Abstract
Since January 2012 we have been monitoring the behavior of sulfur dioxide and water on Venus, using the Texas Echelon Cross-Echelle Spectrograph (TEXES) imaging spectrometer at the NASA InfraRed Telescope Facility (IRTF, Mauna Kea Observatory). We present here the observations obtained between January 2016 and September 2018. As in the case of our previous runs, data were recorded around 1345 cm−1 (7.4 μm). The molecules SO2, CO2, and HDO (used as a proxy for H2O) were observed, and the cloudtop of Venus was probed at an altitude of about 64 km. The volume mixing ratio of SO2 was estimated using the SO2/CO2 line depth ratios of weak transitions; the H2O volume mixing ratio was derived from the HDO/CO2 line depth ratio, assuming a D/H ratio of 200 times the Vienna Standard Mean Ocean Water (VSMOW). As reported in our previous analyses, the SO2 mixing ratio shows strong variations with time and also over the disk, showing evidence of the formation of SO2 plumes with a lifetime of a few hours; in contrast, the H2O abundance is remarkably uniform over the disk and shows moderate variations as a function of time. We performed a statistical analysis of the behavior of the SO2 plumes, using all TEXES data between 2012 and 2018. They appear mostly located around the equator. Their distribution as a function of local time seems to show a depletion around noon; we do not have enough data to confirm this feature definitely. The distribution of SO2 plumes as a function of longitude shows no clear feature, apart from a possible depletion around 100E–150E and around 300E–360E. There seems to be a tendency for the H2O volume mixing ratio to decrease after 2016, and for the SO2 mixing ratio to increase after 2014. However, we see no clear anti-correlation between the SO2 and H2O abundances at the cloudtop, neither on the individual maps nor over the long term. Finally, there is a good agreement between the TEXES results and those obtained in the UV range (SPICAV/Venus Express and UVI/Akatsuki) at a slightly higher altitude. This agreement shows that SO2 observations obtained in the thermal infrared can be used to extend the local time coverage of the SO2 measurements obtained in the UV range.
Highlights
Water and sulfur dioxide are known to drive the atmospheric chemistry of Venus (Krasnopolsky 1986, 2007, 2010; Mills et al 2007; Zhang et al 2012)
In this paper, we presented the data of our SO2 and HDO monitoring at the cloudtop of Venus using the Texas Echelon Cross-Echelle Spectrograph (TEXES) instrument at
– The SO2 plumes are mostly concentrated around the equator, within the (30N–30S) latitude range
Summary
Water and sulfur dioxide are known to drive the atmospheric chemistry of Venus (Krasnopolsky 1986, 2007, 2010; Mills et al 2007; Zhang et al 2012) The clouds, both species are present with volume mixing ratios of about 30 and 130 ppmv, respectively (Bézard & DeBergh 2012; Marcq et al 2018), and at low latitudes are transported upward by Hadley convection. As a complement to these datasets, we have been using ground-based imaging spectroscopy in the thermal infrared since 2012 to map SO2 and H2O at the cloudtop of Venus and to monitor the behavior of these two species as a function of time, both on the short term (a few hours) and the long term (years). The comparative study of the SO2 maps at 7.4 and 18.9 μm, allowing a retrieval of the vertical distribution of SO2, will be performed in a subsequent paper
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