Evidence for SO₂ latitudinal variations below the clouds of Venus

Abstract

Context. Sulphur dioxide (SO₂) is highly variable above the clouds of Venus, yet no spatial or temporal variability below the clouds had been known until now.
Aims: In order to constrain Venus's atmospheric circulation and chemistry (including possible volcanic outgassing), more accurate SO₂ measurements below the clouds are therefore needed.
Methods: We used the high-resolution iSHELL spectrometer located at the NASA IRTF to record thermal night-side spectra, which we fitted using an updated forward radiative transfer model that was previously employed to process SpeX/IRTF and VIRTIS-H/Venus Express spectra.
Results: We report, for the first time, an increase in SO₂ with increasing latitude (+30% between the minimum near 15°S and > 35°N). This is consistent with the interaction between the Hadley-cell circulation and a postulated vertical profile in SO₂ estimated to increase between 30 and 40 km in altitude, as previously suggested by in situ ISAV measurements.
Conclusions: This SO₂ variability challenges our current understanding of Venus's tropospheric thermochemistry and underlines the high scientific return from high-resolution spectroscopy from, for example, future orbiters.