An analysis of potential cloud artifacts in MODIS over ocean aerosol optical thickness products

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Abstract
Using spatially and temporally collocated MODerate Resolution Imaging Spectroradiometer (MODIS) products and data from seven AErosol RObotic NETwork (AERONET) sun‐photometer sites, we explored the relationship between MODIS aerosol optical depth and cloud fraction over remote oceans that have been recently reported in the literature. We show that artifacts such as cloud contamination or adjacency effect contribute to the majority of the relationship in clean marine conditions. This cloud fraction effect could result in a 10–20% overestimation in monthly mean aerosol optical depth or aerosol direct forcing values that are derived using MODIS aerosol products over cloud free oceans. It may also explain some of the high optical depth values derived in the mid‐latitude southern oceans. We also suggest that covariances of meteorological phenomenon such as wind or humidity in cloudy regions while logical might only account for a minor portion of the ensemble relationship.