Regional and Season Variations in Stratus Cloud Properties from MODIS Observations

Marine stratus clouds represent a climatologically significant influence on the global energy and water cycle. By possessing a higher albedo than the underlying ocean surface, these clouds cause a significant decrease in the amount of solar radiation absorbed in the ocean's mixed layer. This radiative impact is influenced by cloud micro- and macrophysical properties that are not fully understood and a realistic representation of their structure and properties is essential to obtain realistic climate model simulations. We use four full years of cloud retrievals from MODIS for five prominent marine stratus regions to compile statistics of stratus cloud macro- and microphysical properties. We employ a rigorous, automated quality control procedure that determines the presence of stratus and removes portions of scenes that are affected by sunglint, contain cirrus or frontal clouds, or contain other retrieval errors. We also investigate the possible effects of partially cloudy pixels by compiling statistics both including and excluding cloud edge pixels. We identify more than 31,000 GCM-grid-sized regions for which we define measures of central tendency and variability of important cloud properties (e.g. optical depth, liquid water path and cloud particle effective radius), and bulk scene properties including the cloud fraction and a measure of mesoscale structure. The analysis explores the seasonal and regional differences in cloud properties, their sub-grid scale properties, and how these vary as a function of cloud macrophysics. Our results show several interesting regional and seasonal differences in cloud properties, which can be used for model validation and development of stratus parameterizations.