Venus Mountain Waves in the Upper Atmosphere Simulated by A Time-Invariant Linear Full-Wave Spectral Model

A 2-D spectral full-wave model is described that simulates the generation and propagation of mountain waves over idealized topography in Venus' atmosphere. Modeled temperature perturbations are compared with the Akatsuki observations. Lower atmosphere eddy diffusivity and stability play a major role in the upward propagation of gravity waves from their mountain sources. Two local times (LT) are considered. For LT = 11 h the waves are blocked by a critical level near 100 km altitude, while for LT = 16 h the waves propagate into the thermosphere. As a result of the small scale height in the Venus thermosphere, for LT = 16 h wave amplitudes grow with increasing altitude up to ~200 km, despite the increasing kinematic viscosity. Although wave amplitudes can become very large in the thermosphere, the value of the total potential temperature gradient suggests that some of these fast waves having extremely large vertical wavelengths may remain convectively stable. Our simulations suggest that the momentum and thermal forcing of the mean state due to the dissipating waves may, at times, be extremely large in the thermosphere. At a given local time, the maximum forcing of the mean state always occurs at an altitude determined by the mean winds and the upper atmospheric viscosity. The surface conditions that determine the forcing (mountain parameters, surface mean wind, eddy diffusivity, and static stability) have little impact on this altitude, but they do significantly impact the magnitude of the forcing.