How does the cloud fraction response to aerosol change over the diurnal cycle?

Stratocumulus clouds play an important role in the Earth’s energy balance due to their widespread spatial coverage and radiative properties. However, the impact of aerosol on stratocumulus cloud fraction (CF) remains poorly constrained resulting in large uncertainties for the effective radiative forcing due to aerosol cloud interactions (ERF_aci). Stratocumuli undergo a strong diurnal cycle driven by variations in cloud top radiative cooling, which alters the processes sustaining the cloud. Despite this, many previous observational studies have only considered the state of the cloud field during the daytime due to the availability of satellite data.

In this work we use a Lagrangian tracking method, combined with geostationary satellite data, to investigate the CF response to aerosol over the entire
diurnal cycle. Strong variations in the cloud response to aerosol are found with the diurnal cycle. This brings satellite-based studies into closer alignment with ground- and insitu-based measurement campaigns, emphasising the importance of nighttime cloud processes for understanding aerosol cloud interactions and constraining the ERF_aci.