An uppermost haze layer above 100 km found over Venus by the SOIR instrument onboard Venus Express

Abstract The Solar Occultation in the InfraRed (SOIR) instrument onboard Venus Express was designed to measure the Venusian atmospheric transmission at high altitudes (65–220 km) in the infrared range (2.2–4.3 μm) with a high spectral resolution. In this work, we investigate the optical properties of Venus’s haze layer above 90 km using SOIR solar occultation observations. Vertical and latitudinal profiles of the extinction coefficient, optical thickness, and mixing ratio of aerosols are retrieved. One of the most remarkable results is that the aerosol mixing ratio tends to increase with altitude above 90 km at both high and low latitudes. We speculate how aerosols could be produced at such high altitudes.