Climatology of SO2 and UV absorber at Venus' cloud top from SPICAV-UV nadir dataset

Following our previous work (Marcq et al., 2013, 2011), we have updated our forward radiative transfer code and processed the whole SPICAV-UV/Venus Express nadir dataset (2006–2014) in order to retrieve SO2 abundance at cloud top – assuming a SO2 decreasing scale height of 3 km and a ratio SO/SO2 tied to 10% – as well as the imaginary index of scattering mode 1 particles, representative of the remaining UV absorption, since the OSSO vertical profile found by Frandsen et al. (2016) cannot account for our observations. Our main results mostly confirm and extend the validity of those discussed by Marcq et al. (2013), namely: (i) long-term variations of low latitude SO2 at 70 km between ∼100 ppbv (2007, 2009) and less than 10 ppbv (2014); (ii) in average, decreasing SO2 with increasing latitude and depletion near the sub-solar point, consistent with a competition between advection and photo-chemical destruction; (iii) secular increase of mode 1 imaginary index at 250 nm, from 10−2 to 5 ⋅ 10−2 between 2006 and 2010; (iv) if not related instead to long-term variability, a possible localized enrichment of SO2 and UV brightness increase above the western slopes of Aphrodite Terra, consistent with Bertaux et al. (2016) supply mechanism through orographic gravity waves. This spatial and temporal variability underlines the need for a long term monitoring of Venus SO2 and cloud top from ground-based facilities until the next generation of Venusian orbiters is operational. •Low latitude SO2 at Venus' cloud top has decreased by ~10× between 2006 and 2014.•Average UV absorption of clouds has increased, hinting at S-atom conversion.•SO2 supply is possibly enhanced on the western slopes of Aphrodite Terra.