Apparent aerosol effects on clouds and precipitation examined via MODIS microphysical regimes

We use a 10 years of MODIS Terra and Aqua Level-3 daily joint histograms of cloud optical thickness (COT) and cloud effective radius (CER) to derive so-called cloud microphysical regimes by means of clustering analysis. The regimes reveal the dominant modes of COT and CER co-variations around the globe for both liquid and ice phases. The clustering analysis exhibits skill in distinguishing between regimes dominated by one of the two water phases. The emerging regimes also show some obvious associations with previously derived "dynamical" regimes. This new type of microphysical regimes serves as an appropriate basis to study possible effects of aerosols on cloud microphysical changes and precipitation. To this end, we employ MODIS aerosol loading measurements either in terms of aerosol index or aerosol optical depth and spatiotemporally matched precipitation (from either GPCP, TRMM or CloudSat) to examine intra-regime variability, regime transitions from morning (Terra) to afternoon (Aqua), and regime precipitation characteristics for locally low, average, and high aerosol loadings. Breakdowns by ocean/land and geographical zone (e.g., tropics vs. midlatitudes) are essential for physical interpretation of the results. The analysis conducted so far reveals notable differences in apparent characteristics of low- and high-cloud dominated microphysical regimes when in different aerosol environments. The presentation will attempt to examine the degree to which the picture painted by our work agrees with prevailing expectations, rooted to either modeling or other observational studies, on how clouds and precipitation respond to distinct aerosol environments.