Modelling the Venusian airglow

Abstract

Context. Modelling of the Venusian ionosphere fluorescence is required, to analyse data being collected by the SPICAV instrument onboard Venus Express. Aims. We present the modelling of the production of excited states of O, CO and N, which enables the computation of nightglow emissions. In the dayside, we compute several emissions, taking advantage of the small influence of resonant scattering for forbidden transitions. Methods. We compute photoionisation and photodissociation mechanisms, and the photoelectron production. We compute electron impact excitation and ionisation, through a multi-stream stationary kinetic transport code. Finally, we compute the ion recombination using a stationary chemical model. Results. We predict altitude density profiles for O(S) and O(D) states, and emissions corresponding to their different transitions. They are found to agree with observations. In the nightside, we discuss the different O(S) excitation mechanisms as a source of green line emission. We calculate production intensities of the O(S) and O(S) states. ForCO, we compute the Cameron bands and the Fourth Positive bands emissions. For N, we compute the LBH, first and Second Positive bands. All values are compared successfully to experiments when data are available. Conclusions. For the first time, a comprehensive model is proposed to compute dayglow and nightglow emissions of the Venusian upper atmosphere. It relies on previous works with noticeable improvements, both on the transport side and on the chemical side. In the near future, a radiative-transfer model will be used to compute optically-thick lines in the dayglow, and a fluid model will be added to compute ion densities. © 2008 ESO.