Venus night airglow and implications for thermospheric composition and dynamics

International audienceSpatially resolved spectra of the NO δ and γ ultraviolet bands have been obtained from 80 to 130 km on the Venus night side with the SPICAV instrument on board Venus Express. This NO airglow emission results from radiative recombination of oxygen and nitrogen atoms created on the dayside and transported by the subsolar to antisolar global circulation. Spectral images of the O2 (1 ∆g ) at 1.27 µm have also been made with the VIRTIS-M instrument both at nadir and at the limb. The O2 (1 ∆g ) emission is produced by three-body recombination of O atoms giving rise to an airglow layer near 96 km. The brightness of both emissions changes by over an order of magnitude. They also show variations in the altitude of the peak emission, with larger variability of the NO airglow. The characteristics of both airglows and their implications on global circulation and vertical transport on the nightside will be discussed. Concurrent observations of both limb airglows will be described. It will be shown that limb observations of the vertical and latitudinal distribution of the 1.27 µm emission make it possible to remotely determine the density of atomic oxygen in the upper mesosphere and improve current atmospheric models. One-dimensional models of the O and N distributions will be presented and global properties of the 1-D parameterization of turbulent transport will be discussed