Letter

Nature 456, 620-623 (4 December 2008) | doi:10.1038/nature07466; Received 4 April 2008; Accepted 16 September 2008

Atmospheric structure and dynamics as the cause of ultraviolet markings in the clouds of Venus

Dmitry V. Titov1,4, Fredric W. Taylor2, Håkan Svedhem3, Nikolay I. Ignatiev1,4, Wojciech J. Markiewicz1, Giuseppe Piccioni5 & Pierre Drossart6

  1. Max Planck Institute for Solar System Research (MPS), Max-Planck-Strasse 2, 37191 Katlenburg-Lindau, Germany
  2. University of Oxford, Sub-Department of Atmospheric, Oceanic and Planetary Physics, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, UK
  3. ESA/ESTEC, PB 299, 2200AG Noordwijk, The Netherlands
  4. Space Research Institute (IKI), 84/32 Profsoyuznaya Str., 117997 Moscow, Russia
  5. Istituto di Astrofisica Spaziale e Fisica Cosmica (INAF-IASF), via del Fosso del Cavaliere 100, 00133 Rome, Italy
  6. LESIA, Observatoire de Paris, 5 place Jules Janssen, 92195 Meudon, France

Correspondence to: Dmitry V. Titov1,4 Correspondence and requests for materials should be addressed to D.V.T. (Email: Titov@mps.mpg.de).

When seen in ultraviolet light, Venus has contrast features that arise from the non-uniform distribution of unknown absorbers within the sulphuric acid clouds1, 2, 3 and seem to trace dynamical activity in the middle atmosphere4. It has long been unclear whether the global pattern arises from differences in cloud top altitude (which was earlier3 estimated to be 66–72 km), compositional variations or temperature contrasts. Here we report multi-wavelength imaging that reveals that the dark low latitudes are dominated by convective mixing which brings the ultraviolet absorbers up from depth. The bright and uniform mid-latitude clouds reside in the 'cold collar', an annulus of cold air characterized by approx30 K lower temperatures with a positive lapse rate, which suppresses vertical mixing and cuts off the supply of ultraviolet absorbers from below. In low and middle latitudes, the visible cloud top is located at a remarkably constant altitude of 72 plusminus 1 km in both the ultraviolet dark and bright regions, indicating that the brightness variations result from compositional differences caused by the colder environment rather than by elevation changes. The cloud top descends to approx64 km in the eye of the hemispheric vortex, which appears as a depression in the upper cloud deck. The ultraviolet dark circular streaks enclose the vortex eye and are dynamically connected to it.

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