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Discussion papers
https://doi.org/10.5194/acp-2019-478
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2019-478
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 07 Jun 2019

Submitted as: research article | 07 Jun 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Investigation of Aerosol-Cloud Interactions under Different Absorptive Aerosol Regimes using ARM SGP Ground-Based Measurements

Xiaojian Zheng1, Baike Xi1, Xiquan Dong1, Timothy Logan2, Yuan Wang3,4, and Peng Wu1 Xiaojian Zheng et al.
  • 1Department of Hydrology and Atmospheric Sciences, University of Arizona, Tucson, AZ, USA
  • 2Department of Atmospheric Sciences, Texas A&M University, College Station, TX, USA
  • 3Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA
  • 4Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA

Abstract. The physicochemical properties of aerosols and their impacts on cloud microphysical properties are examined using data collected from the Department of Energy Atmospheric Radiation Measurement (ARM) facility over the Southern Great Plains region of the United States (ARM-SGP). A total of 16 low-level stratus cloud cases under daytime coupled boundary layer conditions are selected. The aerosol-cloud interaction index (ACIr) is used to quantify the aerosol impacts with respect to cloud-droplet effective radius. The mean value of ACIr calculated from all selected samples is 0.145 ± 0.05 and ranges from 0.09 to 0.24 at a range of cloud liquid water paths (LWP = 20–300 g m−2). The magnitude of ACIr decreases with increasing LWP which suggests a cloud microphysical response to diminished aerosol loading presumably due to enhanced collision-coalescence processes and enlarged particle size. In the presence of weak light-absorbing aerosols, the low-level clouds feature a higher number concentration of cloud condensation nuclei (NCCN) and smaller effective radii (re) while the opposite is true for strong light-absorbing aerosols. Furthermore, the mean activation ratio of aerosols to CCN (NCCN / Na) for weakly (strongly) absorbing aerosols is 0.54 (0.45), owing to the different hygroscopic abilities associated with the dominant aerosol species. In terms of the sensitivity of cloud droplet number concentration (Nd) to aerosol loading, the conversion ratio of Nd / NCCN for weakly (strongly) absorptive aerosols is 0.68 (0.54). Consequently, we expect larger shortwave radiative cooling effect from clouds influenced by weakly absorbing aerosols than strongly absorbing aerosols.

Xiaojian Zheng et al.
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Short summary
A total of 16 continental low-level stratiform cloud cases were selected to investigate the aerosol-cloud interaction under different aerosol absorptive properties. The weakly absorbing aerosols can be more effectively activated as cloud condensation nuclei, which lead to smaller cloud droplets and higher number concentrations than those forming from strongly absorbing aerosols. In general, cloud microphysical properties have relatively stronger sensitivity to weakly absorbing aerosols.
A total of 16 continental low-level stratiform cloud cases were selected to investigate the...
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