An investigation of the SO 2 content of the venusian mesosphere using SPICAV-UV in nadir mode

Abstract

Using the SPICAV-UV spectrometer aboard 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 of R ≃ 200 during 2006 and 2007 in the northern hemisphere. By comparison with a radiative transfer model of the upper atmosphere of Venus, we could derive column abundance above the visible cloud top for SO 2 using its spectral absorption bands near 280 and 220 nm. SO 2 column densities show large temporal and spatial variations on a horizontal scale of a few hundred kilometers. Typical SO 2 column densities at low latitudes (up to 50°N) were found between 5 and 50 μm-atm, whereas in the northern polar region SO 2 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 SO 2 column density in the whole northern hemisphere has been observed in early 2007, possibly related to a convective episode advecting some deep SO 2 into the upper atmosphere.