Stationary Features at the Cloud Top of Venus Observed by Ultraviolet Imager Onboard Akatsuki.

Stationary features indicative of topographic gravity waves were identified at the cloud top of Venus with the 283‐nm channel of the Ultraviolet Imager (UVI) onboard Akatsuki, and their geographical and local time dependences were studied. At this wavelength the absorption by SO2 dominates. To extract stationary structures with respect to the surface, we averaged multiple images to smooth out moving features and applied high‐pass filtering to emphasize small structures. We found that stationary features appear exclusively above highlands and that they tend to appear between noon and evening. The stationary features seem to be synchronized with those observed in the cloud top temperature maps taken by the Longwave Infrared Camera (LIR). It was shown using a gravity wave model that the scale height of SO2 should be smaller than that of the cloud around the cloud top to reproduce the observed phase relationship between the stationary features seen in the Ultraviolet Imager and Longwave Infrared Camera images. Plain Language Summary: Topographic gravity waves, which are atmospheric waves created by winds flowing over mountains, are found to be ubiquitous in the Venus atmosphere. These waves are expected to play crucial roles in the momentum balance of the global‐scale atmospheric circulation. The spatial and temporal variabilities of such waves were studied using 283‐nm images taken by an ultraviolet camera onboard the Venus orbiter Akatsuki. To extract cloud structures related to topographic gravity waves that are stationary with respect to the surface, multiple images were averaged to smooth out moving features. Topographic waves were found to appear above highlands from noon to evening. The vertical distribution of SO2, which is the main absorber at this wavelength, around the cloud top was constrained from the observed wave features based on the modeling of wave‐induced transport. Key Points: Stationary features were observed at the cloud top of Venus in the ultraviolet and attributed to topographic gravity wavesThe features appear above highlands and between noon and the eveningThe scale height of SO2 was constrained based on modeling of the observed features [ABSTRACT FROM AUTHOR]