Environmental Effects on Aerosol-Cloud Interaction in non-precipitating MBL Clouds over the Eastern North Atlantic

• Main Authors: Zheng, Xiaojian, Xi, Baike, Dong, Xiquan, Wu, Peng
• Format: Text
• Language: English
• Published: 2021
• Subjects: North Atlantic
• Online Access: https://doi.org/10.5194/acp-2021-391; https://acp.copernicus.org/preprints/acp-2021-391/

Over the eastern north Atlantic (ENA) ocean, a total of 20 non-precipitating single-layer marine boundary layer (MBL) stratus and stratocumulus cloud cases 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 at 0.2 % supersaturation ( N CCN ,0.2 % ) 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 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-precipitating MBL clouds.