Type-Dependent Aerosol Impact on the Properties of Ice Clouds

The interactions between aerosols and ice and mixed-phase clouds represent one of the largest uncertainties in global radiative forcing from pre-industrial time to the present. A major reason for the substantial uncertainty is the distinct features of different cloud and aerosol types and their complicated interactions. In this study, we investigate the impact of aerosols on properties of ice/mixed-phase clouds and the associated precipitation using 9-year continuous observations from multiple satellite-borne sensors, taking into consideration different cloud and aerosol types. We find that the responses of properties of ice and mixed-phase clouds to aerosols differ significantly according to cloud and aerosol types. For convective clouds and anvil ice clouds generated from them, cloud thickness, cloud optical thickness (COT), and ice cloud fraction increase and decrease with small-to-moderate and high aerosol loadings, respectively. For in-situ formed ice clouds, however, the preceding cloud properties increase monotonically and more sharply with aerosol loadings. When aerosols are decomposed into different types, an increase in the loading of smoke aerosols generally leads to a decrease in COT of convection-generated ice clouds, while the reverse is true for dust and anthropogenic pollution. In contrast, an increase in the loading of any aerosol type can significantly enhance COT of in-situ formed ice clouds. We also show distinct impact of various aerosol types on the precipitation associated with different cloud types. The modulation of the aerosol impacts by cloud/aerosol types is demonstrated and reproduced by simulations using the Weather Research and Forecasting (WRF) model. Adequate and accurate representations of the impact of different cloud/aerosol types in climate models are crucial for reducing the substantial uncertainty in assessment of aerosol-induced radiative forcing and water cycle changes.