Contribution of Thermal Tides to Venus Upper Cloud-Layer Superrotation

Venus's cloud-layer superrotation, characterized by equatorial zonal winds of ∼100 m/s, is sustained by the atmospheric angular momentum (AM) transport induced by atmospheric waves, especially thermal tides, and meridional circulation. However, the overall patterns of thermal tides and their individual components' contribution to superrotation remain poorly understood. Using a 16-year radio occultation data set observed by Venus Express and Akatsuki, we have, for the first time, revealed the thermal tide structure from the cloud base to mesopause (50–90 km) in the southern hemisphere. The tidal patterns are equatorially symmetric and validated by simulations with the Venus Planetary Climate Model, extending tidal insights beyond the northern hemisphere focus of previous studies. The simulation indicates that diurnal tide-induced AM flux divergence is the primary driving force for equatorial cloud-top superrotation, with its meridional and vertical AM flux divergence dominating in the region of ∼5 km above and below the cloud top, respectively.