Aerosol effects on ice clouds: Can the traditional concept of aerosol indirect effects be applied to aerosol-cloud interactions in cirrus clouds?

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Description

Cirrus clouds regularly cover 20-25% of the globe and thus play an important role in the Earth’s radiation budget. This indicates that aerosol effects on cirrus clouds can have a substantial impact on the variation of global radiative forcing if ice-water path (IWP) changes. This study examines the aerosol indirect effect (AIE) through changes in the IWP in a case of cirrus clouds. We use a cloud-system resolving model (CSRM) coupled with a double-moment representation of cloud microphysics. Intensified interactions among the cloud ice number concentration (CINC), deposition, and dynamics play a critical role in the IWP increases due to aerosol increases. Increased aerosols lead to increased CINC, providing the increased surface area of ice crystals where water vapor deposits. This increases deposition and thus depositional heating to produce stronger updrafts, leading to the increased IWP. The conversion of ice crystals to aggregates through auto-conversion and accretion plays a negligible role in the IWP responses to aerosols, as does the sedimentation of aggregates. The sedimentation of ice crystals plays more important role in the IWP response to aerosol increases than the sedimentation of aggregates, but not more than the interactions among the CINC, deposition, and dynamics.