It has been widely recognized that the aerosol indirect effect (AIE) is one of the largest uncertainties of all known climate forcing mechanisms. The AIE is subject to the influences of interactions and feedbacks with aerosol properties (e.g., aerosol vertical distribution, aerosol size distribution, aerosol chemical properties) and dynamical conditions (e.g., vertical velocity and vertical wind shear). Based on the multiple ground- and satellite-based observations, we have investigated such diverse factors and ensuing uncertainties without accounting for them. Major sources of uncertainty were found to stem from the use of aerosol optical quantities as a proxy for the cloud condensation nuclei (CCN), as well as ignorance of the atmospheric dynamics. The AIE and its radiative forcing tends to be underestimated when ambient aerosol optical quantities are used to estimate the AIE. A positive relationship between the AIE and atmospheric stability is derived from surface-based estimation, while the satellite measurements give the opposite relationship. The findings is likely to explain some major discrepancies in past studies concerning aerosol-cloud interactions from the observations and simulations, as well as from surface and satellite-based measurements.
613 Seminar Series Coordinators