# Water and sulfur dioxide thermal mapping on Venus : Long-term monitoring and vertical distribution of SO2 within and above the clouds

Therese Encrenaz, Thomas Greathouse, Rohini Giles, Thomas Widemann, Bruno Bézard, Franck Lefèvre, Maxence Lefèvre, Wenchen Shao, Emmanuel Marcq

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To cite this version:

Therese Encrenaz, Thomas Greathouse, Rohini Giles, Thomas Widemann, Bruno Bézard, et al. Water and sulfur dioxide thermal mapping on Venus: Long-term monitoring and vertical distribution of SO2 within and above the clouds. EPSC-DPS Joint Meeting 2025, Sep 2025, Helsinki, Finland. 10.5194/epsc-dps2025-366. hal-05280755

HAL Id: hal-05280755

https://hal.science/hal-05280755v1

Submitted on 25 Sep 2025

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# Water and sulfur dioxide thermal mapping on Venus : Long-term monitoring and vertical distribution of SO₂ within and above the clouds

Therese Encrenaz<fnref n="1" />, Thomas Greathouse<fnref n="2" />, Rohini Giles<fnref n="2" />, Thomas Widemann<fnref n="1" />, Bruno Bézard<fnref n="1" />, Franck Lefèvre<fnref n="3" />, Maxence Lefèvre<fnref n="3" />, Wenchen Shao<fnref n="4" />, and Emmanuel Marcq<fnref n="3" />

Sulfur and water play a key role in the chemistry, dynamics, and radiative transfer taking place in the atmosphere of Venus. Temporal and local variations in SO₂ and HDO, monitored within or above the clouds, can be indicators of photochemical/thermochemical processes or dynamical changes. Since 2012, ground-based monitoring of the SO₂ v₂ and v₃ bands, centered at 7.4 mm and 18.9 mm respectively, has been performed with TEXES at the IRTF to probe different atmospheric levels atop and within the clouds ; according to the model, the cloud top, probed at 7.4 mm, is at z = 62 km; the lower level, probed at 19 mm, is at z = 57 km. HDO (used as a proxy of H₂O) was simultaneously recorded at 7.4 mm. Since 2021, a third measurement has been systematically added at 8.6 mm to probe a higher atmospheric level (z = 67 km) in the n₁ SO₂ band.

As reported in our previous analyses, the SO₂ mixing ratio shows strong variations as a function of time but also over the disk, indicating the formation of SO₂ plumes. These local maxima appear sporadically on the SO₂ maps and stay visible over a few hours, but less than a day. In contrast, the H₂O abundance is uniform over the disk and shows moderate variations as a function of time (Encrenaz et al. A&A 674, A199, 2023).

Data recorded since 2021 have led to two main results:

1) The long-term variations of H₂O and SO₂ abundances at the cloud top were found to be anticorrelated between 2014 and 2019, but do not show this anticorrelation after 2021. While the disk-integrated H₂O abundances are more or less constant around 750 ppbv, the disk-integrated SO₂ abundances show variations with time by a factor up to 5 (from 100 to 500 ppbv) on a time scale of 2 months.

2) The n₁ SO₂ band observed at 8.6 mm, probing around z = 67 km, is now detected on all datasets for which SO₂ is higher than 300 ppbv at the cloud top. From these data, we infer that the SO₂ volume mixing ratio (vmr) at 67 km is about ten times lower than its value at the cloud top (z = 62 km in our model). The SO₂ vmr gradient is also retrieved from the data at 7.4 mm (z = 62 km) and

<footnote n="1">¹Paris Observatory, LISA, Meudon, France (therese.encrenaz@obspm.fr)</footnote>

<footnote n="2">²SwRI, San Antonio, Texas, USA</footnote>

<footnote n="3">³LATMOS, IPSL, Paris, France</footnote>

<footnote n="4">⁴Department of Space Research and Technology, Denmark</footnote>
18.9 mm. It is found to be close to 0 in most occasions (implying a constant vmr between 57 and 62 km), with a few exceptions where it can be either negative or positive ; the strongest negative values have been found at a period of high plume activity.