First long-term study of the Venus' Cloud Discontinuity with uninterrupted observations

The discontinuity/disruption is a recurrent atmospheric wave observed to propagate during decades at the deeper clouds of Venus (47-56 km above the surface), while its absence at the top of the clouds (~70 km) suggests that it might dissipate at the upper clouds and contribute to the puzzling atmospheric superrotation through wave-mean flow interaction.

Thanks to a campaign of ground-based observations performed in coordination with JAXA's Akatsuki mission since December 2021 until July 2022, we aimed to undertake the longest uninterrupted monitoring of the cloud discontinuity up to date to obtain a pioneering long-term characterization of its main properties and better constrain its recurrence and lifetime. The dayside upper, middle and nightside lower clouds were studied with images taken with suitable filters acquired by Akatsuki/UVI, amateur observers and NASA's IRTF/SpeX, respectively. Hundreds of images were inspected in search of discontinuity events and to measure properties like its dimensions, orientation or rotation period.

We succeeded in tracking the discontinuity at the middle clouds during 109 days without interruption. The discontinuity exhibited properties nearly identical to measurements in 2016 and 2020, with an orientation of 91º±8º, length of 4100±800, width of 500±100 km and a rotation period of 5.11±0.09 days. Ultraviolet images during 13-14 June 2022 suggest that we have witnessed for the first time a manifestation of the discontinuity at the top of the clouds during ~21 hours, facilitated by an altitude change in the critical level for this wave due to slower zonal winds.