Aeronomy of the Venus Upper Atmosphere

We present aeronomical observations collected using remote sensing instruments
on board Venus Express, complemented with ground-based observations and numerical
modeling. They are mostly based on VIRTIS and SPICAV measurements of airglow obtained
in the nadir mode and at the limb above 90 km. They complement our understanding
of the behavior of Venus’ upper atmosphere that was largely based on Pioneer Venus observations
mostly performed over thirty years earlier. Following a summary of recent spectral
data from the EUV to the infrared, we examine how these observations have improved our
knowledge of the composition, thermal structure, dynamics and transport of the Venus upper
atmosphere. We then synthesize progress in three-dimensional modeling of the upper atmosphere
which is largely based on global mapping and observations of time variations of the
nitric oxide and O2 nightglow emissions. Processes controlling the escape flux of atoms to
space are described. Results based on the VeRA radio propagation experiment are summarized
and compared to ionospheric measurements collected during earlier space missions.
Finally, we point out some unsolved and open questions generated by the recent datasets and model comparisons.