Geoengineering marine stratocumulus to increase cloud albedo: where, when and whether to inject aerosols?

Vast areas of the oceanic surface are covered by stratocumulus (Sc) clouds, reducing solar heating to the ocean and marine boundary layer. It has been argued that a 4% increase in the amount or a 0.06 increase in cloud albedo of Sc can offset the warming by atmospheric CO2 doubling. Satellite imagery of marine Sc regions shows the recurrence of striking mesoscale cellular structures exhibiting both closed- and open-cell cloud patterns. The closed cells are more reflective than open cells. Recent observational and modeling studies have suggested that open cells appear to be initiated by precipitation in clean environments while Sc clouds in polluted regions prefer the closed cellular structure. The possibility of mitigation of global warming by injecting aerosols to marine Sc to brighten less reflective clouds, to prevent the formation of open cells or even to transform open cells to closed ones has recently been raised. Using a high-resolution version of the Weather Research and Forecasting (WRF) model, we investigated the impact of aerosol-cloud-precipitation interactions and dynamical feedbacks on the formation and evolution of the aforementioned open and closed cells in the marine Sc regime and examined the effectiveness of different methods for aerosol injection. We will demonstrate how injected aerosol particles can affect cloud microphysics and macrophysics under various meteorological conditions. We will also use simulation results to explore when and where seeding of Sc is most effective and whether an influx of aerosols can transform open cells to closed ones in marine Sc clouds, thereby increasing sunlight reflection and cooling Earth's surface.