Horizontal structures of bow-shaped mountain wave trains seen in thermal infrared images of venusian clouds taken by Akatsuki LIR

Abstract

Bow-shaped stationary gravity waves (mountain waves) have been observed in Venusian cloud images taken by the cameras onboard the Akatsuki spacecraft. The waves are most pronounced in the thermal infrared images taken by the Longwave Infrared Camera (LIR), and have been shown to appear at longitudes where high mountains exist. To better characterize mountain waves in the Venusian atmosphere, we applied a new analysis method to the LIR data. By averaging multiple sequentially obtained images in the geographical coordinates, noise and drifting features were suppressed and stationary features were emphasized, thereby identifying even weak wave features whose amplitudes were smaller than those identified in previous studies. The waves were observed in six highland regions, and two of these wave features have not been previously reported. Each wave packet extends both downstream and upstream by thousands of kilometers from the expected source region. Such characteristics might be attributed to the trapping and horizontal propagation of mountain waves in the low-static stability layers below the clouds.