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HDO and SO2 thermal mapping on Venus. V. Evidence for along-term anti-correlation

Abstract : Since January 2012, we have been monitoring the behavior of sulfur dioxide and water on Venus, usingthe TEXES (Texas Echelon Cross-Echelle Spectrograph) imaging spectrometer at the NASA InfraRed TelescopeFacility (IRTF, Mauna Kea Observatory). Here, we present new data recorded in February and April 2019 inthe 1345 cm−1(7.4μm) spectral range, where SO2, CO2, and HDO (used as a proxy for H2O) transitions wereobserved. The cloud top of Venus was probed at an altitude of about 64 km. As in our previous studies, thevolume mixing ratio (vmr) of SO2was estimated using the SO2/CO2line depth ratio of weak transitions; theH2O volume mixing ratio was derived from the HDO/CO2line depth ratio, assuming a D/H ratio of 200 timesthe Vienna standard mean ocean water (SMOW). As reported in our previous analyses, the SO2mixing ratioshows strong variations with time and also over the disk, showing evidence for the formation of SO2plumes with alifetime of a few hours; in contrast, the H2O abundance is remarkably uniform over the disk and shows moderatevariations as a function of time. We have used the 2019 data in addition to our previous dataset to study thelong-term variations of SO2and H2O. The data reveal a long-term anti-correlation with a correlation coefficientof -0.80; this coefficient becomes -0.90 if the analysis is restricted to the 2014-2019 time period. The statisticalanalysis of the SO2plumes as a function of local time confirms our previous result with a minimum around 10:00and two maxima near the terminators. The dependence of the SO2vmr with respect to local time shows a higherabundance at the evening terminator with respect to the morning. The dependence of the SO2vmr with respectto 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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https://hal-insu.archives-ouvertes.fr/insu-02637956
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Submitted on : Thursday, May 28, 2020 - 8:39:20 AM
Last modification on : Friday, June 12, 2020 - 5:38:05 PM

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Thérèse Encrenaz, Thomas K. Greathouse, Emmanuel Marcq, H. Sagawa, Thomas Widemann, et al.. HDO and SO2 thermal mapping on Venus. V. Evidence for along-term anti-correlation. Astronomy and Astrophysics - A&A, EDP Sciences, 2020, (in press). ⟨10.1051/0004-6361/202037741⟩. ⟨insu-02637956⟩

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