Simulations of Wave Features in Venus' Deep Atmosphere Associated with Topography, Using a Venus GCM

Abstract:

Venus' cloud-level atmosphere is characterized by the presence of waves with a range of periods and scale sizes. Wave phenomena can have important dynamical effects and may deposit significant momentum and energy into the atmosphere. Fluctuations with scale sizes of a few km to 10's of km have been observed at cloud altitudes in temperatures, winds or UV images from Mariner 10, Pioneer Venus, Venera 9, Magellan and Venus Express, suggesting the presence of gravity waves. Measurements of Venus' cloud level atmosphere have also identified planetary scale waves, with periods of around 4 to 5 days, which have been associated with Rossby or Kelvin waves. Longer term variations have also been observed in wind velocities at cloud heights, with periods of the order of several years. Planetary scale waves or gravity waves at cloud altitudes may be generated by a number of different mechanisms, for example by instabilities such as the Kelvin-Helmholtz instability or convective instability below the upper cloud layer, or they may be generated at lower altitudes and propagate upwards. Recent analyses from Venus Express observations suggest an association of gravity waves at cloud heights with significant topographical features. Although many measurements are available at cloud altitudes, little is known about waves in the poorly measured deep atmosphere. In order to explore the characteristics of waves generated near the surface we perform numerical simulations using the Venus Community Atmosphere Model general circulation model, which includes realistic topography based on measurements from the Magellan mission. We examine the influence of topography in generating waves near the surface associated with topographical features and the vertical development of simulated waves.