Evidence for secondary ice production in Southern Ocean open cellular convection

Abstract

Ice particles present at temperatures warmer than −9 °C were encountered in unexpectedly high number concentrations (up to 54 L−1) by an instrumented aircraft over the Southern Ocean (SO), off the southwest coast of Tasmania, Australia, on 7 September 2013. The sampled clouds were precipitating, characterized by mixed-phase, open-cellular shallow convection. These clouds were present within a large-scale environment characterized by cold air advection, in a pristine air mass for over 72 h. Using a Cloud and Aerosol Spectrometer, aerosol particles (diameters > 0.6 µm) size and number concentrations were measured and ice nucleating particle (INP) number concentrations were estimated with a rec..