Two-dimensional time-dependent model of the transport of minor species in the Venus night side upper atmosphere

Abstract

a b s t r a c tWe present a numerical tool developed to quantify the role of processes controlling the spatio-temporal distribution of the NO ultraviolet and O 2 ð 1 D g Þ infrared nightglows in the Venus night side upper atmosphere, observed with the VIRTIS and SPICAV instruments on board Venus Express. This numerical tool consists in a two-dimensional chemical-transport time-dependent model which computes in a hypothetical rectangular solving domain the spatio-temporal distributions of the number densities of the four minor species at play in these two nightglow emissions. The coupled nonlinear system of the four partial differential equations, describing the spatio-temporal variations of the minor species, has been solved using a finite volume method with a forward Euler method for the time integration scheme. As an application, we have first simulated a time-constant supply of atoms through the upper boundary of the solving domain. The fluxes are inhomogeneous relative to its horizontal direction, in order to simulate regions of enhanced downward flow of oxygen and nitrogen giving rise to NO and O 2 brightening. Given that these two emissions show large time variations, we have also simulated a timedependent downward flux of O and N atoms. It results from these simulations that the lack of correlation between the NO and O 2 ð 1 D g Þ nightglows largely result from to the coupling between horizontal and vertical transport processes and the very different chemical lifetimes of the two species. In particular, we have quantified the role of each process generating spatio-temporal de-correlations between the NO and O 2 ð 1 D g Þ nightglows.

The vertical distribution of the Venus NO nightglow: Limb profiles inversion and one-dimensional modeling

“…In all profiles analyzed, no correlation has been found between the presence of multiple peaks in the NO and O 2 emissions. This is in perfect agreement with Gérard et al (2009a) and Collet et al (2010) who both described the lack of correlation between the two emission peaks.…”

“…This intensity is too bright and peaks 6 km above those derived from VIRTIS observations (Gérard et al, 2009b;Soret et al, 2012). The distance between the two peaks of NO and O 2 emissions was discussed in Collet et al (2010) and Brecht et al (2011). They both modeled a distance smaller than determined from observations.…”

Venus nitric oxide nightglow mapping from SPICAV nadir observations

“…7 sketches the downward transport of atoms that recombine and generate airglow layers in different altitude regimes. The two-dimensional transport model by Collet et al (2010) reproduced the separation between the NO and O 2 (a 1 D) emissions following localized injection of a blob of O and N atoms. It is a consequence of the coupling between the horizontal and vertical transport processes.…”

Understanding the variability of nightside temperatures, NO UV and O2IR nightglow emissions in the Venus upper atmosphere

“…Furthermore, Gérard et al [2009b] have shown the first concurrent observations of the O 2 IR and NO UV night airglow with VIRTIS and SPICAV data. They concluded that the two nightglow emissions are not spatially correlated, giving rise to the idea that each emission is controlled by different dynamical processes [ Collet et al , 2010]. Recent publications [ Gérard et al , 2008b, 2008c, 2009a, 2009b, 2010; Bertaux et al , 2007; Piccioni et al , 2009] detailing observations made by these instruments are discussed in section 4.…”