Concurrent observations of the ultraviolet nitric oxide and infrared O₂ nightglow emissions with Venus Express

Abstract

[1] Two prominent features of the Venus nightside airglow are the nitric oxide d and g bands produced by radiative association of O and N atoms in the lower thermosphere and the O 2 infrared emission generated by three-body recombination of oxygen atoms in the upper mesosphere. The O 2 airglow has been observed from the ground, during the Cassini flyby, and with VIRTIS on board Venus Express. It now appears that the global structure of the two emissions shows some similarities, but the statistical location of the region of strongest emission is not coincident. The Spectroscopy for Investigation of Characteristics of the Atmosphere of Venus (SPICAV) ultraviolet spectrograph has collected a large number of spectra of the Venus nitric oxide nightside airglow. Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) images have been obtained at the limb and in the nadir-viewing mode and have provided new information on the horizontal and vertical distribution of the emission. We present the first concurrent observations of the two emissions observed with Venus Express. We show that nadir observations generally indicate a low degree of correlation between the two emissions observed quasi-simultaneously at a common location. A statistical study of limb profiles indicates that the altitude and the brightness of the two airglow layers generally do not covary. We suggest that this lack of correlation is explained by the presence of strong horizontal winds in the mesosphere-thermosphere transition region. They carry the downflowing atoms over large distances in such a way that regions of enhanced NO emission generally do not coincide with zones of bright O 2 airglow.

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.…”

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

“…A similar conclusion was reached by Piccioni et al (2009). Observations by VIRTIS in the nadir mode have been used to construct statistical maps of the Venus atmosphere in the O 2 emission band (Gé rard et al, 2008b;Piccioni et al, 2009). These maps indicate the region of enhanced emission is centered on the antisolar point.…”

“…The shift of this statistical bright spot was interpreted as an indication of the presence of a super-rotation wind component at or above the altitude of the NO emission peak. The altitude of the emission peak was determined from PV-OUVS observations from periapsis by Gé rard et al (1981) who concluded that the emission peak is located at 115 7 2 km. A much larger set of limb observations of the NO d and g bands nightglow was made with the SPICAV ultraviolet spectrometer (Bertaux et al, 2007) Express.…”

Mapping zonal winds at Venus’s cloud tops from ground-based Doppler velocimetry

“…The wind velocity on SS-AS cells show a strong variability on its zonal component over different time scales, as revealed by several complementary observing techniques such as ground-based wind measurements from Dopplershifted infrared, sub-mm and millimeter lines (Goldstein et al, 1991;Lellouch et al, 1994Lellouch et al, , 2008Clancy et al, 2008;Rengel et al, 2008;Sornig et al, 2008Sornig et al, , 2012Clancy et al, 2012), ground-based and Venus Express/SPICAV observations of non-LTE airglow emission variability on the night side (Ohtsuki et al, 2008;Gérard et al, 2009;Soret et al, 2010Soret et al, , 2012 as well as modeling constraints of the upper mesosphere and lower thermosphere in terms of vertical and latitudinal extension of the cyclostrophic balance approximation Mueller-Wodarg et al, 2006;Brecht et al, 2012). In the upper cloud region the wind variability may be caused by intrusions of the SS-AS return branch, superimposed to the mean zonal flow at low and midlatitudes (Widemann et al, 2007) or, in the polar region, by tidal effects .…”