New insight on the global dynamics in the "transition region" of Venus atmosphere (80-130 km) with a 3D model

Abstract

International audienceVenus’ atmosphere layers between 80 km and 130 km mark the transition between the superrotation and the day-to-night circulation regimes. Accurately modeling this layer is essential to better understand the planet’s atmospheric dynamics. However, this re-gion remains poorly constrained by observations, and its variability is not yet fully captured by current 3D models. Here we use the latest version of the Venus Planetary Climate Model (V-PCM), a ground-to-thermosphere global circulation model, to investigate possible scenarios relevant to future EnVision observations above the cloud tops. We focus on current data-model biases and provide a tentative interpretation of their origin. Benchmark simulations by Martinez et al. (2024) overestimate the nightside O airglow emission by a factor of two and place the emission peak 5–7 km higher than observed. Furthermore, the emission distribution is not centered around midnight, but shifted to LT=4h, likely due to a strong (∼100 m/s) zonal wind component below 105 km. We performed sensitivity tests on unconstrained parameters (e.g. gravity wave drag and eddy diffusion) to evaluate their impact on the dynamical structures. Results show that reducing non-orographic gravity wave forcing below 105 km weakens that superrotation wind component, and recenter the emission around midnight. However, the altitude bias appears linked to insufficient vertical transport in the model. These findings underline the need for future space missions capable of continuously monitoring mesospheric gravity waves and O2 nightglow to better constrain their spatial and temporal variability and improve the representation of key dynamical processes in Venus’ upper atmosphere