Aerosol-Cloud Interactions in Marine Boundary Layer Clouds based on Aircraft and Ground-based Measurement over Eastern North Atlantic

The aerosol-cloud interactions in marine boundary layer (MBL) clouds over the Eastern North Atlantic (ENA) ocean are examined using the aircraft in-situ measurements from the DOE ARM ACE-ENA field campaign during Summer 2017 and Winter 2018, and the ground-based measurements and retrievals from ARM ENA site during 2015 - 2019. The combined measurements are used to investigate the relationships between surface measured cloud condensation nuclei (CCN) number concentration (N_CCN) and the cloud droplet number concentration (N_c). The effective supersaturation (S_eff) of each period is determined by comparing the surface measured N_CCN spectra to the in-situ measured in-cloud N_c. Preliminary results show that the S_eff is positively correlated with the strength of boundary layer turbulence. On the one hand, a well-mixed boundary layer more frequently occurs in winter, which is characterized by the higher near-cloud-base updraft as well as larger variation of below-cloud vertical velocity, is favorable to produce higher S_eff. On the other hand, the summertime MBL aerosols over ENA is dominated by sulfate and organic particles which are more readily activated to become CCN, thus, the MBL clouds can be formed at a relative lower during summer. In addition, to study the aerosol-cloud interactions using continuous ground-based measurement, we plan to examine the quantitative relations under different boundary layer turbulence regimes, as well as the influences of thermodynamic forcing, which can be indicated by indexes such as LTS, EIS, and M factor, on the aerosol-cloud interaction, because these indexes are easy to be parameterized.