Convectively Generated Internal Gravity Waves in the Lower Atmosphere of Venus. Part II: Mean Wind Shear and Wave–Mean Flow Interaction

Abstract

This paper is the second of a two-part study that numerically investigates internal gravity wave generation by convection in the lower atmosphere of Venus. Part I of this study considers gravity wave generation and propagation in the absence of mean wind shear. In Part II, the Venus westward superrotation is included, and wave–mean flow interaction is assessed. Both lower-atmosphere convection and cloud-level convection play active roles in the dynamics of the stable layer from 31- to 47-km altitude when mean wind shear is present. This result contrasts with the simulation without mean wind shear presented in Part I where cloud-level convection was primarily responsible for gravity wave generation in the stable layer. In the presence of mean wind shear, upward entrainment from lower-atmosphere convection and downward penetration from cloud-level convection are comparable in magnitude. Convectively generated internal gravity waves have horizontal wavelengths (∼25–30 km) comparable to horizontal scales in both convection layers. Quasi-stationary gravity waves (with respect to the lower convection layer) occur in the lower part of the stable layer, while both eastward- and westward-propagating waves generated by cloud-level convection exist in the upper part of the stable layer. Simulated wave amplitudes and vertical wavelengths agree well with observations. Eastward-propagating waves generated by cloud-level convection experience critical level absorption in the stable layer and thus decelerate the Venus westward superrotation below the clouds. The deceleration is comparable in magnitude to zonal accelerations above the clouds by thermal tides.