Negative Aerosol-Cloud r_e Relationship From Aircraft Observations Over Hebei, China

Using six flights observations in September 2015 over Hebei, China, this study shows a robust negative aerosol-cloud droplet effective radius (r_e) relationship for liquid clouds, which is different from previous studies that found positive aerosol-cloud r_e relationship over East China using satellite observations. A total of 27 cloud samples was analyzed with the classification of clean and polluted conditions using lower and upper 1/3 aerosol concentration at 200 m below the cloud bases. By normalizing the profiles of cloud droplet r_e, we found significant smaller values under polluted than under clean condition at most heights. Moreover, the averaged profiles of cloud liquid water content (LWC) show larger values under polluted than clean conditions, indicating even stronger negative aerosol-cloud r_e relationship if LWC is kept constant. The droplet size distributions further demonstrate that more droplets concentrate within smaller size ranges under polluted conditions. Quantitatively, the aerosol-cloud interaction is found around 0.10–0.19 for the study region.