Observing aerosol impacts on tropical deep convective clouds

The indirect effects of aerosols on cloud microphysics and dynamics are complex and not fully understood. An especially challenging part of this problem is the difference in the responses seen in deep convection. While the first aerosol indirect effect seems to be relatively consistent in shallow clouds, the precipitation response in deep convective clouds has at times been found to not be in keeping with aerosol indirect theory. The reduction in warm rain predicted by the second aerosol indirect effect is often mitigated, or even canceled out, by dynamic feedbacks due to changes in the ice phase of the storms. The Cloud Profiling Radar on CloudSat can offer detailed information about the vertical structure of convective clouds. CloudSat data can be combined with the MODIS aerosol index in order to examine any differences in the characteristics of convective clouds that occur with an increase in the background aerosol concentration. The combination of CloudSat and MODIS data has been used successfully to look at the impact of aerosols on shallow clouds. Currently, this idea is being extended to investigate aerosol impacts on deep convective clouds in the tropics, particularly in the regions near the West Pacific warm pool and off the western coast of Africa. It has been seen previously that continental convection tends to have higher reflectivity and deeper mixed phase zones than oceanic clouds. A similar difference should be seen between polluted and clean deep convective clouds. As the ice phase plays an important role in producing convective precipitation, understanding the changes in the ice phase in convective clouds will help move toward a more complete understanding of how convective precipitation responds to changes in aerosol concentration.