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The Many Faces of the Venus Polar Vortex

Press Release From: ESA Venus Express Mission
Posted: Thursday, September 23, 2010

image A new animation using data from ESA's Venus Express spacecraft shows that the double eye of the giant vortex at Venus's South pole has disappeared. Results of a study that shows the complex, variable dynamics at the Venusian south pole is being presented by Dr. Giuseppe Piccioni at the European Planetary Science Congress, on Thursday 23d September.

Orbiting around Venus since April 11, 2006, the ESA mission Venus Express is providing an extensive and unique dataset of great scientific importance, spanning from the surface to the atmosphere and its interaction with the solar wind. The VIRTIS (Visible and InfraRed Thermal Imaging Spectrometer) instrument studies Venus from orbit through atmospheric 'windows', which are transparent at certain infrared wavelengths and thus able to transmit the thermal radiance from very deep regions in the Venusian atmosphere. It also provides information about temperature of the atmosphere and the cloud tops, from which it is possible to study the dynamics and in particular the polar vortex.

In 1979, the Pioneer Venus mission observed a similar polar vortex with two apparent centers of rotation in the Venusian northern hemisphere. This was labeled the dipole of Venus. The VIRTIS instrument, right at the beginning of the Venus Express mission, observed a very similar shape in the southern hemisphere. This discovery revealed a north-south symmetry on Venus and, at a first glance, confirmed the stability of the dipole. However, in the course of the mission, systematic observations with VIRTIS showed a large number of different shapes of the vortex, with complex configurations and not well identified stable features.

"We had ironically observed it in a dipole configuration right at the beginning of the mission. But we soon discovered that this was just a coincidence, since the dipole in reality is not a stable feature on Venus but just one shape among others," says Dr. Piccioni.

Dr. Piccioni and colleagues also tracked the clouds in the Venusian atmosphere in order to measure the wind speeds of the significant atmospheric 'super-rotation' rotating 60 times faster than planet underneath. Observing at different wavelengths, they were able to probe different altitude levels within the atmosphere.

"We found a significant vertical shear, or change of winds with height, at low latitudes, with winds doubling from the lower clouds to the cloud tops," says Dr. Piccioni. "However, the shear disappeared at higher latitudes, in combination with a decreasing wind speed toward the pole," he adds.

In fact, the polar region of Venus has peculiar dynamics, quite different than the rest of the planet. A permanent giant vortex, extending more than 3000 km, dominates which, on average, rotates almost like a solid body. This is quite contrary to the vertical shear in the mid-to-low latitudes, observed by Dr. Piccioni's team. The ring surrounding the polar region, known as cold collar, acts as a barrier separating the two rotation zones.

Starting from this December, Venus Express will be joined in around Venus by the Japanese mission Planet-C, launched last May. Together, they will continue the adventure of exploring Earth's mysterious sister planet.

Images and Animations

Image 1: Comparison of 3D prospective views of the Venus' south polar vortex showing the vortex as it is now (left) and with the dipole configuration (right). The vertical scale represents the temperature of the clouds' top, correlated with its altitude. The center of the vortex is the deepest zone, estimated to be a few km lower than its surroundings. Credits: ESA/VIRTIS/INAF-IASF/Obs. de Paris-LESIA http://www.europlanet-eu.org/outreach/images/stories/ep/news/epsc2010/vortex_comparison.jpg

Animation 1: A 3D prospective view of the Venus' south polar vortex at 3.8 microns acquired by VIRTIS. The vertical scale represents the temperature of the clouds' top, correlated with its altitude. The center of the vortex is the deepest zone, estimated to be a few km lower than its surroundings. Credits: ESA/VIRTIS/INAF-IASF/Obs. de Paris-LESIA http://www.europlanet-eu.org/outreach/images/stories/ep/news/epsc2010/piccionianimation1.gif

Animation 2: A 3D prospective view of the Venus' south polar vortex with the dipole configuration. The vertical scale represents the temperature of the clouds' top, correlated with its altitude. The center of the vortex is the deepest zone, estimated to be a few km lower than its surroundings. Credits: ESA/VIRTIS/INAF-IASF/Obs. de Paris-LESIA http://www.europlanet-eu.org/outreach/images/stories/ep/news/epsc2010/vortex_3d_dipole.gif

Image 2: A set of images of the Venus south polar vortex at 3.8 microns acquired by VIRTIS. The images show the temperature of the clouds top at about 65 km altitude. A darker region corresponds to higher temperature and thus lower altitude. The center of the vortex, approximately at a temperature of about 250K, is the deepest zone, exhibiting the highest temperature of the Venus clouds' top. Credits: ESA/VIRTIS/INAF-IASF/Obs. de Paris-LESIA http://www.europlanet-eu.org/outreach/images/stories/ep/news/epsc2010/piccioniimage2.jpg

Animation 3: A movie of the Venus south polar vortex at 3.8 microns acquired by VIRTIS. The set of images show the temperature of the clouds' top. A darker region corresponds to higher temperature and thus lower altitude. The temperature contrast is the reason of the three dimensional effect of the images. Credits: ESA/VIRTIS/INAF-IASF-/Obs. de Paris-LESIA http://www.europlanet-eu.org/outreach/images/stories/ep/news/epsc2010/piccionianimation3.gif

Animation 4: A movie of the Venus' south polar vortex at 3.8 microns acquired by VIRTIS. The set of images are projected and compensated for the vortex rotation, to show the dynamics within the vortex, which is very complex. It is thus possible to see atmospheric flow with different direction and speed. Credits: ESA/VIRTIS/INAF-IASF/Obs. de Paris-LESIA/Univ. of Oxford http://www.europlanet-eu.org/outreach/images/stories/ep/news/epsc2010/piccionifigure4.gif

Figure 5: A movie of the Venus' south polar vortex at 3.8 microns acquired by VIRTIS. The set of images are projected and compensated for the vortex rotation, to show the dynamics within the vortex, which is very complex. It is possible to see some structure of planetary waves rotating around the vortex. Credits: ESA/VIRTIS/INAF-IASF/Obs. de Paris-LESIA/Univ. of Oxford http://www.europlanet-eu.org/outreach/images/stories/ep/news/epsc2010/piccionifigure5.gif

Science Contact:

Dr. Giuseppe Piccioni
Institute: IASF-Rome of the Instituto Nazionale di Astrofisica
(National Institute for Astrophysics)
+39 06 45488 445
Giuseppe.piccioni@iasf-roma.inaf.it

Dr. Piccioni can be contacted through the EPSC Press Office from 20-24
September.

Useful links:
* http://virtis-vex.iasf-roma.inaf.it/
* http://venus.esa.int/
* http://sci.esa.int/home/venusexpress

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