Carbon monoxide observed in Venus’ atmosphere with SOIR/VEx

Abstract

The SOIR instrument on board the ESA Venus Express mission has been operational during the complete duration of the mission, from April 2006 up to December 2014. Spectra were recorded in the IR spectral region (2.2–4.3µm) using the solar occultation geometry, giving access to a vast number of ro-vibrational lines and bands of several key species of the atmosphere of Venus. Here we present the complete set of vertical profiles of carbon monoxide (CO) densities and volume mixing ratios (vmr) obtained during the mission. These profiles are spanning the 65–150km altitude range. We discuss the variability which is observed on the short term, but also the long term trend as well as variation of CO with solar local time and latitude. Short term variations can reach one order of magnitude on less than one month periods. SOIR does not observe a marked long term trend, except perhaps at the beginning of the mission where an increase of CO density and vmr has been observed. Evening abundances are systematically higher than morning values at altitudes above 105km, but the reverse is observed at lower altitudes. Higher abundances are observed at the equator than at the poles for altitude higher than 105km, but again the reverse is seen at altitudes lower than 90km. This illustrates the complexity of the 90–100km region of the Venus’ atmosphere where different wind regimes are at play.