Understanding physical mechanisms of aerosol-driven liquid water path adjustments in marine stratocumulus observed in ARM EPCAPE using large-eddy simulations
Dr. Haipeng Zhang, Goddard Earth Sciences Technology and Research II (GESTAR II) Center.
Marine stratocumulus clouds exert a large and uncertain negative radiative forcing on Earth’s climate, yet the physical mechanisms underlying aerosol-driven liquid water path (LWP) adjustments remain poorly understood. Recent analysis of ARM Eastern Pacific Cloud Aerosol Precipitation Experiment (EPCAPE) observations using an explainable machine learning framework has revealed a negative LWP response to increasing cloud droplet number concentration, consistent with entrainment drying effects, and demonstrated that this response varies nonlinearly with the thermodynamic environment. However, these statistical approaches cannot establish robust causality or isolate the individual physical processes responsible for the observed sensitivities and their meteorological dependence. This project addresses these limitations by conducting a suite of observation-constrained large-eddy simulations initialized from EPCAPE cases with cloud droplet number concentration perturbations across a range of thermodynamic conditions. The results will provide process-level mechanistic understanding of LWP adjustments and their dependence on the thermodynamic environment, directly complementing and extending the observational findings from EPCAPE, and offering physical insights needed to improve aerosol–cloud interaction parameterizations in Earth System Models.