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Title: Environmental Effects on Aerosol-Cloud Interaction in non-precipitating MBL clouds over the Eastern North Atlantic
Over the eastern north Atlantic (ENA) ocean, a total of 21 non-drizzling single-layer marine boundary layer (MBL) stratus and stratocumulus cloud caseperiods are selected in order to investigate the impacts of the environmental variables on the aerosol-cloud interaction (ACI_r) using the ground-based measurements from the Department of Energy Atmospheric Radiation Measurement (ARM) facility at the ENA site during the period 2016 – 2018. The ACI_r represents the relative change of cloud-droplet effective radius r_e with respect to the relative change of cloud condensation nuclei (CCN) number concentration (N_CCN) in the water vapor stratified environment. The ACI_r values vary from -0.004 to 0.207 with increasing precipitable water vapor (PWV) conditions, indicating that r_e is more sensitive to the CCN loading under sufficient water vapor supply, owing to the combined effect of enhanced condensational growth and coalescence processes associated with higher N_c and PWV. The environmental effects on ACI_r are examined by stratifying the data into different lower tropospheric stability (LTS) and vertical component of turbulence kinetic energy (TKE_w) regimes. The higher LTS normally associates with a more adiabatic cloud layer and a lower boundary layer and thus results in higher CCN to cloud droplet conversion and ACI_r. The ACI_r values under more » a range of PWV double from low TKE_w to high TKE_w regime, indicating a strong impact of turbulence on the ACI_r. The stronger boundary layer turbulence represented by higher TKE_w strengthens the connection and interaction between cloud microphysical properties and the underneath CCN and moisture sources. With sufficient water vapor and low CCN loading, the active coalescence process broadens the cloud droplet size distribution spectra, and consequently results in an enlargement of r_e. The enhanced N_c conversion and condensational growth induced by more intrusions of CCN effectively decrease r_e, which jointly presents as the increased ACI_r. The TKE_w median value of 0.08 m^2 s^(-2) suggests a feasible way in distinguishing the turbulence-enhanced aerosol-cloud interaction in non-drizzling MBL clouds. « less
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