Radiative Properties of Layered Cloud Systems as Deduced from Satellite Observations

Abstract

NOAA-AVHRR imagery data is used to probe the physical and radiative properties of single-layered cloud systems over the Pacific Ocean. Such systems constitute approximately 30% of the observations for (250km)² regions and thus represent a significant component of the global cloud system. Nighttime observations of thermal emission at 3.7 and 11 μm indicate that these systems are often optically thick at both wavelengths. Daytime observations of reflected solar radiation at 3.7 μm indicate that the sides of clouds reflect more radiation than the interiors do. Calculations of reflected radiation suggest that the enhanced reflectivity may be caused either by cloud geometry or by a systematic shift in droplet sizes from larger sizes in the interior to smaller sizes at cloud edges. The influence of droplet size on the 3.7 μm reflectivity is clearly evident in images showing the effect of ship stack gases on the sunlight reflected by low-level clouds.