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Abstract: The Venus Express (VEX) Radio Science experiment VeRa utilizes radio occultation techniques to investigate the Venus atmosphere over a wide range of latitudes. Radio attenuation measurements with the VEX 3.6cm (X-band) signal provide information on the absorptivity distribution within the Venus cloud deck. The combined results from 6years of occultation measurements reveal a distinct latitudinal variation in absorptivity in the altitude range from 50 to 55km. Enhanced absorptivity is observed at equatorial and mid-latitudes (0–50°S), exceeding 0.008dB/km on the dayside and 0.01dB/km on the nightside of the southern hemisphere. Poleward of 50°S latitude a decrease in the absorptivity is observed, reaching minimal values at polar latitudes (>70°S), where the absorptivity did not exceed 0.005dB/km on the dayside and 0.004dB/km on the nightside. The main absorber of radio waves in the Venus atmosphere, gaseous sulfuric acid, can serve as a tracer for atmospheric motions. The inferred absorptivity was used to determine the abundance of gaseous sulfuric acid. Abundances of about 1–2ppm are found between 0°S and 70°S latitude in the altitude range from 50 to about 52km, sometimes increasing to values of about 3ppm on the dayside and 5ppm on the nightside near 50km. The abundance at polar latitudes (>70°S) did not exceed 1ppm within the considered altitude range. The absorptivity and gaseous sulfuric acid height profiles are compared with previous measurements. [Copyright &y& Elsevier]

The SOIR instrument on board Venus Express regularly sounds the Venus atmosphere using the solar occultation technique. The density and temperature profiles are inferred from SOIR spectra recorded in the infrared. The method has been described in a previous publication (Mahieux et al., 2012. J. Geophys. Res. 117. doi:10.1029/2012JE004058.). This paper is devoted to the update of the VAST (Venus Atmosphere from SOIR measurements at the Terminator) compilation that was initiated in the above cited work, which gives the mean CO 2 number density and temperature profiles for different latitude bins. The method has been improved and has been applied to more data. The new compilation which is given on the same latitudinal grid now distinguishes between the two sides of the terminator. The compilation also confirms the main thermal layering characteristics that were identified in the earlier version: the succession of a warm layer (230±30 K, 1− σ standard deviation) at a pressure level of 3.2×10 −7 mbar (~140 km), a very cold layer (125±32 K) at 2.5×10 −5 mbar (~123 km), a warm layer (204±17 K) at 0.01 mbar (~102 km) and finally a colder layer at 0.4 mbar (171±34 K, ~87 km). The layering of all the temperature profiles is explained by radiative rather than dynamical processes. The temporal temperature variation is larger than the mean latitudinal temperature variation. VAST is compared with temperature profiles obtained from other Venus Express instruments, VeRa and SPICAV–UV, and ground based measurements. [ABSTRACT FROM AUTHOR]

Profiles of electron density versus height obtained by the radio occultation experiment on Venus Express provide an observational data base suitable for semi-empirical modeling. The basic equations of photo-chemical-equilibrium (PCE) theory can be applied to the altitude range 100–170 km of Venus' ionosphere (Peter et al., 2014). Within that domain, the maximum electron density (N max) and total electron content (TEC) show very high correlations (0.98) with parameterizations of solar flux and solar zenith angle. Validation using independent profiles from the Venera 15/16 radio occultation experiments yielded an even higher correlation (0.99). Such dominance of PCE ionospheric processes at Venus is the highest in the solar system. This allows for N max and TEC to be used to derive estimates of the exospheric temperature of Venus' thermosphere at ~170 km. • Venus has the Solar System ionosphere most controlled by photochemical equilibrium. • Venus Express radio occultation observations used to model Nmax and TEC • Venus Ionospheric model validated by Venera 15/16 observations • Slab thickness and exospheric temperature are derived from Nmax and TEC. • Exospheric temperature is essentially constant throughout the daytime period. [ABSTRACT FROM AUTHOR]