Ground-based HDO and SO2 thermal mapping on Venus between 2012 and 2022: : 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. Sixteen runs have been performed between 2012 and 2022. Maps have been recorded around 1345 cm^-1 (7.4 microns, z = 62 km), where SO₂, CO₂ and HDO are observed, and around 530 cm^-1 (19 microns, z = 57 km) where SO₂ and CO₂ are observed, as well as around 1162 cm^-1 (8.6 microns, z = 66 km) where CO₂ is observed. From the early beginning, SO₂ plumes have been identified with an evolution time scale of a few hours. In 2020, an anti-correlation has been found in the long-term evolution of H₂O and SO₂; in addition,  the SO₂ plume appearance 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 two years of interruption due to the pandemia, new observations have been performed in July 2021, September 2021, November 2021, and February 2022.   The main results of the new observations are listed below. (1)The SO₂ abundance, which had been globally increasing from 2014 until 2019, has now decreased with respect to its maximum value. (2) The anti-correlation between H₂O and SO₂, which was maximum between 2014 and 2019 (cc = - 0.9) does not appear clearly in the recent observations. (3) The maximum appearance of the SO₂ plumes at the equator and the terminators is confirmed, but appears stronger on the morning side.(4) A strong activity of the SO₂ plumes is observed in September and November 2021, at a time when the disk-integrated SO₂ abundance is low. At the same time, thermal maps at 1162 cm^-1 (8.6 microns, z = 66 km) show a polar enhancement. This behavior could possibly be associated with the topography.