Stratocumulus clouds, a key component of global climate, are sensitive
to aerosol properties. Aerosol-cloud-precipitation interactions in these
clouds influence their closed-to-open cell dynamical transition and
hence cloud cover and radiative forcing. This study uses large-eddy
simulations with Lagrangian super-particle and bin microphysics schemes
to investigate impacts of aerosol scavenging and physical processing by
clouds on drizzle initiation and the cellular transition process. The
simulation using Lagrangian microphysics with explicit representation of
cloud-borne aerosol and scavenging shows significant aerosol processing
that impacts precipitation generation and consequently the
closed-to-open cell transition. Sensitivity simulations using the bin
scheme and their comparison with the Lagrangian microphysics simulation
suggest that reduced aerosol concentration due to scavenging is a
primary microphysical catalyst for enhanced precipitation using the
Lagrangian scheme. However, changes in the aerosol distribution shape
through processing also contribute appreciably to the differences in
precipitation rate. Thus, both aerosol scavenging and processing drive
earlier rain formation and the transition to open cells in the
simulation with Lagrangian microphysics. This study also highlights a
shortcoming of Eulerian bin microphysics producing smaller mean drop
radius and cloud water mixing ratios owing to numerical diffusion.
Initially larger mean radius and cloud mixing ratios using the
Lagrangian scheme induce faster rain development compared to the bin
scheme. A positive feedback in turn accelerates aerosol removal and
further rain production using the Lagrangian scheme and, consequently,
reduced cloud droplet number, increased mean size, and increased droplet
spectral width.