The three-dimensional structure of cumulus clouds over the ocean

Thermal channel (channel 6, 10.4-12.5 μm) images of five LANDSAT Thematic Mapper (TM) cumulus scenes over the ocean are examined. A technique is developed to recognize individual cells within a cloud. It is found that unicellular clouds are generally smaller (⩽1 km) and have smaller fractal dimensions, while multicellular clouds are larger (⩾1 km) and have larger fractal dimensions, cell structural statistics are similar to those of the smaller clouds. Each cell is approximated as a quadric surface using a linear least-squares fit. Most cells are found to have the shape of a hyperboloid of one sheet. However about 15% of the cells are best modeled by a hyperboloid of two sheets, and less than 1% are found to be ellipsoidal. The number of cells in a cloud increases slightly faster than linearly with increasing cloud size. The mean nearest neighbor distance between cells in a cloud, however, appears to increase linearly with increasing cloud size and to reach a maximum when the cloud effective diameter is about 10 km; then it decreases with increasing cloud size. Sensitivity studies of threshold and lapse rate show that neither has a significant impact upon the results