Clustering, randomness, and regularity in cloud fields. 5. The nature of regular cumulus cloud fields

Abstract

This study focuses on the nature of regularity in cumulus cloud fields at the spatial scales suggested by Weger et al. [1993]. We analyzed cumulus cloud fields from Landsat, advanced very high resolution radiometer, and GOES satellite imagery for regularity, using nearest-neighbor cumulative distribution statistics. We found that the spatial scales over which regularity is observed vary from 20 km to 150 km in diameter. Clouds involved in regularity range in radius from about 300 m to 1.5 km. For the cases analyzed, we observed regularity in about 20% of the scenes, while randomness was the dominant spatial distribution for cumulus cloud fields; in addition, we frequently observed a tendency toward regularity. For regions in which we observed either regularity or randomness with a tendency toward regularity, small clouds were inhibited up to a distance of 3 cloud radii from the center of the large cloud. We also determined the size distributions of clouds, using a power law. For clouds larger than 1.5 km radius the exponent of the power law was correlated to the type of spatial distribution of the clouds. The exponent has largest values for regular spatial distributions, smallest values for clustered distributions, and in-between values for random spatial distributions. Analysis of GOES scenes shows that the spatial distribution tends to be clustered in the early stages of the cloud field. During the mature phase it becomes either random, regular, or random with tendency toward regularity. During the later stages of cloud field development the spatial distribution once again becomes clustered.