Resembling a frosted window on a cold winter's day, this lacy pattern of marine clouds was captured off the coast of Peru in the Pacific Ocean by NASA´s Terra satellite on September 4, 2003. The true-color MODIS image reveals both open- and closed-cell cumulus cloud patterns. These cells, or parcels of air, often occur in roughly hexagonal arrays in a layer of fluid (the atmosphere often behaves like a fluid) that begins to "boil," or convect, due to heating at the base or cooling at the top of the layer.
In "closed" cells warm air is rising in the center, and sinking around the edges, so clouds appear in cell centers, but evaporate around cell edges. This produces cloud formations like those that dominate the upper right. The reverse flow can also occur: air can sink in the center of the cell and rise at the edge. This process is called "open cell" convection, and clouds form at cell edges around open centers, which creates a lacy, hollow-looking pattern like the clouds in the lower left.
Closed and open cell convection represent two stable atmospheric configurations — two sides of the convection coin. But what determines which path the "boiling" atmosphere will take? Apparently the process is highly chaotic, and there appears to be no way to predict whether convection will result in open or closed cells. Indeed, the atmosphere may sometimes flip between one mode and another in no predictable pattern.