Aerosol Impacts on Idealized Subtropical Marine Clouds: From Overcast Stratocumulus to Broken Cloud Transitions

Subtropical marine clouds are a focal area in climate research due to their pivotal role in shaping the Earth's energy balance. The cooling influence of overcast low marine clouds is marked by their emission of outgoing longwave radiative flux, comparable in intensity to the ocean surface, and efficient reflection of solar insolation. These clouds, however, undergo cloud breakup within a few days driven by rising sea surface temperatures (SST) and evolving meteorological dynamics as air masses flow equatorward along the trade winds. Notably, the properties of subtropical marine clouds exhibit sensitivity to aerosol, fundamentally modifying cloud physics and dynamics that determine cloud albedo and lifetime.

In this study, we present a concise summary of outcomes from large-eddy simulations involving two distinct yet representative idealized scenarios of subtropical marine clouds. Encompassing a range of meteorological conditions, the scenarios encompass overcast steady clouds and clouds undergoing transition via breakup with increasing SST and evolving large-scale conditions. These scenarios are systematically examined through simulations both with and without aerosol injections, providing insights into the intricate response to aerosol perturbations. Our findings underscore the contrasting nature of key processes inherent in these two cloud scenarios. Within the overcast shallow stratocumulus, where boundary layers are well mixed, intensified cloud-top entrainment by aerosol perturbation leads to negative cloud adjustments, partially offset or excessively countered by compensatory adjustment in surface heat fluxes and precipitation. In transitioning clouds, a significant interplay emerges between aerosol-cloud interactions and large-scale circulation. This intricate interaction, driven by buoyancy adjustments, exerts a profound influence on the transition mode. As clouds transition, the influence of cloud-top entrainment adjustment diminishes due to weak turbulence generation from cloud top while the dominance of surface buoyancy production adjustment becomes more pronounced.

This presentation unveils the intricate interplay between clouds and aerosols in scenarios ranging from overcast shallow clouds to transitioning clouds during breakup, with various background meteorological conditions. By shedding light on these complex dynamics, we better understand the relationship between aerosol perturbations and the behavior of subtropical marine clouds.