Background

Multilayered, overlapping cloud layers occur in more than half of cloud observations, as shown by the synoptic cloud observation studies by Hahn et al. (1982, NCAR Tech. Note TN-201; 1984,NCAR Tech. Note TN-241) and Warren et al. (J. Climate Appl. Meteor., 24, 658-667, 1985). Multilayered clouds occur commonly in the vicinity of fronts and also in the vicinity of deep tropical convection. Over tropical oceans, thin cirrus often overlies broken boundary layer clouds. In a study performed over the north Atlantic Ocean, Tian and Curry (J. Geophys. Res., 94, 9925-9935, 1989) showed that a majority of the multilayered cloud cases consisted of two-layer cloud systems at a spatial scale of approximately 45 km. Three-layer cases began to dominate over larger scales of approximately 200 km.

By necessity, operational cloud retrieval algorithms are based on the simplifying assumption that each satellite field of view (FOV) contains only a single cloud layer. For scenes in which a high-level transmissive cirrus cloud overlies a boundary layer stratus cloud, the retrieved cloud height is typically between the cirrus and stratus cloud heights (e.g., Menzel et al., J. Appl. Meteor., 31, 370-385, 1992; Baum and Wielicki, J. Appl. Meteor., 33, 107-117 1994), depending on the optical depth of the uppermost cloud layer.

Based on our recent research involving multispectral satellite imagery, we are now able to identify where optically thin cirrus overlies a lower-level water cloud with some success. Our emphasis is twofold:

• to transition the methodology from research mode to operational mode by applying the method to direct-broadcast MODIS data at the University of Wisconsin-Madison, and
• subsequently use this information to improve the accuracy of the retrieved cloud heights and other cloud properties.