EC-16. On the geographical uniqueness of meteorological covariability in affecting low cloud albedo susceptibility

Marine low-level clouds cool the Earth effectively due to their high reflectiveness of the incoming solar radiation and persistent occurrence. The sensitivity of their solar reflectivity (cloud albedo) to perturbation in cloud droplet number concentration (Nd), termed as albedo susceptibility (S0), is modulated primarily by the states they are in (e.g. the amount of liquid water and droplets in the clouds, precipitating or not), governed by the large-scale meteorological conditions. We derived 3 years of albedo susceptibility for global marine low clouds (60°S – 60°N) from individual satellite (Terra & Aqua) snapshots (over 1° by 1° area). Existing literatures have shown that individual meteorological factors affect cloud adjustments to aerosol perturbations, however, the covariability among meteorological factors and its geographical distribution are often overlooked. Here we show that large-scale meteorological factors (from ERA5 reanalysis), including lower-tropospheric stability (LTS), free-tropospheric relative humidity (RHft), and sea surface temperature (SST), have their unique covariability over each eastern subtropical ocean basins where marine stratocumulus prevail. This leads to drastically different monthly evolutions in albedo susceptibility over each basin. Our work suggests that meteorology-susceptibility relationship drew from global data can be biased when a particular region is concerned, or in other words, ‘equifinality’ obscures the direct pathways from individual meteorological conditions to low cloud albedo susceptibility. This study points to not only the necessity of considering meteorological covariability but also the geographical uniqueness of such covariability when assessing the governing role of large-scale meteorology in aerosol-cloud interactions.