Weird Weather on a Global Scale
Swirling at the south pole of Venus is a vortex that's not only huge (2,000 kilometers wide) but a shape-shifter as well. Researchers have known about this hurricane-like structure since 1979, when Pioneer spotted it, but they're learning more thanks to Venus Express. Between Feb. 26 and Feb. 27 of last year, for example, they saw the vortex change from hourglass-shaped to near-circular. At other times, the swirl takes on an oval shape. The storm also has complex circulation patterns, with gases at different altitudes flowing in from different directions.
At right: images of Venus cloud cover at two infrared wavelengths. Image credit: http://sci.esa.int/science-e-media/img/00/Cloud-tracking_infrared.jpg, Copyright: ESA/VIRTIS/INAF-IASF/Obs. de Paris-LESIA
As quickly as Venus' southern vortex can change, so too can the planet's global weather. Venus Express has observed bright hazes of sulfuric acid engulf nearly the whole southern hemisphere then disappear again over the course of a few days. "Such 'global weather,' unlike anything on Earth, has given scientists a new mystery to solve," says the ESA.
"You cannot understand the Venusian weather and atmosphere by comparing them to Earth's," the ESA says. "Scientists are unable to explain some of the more extreme atmospheric phenomena that take place on Venus. For example, the planet only rotates once every 243 Earth days. However, in the upper atmosphere, hurricane-force winds sweep around Venus, taking just 4 Earth days to circumnavigate the planet."
At left: false-color, infrared images of Venus' south pole vortex. Image credit: http://sci.esa.int/science-e-media/img/0b/VIRTIS_south-pole_composite.jpg