2026/06/05 by Kamal Kant Chandrakar, Hugh Morrison
Environmental Science · Earth and Planetary Sciences · #Atmospheric aerosols and clouds #Atmospheric chemistry and aerosols #Meteorological Phenomena and Simulations
paper · doi:10.1175/jas-d-25-0226.1
Abstract 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 superparticle and bin microphysics schemes to investigate the impacts of aerosol scavenging and physical processing by clouds on drizzle initiation and the cellular transition process. The Lagrangian microphysics simulation with explicit representation of cloud-borne aerosol and scavenging shows significant aerosol processing. Sensitivity simulations using the bin scheme and their comparison with the Lagrangian microphysics simulations suggest that reduced aerosol concentration due to scavenging is a primary microphysical driver for enhanced precipitation and earlier transition to open cells using the Lagrangian scheme. Changes in the aerosol distribution shape through processing do not contribute appreciably to the differences in precipitation rate in a clean condition. A lower droplet activation rate, larger mean radius, and higher cloud water mixing ratios are the initial triggers for faster rain development using the Lagrangian scheme compared to the bin scheme. A positive feedback then accelerates aerosol removal and further rain production using the Lagrangian scheme and, consequently, reduces cloud droplet number, increases mean size, and increases droplet spectral width, leading to a rapid transition to open cellular convection. These results highlight how enhanced droplet activation, likely from the equilibrium assumption for droplet activation, and higher cloud droplet number initially using the Eulerian bin scheme delay open cell formation compared to simulations using the Lagrangian scheme. Significance Statement Stratocumulus clouds play a vital role in Earth system by reflecting solar radiation due to their extensive coverage. Two-way interactions between aerosol particles and clouds influence drizzle formation and the transition from closed cells with solid cloud cover to less-reflective open cells. Traditional cloud models do not explicitly track aerosol mass within cloud and drizzle drops, while newer particle-based models overcome these limitations. Using both model types, this study demonstrates that decreased aerosol concentration from scavenging by cloud and drizzle drops is a primary driver of rain formation and the transition to open cellular structure, while changes in aerosol particle size from processing by cloud and drizzle drops are relatively unimportant in clean aerosol conditions.