Effects of Aerosols on Cloud Dynamics and Microphysics simulated numerically

A state-of-the-art hybrid bulk/bin microphysics scheme was developed and coupled to the WRF model. The scheme was rigorously validated against observations from two contrasting cases (a tropical maritime and a mid-latitude continental). The aerosol-cloud model treats all the known modes of cloud droplet initiation and ice-crystal activation. It directly links these nucleation processes with aerosol chemistry and loading. This scheme was used to investigate salient microphysical mechanisms of aerosol indirect effects with focus on glaciated clouds - glaciated clouds aerosol indirect effects.

Results showed that more soluble aerosols inhibit warm rain processes and promote homogeneous droplet and aerosol freezing. This homogeneous freezing raised crystal number concentrations in the upper-troposhphere. The latent heating released during homogeneous freezing of cloud droplets caused strong up-drafts which force up the cloud-top height. Although warm rain production was significantly weakened by more soluble aerosols, snow and graupel production strongly increased in completely glaciated clouds. Thus the total amount precipitation reaching the ground was not significantly altered in continental clouds. However in maritime clouds, the invigoration effect was weak. This is primarily because anthropogenic aerosol increases in maritime atmospheres are not yet high enough to have a strong impact on cloud's microphysical processes compared to their continental counterparts which may have reached saturation.