White formations of cloud and ice feature prominently in this image of the Southern Ocean, captured by the MODIS on the Terra satellite on September 10, 2009. The Southern Ocean is also sometimes known as the Antarctic Ocean. Sea ice is visible in the bottom left-corner. Clouds dominate much of the rest of the image.
The lines of clouds are called "cloud streets." These cumulous clouds result from thermals, or rising columns of warmed air. Thermals themselves form when the ground surface is a little warmer than its surroundings. If the thermal produces a consistent flow of warm air, and steady wind carries that air away, lines of clouds can form along the direction of the wind. An irregular surface like the edge of the sea ice observed in this image may provide the perfect conditions for creating steady streams of warm air interspersed with areas of cooler air.
At the point where the clouds first form streets, they're very narrow and well-defined. But as they age, they lose their definition, and begin to spread out and rejoin each other into a larger cloud mass.