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

Friday, 18 December 2015
Poster Hall (Moscone South)
Reuven Haim Heiblum1, Ilan Koren2, Orit Altaratz2, Graham Feingold3, Alexander B Kostinski4, Alexander Khain5, Mikhail Ovchinnikov6, Erick Fredj7 and Guy Dagan1, (1)Weizmann Institute of Science, Earth and Planetary Sciences, Rehovot, Israel, (2)Weizmann Institute of Science, Rehovot, Israel, (3)NOAA Boulder, Boulder, CO, United States, (4)Michigan Technological University, Houghton, MI, United States, (5)Hebrew University of Jerusalem, Jerusalem, Israel, (6)Pacific Northwest National Laboratory, Richland, WA, United States, (7)The Jerusalem College of Technology, Jerusalem, Israel
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.