New Understanding of Regime Dependence and Contrasting Observations of Aerosol-Cloud Interactions

 

Authors

Yangang Liu — Brookhaven National Laboratory
Jingyi Chen — Stony Brook University
Jiannong Quan — Institute of Urban Meteorology
Chunsong Lu — Nanjing University of Information Science and Technology

Category

Warm low clouds, including aerosol interactions

Description

It has been increasingly recognized that aerosol indirect effects and associated large uncertainties depend strongly on the regime of aerosol-cloud interactions (i.e., cloud droplet concentration depends nonlinearly on pre-cloud aerosol concentration and updraft velocity), and on the treatment of dispersion effect. We have recently extended the conventional regime dependence of droplet concentration to consider dispersion effect as well, and shown that dispersion effect exhibits a stronger regime dependence than that of the droplet number effect, varying from warming effect in the aerosol-limited regime to cooling effect in the updraft-limited regime. The objective of this study is two-fold. First, we further extend the regime dependence of aerosol-cloud interactions to consider the height above cloud base. Second, pieces of observational evidence 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, awaiting sound physical explanations. The second objective is to address this perplexing topic. We will show that a unified consideration of the regime dependence of droplet concentration, dispersion effect and cloud height can explain away at least some of these conflicting observations. The role of entrainment-mixing processes will also be explored. A major thrust of this study lies in a comprehensive investigation and physical understanding of regime-dependence of aerosol-cloud interactions and related contrasting observations.