Gravity Wave Packets in the Venusian Atmosphere Observed by Radio Occultation Experiments: Comparison With Saturation Theory. Issue 9 (10th September 2021) - Mori, Ryota
Abstract: The characteristics of gravity wave packets in the Venusian atmosphere were studied using high‐vertical‐resolution temperature profiles obtained by ESA's Venus Express and JAXA's Akatsuki radio occultation experiments with radio holographic methods. Localized disturbances were detected by applying a wavelet transform to the temperature profiles. The packet lengths were found to be distributed over 0.6–10 km, in which typically 1.5–4.0 oscillations are included. The number of oscillations per wave packet was found to have only a slight dependence on the wavelength, which is consistent with the −3 power law dependence of the spectral density on the wavenumber in the saturation model. The spectral densities of the wave packets are roughly aligned with the power law of the saturation model, while the saturation ratio for each quasi‐monochromatic wave is low. This suggests that the saturated spectrum is produced by the superposition of individually unsaturated quasi‐monochromatic waves. Waves with short vertical wavelengths (<1.5 km) were found to be more prevalent at lower altitudes than at higher altitudes, implying an effect of radiative damping during upward propagation. The amplitude was found to be larger at higher latitudes, which might be attributed to an increase in background static stability at high latitudes, which allows larger saturation amplitudes. Plain Language Summary: Although gravity waves are thought to play crucial roles in transporting momentum and energy in the Venusian atmosphere, their characteristics are not well constrained from observations. Here the characteristics of Venusian gravity waves were studied by extracting wave packets from temperature profiles obtained by radio occultation experiments using Venus orbiters. The number of oscillations per wave packet was found to have only a slight dependence on the wavelength. The observed amplitudes and the vertical wavenumber spectra suggest that the superposition of quasi‐monochromatic waves causes convective instability to limit their amplitudes. The decrease of short vertical‐scale waves with altitude is thought to be caused by radiative dampling, and the increase of the amplitude at high latitudes is attributed to an effect of the background static stability. The finding that the wave amplitude is mostly limited by convective instability serves as the basis for gravity wave parameterization in numerical models. Key Points: Gravity wave packets in the Venusian atmosphere were detected in radio occultation temperature profiles using wavelet transform The characteristics of quasi‐monochromatic wave packets were studied in terms of the consistency with the saturation model Altitude and latitude dependences might be caused by radiative damping and the latitudinal variation of static stability, respectively