Testing sea salt injections into marine stratocumulus as a geoengineering option

The negative radiative forcing of the global climate system imposed by marine boundary layer clouds is largely controlled by their macrophysical properties such as the cloud cover, thickness and albedo. Changes in aerosols are known to influence the microphysics of stratocumulus clouds thereby affecting the macrophysical properties through complex interactions between the aerosols, the cloud microphysics and the cloud dynamics.

Geoengineering approaches have been suggested that utilize the indirect aerosol effects on clouds (i.e., the cloud albedo and cloud lifetime effect) to counteract global warming artificially by injecting additional sea salt aerosols into marine stratocumulus clouds. Yet, the complex interactions between aerosols, clouds and radiation are not very well understood which in turn questions the outcome of this geoengineering proposal.

In this contribution we aim to simulate the response of marine stratocumulus clouds to artificial aerosol perturbations in the marine boundary layer with a numerical model and investigate the change in radiative forcing imposed by the geoengineered clouds.

For the control simulation we focus on a case study from the VOCALS-Rex campaign in the South-east Pacific during October 2008 where detailed observations from in situ and remote sensing platforms are available for model evaluation. We then conduct several sensitivity experiments by changing the aerosol emissions to assess the effect of the aerosol perturbations on the cloud radiative forcing and the mesoscale circulations. The numerical simulations are performed with a mesoscale regional model with a coupled double-moment aerosol-cloud-microphysics parameterization. The model is driven by meteorological initial and boundary conditions from the ECMWF analysis archive.