Dr. Thomas Navarro - Dynamical surface-atmosphere coupling of Venus: consequences for length of day variations and transport of atmospheric angular momentum

Akatsuki, the only spacecraft currently active at Venus, recently discovered massive 10,000 km long stationary atmospheric mountain waves at the planet’s cloud top, challenging the long-held view that the cloud deck in superrotation (with a period of 5 days) is dynamically uncorrelated with the slowly rotating surface (243 days). Investigating this structure with a state-of-the-art numerical model of the atmosphere explains how, where, and when it is formed, in agreement with Akatsuki’s observations. These results reveal that mountain waves transfer substantive amounts of angular momentum to the solid body, and are the lead cause of the variations of the Venus length of day (LOD). Two main research directions ensue from these findings. First, monitoring the LOD fluctuations, while being able to quantify this atmospheric forcing mechanism, will ultimately constrain the interior of Venus for which we desperately lack data. Second, mountain waves can transport angular momentum from the surface to the upper atmosphere, and may play a role in the origin of the mysterious atmospheric superrotation.