SO2 above The clouds of Venus as measured by SPICAV-UV In Nadir
Résumé
Using the SPICAV-UV spectrometer on-board Venus Express in nadir mode, we were able to derive spectral radiance factors in the middle atmosphere of Venus in the 170-320 nm range at a spectral resolution R 200 during 2006 and 2007 in the northern hemisphere. By comparison with a radiative transfer model, we could derive column abundance above the visible cloud top for SO2 using its spectral absorption bands near 280 and 220 nm. SO2 column densities show large temporal and spatial variations on a horizontal scale of a few hundred kilometers. Typical SO2 column densities at low latitudes (up to 50°N) were found between 5 and 50 µm-atm, whereas in the northern polar region SO2 content was usually below 5 µm-atm. The observed latitudinal variations follow closely the cloud top altitude derived by SPICAV-IR and are thought to be of dynamical origin. Also, a sudden increase of SO2 column density in the whole northern hemisphere has been observed in early 2007, possibly related to a convective episode advecting some deep SO2 into the upper atmosphere. These results have been submitted to Icarus journal for publication.