Aerosol-Mediated Glaciation of Mixed-Phase Clouds: Steady-State Laboratory Measurements

Abstract

What concentration of ice-nucleating particles is required to completely glaciate a typical atmospheric supercooled liquid cloud? This seemingly esoteric question has far reaching implications, as the ratio of liquid to ice in these clouds governs, for example, their influence on Earth's radiation budget and their precipitation efficiency. Microphysical properties of steady-state mixed-phase clouds formed in a laboratory convection chamber are observed using digital holography. It is observed that the ratio of ice to total water content of steady-state mixed-phase clouds is determined by the concentration of ice-nucleating aerosol particles. Existing theory is adapted to show such clouds result from a balance between the thermodynamic forcing (i.e., the source of excess water vapor that is condensing to liquid and ice) and the number and size of particles that become ice (i.e., the ice integral radius). The measurements quantitatively support the Korolev-Mazin conditions for existence of mixed-phase clouds.