Height Dependence of Aerosol–Cloud Interactions and Important Implications for Developing Parameterizations

Despite decades of research, many aspects of aerosol-cloud interactions remain elusive. For example, contrasting relationships between key cloud microphysical properties (e.g., droplet concentration, relative dispersion, or effective radius) and aerosol properties (e.g., aerosol concentration or aerosol optical depth) have been reported, and awaiting physical explanation. Particularly understudied is the dependence of aerosol-cloud interactions on the height above cloud base, which is the focus of this work. Our observational analysis shows that the Key microphysical relationships (e.g., droplet concentration vs. aerosols, relative dispersion vs aerosols, and liquid water content vs. aerosols) exhibit strong height dependence. Also examined is the dependence of cloud thickness on aerosols. A theoretical framework is presented to provide physical explanation for the observations; implications for improving aerosol-cloud interaction parameterization are discussed.