Morphology of the cloud tops as observed by the Venus Express Monitoring Camera |
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| Authors: | Dmitrij V Titov Wojciech J Markiewicz Nikolay I Ignatiev Li Song Sanjay S Limaye Agustin Sanchez-Lavega Jonas Hesemann Miguel Almeida Thomas Roatsch Klaus-Dieter Matz Frank Scholten David Crisp Larry W Esposito Stubbe F Hviid Ralf Jaumann Horst U Keller Richard Moissl |
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| Institution: | 1. Max Planck Institute for Solar System Research, Max-Planck-Str. 2, 37191 Katlenburg-Lindau, Germany;2. ESA/ESTEC, PB 299, 2200AG Noordwijk, The Netherlands;3. Space Research Institute (IKI), Profsoyuznaya 84/32, 117997 Moscow, Russia;4. Space Science and Engineering Centre, University of Wisconsin, Madison, WI 53706, USA;5. Universidad del País Vasco, ETSI, Alameda Urquijo s/n, 48013 Bilbao, Spain;6. ESA/ESAC, SRE-OS, P.O. Box 78, 28691 Villanueva de la Cañada, Madrid, Spain;7. Institute for Planetary Exploration (DLR), Rutherfordstrasse 2, 12489 Berlin, Germany;8. 183-501, Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109, USA;9. LASP, 392 UCB, University of Colorado, Boulder, CO 80309-0392, USA;1. Cornell University, Dept of Astronomy, 318 Space Sciences Building, Ithaca, NY, 14853, USA;2. Observatoire de Paris, LESIA, 5 Place Jules Janssen, 92195 Meudon Cedex, France;3. University of Wisconsin-Madison, Space Science and Engineering Center, 1225 West Dayton Street, Madison, WI 53706, USA;4. Jet Propulsion Laboratory, M/S 183-501, 4800 Oak Grove Drive, Pasadena, CA 91109 USA |
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| Abstract: | Since the discovery of ultraviolet markings on Venus, their observations have been a powerful tool to study the morphology, motions and dynamical state at the cloud top level. Here we present the results of investigation of the cloud top morphology performed by the Venus Monitoring Camera (VMC) during more than 3 years of the Venus Express mission. The camera acquires images in four narrow-band filters centered at 365, 513, 965 and 1010 nm with spatial resolution from 50 km at apocentre to a few hundred of meters at pericentre. The VMC experiment provides a significant improvement in the Venus imaging as compared to the capabilities of the earlier missions. The camera discovered new cloud features like bright “lace clouds” and cloud columns at the low latitudes, dark polar oval and narrow circular and spiral “grooves” in the polar regions, different types of waves at the high latitudes. The VMC observations revealed detailed structure of the sub-solar region and the afternoon convective wake, the bow-shape features and convective cells, the mid-latitude transition region and the “polar cap”. The polar orbit of the satellite enables for the first time nadir viewing of the Southern polar regions and an opportunity to zoom in on the planet. The experiment returned numerous images of the Venus limb and documented global and local brightening events. VMC provided almost continuous monitoring of the planet with high temporal resolution that allowed one to follow changes in the cloud morphology at various scales.We present the in-flight performance of the instrument and focus in particular on the data from the ultraviolet channel, centered at the characteristic wavelength of the unknown UV absorber that yields the highest contrasts on the cloud top. Low latitudes are dominated by relatively dark clouds that have mottled and fragmented appearance clearly indicating convective activity in the sub-solar region. At ～50° latitude this pattern gives way to streaky clouds suggesting that horizontal, almost laminar, flow prevails here. Poleward from about 60°S the planet is covered by almost featureless bright polar hood sometimes crossed by dark narrow (～300 km) spiral or circular structures. This global cloud pattern can change on time scales of a few days resulting in global and local “brightening events” when the bright haze can extend far into low latitudes and/or increase its brightness by 30%. Close-up snapshots reveal plenty of morphological details like convective cells, cloud streaks, cumulus-like columns, wave trains. Different kinds of small scale waves are frequently observed at the cloud top. The wave activity is mainly observed in the 65–80° latitude band and is in particular concentrated in the region of Ishtar Terra that suggests their possible orographic origin. The VMC observations have important implications for the problems of the unknown UV absorber, microphysical processes, dynamics and radiative energy balance at the cloud tops. They are only briefly discussed in the paper, but each of them will be the subject of a dedicated study. |
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