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. Marine boundary layer clouds, including the transition fromstratocumulus to cumulus, are poorly represented in numerical weatherprediction and general circulation models. Further uncertainties in thecloud structure arise in the presence of biomass burning carbonaceousaerosol, as is the case over the southeast Atlantic Ocean, where biomassburning aerosol is transported from the African continent. As the aerosolplume progresses across the southeast Atlantic Ocean, radiative heatingwithin the aerosol layer has the potential to alter the thermodynamicenvironment and therefore the cloud structure; however, limited work hasbeen done to quantify this along the trajectory of the aerosol plume in theregion. The deployment of the first Atmospheric Radiation Measurement (ARM) MobileFacility (AMF1) in support of the Layered Atlantic Smoke Interactions with Cloudsfield campaign provided a unique opportunity to collect observations ofcloud and aerosol properties during two consecutive biomass burning seasonsduring July through October of 2016 and 2017 over Ascension Island (7.96∘ S, 14.35∘ W). Using observed profiles of temperature,humidity, and clouds from the field campaign alongside aerosol opticalproperties from Modern-Era Retrospectiveanalysis for Research and Applications, Version 2 (MERRA-2), as input for the Rapid Radiation Transfer Model (RRTM),profiles of the radiative heating rate due to aerosols and clouds werecomputed. Radiative heating is also assessed across the southeast AtlanticOcean using an ensemble of back trajectories from the Hybrid Single ParticleLagrangian Integrated Trajectory (HYSPLIT) model. Idealized experiments using theRRTM with and without aerosols and a range ofvalues for the single-scattering albedo (SSA) demonstrate that shortwave (SW) heatingwithin the aerosol layer above Ascension Island can locally range between 2and 8 K d−1 depending on the aerosol optical properties, though impactsof the aerosol can be felt elsewhere in the atmospheric column. Whenconsidered under clear conditions, the aerosol has a cooling effect at theTOA, and based on the observed cloud properties at Ascension Island, thecloud albedo is not large enough to overcome this. Shortwave radiativeheating due to biomass burning aerosol is not balanced by additionallongwave (LW) cooling, and the net radiative impact results in a stabilization ofthe lower troposphere. However, these results are extremely sensitive to thesingle-scattering albedo assumptions in models.

Radiative heating rate profiles over the southeast Atlantic Ocean during the 2016 and 2017 biomass burning seasons