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

• Published in: Nature 2008-12, Vol.456 (7222), p.620-623
• Main Authors: Titov, Dmitry V., Taylor, Fredric W., Svedhem, Håkan, Ignatiev, Nikolay I., Markiewicz, Wojciech J., Piccioni, Giuseppe, Drossart, Pierre
• Format: Article
• Language: English
• Subjects: Alternative energy sources; Altitude; Analysis; Astronomical research; Astrophysics; Atmosphere; Clouds; Environmental aspects; Humanities and Social Sciences; Latitude; letter; Low temperature; Meteorology; multidisciplinary; Natural history; Physics; Planets; Remote sensing; Science; Solar energy; Sulfuric acid; Temperature; Turbulent flow; Ultraviolet radiation; Venus; Venus (Planet); Wind shear
• ISSN: 0028-0836; 1476-4687; 1476-4679
• DOI: 10.1038/nature07466

The atmosphere on Venus: reading the clouds Details about the atmosphere on Venus are gradually emerging from the once apparently impenetrable global cloud cover. Simultaneous imaging in the ultraviolet and infrared by Venus Express provides a new view of the ultraviolet patterns seen in the cloud tops. The picture that emerges is one of dark low latitudes dominated by convective mixing in the sulphuric acid clouds, bringing unknown ultraviolet absorbers up from the lower atmosphere. The cloud-top morphology revealed in the southern hemisphere by Venus Express resembles that found earlier by Pioneer Venus and Venera-15 in the north, suggesting global symmetry between the two hemispheres. When seen in ultraviolet light, Venus has contrast features that arise from the non-uniform distribution of unknown absorbers within the sulphuric acid clouds. This paper reports multi-wavelength imaging that reveals that the dark low latitudes are dominated by convective mixing that brings the ultraviolet absorbers up from depth. The bright and uniform mid-latitude clouds reside in the 'cold collar', which suppresses vertical mixing. In low and middle latitudes, the visible cloud top is located at a constant altitude of 72 ± 1 km in both the ultraviolet dark and bright regions, indicating that the brightness variations result from compositional differences caused by the colder environment. When seen in ultraviolet light, Venus has contrast features that arise from the non-uniform distribution of unknown absorbers within the sulphuric acid clouds 1 , 2 , 3 and seem to trace dynamical activity in the middle atmosphere 4 . It has long been unclear whether the global pattern arises from differences in cloud top altitude (which was earlier 3 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 ∼30 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 ± 1 km in both the ultraviolet dark and bright regions, indicating that the brightness variations result from compositional differences caus