Cloud vortices off Heard Island, south Indian Ocean

Delicate swirls of cloud trail behind the ice-covered Heard Island in this Moderate Resolution Imaging Spectroradiometer (MODIS) image. The swirling pattern—a cloud vortex (plural: vertices)—is produced by the circular flow of air in the atmosphere. Like curling eddies in the lee of a rock in a smooth-flowing river, the vortices in this image were formed by the turbulence created when air flows over Heard Island.

The clouds that form in the spinning air assume its shape. The clouds are made up of many small droplets of water or ice crystals that gather around a condensation nucleus, which might be a small particle of dust, ash, or smoke. Since clouds reflect all visible wavelengths of sunlight, they appear white. To the human eye, however, clouds sometimes appear gray or even black. This is caused by the process of accumulation, where droplets within the cloud merge with others, forming larger droplets. The space between droplets then becomes larger, allowing more light to be absorbed within the cloud, making it appear darker to the naked eye.

Heard Island (visible in the lower right portion of the image) is located in the Indian Ocean, about two-thirds of the way from Madagascar to Antarctica. The island is uninhabited by humans, although it is home to many birds and seals. As this image shows, Heard Island is rugged and mountainous, and is mostly covered with ice. It is also home to an active volcano, Mawson Peak. The island has been a territory of Australia since 1947.

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Jeff Schmaltz, MODIS Rapid Response Team, NASA/GSFC

Published August 5, 2005
Data acquired July 24, 2005

Source:

Terra > MODIS