NASA: High-Altitude Haze and Vortex At South Pole of Saturn's Moon Titan

PASADENA, Calif. — Images from NASA’s Cassini spacecraft show a concentration of high-altitude haze and a vortex materializing at the south pole of Saturn’s moon Titan, signs that the seasons are turning on Saturn’s largest moon. “The structure inside the vortex is reminiscent of the open cellular convection that is often seen over Earth’s oceans,” said Tony Del Genio, a Cassini team member at NASA’s Goddard Institute for Space Studies, N.Y. “But unlike on Earth, where such layers are just above the surface, this one is at very high altitude, maybe a response of Titan’s stratosphere to seasonal cooling as southern winter approaches. But so soon in the game, we’re not sure.

Cassini first saw a “hood” of high-altitude haze and a vortex, which is a mass of swirling gas around the pole in the moon’s atmosphere, at Titan’s north pole when the spacecraft first arrived in the Saturn system in 2004. At the time, it was northern winter. Multiple instruments have been keeping an eye on the Titan atmosphere above the south pole for signs of the coming southern winter.

While the northern hood has remained, the circulation in the upper atmosphere has been moving from the illuminated north pole to the cooling south pole. This movement appears to be causing downwellings over the south pole and the formation of high-altitude haze and a vortex.”

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For those unfamiliar, a Polar Vortex is “caused when an area of low pressure sits at the rotation pole of a planet. This causes air to spiral down from higher in the atmosphere, like water going down a drain.” Universe Today

“A polar vortex is a persistent, large-scale cyclone located near one or both of a planet’s geographical poles.” “The vortex is most powerful in the hemisphere’s winter, when the temperature gradient is steepest, and diminishes or can disappear in the summer. The Antarctic polar vortex is more pronounced and persistent than the Arctic one; this is because the distribution of land masses at high latitudes in the northern hemisphere gives rise to Rossby waves which contribute to the breakdown of the vortex, whereas in the southern hemisphere the vortex remains less disturbed. The breakdown of the polar vortex is an extreme event known as a Sudden stratospheric warming, here the vortex completely breaks down and an associated warming of 30-50 degrees Celsius over a few days can occur. The Arctic vortex is elongated in shape, with two centres, one roughly over Baffin Island in Canada and the other over northeast Siberia. In rare events, the vortex can push further south as a result of axis interruption, see January 1985 Arctic outbreak. Wikipedia

These Wired and NASA articles and associated imagery, including the one at the top of this article, help to demonstrate the dynamical effect of the polar vortex on Venus’s south pole.

This animation shows Earth’s Winter 2008 – 09 Arctic Polar Vortex and a Sudden Stratospheric Warming, which occurs when the Polar Vortex splits or breaks-up:

Within the Polar Vortex, “Air from very high altitudes descends vertically through the center of the vortex, moving air to lower altitudes over several months.” NASA

“The walls of the polar vortex act as the boundaries for the extraordinary changes in chemical concentrations. Now the polar vortex can be considered a sealed chemical reactor bowl, containing a water vapor hole, a nitrogen oxide hole and an ozone hole, all occurring simultaneously (Labitzke and Kunze 2005)” Stratosphere troposphere interactions: an introduction

There are also “measurements of low methane concentrations in the vortex made by the HALOE instrument on board the Upper Atmosphere Research Satellite.” Rapid descent of mesospheric air into the stratospheric polar vortex, AGU 1993

To learn more about Polar Vortices on Earth see the WUWT Polar Vortex Reference Page.