6.4 Deep convective cloud system size and structure: thermodynamic forcing and modification by aerosols

Wednesday, 9 January 2013: 4:45 PM
Room 5ABC (Austin Convention Center)
Eric M. Wilcox, DRI, Reno, NV; and T. Yuan and D. J. Posselt

It has been suggested that the modification of deep convective clouds by aerosols can impact the spatial coverage of anvil and cirrus clouds detraining in the upper-troposphere. The factors influencing the variability of convective cloud scale and structure, however, are poorly understood. Here we explore the relationships among cloud system horizontal scale and structure, environmental convective available potential energy (CAPE), vertical shear of horizontal wind, and aerosol optical thickness (AOT) using collocated MODIS, AMSR-E and MERRA data. The distribution of infrared and microwave brightness temperatures within clouds provide both an objective measure of cloud system scale and clues to the internal structure of the cloud system. It is a combination of the thermodynamic structure of the cloudy environment, the mesoscale structure of cloud systems, and the cloud microphysics that conspire to produce cloud systems of a particular horizontal scale. Using a data base of hundreds of thousands of clouds over the Indian Ocean and South Asia during the winter and summer monsoons a strong quantitative relationship is established between the horizontal scale of cloud systems and the CAPE and shear of the environment. These relationships are distinct for oceanic cloud systems compared to land systems, as well as for daytime compared to nighttime systems over land. Systematic differences in cloud system horizontal scale are also apparent for cloud systems associated with high AOT compared to those associated with low AOT, however the magnitude and even the sign of the difference depends on the CAPE and shear of the environment. This presentation will discuss the physics underlying the differing responses of deep convective cloud system size to aerosols for different thermodynamic environments. We also discuss a strategy for verifying this physics in cloud-resolving models using simulated satellite brightness temperatures.
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