Near-Surface Water Vapor Content Based on Spicav IR/VEx Observations in the 1.1- and 1.18-μm Transparency Windows

The SPICAV IR spectrometer on board the Venus Express mission measured spectra of the 1.1- and 1.18-μm atmospheric transparency windows at the Venus night side. The H2O volume mixing ratio in the deep Venus atmosphere at about 10-16 km has been retrieved for the entire SPICAV IR dataset using a radiative transfer model with multiple scattering. One of the challenges in modeling Venus’ night-side thermal emission in transparency windows is the deviation of the far wings of H2O and CO2 absorption lines from the Lorentz profile. Depending on the chosen approach to calculate the H2O absorption, the volume mixing ratio is: 27.1±1.1 ppmv for the Voigt profile, 26.9 ± 1.0 for the semi-empirical MT_CKD water vapor continuum model, 23.6±1.0 ppmv for the super-Lorentzian line profile. The zonal mean of the water vapor VMR do not vary significantly from 60°S to 70°N. Observations of polar latitudes are characterized by the increased noise level and might show a slight H2O mixing ratio decrease of 2 ppmv. No prominent long-term change on the time scale of 8 years nor local time variations of water vapor were detected.