  An improved high-resolution ground-to-thermosphere version of the Institut
Pierre-Simon Laplace (IPSL) Venus General Circulation Model (VGCM), including
non-orographic gravity waves (GW) parameterization and fine-tuned non-LTE
parameters, is presented here. We focus on the validation of the model built
from a collection of data mostly from Venus Express experiments and coordinated
ground-based telescope campaigns, in the upper mesosphere/lower thermosphere of
Venus. These simulations result in an overall better agreement with temperature
observations above 90 km, compared with previous versions of the VGCM. Density
of CO2 and light species (CO and O) are also comparable with observations in
terms of trend and order of magnitude. Systematic biases in the temperature
structure are found at about 80-100 km and above 130 km at the terminator,
possibly due to assumptions on the CO2 mixing ratio made for stellar/solar
occultation retrievals and uncertainties on the collisional rate coefficients
used in the non-LTE parameterization, respectively. Diurnal and latitudinal
distribution of dynamical tracers are also analyzed. Overall, our simulations
indicate that a weak westward retrograde wind is present up to about 120 km,
producing the CO bulge displacement toward 2h-3h in the morning, instead of
piling up at the anti-solar point, as for an idealised SS-AS circulation. This
retrograde imbalance is suggested to be produced by perturbations of about 5
days Kelvin wave impacting the mesosphere up to 110 km (see the companion paper
Navarro et al. 2021), combined with GW westward acceleration mostly above 110
km. On the whole, these model developments point to the importance of the
inclusion of the lower atmosphere, higher resolution and finely tuned
parameterizations in GCM of the Venusian upper atmosphere, in order to shed
light on existing observations.
