Precipitating cloud-system response to aerosol perturbations

Description

We simulate aerosol effects on a tropical western Pacific mixed-phase convective cloud system of two-day duration that is well constrained by observations. This facilitates exploration of aerosol-induced changes in precipitation pathways. A tenfold increase in aerosol produces a small (9 %) increase in the simulated precipitation due to an enhancement in convective rain countering a reduction in stratiform rain. A more distinct feature is that in stratiform clouds, precipitation efficiency (PE) and scavenging efficiency (SE) decrease significantly with increasing aerosol. There is very close agreement between PE and SE both temporally and for stratiform versus convective rain. The time required for a perturbed system to relax back to the unperturbed aerosol state is ~10 days, with only weak sensitivity to the magnitude of the aerosol perturbation and the modeled increase (or decrease) in precipitation. The upper tropospheric relaxation time is substantially longer, with implications for direct forcing and heterogeneous chemistry.