(Invited Speaker) A process-modeling study of aerosol-cloud-precipitation interactions in response to controlled seawater spray in marine boundary layer

Vast areas of the oceanic surface are covered by stratocumulus (Sc) clouds. They significantly enhance the reflection of incoming solar radiation back to space, leading to a considerable cooling of the Earth-atmosphere system. It has been argued that a 4% increase in the areal coverage or a 0.06 increase in cloud albedo of Sc clouds can offset the warming by atmospheric CO₂ doubling (Randall et al. 1984; Latham et al. 2008). Acting as cloud condensation nuclei (CCN), aerosol particles can modify cloud albedo, cloud longevity and precipitation efficiency. Recent observational and modeling studies have suggested that aerosol, through its effect on precipitation, can alter cloud cellular structures in marine Sc region, representing a powerful modification of clouds by aerosol.

The possibility of mitigating global warming by spraying sea-salt particles into marine boundary layer to brighten Sc clouds was raised by Latham (1990). The idea has been evaluated by several global climate model studies but their inability to represent cloud-scale dynamics and microphysics raises questions about the validity of the results. Using a high-resolution version of the Weather Research and Forecasting (WRF) model, we investigate the impact of seawater spray on the formation and evolution of marine Sc through aerosol-cloud-precipitation interactions and dynamical feedback. We will demonstrate how injected aerosol particles are transported from the ocean surface into clouds and affect cloud microphysics and macrophysics under various meteorological conditions. We will also use simulation results to explore whether the influx of sea-salt aerosols always enhances cloud albedo and how the performance depends on the distribution of sprayers.