It is mid-summer in the northern hemisphere of Mars--a time of enhanced heating that leads to the release of water vapor into the atmosphere. In the north polar region, temperature differences between bright areas of year-round ice and dark areas of sand and rock create strong winds that mix the atmosphere and create waves of clouds that swirl around the polar cap. Sometimes, as seen during the Viking mission, these winds form tight cyclones; other times, they weave an intricate pattern reflecting the turbulence of the circulation of the atmosphere.
This animation shows four days of observations of a representative portion of the northern hemisphere. Five Mars Orbiter Camera (MOC) wide angle image pairs(red/blue filters) were combined. These image pairs were warped to create a polar stereographic map projection, which is used by cartographers to present polar areas as if viewed from above. The edges of the pictures move back and forth because of the slightly different path taken by the Mars Global Surveyor spacecraft on each of the five orbits used in this sequence. Seen in the right-hand side of the image is the permanent ice cap and the dark areas that surround it.
The motion of the clouds viewed in this image is typical for this season on Mars, and shows forms often seen on Earth. Waves of clouds are moving from the upper portion of the frame towards the bottom (towards the east northeast). This motion is most likely the movement of a moister portion of the martian atmosphere under the influence of circumpolar winds. Early in the sequence, a prominent circular band of clouds moves almost due east, rotating slightly counter-clockwise. Towards the end of the sequence, the circle dissipates and a linear set of clouds propagates towards the bottom of the frame. Linear cloud speeds vary from day today, averaging about 16 km/hr (10 miles/hr); rotational rates appear to have been less than 10 km/hr (6 miles/hr).
Malin Space Science Systems and the California Institute of Technology built the MOC using spare hardware from the Mars Observer mission. MSSS operates the camera from its facilities in San Diego, CA. The Jet Propulsion Laboratory's Mars Surveyor Operations Project operates the Mars Global Surveyor spacecraft with its industrial partner, Lockheed Martin Astronautics, from facilities in Pasadena, CA and Denver, CO.