Gravity Wave Packets in the Venusian Atmosphere Observed by Radio Occultation Experiments: Comparison With Saturation Theory

摘要

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.