Aerosol effects on warm cumulus cloud fields using a center-of-gravity vs. water mass phase space

Abstract:

Warm convective cloud fields are studied using large eddy simulations. Individual clouds were tracked a posteriori from formation to dissipation using a 3D cloud tracking algorithm and results are presented in the phase-space of center of gravity altitude versus cloud liquid water mass (CvM space). The CvM space (see the figure below) is shown to contain rich information on cloud field properties, such as interactions between clouds, partition to growing, precipitating, and dissipating clouds, degree of adiabaticity, common dissipation pathways, and precipitation efficiency and yields.

We show clear effect of the aerosol loading on the shape and size of CvM clusters, with the majority of water mass in the clean case (panel a) attributed to precipitating clouds and the majority of water mass in the polluted case (panel b) attributed to growing clouds. We also find fundamental differences in the CvM space between simulations results using bin versus bulk microphysical schemes, with bin scheme expressing much higher sensitivity to changes in aerosol concentrations.

Using the bin microphysical scheme, we find that the increase in cloud center of gravity altitude with increase in aerosol concentrations occurs for a wide range of cloud sizes, except for the smallest clouds. This is attributed to reduced sedimentation, increased buoyancy and vertical velocities, and increased environmental instability, all of which are tightly coupled to inhibition of precipitation processes and subsequent feedbacks of clouds on their environment.