Numerical simulations of the effects of deep convection on the concentration and size-distribution of aerosol particles at the upper troposphere

A spectral bin microphysical scheme has been implemented into a cloud resolving model to investigate the effects of aerosol layers on cloud development and vertical transport of aerosols by deep convection. The parameterization of ice formation proposed by DeMott et al. (2010) is used for prediction of ice crystals. A convective cloud event occurred on 1 December 2005 in Darwin, Australia is simulated using the coupled model, and is compared with available radar measurements. The results show that the main characteristics of the storm is well reproduced by the model, especially for the horizontal and vertical structure of convective core. Aerosol layers located at five different altitudes are added purposely in order to understand how the aerosols transported to the UT by deep convection are sensitive to origin of the aerosol layers and the effect of aerosol layers on cloud development and dynamic structure of the cloud. The sensitivity tests show that aerosol particles originated from the boundary layer (case LAYER1) can be transported upward more efficiently as compared to that from mid-troposphere, due to the significantly increased vertical velocity in the development stage of convection through reinforced homogeneous freezing of drops. Aerosols enhanced at the altitudes above boundary layer, i.e., cases LAYER2 to LAYER5 have little influence on the cloud dynamical processes, but precipitation increases in most of the cases when an aerosol layer presents, except for the case when the added aerosol appears at 5.4-8.0 km (case LAYER3), in this case, the smaller graupel mass resulted in less precipitation. For aerosol layers at mid-troposphere, the vertical profiles of aerosol appear two peak values after cloud processing, one at their initial layers and the other at the altitude of 12-14 km. Aerosol concentrations at the altitudes of 13.5 km are enlarged by factors of 7.71, 5.36 and 5.16 when aerosol layer exist at 0-2.2 km, 2.2-5.4 km and 5.4-8.0 km, respectively, and Aitken mode and part of accumulation mode (0.1-0.2 μm) particles can be transported to UT. When the layer lofted at the altitude above 12.6 km, upward convective transport has almost no influence on the size distribution of the aerosols at its initial level.