Zonal-flow variability associated with meridional circulation at the cloud top in a Venus atmospheric general circulation model

Internal variability of cloud-top super-rotation with periods of about a Venus day is found in a Venus AORI (Atmosphere and Ocean Research Institute, The University of Tokyo) GCM (General Circulation Model), along with diurnal variations of the meridional circulation and long-wave radiative cooling. In the diurnal cycle of the cloud-top zonal flow, the high-latitude jets increase, while the meridional circulation enhances the poleward momentum flux. Subsequently, the equatorial super-rotation becomes its maximum after the high-latitude jets reach their maximum. The present study reveals the formation of the diurnal cycle of the zonal flow by the meridional circulation and the destruction of the diurnal cycle by the amplified Eliassen-Palm (EP) flux in the model. Although the variability of the meridional circulation is stably diurnal throughout the simulation, the periodicity of the EP flux is not always diurnal. The diurnal cycle of the zonal flow becomes weak and the periodicities of ∼two Venus days appear in the model, when the zonal-flow acceleration by the EP flux is stronger than that by the meridional circulation at the equator and at the high-latitude jet cores. Moreover, when cyclic data gaps of cloud-tracking observation are considered in this study, the diurnal cycle of the zonal flow is unclear, and the peak-to-peak intervals of the zonal-wind maxima appear to be ∼two Venus days. • Variability of cloud-top super-rotation is examined in a Venus AORI GCM. • Diurnal cycle of meridional circulation is apparent in the presence of topography. • Diurnal cycle of zonal flow is formed by the meridional circulation. • Diurnal cycle of zonal flow is destroyed by the amplified Eliassen-Palm flux. • Periodicities of ∼two Venus days also appear in the GCM.