Cloud response and feedback processes in stratiform mixed-phase clouds perturbed by ship exhaust

Stratiform mixed-phase clouds (MPCs), which contain both supercooled liquid and ice, play a key role in the energy balance of the Arctic and are a major contributor to surface precipitation. As Arctic shipping is projected to increase with climate change, these clouds may frequently be exposed to local aerosol perturbations of up to 15,000 cm(-3). Yet little consensus exists within the community regarding the key feedback mechanisms induced in MPCs perturbed by ship exhaust, or aerosol in general. Here we show that many known processes identified in the warm-phase stratocumulus regime can be extrapolated to the MPC regime. However, their effect may be compensated, or even undermined, by the following two most relevant processes unique to the MPC regime: (i) increased cloud glaciation via immersion freezing due to cloud condensation nuclei (CCN) induced cloud top radiative cooling and (ii) the continued cycling of ice nucleating particles (INPs) through the cloud and subcloud layer.