Marine boundary layer (MBL) clouds are important to the planetary energy balance because they cover large regions of the oceans and possess an albedo that is considerably larger than the underlying ocean surface; however, their albedo is poorly simulated by global climate models (GCMs).

To aid in understanding the role MBL clouds play in climate and assist in improving their representation in GCMs we quantify their long-term macro- and microphysical properties using six years of observations from the Moderate Resolution Imaging Spectraradiometer (MODIS) instrument aboard the NASA Earth Observing System Terra and Aqua satellites over five oceanic regions where MBL clouds are prevalent. For GCM-sized grids (300 km x 300 km) primarily containing marine boundary layers clouds (i.e. little to no contamination from other cloud types), we characterize the macro-scale cloud organization using cloud fraction and effective cloud diameter, in addition to the central tendencies and deviations of key microphysical properties including optical depth, liquid water path, and cloud particle effective radius. The results show a seasonal dependence where a greater fraction of overcast cloud scenes with larger optical depth and liquid water path tend to occur during the months of peak MBL cloud occurrence for all regions. We do however find distinct differences between regions in relationships between cloud mesoscale structure and drizzle frequency.

This study is further complemented by analysis of GOES-10 pixel level data products of MBL clouds off the coast of California during the Atmospheric Radiation Measurement (ARM) Mobile Facility deployment at Pt. Reyes, California (March to October 2005). We relate the micro- and macro-physical cloud properties to visual identification and radiometric proxies of “pockets of open cells” within overcast stratocumulus throughout the diurnal cycle.