Difference in cloud effect on maritime aerosol optical depth between MODIS and CALIPSO-CloudSat cloud fraction over the CERES footprint

Passively sensed aerosol with MODIS data has shown an increase in Aerosol Optical Depth (AOD) over ocean of approximately 100% between clear and overcast when plotted against cloud fraction also obtained from MODIS data over the CERES footprint. This result is consistent using either the MODIS provided AOD or the NESDIS algorithm using MODIS data. There is uncertainty whether this is due to increasing cloud contamination in the retrieval or an actual cloud-effect in the AOD. To improve cloud detection, CALIPSO cloud and aerosol and CloudSat cloud data has been matched with MODIS and then convolved within the CERES footprint. When the MODIS derived AOD is plotted against the CALIPSO-CloudSat derived cloud fraction, the increase of AOD with cloud fraction is significantly reduced; the increase in AOD by changing scenes from 100% clear over a CERES footprint to more than 90% cloud cover is less than 50 percent. When CALIPSO derived AOD is screened by the aerosol type, clean maritime AOD shows a consistent increase with cloud fraction compared to MODIS derived AOD. In this presentation, an understanding of how the AOD distribution changes between binning with the MODIS and the CALIPSO and CloudSat derived cloud fraction will be discussed. In addition, the solar zenith angle dependence of the AOD and cloud fraction relationship will be discussed. Whether or not the relationship depends on solar zenith angle possibly provides key information of the impact of 3D radiative transfer effects to the relationship between cloud fraction and MODIS derived AOD.