Ground-based HDO and SO2 thermal mapping on Venus : An update

Since 2012, we have been monitoring SO₂ and H₂O (using HDO as a proxy) at the cloud top of Venus, using the TEXES high-resolution imaging spectrometer at the NASA InfraRed Telescope Facility (IRTF) at Maunakea Observatory. Maps have been recorded around 1345 cm^-1 (7.4 microns), where SO₂, CO₂ and HDO are observed, and around 530 cm^-1 (19 microns) where SO₂ and CO₂ are observed. An anti-correlation has been found in the long-term evolution of these two species and SO₂ plumes have been identified with an evolution time scale of a few hours. The SO₂ distribution as a function of local time seems to show two maxima around the terminator, indicating the possible presence of a semi-diurnal wave (Encrenaz et al. A&A 639, A69, 2020). After a year of interruption due to the Covid crisis, new observations have been performed in July and September 2021.   They show that the SO₂ abundance, which had been globally increasing from 2014 until 2019, has now decreased with respect to its maximum value. The new data will be analyzed in the context of the whole dataset.