Actinoform clouds have intriguing structures that are visually interesting examples of the self-organization possible in a convective fluid. These structures also act as indicators of air-sea interaction within the marine boundary layer and may help in the development of improved parameterizations of the albedo of marine boundary layer clouds for climate studies.

We have being studying some of the more frequent and striking examples of actinoform clouds that form in the marine boundary layer over the westward extension of the Peruvian current in the tropical South Pacific. Observed from space using a combination of GOES-10 and MISR (Multiangle Spectroradiometer on Terra) imagery, the self-organization of these clouds is shown to extend at times over distances greater than 2000 km. On scales of about 200 km they take on structures variously described as "leaf" (see figure below), "spider" and "millipede". These, and other South Pacific examples, indicate that the highest degree of self-organization occurs in undisturbed air masses far from continental influence. Contrary to an earlier hypothesis, we see little evidence that actinoform clouds represent a transition zone between closed and open cell structures.

Analysis of cloud heights using stereo retrieval, and of cloud properties using reflected spectral radiance, indicates that the microphysical structure of these clouds changes systematically over distances of only a few kilometers. We also use the satellite measurements to determine the albedo and cloud radiative forcing typical of actinoform clouds, and address the issue of parameterizing these findings in the context of climate modeling.