Convectively Generated Internal Gravity Waves in the Lower Atmosphere of Venus. Part I: No Wind Shear

Abstract

This paper is the first of a two-part study that investigates internal gravity wave generation by convection in the lower atmosphere of Venus. A two-dimensional, nonlinear, fully compressible model of a perfect gas is employed. The calculations consider the lower atmosphere from 12- to 60-km altitude, thereby including two convection regions: the lower atmosphere convection layer from roughly 18- to 30-km altitude and the cloud-level convection layer from roughly 48- to 55-km altitude. The gravity waves of interest are located in the stable layer between these two convection regions. Part I of this study considers gravity wave generation and propagation in the absence of mean wind shear. In the absence of mean wind shear, internal gravity waves are primarily generated by cloud-level convection. Horizontal wavelengths (?10?15 km) are similar to dominant horizontal scales in the cloud-level penetrative region, and intrinsic horizontal phase speeds are comparable to cloud-level downdraft velocities. Without mean wind shear, there is no effective coupling between the lower atmosphere below 34-km altitude and the overlying stable layer. Simulated wave amplitudes and vertical wavelengths agree well with spacecraft observations, suggesting that gravity waves generated by cloud-level convection through the ?mechanical oscillator? effect may be responsible for observed variations in the stable layer.