HDO and SO₂thermal mapping on Venus

Abstract

Since January 2012, we have been monitoring the behavior of sulfur dioxide and water on Venus, using the Texas Echelon Cross-Echelle Spectrograph imaging spectrometer at the NASA InfraRed Telescope Facility (IRTF, Mauna Kea Observatory). Here, we present new data recorded in February and April 2019 in the 1345 cm −1 (7.4 μ m) spectral range, where SO 2 , CO 2 , and HDO (used as a proxy for H 2 O) transitions were observed. The cloud top of Venus was probed at an altitude of about 64 km. As in our previous studies, the volume mixing ratio (vmr) of SO 2 was estimated using the SO 2 /CO 2 line depth ratio of weak transitions; the H 2 O volume mixing ratio was derived from the HDO/CO 2 line depth ratio, assuming a D/H ratio of 200 times the Vienna standard mean ocean water. As reported in our previous analyses, the SO 2 mixing ratio shows strong variations with time and also over the disk, showing evidence for the formation of SO 2 plumes with a lifetime of a few hours; in contrast, the H 2 O abundance is remarkably uniform over the disk and shows moderate variations as a function of time. We have used the 2019 data in addition to our previous dataset to study the long-term variations of SO 2 and H 2 O. The data reveal a long-term anti-correlation with a correlation coefficient of −0.80; this coefficient becomes −0.90 if the analysis is restricted to the 2014–2019 time period. The statistical analysis of the SO 2 plumes as a function of local time confirms our previous result with a minimum around 10:00 and two maxima near the terminators. The dependence of the SO 2 vmr with respect to local time shows a higher abundance at the evening terminator with respect to the morning. The dependence of the SO 2 vmr with respect to longitude exhibits a broad maximum at 120–200° east longitudes, near the region of Aphrodite Terra. However, this trend has not been observed by other measurements and has yet to be confirmed.

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