Preprints
https://doi.org/10.5194/acp-2021-391
https://doi.org/10.5194/acp-2021-391

  07 Jun 2021

07 Jun 2021

Review status: a revised version of this preprint is currently under review for the journal ACP.

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

Xiaojian Zheng1, Baike Xi1, Xiquan Dong1, and Peng Wu2 Xiaojian Zheng et al.
  • 1Department of Hydrology and Atmospheric Sciences, University of Arizona, Tucson, AZ, USA
  • 2Pacific Northwest National Laboratory, Richland, WA, USA

Abstract. 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 (ACIr) 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 ACIr represents the relative change of cloud-droplet effective radius re with respect to the relative change of cloud condensation nuclei (CCN) number concentration at 0.2 % supersaturation (NCCN,0.2 %) in the water vapor stratified environment. The ACIr values vary from −0.004 to 0.207 with increasing precipitable water vapor (PWV) conditions, indicating that re 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 NC and PWV. The environmental effects on ACIr are examined by stratifying the data into different lower tropospheric stability (LTS) and vertical component of turbulence kinetic energy (TKEw) 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 ACIr. The ACIr values under a range of PWV double from low TKEw to high TKEw regime, indicating a strong impact of turbulence on the ACIr. The stronger boundary layer turbulence represented by higher TKEw 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 re. The enhanced NC conversion and condensational growth induced by more intrusions of CCN effectively decrease re, which jointly presents as the increased ACIr. The TKEw median value of 0.08 m2 s−2 suggests a feasible way in distinguishing the turbulence-enhanced aerosol-cloud interaction in non-precipitating MBL clouds.

Xiaojian Zheng et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-391', Anonymous Referee #1, 21 Jun 2021
  • RC2: 'Comment on acp-2021-391', Anonymous Referee #2, 02 Jul 2021
  • RC3: 'Comment on acp-2021-391', Anonymous Referee #3, 08 Jul 2021

Xiaojian Zheng et al.

Xiaojian Zheng et al.

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Short summary
This study uses ground-based observations to investigate the physical processes in the aerosol-cloud interactions in the non-precipitating marine boundary layer clouds, over the eastern north Atlantic ocean. Results show that the cloud responses to the aerosols are diminished with limited water vapor supply, while are enhanced with increasing water vapor availability. The clouds are found to be most sensitive to the aerosol under sufficient water vapor and strong boundary layer turbulence.
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