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Published October 1, 2004 | public
Journal Article Open

Overlooked examples of cloud self-organization at the mesoscale


Stratocumulus clouds are common in the tropical and subtropical marine boundary layer, and understanding these clouds is important due to their significant impact on the earth's radiation budget. Observations show that the marine boundary layer contains complex, but poorly understood processes, which, from time to time, result in the observable self-organization of cloud structures at scales ranging from a few to a few thousand kilometers. Such shallow convective cloud features, typically observed as hexagonal cells, are known generally as mesoscale cellular convection (MCC). Actinoform clouds are rarer, but visually more striking forms of MCC, which possess a radial structure. Because mesoscale cloud features are typically too large to be observed from the ground, observations of hexagonal cells historically date only to the beginning of satellite meteorology. Examples of actinoform clouds were shown in the venerable "Picture of the Month" series in Monthly Weather Review in the early 1960s, but these clouds were generally forgotten as research focused on hexagonal cells. Recent high-resolution satellite images have, in a sense, "rediscovered" actinoform clouds, and they appear to be much more prevalent than had been previously suspected. We show a number of examples of actinoform clouds from a variety of locations worldwide. In addition, we have conducted a detailed case study of an actinoform cloud system using data from the Multiangle Imaging SpectroRadiometer (MISR) and the Geostationary Operational Environmental Satellite (GOES), including analysis of cloud heights, radiative properties, and the time-evolution of the cloud system. We also examine earlier theories regarding actinoform clouds in light of the new satellite data.

Additional Information

© Copyright by American Meteorological Society 2004. In final form 11 April 2004. The research described in this paper was performed at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. We would like to thank Shawn Ewald for his assistance in compiling a GOES database of actinoform clouds. Special thanks to David J. Diner for his continual support of this effort. Additional thanks is due to James F. W. Purdom for his insightful comments and for his GOES animations of an actinoform cloud case. Finally, a number of reviewers helped improve the clarity of the manuscript and, in particular, pointed out the online study of a 1997 actinoform cloud case referenced in the paper.


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