Mesoscale modeling of Venus' bow-shape waves

Abstract

The Akatsuki instrument LIR measured an unprecedented wave feature at the top of Venusian cloud layer. Stationary bow-shape waves of thousands of kilometers large lasting several Earth days have been observed over the main equatorial mountains. Here we use for the first time a mesoscale model of the Venus's atmosphere with high-resolution topography and fully coupled interactive radiative transfer computations. Mountain waves resolved by the model form large-scale bow shape waves with an amplitude of about 1.5 K and a size up to several decades of latitude similar to the ones measured by the Akatsuki spacecraft. The maximum amplitude of the waves appears in the afternoon due to an increase of the near-surface stability. Propagating vertically the waves encounter two regions of low static stability, the mixed layer between approximately 18 and 30 km and the convective layer between 50 and 55 km. Some part of the wave energy can pass through these regions via wave tunneling. These two layers act as wave filter, especially the deep atmosphere layer. The encounter with these layers generates trapped lee waves propagating horizontally. No stationary waves is resolved at cloud top over the polar regions because of strong circumpolar transient waves, and a thicker deep atmosphere mixed layer that filters most of the mountain waves.