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The Many Faces of the Venus Polar Vortex
A new animation using data from ESA'sVenus 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 will be 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, in particular the VIRTIS (Visible and InfraRed Thermal Imaging Spectrometer) instrument on board, 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. VIRTIS is perfectly suited to study Venus from orbit through so called infrared atmospheric windows (very narrow holes at selected wavelengths almost transparent and thus able to transmit the thermal radiance from very deep regions into the Venusian atmosphere). Also, it provides information about temperature of the atmosphere and the clouds’ top, from which it is possible to study its dynamics and in particular the polar vortex.
The Pioneer Venus mission observed for the first time in 1980 the elliptical shape of a polar vortex with two apparent centres of rotation, in the Venusian northern hemisphere labelling it the dipole of Venus. The VIRTIS instrument, right at the beginning of the Venus Express mission, observed for the first time 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, complex configurations with a not well identified stable feature.
“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 its solid body. Measuring the solar light as is reflected or transmitted at different wavelengths they were able to probe different altitude levels within the atmosphere. “We found a significant vertical shear (change of winds with height) at low latitudes, with winds doubling from the lower clouds to the clouds’ top,” 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 is known for its very peculiar dynamics, quite different than the rest of the planet. A permanent giant vortex, extending more than 3000 km, dominates its dynamics with, on average, an almost solid body rotation. 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 real barrier of separation between the two rotation zones.
Starting from this December, Venus Express will not be alone any more orbiting around Venus, because the Japanese mission Planet-C, launched last May, will join it into the adventure of exploring the mysterious sister planet.
Images and Movies
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 centre 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
Animation 1 (gif): 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 centre 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
Animation 2 (gif): 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 centre 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
Image 2 (tif): 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 centre 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
Animation 3 (gif): 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
Animation 4 (gif): 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
Figure 5 (gif): 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
South-polar features on Venus similar to those near the North Pole, Piccioni, G.; Drossart, P., 2007, NATURE 450(7170), 637-640
Variable winds on Venus mapped in three dimensions, Sanchez-Lavega, A.; Hueso, R.; Piccioni, G.; Drossart, P.; Peralta, J.; Perez-Hoyos, S.; Wilson, C. F.; Taylor, F. W.; Baines, K. H.; Luz, D.; Erard, S. & Lebonnois, S., 2008, GRL 35(13)
Atmospheric structure and dynamics as the cause of ultraviolet markings in the clouds of Venus, Titov, D. V., Taylor, F. W., Svedhem, H., Ignatiev, N. I, Markiwicz, W. J., Piccioni, G., and Drossart, P., 2008, NATURE, Vol. 456, pp. 620-623
Altimetry of the Venus cloud tops from the Venus Express observations, Ignatiev, N. I., Titov, Piccioni, G., Drossart, P., Markiewicz, W. J., Cottini, V., Roatsch, Th., Almeida, M., and Manoel, 2009, N.:, J. Geophys. Res., Vol. 114, E00B43
European Planetary Science Congress (EPSC) 2010
EPSC 2010 is organised by Europlanet, a Research Infrastructure funded under the European Commission’s Framework 7 Programme, in association with the European Geosciences Union. It is the major meeting in Europe for planetary scientists. The programme comprises more than 50 sessions and workshops covering a wide range of planetary topics. EPSC 2009 is taking place at the Angelicum Center – Pontifical University of St. Thomas Aquinas, Rome, Italy from Sunday 19 September to Friday 24 September 2010.
For further details, see the meeting website: http://meetings.copernicus.org/epsc2010/
Europlanet Research Infrastructure (RI)
Europlanet Research RI is a major (€6 million) programme co-funded by the European Union under the Seventh Framework Programme of the European Commission.
Europlanet RI brings together the European planetary science community through a range of Networking Activities, aimed at fostering a culture of cooperation in the field of planetary sciences, Transnational Access Activities, providing European researchers with access to a range of laboratory and field site facilities tailored to the needs of planetary research, as well as on-line access to the available planetary science data, information and software tools, through the Integrated and Distributed Information Service. These programmes are underpinned by Joint Research Activities, which are developing and improving the facilities, models, software tools and services offered by Europlanet
Europlanet Project website: http://www.europlanet-ri.eu/
Europlanet Outreach/Media website: http://www.europlanet-ri.eu/
Dr. Giuseppe Piccioni
Institute: IASF-Rome of the Instituto Nazionale di Astrofisica (National Institute for Astrophysics)
Tel: +39 06 45488 445
Europlanet Press Officer
Phone: +30 697 2235681
Dr Piccioni can be contacted through the EPSC Press Office from 20-24 September.