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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.

HDO and SO2thermal mapping on Venus

HDO and SO₂thermal mapping on Venus