The astronomers in the UPV/EHU’s Planetary Science Group have completed a study of the atmospheric vortex of the south pole of Venus, a huge whirlwind the size of Europe similar to Jupiter's 300-year-0ld Great Red Spot and the South Pole Vortex on Saturn. In the atmosphere there are two main cloud layers separated by a distance of 20km. The astronomers have been closely monitoring the movement of the vortex on both levels, and have been able to confirm the erratic nature of this movement.
The centers of rotation of the upper and lower vortex rarely coincide in their position with respect to the vertical, yet they form a constantly evolving permanent structure on the surface of Venus. Long-term vortices are a frequent phenomenon in the atmospheres of fast rotating planets, like Jupiter and Saturn, for example. Venus rotates slowly, yet it has permanent vortices in its atmosphere at both poles. What is more, the rotation speed of the atmosphere is much greater than that of the planet.
“We’ve known for a long time that the atmosphere of Venus rotates 60 times faster than the planet itself, but we didn’t know why," says Garate-Lopez. "The difference is huge; that is why it’s called super-rotation. And we‘ve no idea how it started or how it keeps going.” The image below shows a thin cloud layer near the South Pole.
The permanence of the Venus vortices contrasts with the case of the Earth. “On the Earth there are seasonal effects and temperature differences between the continental zones and the oceans that create suitable conditions for the formation and dispersal of polar vortices. On Venus there are no oceans or seasons, and so the polar atmosphere behaves very differently,” added Garate-Lopez.
The UPV/EHU team has been able to monitor the evolution of the south pole vortex thanks to one of the instruments on board the European Space Agency’s Venus Express spacecraft, which has been orbiting our neighboring planet since April 2006. The orbit of this craft is very elliptical: it gets very close to the North pole and South pole, yet the planet is observed from a greater distance, which allows a more global vision to be obtained. Also needed was a more extended view offering a detailed view of the planet's south pole, whereas the north pole is observed from much shorter distances, which prevents it from being observed globally," explains Garate-Lopez.
The UPV/EHU astronomers have been using the VIRTIS-M infrared camera on the Venus Express probe and have been analysing data obtained in the course of 169 earth days, and in particular, they have been studying in great detail the data on the 25 most representative orbits.
“This camera doesn’t take individual photos like an ordinary camera, it divides the light into different wave lengths that enable various vertical layers of the planet’s atmosphere to be observed simultaneously, says Garate-Lopez. Besides, we have compared images separated by one-hour intervals and this has enabled us to monitor the speed at which the clouds move."
Recent images from Venus Express shown at the top of the page do not confirm previous sightings of a double storm system there (shown belwo), but rather found a single unusual swirling cloud vortex. In the above recently released image sequence taken in infrared light and digitally compressed, darker areas correspond to higher temperatures and hence lower regions of Venus' atmosphere. Also illuminating are recently released movies, which show similarities between Venus' southern vortex and the vortex that swirls over the South Pole of Saturn. Understanding the peculiar dynamics of why, at times, two eddies appear, while at other times a single peculiar eddy appears, may give insight into how hurricanes evolve on Earth, and remain a topic of research for some time.
Image credits: ESA, Venus Express, VIRTIS, INAF-IASF, Obs. de Paris-LESIA