Diurnal Patterns in the Observed Cloud Liquid Water Path Response to Droplet Number Perturbations

Aerosol-cloud-interactions remain a large climate uncertainty; especially uncertain is the liquid water path (LWP) adjustment to varying aerosol concentrations in stratocumulus (StCu). Physically, LWP can take two pathways depending on initial aerosol state: 1) LWP may increase with increasing aerosol concentrations due to precipitation suppression or 2) LWP may decrease with increasing aerosol concentrations due to cloud-top entrainment. Therefore, observations of the real-world evolution of LWP in varying aerosol environments are needed to resolve the nature of the correlation between LWP and aerosol. We address this by analyzing a large ensemble of 3-day parcel trajectories over the southeast Pacific within the GOES-16 field of regard. Following StCu that are less likely to be precipitating (lowest initial LWP), we find that LWP decreases faster at high initial cloud droplet number concentrations (N_d) than at low N_d (i.e. a negative LWP adjustment). While this is consistent with prior idealized nocturnal LES, the overall adjustment of LWP to N_d is faster than and never reaches the magnitudes of that from LES.