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. Aerosol–cloud interaction continues to be one of the leadinguncertain components of climate models, primarily due to the lack ofadequate knowledge of the complex microphysical and radiative processes ofthe aerosol–cloud system. Situations when light-absorbing aerosols suchas carbonaceous particles and windblown dust overlay low-level cloud decksare commonly found in several regions of the world. Contrary to the knowncooling effects of these aerosols in cloud-free scenario over darkersurfaces, an overlapping situation of the absorbing aerosols over the cloudcan lead to a significant level of atmospheric absorption exerting a positiveradiative forcing (warming) at the top of the atmosphere. We contribute to thistopic by introducing a new global product of above-cloud aerosol opticaldepth (ACAOD) of absorbing aerosols retrieved from the near-UV observationsmade by the Ozone Monitoring Instrument (OMI) onboard NASA's Aura platform.Physically based on an unambiguous “color ratio” effect in the near-UVcaused by the aerosol absorption above the cloud, the OMACA (OMI above-cloudaerosols) algorithm simultaneously retrieves the optical depths of aerosolsand clouds under a prescribed state of the atmosphere. The OMACA algorithmshares many similarities with the two-channel cloud-free OMAERUV algorithm,including the use of AIRS carbon monoxide for aerosol typeidentification, CALIOP-based aerosol layer height dataset, and an OMI-basedsurface albedo database. We present the algorithm architecture, inversionprocedure, retrieval quality flags, initial validation results, and resultsfrom a 12-year long OMI record (2005–2016) including global climatology ofthe frequency of occurrence, ACAOD, and aerosol-corrected cloud opticaldepth. A comparative analysis of the OMACA-retrieved ACAOD, collocated withequivalent accurate measurements from the HSRL-2 lidar for the ORACLES PhaseI operation (August–September 2016), revealed a good agreement( R =  0.77, RMSE  =  0.10). The long-term OMACA record reveals severalimportant regions of the world, where the carbonaceous aerosolsfrom the seasonal biomass burning and mineral dust originated over thecontinents are found to overlie low-level cloud decks with moderate(0.3 < ACAOD < 0.5, away from the sources) to higherlevels of ACAOD (> 0.8 in the proximity to the sources), including the southeastern Atlantic Ocean,southern Indian Ocean, Southeast Asia, the tropical Atlantic Ocean off the coastof western Africa, and northern Arabian sea. Nosignificant long-term trend in the frequency of occurrence of aerosols abovethe clouds and ACAOD is noticed when OMI observations that are free from the“row anomaly” throughout the operation are considered. If not accounted for,the effects of aerosol absorption above the clouds introduce low bias in theretrieval of cloud optical depth with a profound impact on increasing ACAODand cloud brightness. The OMACA aerosol product from OMI presented in thispaper offers a crucial missing piece of information from the aerosol loadingabove cloud that will help us to quantify the radiative effects of cloudswhen overlaid with aerosols and their resultant impact on cloud properties andclimate.

A 12-year long global record of optical depth of absorbing aerosols above the clouds derived from the OMI/OMACA algorithm