Nighttime photochemical model and night airglow on Venus

The photochemical model for the Venus nighttime atmosphere and night airglow (Krasnopolsky, 2010, Icarus 207, 17–27) has been revised to account for the SPICAV detection of the nighttime ozone layer and more detailed spectroscopy and morphology of the OH nightglow. Nighttime chemistry on Venus is induced by fluxes of O, N, H, and Cl with mean hemispheric values of 3×1012, 1.2×109, 1010, and 1010 cm−2 s−1, respectively. These fluxes are proportional to column abundances of these species in the daytime atmosphere above 90 km, and this favors their validity. The model includes 86 reactions of 29 species. The calculated abundances of Cl2, ClO, and ClNO3 exceed a ppb level at 80–90 km, and perspectives of their detection are briefly discussed. Properties of the ozone layer in the model agree with those observed by SPICAV. An alternative model without the flux of Cl agrees with the observed O3 peak altitude and density but predicts an increase of ozone to 4×108 cm−3 at 80 km. Reactions H+O3 and O+HO2 that may excite the OH nightglow have equal column rates. However, the latter is shifted to 92–94 km, and the models agree better with the nightglow observations if O+HO2 does not contribute to the OH excitation. Schemes for quenching of the OH vibrational quanta by CO2 are chosen to fit the observed band distribution in the Δv=1 sequence at 2.9 μm. The models agree with all observational constraints for the mean nighttime atmosphere. Analytic relationships between the nightglow intensities, the ozone layer, and the input fluxes of atomic species are given. The model results are compared with those of three-dimensional models for the Venus thermosphere.