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. All-sky direct aerosol radiative effects (DARE) play a significantyet still uncertain role in climate. This is partly due to poorly quantifiedradiative properties of aerosol above clouds (AAC). We compute globalestimates of shortwave top-of-atmosphere DARE over opaque water clouds(OWCs), DARE OWC , using observation-based aerosol and cloud radiativeproperties from a combination of A-Train satellite sensors and a radiativetransfer model. There are three major differences between ourDARE OWC calculations and previous studies: (1) we use thedepolarization ratio method (DR) on CALIOP (Cloud–Aerosol Lidar withOrthogonal Polarization) Level 1 measurements to compute the AAC frequenciesof occurrence and the AAC aerosol optical depths (AODs), thus introducingfewer uncertainties compared to using the CALIOP standard product; (2) weapply our calculations globally, instead of focusing exclusively on regionalAAC “hotspots” such as the southeast Atlantic; and (3) instead of thetraditional look-up table approach, we use a combination of satellite-basedsensors to obtain AAC intensive radiative properties. Our results agree withprevious findings on the dominant locations of AAC (south and northeastPacific, tropical and southeast Atlantic, northern Indian Ocean and northwest Pacific), the season of maximum occurrence and aerosol optical depths (amajority in the 0.01–0.02 range and that can exceed 0.2 at 532 nm) across the globe. We find positive averages of global seasonal DARE OWC between0.13 and 0.26 W m −2 (i.e., a warming effect on climate). Regionalseasonal DARE OWC values range from −0.06  W m −2 in theIndian Ocean offshore from western Australia (in March–April–May) to2.87 W m −2 in the southeast Atlantic (inSeptember–October–November). High positive values are usually paired withhigh aerosol optical depths ( >0.1 ) and low single scattering albedos ( ), representative of, for example, biomass burning aerosols. Because we usedifferent spatial domains, temporal periods, satellite sensors, detectionmethods and/or associated uncertainties, the DARE OWC estimates inthis study are not directly comparable to previous peer-reviewed results.Despite these differences, we emphasize that the DARE OWC estimatesderived in this study are generally higher than previously reported. Theprimary reasons for our higher estimates are (i) the possible underestimateof the number of dust-dominated AAC cases in our study; (ii) our use of Level1 CALIOP products (instead of CALIOP Level 2 products in previous studies)for the detection and quantification of AAC aerosol optical depths, whichleads to larger estimates of AOD above OWC; and (iii) our use of gridded 4 ∘ × 5 ∘ seasonal means of aerosol and cloud properties in ourDARE OWC calculations instead of simultaneously derived aerosol andcloud properties from a combination of A-Train satellite sensors. Each ofthese areas is explored in depth with detailed discussions that explain boththe rationale for our specific approach and the subsequent ramifications for ourDARE calculations.

Estimations of global shortwave direct aerosol radiative effects above opaque water clouds using a combination of A-Train satellite sensors