Abstract
Understanding how entrainment and mixing shape the cloud droplet size
distribution (DSD) is crucial for understanding the optical properties
and precipitation efficiency of clouds. Different mixing scenarios,
mainly homogeneous and inhomogeneous, shape the DSD in a distinct way
and alter the cloud’s impact on climate. However, the prevalence of
these mixing scenarios and how they vary in space and time is still
uncertain, as underlying processes are commonly unresolved by
conventional numerical models. To overcome this challenge, we employ the
$L^3$ model, which considers supersaturation fluctuations and
turbulent mixing down to the finest relevant lengthscales, making it
possible to represent different mixing scenarios realistically. We
investigate the spatial and temporal evolution of mixing scenarios over
the life cycle of shallow cumulus clouds for varying boundary layer
humidities and aerosol concentrations. Our findings suggest homogeneous
mixing is generally predominant in cumulus clouds, while different
mixing scenarios occur concurrently in the same cloud. Notably,
inhomogeneous mixing increases over the cloud life cycle across all
analyzed cases. The mean and standard deviation of supersaturation are
found to be the most capable indicators of this evolution, providing a
comprehensive insight into the characteristics of mixing scenarios.
Finally, we show inhomogeneous mixing is more prevalent in drier
boundary layers and for higher aerosol concentrations, underscoring the
need for a more comprehensive investigation of how these mixing dynamics
evolve in a changing climate.