Angular Momentum Balance of Superrotation in Venus's Middle and Upper Atmosphere Simulated by AFES‐Venus

Abstract Based on simulations of the Venusian atmosphere using the AFES‐Venus GCM, we investigated the angular momentum (AM) balance that maintains the atmospheric superrotation (SR) at 35–90 km altitudes. In and above the cloud layer, the Eulerian‐mean meridional circulation consists of Hadley‐like cells at low latitudes and Ferrel‐like cells at middle to high latitudes, while the residual mean meridional circulation (RMMC) consists of a single Hadley‐like cell extending from the equator to the poles. Horizontally integrated AM and Eliassen‐Palm (EP) fluxes show that, at 46–90 km, SR is primarily accelerated by RMMC‐induced upward AM transport. This acceleration is counterbalanced by wave‐induced downward transport; however, the thermal tides significantly accelerate SR at 50–60 and 67–75 km. Thus, SR is maintained by both the meridional circulation and thermal tide mechanisms, which contribute approximately 70% and 30%, respectively, in the cloud layer. Regionally integrated AM and EP fluxes indicate that the RMMC transports substantial AM upward across the 54‐km level at low latitudes, with its upper branch subsequently carrying most of this AM poleward within 54–73 km. Although part of the poleward‐transported AM is returned equatorward by waves, the amount is much smaller than the poleward transport. Instead, wave‐induced downward transport at high latitudes, primarily associated with poleward eddy heat flux, is crucial for the AM budget. Our results provide a more detailed interpretation of the AM balance and clarify the respective roles of the MMC, thermal tides, and planetary‐scale waves than those presented in the so‐called classical theories.