Letter to the Editor

Venus cloud discontinuity in 2022

The first long-term study with uninterrupted observations

¹ Facultad de Física, Universidad de Sevilla, Av. Reina Mercedes s/n, 41012 Sevilla, Spain
e-mail: jperalta1@us.es
² Associação Portuguesa de Astrónomos Amadores (APAA), Portugal
³ AstroCampania, Italy
⁴ British Astronomical Association, UK
⁵ Astronomical Society of Southern Africa (ASSA), South Africa
⁶ Science and Technology Corp., Boulder, CO, USA
⁷ Southwest Research Institute, Boulder, CO, USA
⁸ Escuela de Ingeniería de Bilbao, Universidad del País Vasco (UPV/EHU), Bilbao, Spain
⁹ Faculty of Environmental Earth Science, Hokkaido University, Sapporo, Japan
¹⁰ Graduate School of Frontier Sciences, The University of Tokyo, Tokyo, Japan
¹¹ Hellenic Amateur Astronomy Association, Athens, Greece
¹² Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency (JAXA), Sagamihara, Japan
¹³ Hokkaido Information University, Ebetsu, Japan

Received: 27 August 2022
Accepted: 7 February 2023

Abstract

Context. First identified in 2016 by the Japan Aerospace eXploration Agency (JAXA) Akatsuki mission, the discontinuity or disruption is a recurrent wave observed to propagate over 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 dissipates at the upper clouds and contributes to the maintenance of the puzzling atmospheric superrotation of Venus through wave-mean flow interaction.

Aims. Taking advantage of the campaign of ground-based observations undertaken in coordination with the Akatsuki mission from December 2021 until July 2022, we undertook the longest uninterrupted monitoring of the cloud discontinuity to date to obtain a pioneering long-term characterisation of its main properties and to better constrain its recurrence and lifetime.

Methods. The dayside upper, middle, and nightside lower clouds were studied with images acquired by the Akatsuki Ultraviolet Imager (UVI), amateur observers, and SpeX at the NASA Infrared Telescope Facility (IRTF). Hundreds of images were inspected in search of the discontinuity events and to measure key properties such as its dimensions, orientation, and rotation period.

Results. 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 91° ±8°, length of 4100 ± 800 km, width of 500 ± 100 km, and a rotation period of 5.11 ± 0.09 days. Ultraviolet images during 13–14 June 2022 suggest that the discontinuity may have manifested at the top of the clouds during ∼21 h as a result of an altitude change in the critical level for this wave, due to slower zonal winds.