NASA/JPL/University of Arizona

This brief animation shows the motion of the clouds in the Jovian atmosphere. Most notable is the dark, oval-shaped Great Red Spot. The animation was compiled from blue filter images taken using the narrow-angle camera on NASA's Cassini spacecraft during seven rotations of Jupiter between October 1 and October 5, 2000. The images reveal an area on Jupiter centered on the equator that extends about 50° north and south and covers 100° east-west (about a quarter of Jupiter's circumference).

Video: 428 kB, Animated GIF

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The dynamics of the Jovian atmosphere

Jupiter's atmosphere is driven by strong zonal winds, analogous to the jet stream on Earth. However, unlike Earth, the atmosphere is made up of an array of belts and zones which rotate in an east-west direction. The light zones are regions of upwelling air, forming ammonia cirrus clouds. The dark belts are regions where the cooler the circulation moves downward. Because there are no ammonia clouds, we can see deeper into the atmosphere in these regions. The speed of the main equatorial jet is about 300 km/hr and these speeds have not changed for hundreds of years.

The Great Red Spot

Jupiter's Great Red Spot is a storm that has been present for centuries, first observed by Galileo 400 years ago. The storm lies in the southern hemisphere and is about 30,000 kilometers by 14,000 kilometers, much larger than the planet Earth! It is an anticyclonic storm and has a high-pressure center (unlike storms on Earth that have low-pressure centers). Its winds rotate counterclockwise and have a period of about 6 days. Scientists do not know what drives the storm or if the storm will ever dissipate. One theory suggests the Great Red Spot is continually fueled by the smaller storms that merge with the giant storm.

Ellen Cohen