Entrainment and associated mixing (i.e., entrainment-mixing) have been shown to impact drop size distributions. However, most past studies have focused on warm clouds and have not considered the impacts on mixed phase clouds (i.e., those containing liquid and ice particles). This study characterizes the impacts of entrainment-mixing on mixed phase cloud properties over the Southern Ocean using in situ observations. By taking advantage of strong correlations between droplet clustering and entrainment-mixing, a clustering metric is used as a proxy to assess the degree of mixing. This maximizes the available sample size for a statistical analysis of entrainment-mixing impacts on mixed phase properties. A positive relationship is found between the magnitude of droplet clustering and large ice concentrations (those with maximum dimensions greater than similar to 300 mu m), suggesting entrainment-mixing enhances the Wegener-Bergeron-Findeisen (WBF) process. Particle size distributions are averaged over different ranges of liquid (liquid water content (LWC)) to total water content (TWC) ratio. Since the ratio is expected to transition from 1 to 0 during glaciation, differences in the distributions provide insight into the relation of entrainment-mixing to mixed phase cloud evolution. Mixed phase samples with the greatest large ice concentrations occur at LWC/TWC < 0.4 in low clustering regions. However, these samples are relatively few, whereas high clustering regions have a greater frequency of samples with LWC/TWC < 0.4. This suggests sublimation/vapor sinks associated with entrainment can counteract the enhanced WBF. In high clustering regions, distributions of small droplets are relatively constant and large droplets (>30 mu m) are preferentially removed as LWC/TWC transitions from 1 to 0. Mixed phase clouds (i.e., liquid and ice particles within the same sample volume) have been notoriously difficult to represent in weather and climate models. To improve simulations, continued exploration of mixed phase properties and processes using high resolution observations is necessary. This study uses in situ observations to explore the potential impacts of entrainment and the associated mixing (i.e., entrainment-mixing) on mixed phase microphysical properties. In situ observations are taken primarily from low-level clouds over the Southern Ocean acquired during the Southern Ocean Cloud-Radiation Aerosol Transport Experimental Study. This study takes advantage of the fact that cloud drop clustering is strongly correlated with entrainment-mixing. Namely, drop clustering is used as a proxy variable to diagnose entrainment-mixing and the associated impacts on mixed phase clouds. Results suggest entrainment-mixing can result in an enhanced Wegener-Bergeron-Findeisen (WBF) process, as seen by a positive relationship between drop clustering and large ice concentrations. However, the enhanced WBF process can be offset by sufficiently strong entrainment-mixing.
