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Thermal mapping of HDO and SO2 on Venus: results from the 2021-2023 observations

Presentation #406.03 in the session Venus (Poster)

Published onOct 23, 2023
Thermal mapping of HDO and SO2 on Venus: results from the 2021-2023 observations

Since 2012, water vapor and sulfur dioxide have been monitored at the cloud top of Venus using the TEXES (Texas Echelon Cross Echelle Spectrograph) imaging spectrometer at the NASA IRTF (InfraRed Telescope Facility, Mauna Kea Observatory). Mixing ratios of the two species were inferred from weak transitions of HDO (used as a proxy from H2O), SO2 and CO2. The H2O maps are always uniform over the disk and show moderate temporal variations. Over the long term, SO2 exhibits variations by a factor as large as 10, while the H2O variations do not exceed a factor 3. Between 2014 and 2019, the two molecules exhibited a clear anti-correlation which is no more observed after 2021. Reasons for this change are not clear. The anti-correlation might result from photochemical processes, while convective motions might favor the mixing of the two species. In addition, unlike H2O, SO2 exhibits strong short-term variations in the form of episodic plumes with a life time shorter than a day. They are mostly observed around the equator and in the vicinity of the terminators. Between 2021 and March 2023, the SO2 content has been especially low, but the plume activity has been strongly variable (high in November 2022 and weak in March 2023). Observing SO2 simultaneously at two different wavelengths (7.4 and 19 microns) has allowed us to probe the SO2 abundance at two different altitudes, at the cloud top (z = 62 km, at 7.4 microns) and a few kilometers below within the cloud (z = 57 km, at 19 microns). In most of the cases, the SO2 gradient has been found more or less constant, but in a few occasions, the SO2 gradient can be either positive or negative. Above the cloud top, the SO2 mixing ratio decreases rapidly, as illustrated by the widths of the SO2 lines, broader than the CO2 lines. Finally, the temperature fields retrieved from continuum maps at 7.4, 19 and 8.6 microns (z = 67 km) in September and November 2021 show an unusual structure, possibly associated with gravity waves, as previously observed by the LIR camera aboard the Akatsuki spacecraft.

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