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(7.4μm) spectral range, where SO2, CO2, and HDO (used as a proxy for H2O) 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 SO2was estimated using the SO2/CO2line depth ratio of weak transitions; the H2O volume mixing ratio was derived from the HDO/CO2line depth ratio, assuming a D/H ratio of 200 times the Vienna standard mean ocean water. As reported in our previous analyses, the SO2mixing ratio shows strong variations with time and also over the disk, showing evidence for the formation of SO2plumes 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 have used the 2019 data in addition to our previous dataset to study the long-term variations of SO2and H2O. 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 SO2plumes 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 SO2vmr with respect to local time shows a higher abundance at the evening terminator with respect to the morning. The dependence of the SO2vmr 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.
Highlights
The atmospheric chemistry of Venus is driven by the cycles of water and sulfur dioxide (Krasnopolsky 1986, 2007, 2010; Mills et al 2007; Zhang et al 2012)
Two SO2 maps, recorded on April 20, 2019 and separated by about one hour, show a very high SO2 vmr all over the disk, with a local maximum, higher than 1 ppmv, near the sub-solar point, which decreases within a time scale of one hour
The short-term variations of SO2 observed in 2018 and 2019 tend to be stronger than in the previous years. This suggest that the long-term evolution of the SO2 abundance at the cloud top is associated with the short-term activity of the SO2 plumes, as observed by SPICAV aboard Venus Express (Marcq et al 2020)
Summary
T. Encrenaz1, T. K. Greathouse2, E. Marcq3, H. Sagawa4, T. Widemann1, B. Bézard1, T. Fouchet1, F. Lefèvre3, S. Lebonnois5, S. K. Atreya6, Y. J. Lee7, R. Giles8, S. Watanabe9, W. Shao10, X. Zhang10, and C. J. Bierson10 05, France 6 Planetary Science Laboratory, University of Michigan, Ann Arbor MI 48109-2143, USA 7 Zentrum fuer Astronomie und Astrophysik, Technische Universitaet Berlin, Hardenbergstr. 36, 10623 Berlin, Germany 8 Jet Propulsion Laboratory, Pasadena, CA 91109, USA 9 Hokkaido Information University, Hokkaido 069-8585, Japan 10 Department of Earth and Planetary Sciences, University of California, Santa Cruz, CA 95064, USA
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