Quantification of aerosol influence on day-to-day mesoscale variability of shallow convection

A major uncertainty in the cloud-feedback to a warming climate can be attributed to shallow convection in the trades. With recent advances in observational and computational resources, the potential impact of the mesoscale organization of these clouds became apparent. While the processes leading to the mesoscale organization are not resolved in current climate models, observations of these features and more importantly their interaction with different scales became available through field campaigns like EUREC4A.

This study quantifies the ability of large-domain large-eddy simulations to represent the observed mesoscale variability in cloudiness. By using forward operators to mimic the observations, we show that the stratiform cloud amount and precipitation frequency remain challenging to simulate at hectometre resolutions. Despite these challenges, the simulations show a similar sensitivity in cloud distribution to environmental conditions.

By perturbing the 41 days simulation with a 13-fold increase in CCN concentration we quantify the sensitivity of the mesoscale cloud organisation to changes in precipitation and show the strong influence on the cold-pool driven cloud formations. We further emphasise the importance to correctly represent the mesoscale processes in climate simulations by showing that changes in cloud-radiative effects due to aerosol changes vary day-by-day with varying contributions from changes in cloud albedo and cloud fraction.