Viability of mixed-phase cloud thinning with prognostic mineral dust in CESM2

Abstract. Mixed-phase cloud thinning (MCT) has been proposed as a regional climate intervention method to offset Arctic warming by reducing the longwave cloud radiative effect of high-latitude winter clouds. While initial studies suggested that MCT could achieve meaningful Arctic cooling using idealized MCT scenarios with prescribed ice-nucleating particle (INP) concentrations, the radiative impact of a more realistic, prognostic seeding aerosol has remained largely unexplored so far. Here we evaluate the viability of MCT using prognostic mineral dust in a global climate model. We conducted a set of 16 sensitivity experiments in the Arctic during the boreal winter (Nov–Feb), varying the dust injection altitude and the seeding rate relative to a control simulation. Mineral dust seeding triggers glaciation of mixed-phase regime clouds, producing a net negative top-of-atmosphere radiative effect, that strengthens with seeding rate, driven by a competition between a positive longwave effect arising from aerosol-radiation interactions (LW ARI), a negative shortwave effect arising from aerosol-radiation interactions (SW ARI), and effects from aerosol-cloud interactions (ACI). Lower seeding altitudes retain more of the seeded dust within the target region and activate a larger fraction of it into cloud droplets, yet produce weaker cloud glaciation and thinning than high-altitude injections. Overall, these results indicate that MCT can produce a meaningful negative top-of-atmosphere radiative forcing over the target region, consistent with the surface-cooling potential suggested by earlier studies, but that both injection altitude and rate influence its efficacy and its side effects.