Images taken 18 August 2009 from a European Space Agency satellite stationed in a geosynchronous orbit above the equator and prime meridian show a typical pattern of cloud cover off Africa’s west coast. Sprawling marine stratocumulus clouds are visible in two familiar forms: a so-called closed-cellular field, a densely packed layer of clouds separated by thin rings of clear sky; and a more sparsely populated open-cellular field, a honeycomb-like lattice of rings of clouds encircling large pockets of clear sky.
When scientists led by Graham Feingold (National Oceanic and Atmospheric Administration, Boulder, Colorado) zoomed in on the satellite images, they saw intriguing behavior.1 After accounting for wind advection, they noticed that now and then, a cloud in the open-cellular field would vanish, leaving clear sky. Kilometers away, a new cloud would form. Every hour or so, the disappearing act would repeat.
The oscillations Feingold and his colleagues observed are...
