 0.020 for SS. AODs of the CALIOP-MODIS retrieval were between those of the CALIPSO and MODIS standard products in 2010. The global means of SSA and AF were 0.940 &plusmn; 0.038 and 0.718 &plusmn; 0.037; these values are in the range of those reported by previous studies. The horizontal distribution of each aerosol component was reasonable; for example, DS was large in desert regions, and LA was large in the major regions of biomass-burning and anthropogenic aerosol emissions. The AOD, SSA, AF, and fine and coarse median radii of the CALIOP-MODIS retrieval were compared with those of the AERONET products. AOD at 532 and 1064 nm of the CALIOP-MODIS retrieval agreed well with the AERONET products. SSA, AF, and fine and coarse median radii of the CALIOP-MODIS retrieval were not far from those of the AERONET products, but the variations were large, and the coefficients of determination for linear regression between them were small. In the retrieval results for 2010, the clear sky SDRF values for aerosols at the top and bottom of the atmosphere were &ndash;4.99 &plusmn; 3.42 and &ndash;13.10 &plusmn; 9.93 W m^&ndash;2, respectively, and the impact of aerosols on the heating rate was from 0.0 to 0.5 K day^&ndash;1. These results are generally similar to those of previous studies, but the SDRF at the bottom of the atmosphere is larger than that reported previously. Comparison with previous studies showed that the CALIOP-MODIS retrieval results were reasonable with respect to aerosol composition, optical properties, and the SDRF.