Cloud Response and Feedback processes in stratiform mixed-phase clouds perturbed by ship exhaust

A. Possner, A.M.L. Ekman, U. Lohmann

Stratiform mixed-phase clouds, which contain both liquid and ice, play a key role in the energy balance of the Arctic climate 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 aerosol perturbations of up to 15’000 cm-3 (locally). Yet, little consensus exists within the community regarding the key feedback mechanisms induced in mixed-phase clouds perturbed by ship exhaust, or aerosol in general. Here we show that many well understood processes identified in the warm-phase stratocumulus regime can be extrapolated to the mixed-phase regime. However, their effect may be compensated, or even undermined, by the following two most relevant processes unique to the mixed-phase stratocumulus regime: (i) increased cloud glaciation via immersion freezing due to CCN induced cloud top radiative cooling and (ii) the continued cycling of INP through the cloud and sub-cloud layer.

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