Regional assessment of microphysical properties of marine boundary layer cloud using the PATMOS-x dataset

Cloud droplet number concentration and geometrical thickness of marine boundary layer clouds are inferred from 25 years of National Oceanic and Atmospheric Administration's AVHRR Pathfinder Atmospheres-Extended (PATMOS-x) Level 2b retrievals of optical thickness and cloud droplet effective radius over the period 1982 through 2009. A novel approach to addressing nonphysical values of cloud droplet number concentration N owing to satellite orbital drift is applied by normalizing estimated droplet number concentrations with respect to local observation time. Cloud geometrical thickness H is also normalized to a common reference time by scaling H against diurnal values from a passive microwave liquid water path climatology. The effectiveness of the methods applied to correct N and H are evaluated. Both quantities are spatially and temporally characterized in several subtropical subsidence regions for likely drizzle-free observations. Estimated liquid water path from PATMOS-x is further validated against 20 years of liquid water path values from the Special Sensor Microwave/Imager (SSM/I). Good agreement between SSM/I and PATMOS-x is found in coastal regions. Cloud droplet number concentrations in excess of 300 cm(-3) are found along the western boundaries of the American and African continents, with greatly lower values found further out to sea with no observed long-term trends in cloud properties.