Clouds over Sumatra: Gorgeous photographs of astronauts captured thunderstorms and anvil clouds

Moist ocean air and steady winds have piled up anvil-like clouds around Indonesia. An astronaut aboard the International Space Station took this panoramic westward looking westward view of the clouds surrounding Sumatra, one of Indonesia's largest islands. The photo also shows the smaller, adjacent islands of Banga and Belithorn, the Java Sea and the west coast of Borneo (above the rightmost edge of the solar panels).

Long, bright clouds are where thunderstorms occur, casting black shadows on the land and sea below. The brightest area (sunglint) where the sun reflects on the water highlights the narrow strait between Sumatra and these islands, and the Lion City of Singapore hides under thunderstorms.

On the day this photo was taken, the wind blew from the northeast (right to left in this perspective). After crossing the Java Sea, moist air rises as it is heated. This heating can lead to the formation of thunderstorms on each island.

The tops of some storms were blown away by the wind, forming flattened clouds on the upper surface; these were called anvil clouds. Winds can extend cumulus clouds far away, forming long, narrow tails. The large anvil, which began over The island of Banga, stretched about 200 kilometers (120 miles) across Sumatra into the Indian Ocean. Over the tall Barissan Mountains off the southwest coast of Sumatra, air is forced to rise, forming other anvil-like clouds (far left), with smaller cumulus also forming on the island chain of the Mintawe Islands (top left).

Cloudless zones appear over the Java Sea and the Indian Ocean. Both areas are located in the downwinds of land (Borneo and Sumatra) where air drops significantly to the surface of the sea on this day, and the falling air usually inhibits the formation of clouds.