Toward understanding the nature of the “Disruption” and “Enormous Cloud” seen by Akatsuki in the Venus atmosphere

Night side near infrared imagery by the IR2 camera on JAXA’s Akatsuki spacecraft revealed an unusually large and sharply-defined opacity feature. Examination of past observations by numerous spacecraft and ground-based observatories, it was found that morphologically-similar counterparts to the Akatsuki-viewed feature could be reliably found since the 1980’s, when the technique of near-infrared night side imaging of Venus was pioneered. This feature was observed to circle the planet with an average speed of 4.9 days per rotation, consistent with zonal winds near the cloud tops. Although previous work suggested that the night side near infrared contrasts were driven largely by opacity variations in the lower cloud, this feature appeared to be travelling at speeds that were closer in magnitude to the zonal winds observed in the upper clouds. Taking advantage of the spectroscopic analysis made possible by VIRTIS on Venus Express, we explore the nature of this feature observed in Akatsuki data by assuming that the morphologically-similar features are comparable. Following previous analysis, we derive maps of cloud particle acid mass fraction, mixing ratios of water vapor and carbon monoxide, particle size parameter, and cloud base altitude for an instance of this feature seen by VIRTIS on Venus Express.