Regional model simulations of aerosol-cloud interactions in the Southeast Pacific

Satellite observations show a variety of stratocumulus (Sc) cloud morphologies in the Southeast Pacific region ranging from homogeneous, overcast Sc decks to organized broken/unbroken Sc cells with open/closed cellular convection. The rapid transitions in cloud morphologies as they are observed as pockets of open cells (POCs) are often accompanied by strong contrasts in microphysics and precipitation. The cause for POC formation and rapid transitions in cloud microphysical and macrophysical properties are not very well understood and may be linked to mesoscale dynamical feedbacks induced by aerosols.

In this contribution we will investigate the potential of aerosols as well as mesoscale dynamical perturbations in triggering transitions in Sc cloud morphologies in the Southeast Pacific region. We will simulate a POC case that has been observed and sampled by the NCAR/NSF C-130 aircraft during the VOCALS-REx field campaign in October 2008. We will compare the simulated microphysical and macrophysical cloud properties against the in situ microphysical measurements from the aircraft and against satellite observations.

The simulations will be performed with a high-resolution (2 km horizontal grid spacing) regional model, which accounts for aerosol-cloud interactions and local aerosol emissions from the ocean as well as anthropogenic emissions from South America. Sensitivity studies and trajectory analysis will enable us to determine whether the observed POC has been triggered by dynamical feedbacks induced by aerosols or by synoptic-scale/mesoscale dynamical perturbations. Furthermore, we will be able to tell whether the aerosol involved originated from natural or anthropogenic sources.