Aerosol First Indirect Effects: Uncertainties and Influential Factors as Inferred from Ample Measurements

By using the extensive measurements of aerosol, cloud, and meteorological variables from multiple Atmospheric Radiation Measurement (ARM) Climate Research Facility (ACRF) sites and satellite sensors, the uncertainties of AIE and its influence factors (e.g. larger scale dynamic and thermodynamic conditions, aerosol swelling effects, aerosol composition, etc.) were systematically investigated. The significant AIEs were observed from surface measurements over southeastern China, while satellite results usually given the opposite results. A opposite dependence of AIE on atmospheric stability estimated from surface and satellite cloud property retrievals was found, which likely explains some major discrepancies in past studies concerning aerosol-cloud interactions from surface and satellite-based measurements. The magnitude of the FIE for aerosol particles with stronger aerosol hygroscopicity (higher inorganic fraction) is systematically larger than that for aerosol particles with weaker aerosol hygroscopicity (lower inorganic fraction). A one-unit enhancement in the aerosol scattering coefficient by the swelling effect leads to a systematic underestimation of the FIE by about 23%. This likely contributes significantly to the systematic difference between observation-based, especially satellite-based, estimates of the FIE and those simulated by general circulation models.