Correlations between cloud thickness and sub-cloud water abundance on Venus

• Published in: Geophysical research letters Vol. 37; no. 2
• Main Authors: Tsang, Constantine C. C., Wilson, Colin F., Barstow, Joanna K., Irwin, Patrick G. J., Taylor, Fredric W., McGouldrick, Kevin, Piccioni, Giuseppe, Drossart, Pierre, Svedhem, Håkan
• Format: Journal Article
• Language: English
• Published: Washington, DC Blackwell Publishing Ltd 01.01.2010; American Geophysical Union; John Wiley & Sons, Inc
• Subjects: Astrophysics; Atmosphere; Earth sciences; Earth, ocean, space; Exact sciences and technology; Meteorology; Physics; Planetology; Planets; Remote sensing; Sciences of the Universe; Venus; wavelength; altitude; time variations; thickness; abundance; Latitudinal gradient; Spectral window; clouds; sounding; variability; convection; genesis; correlation; water vapor; Venus; spatial resolution; spatial variations; refractive index; Opacity; particles
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2009GL041770

Past spacecraft observations of Venus have found considerable spatial and temporal variations of water vapour abundance above the clouds. Previous searches for variability below the clouds at 30–45 km altitude found no large scale latitudinal gradients, but lacked the spatial resolution to detect smaller scale variations. Here we interpret results from the VIRTIS imaging spectrometer on Venus Express, remotely sounding at near‐infrared ‘spectral window’ wavelengths, as indicating that the water vapour abundance at 30–40 km altitude varies from 22 to 35 ppmv (±4 ppmv). Furthermore, this variability is correlated with cloud opacity, supporting the hypothesis that its genesis is linked to cloud convection. It is also possible to fit the observations without requiring spatial variation of water abundance, but this places a strong constraint on the spectral dependence of the refractive index data assumed for the lower cloud particles, for which there is as yet no supporting evidence.