[P-PS04] Advancing the science of Venus in the golden age of exploration

[PPS04-09] Meridional distribution of gravity waves in the Venusian atmosphere revealed by radio occultation

Fukuoka Seiki¹, *Takeshi Imamura¹, Hiroki Ando², Bernd Häusler³, Martin Pätzold⁴, Silvia Tellmann⁴ (1.Graduate School of Frontier Sciences, The University of Tokyo, 2.Kyoto Sangyo University, 3.Universitat der Bundeswehr Munchen, Germany, 4.Universitat zu Koln, Germany)

Keywords:Venus, atmospheric gravity wave, radio occultation

Atmospheric gravity waves are thought to play crucial roles in the vertical transport of energy, momentum and chemical species in the atmospheres of the planets including Venus. Venusian gravity waves have been extensively studied with radio occultation observations in NASA’s Magellan mission, ESA’s Venus Express mission and JAXA’s Akatsuki mission [e.g., Hinson and Jenkins 1995; Tellmann et al. 2012; Mori et al. 2021]. An increase of the amplitude at high latitudes was found and attributed to the effect of topography or the possible enhancement of cloud-level convection at high latitudes. The decay of the amplitude with height was also suggested and attributed to the effect of radiative damping. In order to quantitatively assess the role of gravity waves, more detailed distribution of gravitational waves over wide latitude and altitude ranges and its wavelength dependence need to be known.
In this study, the radio occultation data taken in Akatsuki and Venus Express missions were analyzed by Full Spectrum Inversion [Jensen et al., 2003] to achieve a vertical resolution of around 100 m, which is higher than those achieved by the conventional geometric optics method. This enables us to obtain the meridional distribution of gravitational waves for different vertical wavelengths including those less than 1 km. The meridional distribution was found to be qualitatively similar among the wavelength ranges. The temperature amplitude is relatively large in the upper part of the cloud layer at altitudes of 60–70 km, especially at high latitudes where the static stability of the background atmosphere is high. It was also found that the amplitude increases with altitude above 75 km at low latitudes. The local time dependence in the low latitude shows a tendency that the amplitude increases during daytime around 60 km altitude where the static stability is relatively high. These results suggest that the temperature amplitude tends to be larger in regions where the static stability of the background atmosphere is higher. A linear model of monochromatic waves taking into account the static stability of the background atmosphere and radiative damping was developed to show that the observed meridional distribution of the temperature amplitude can be qualitatively explained by the distribution of the static stability.