Determination of the Venus eddy diffusion profile from CO and CO2 profiles using SOIR/Venus express observations

Abstract We present a study of the SOIR/Venus Express CO2 and CO profiles in order to constrain the eddy diffusion profile in the Venus mesosphere (80 to 130 km of altitude). We compute the mean number density profile of both species, and the hydrostatic temperature based on the CO2 mean density profile. We use a 1D-photochemical/diffusion model to adjust the eddy diffusion profile such that the 1D-model and SOIR CO profiles best agree. We compare our results with eddy diffusion profiles found in the literature. We use our approach to revisit the He and CO2 profiles from Pioneer Venus probe mass spectrometer in order to derive an eddy diffusion profile extending from 80 to 200 km of altitude. Our eddy diffusion profile is different in shape and in magnitude compared to the Pioneer Venus profile: it is equal to 3.6 × 106 cm2/s at 110 km, 7.5 × 106 cm2/s at 120 km, 0.4 × 106 cm2/s at 130 km, and 201 × 106 cm2/s at 140 km, and constant below 110 km and above 140 km. This new eddy diffusion profile can be used in Venus Global Circulation Models as well as 1D-photochemical models.