Aerosol effects on the lifetime of shallow cumulus

Analysis of hundreds of shallow cumulus clouds generated by large eddy simulations suggests that the effect of aerosol on the lifetime of these clouds is negligible, and much smaller than the variability in cloud lifetime associated with clouds at any given aerosol concentration. Individual clouds, as simulated in a twodimensional single cloud model show a reduction in cloud lifetime with increasing aerosol. It is suggested that evaporation-entrainment feedbacks discussed by Wang et al. (2003), Xue and Feingold (2006), and Jiang et al. (2006) may be responsible for this unexpected result. Higher aerosol concentrations result in higher evaporation rates that tend to increase the vortical circulation around the core of a cumulus cloud and enhance entrainment. This hypothesis will need to be tested against detailed simulations using PDF methods (e.g. Jeffery and Reisner, 2006) and observations.