Science and Exploration

New Study About The ‘Tsunami’ In Venus’ Clouds

By Keith Cowing
Press Release
University of Seville
March 24, 2023
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New Study About The ‘Tsunami’ In Venus’ Clouds
A.1. Geometrical projections of discontinuity events during 2022. This Supporting Figure displays the same examples of discontinuity as in Figure 1 but as equirectanguar (cylindrical) projections with an angular resolution of 0.75◦ per pixel. The images are projected for latitudes 90◦N–90◦S (vertical axis) and local hour coordinates (horizontal axis). The discontinuity was apparent on the nightside lower clouds with 2.26−µm images from IRTF/SpeX taken in February 4, and on the dayside middle clouds as observed with images by amateur observers taken with filters covering wavelengths 700–900 nm during May 5,15,25,30, June 14,19,24 and July 13,18,23,28. Exceptionally, the discontinuity seemed to manifest at the top of the dayside clouds with Akatsuki/UVI images at 365 nm during June 14. The red rectangles represent the areas where we expect to find the discontinuity when considering June 14 as the reference position and mean rotation period 5.11 ± 0.09 terrestrial days. — astro-ph.EP

A group of scientists from the University of Seville, in collaboration with experts from the University of the Basque Country, has led the first detailed study of the evolution of the discontinuity of Venus’s clouds, a gigantic atmosphere wave with the appearance of a “tsunami” that is propagated in the planet’s deepest clouds and which, it is believed, may be playing a very significant role in the acceleration of Venus’s fast-moving atmosphere.

The observations were carried out non-stop for more than 100 days. “This observational feat was possible thanks to the collaboration of amateur astronomers from various countries, who have been the leading lights in the worldwide campaign of observations coordinated with the Japanese mission Akatsuki in 2022,” explains the University of Seville researcher and member of this mission, Javier Peralta.

This paper published in Astronomy & Astrophysics has also revealed a truly unexpected event, since the ultraviolet images taken in June by the UVI camera on board the Akatsuki mission (which allows us to see the highest clouds in Venus) seem to reflect the fact that the discontinuity was capable of propagating for a few hours to around 70 km above the surface of Venus. “This is surprising, because until now the discontinuity appeared ‘trapped’ in the deepest clouds and we had never observed it at such a high altitude,” explains Peralta.

The astrophysicist Javier Peralta was responsible for designing in 2022 the strategy for WISPR’s Venus observations during the spacecraft’s approach/departure manoeuvres during Parker’s flybys. He also contributed to physical interpretation of the observations, comparing thermal emission images of the surface of Venus taken by WISPR (NASA-Parker) and the IR1 camera (JAXA-Akatsuki).

In this vein, the Akatsuki images not only point to the fact that the discontinuity may have propagated to Venus’ upper clouds, but also help us to understand the reasons for this displacement. In general, regions where winds have the same speed as a wave act as a physical “barrier” for the propagation of that wave. Because winds gradually increase with height on Venus and have higher speeds than the discontinuity at the peak of the clouds, the discontinuity attempts to propagate upwards from the deep clouds, but meets this obstacle on its way and eventually dissipates. Thus, experts were surprised when they measured the winds in the high clouds with Akatsuki: they found that they were unusually slow in the first half of 2022, several times slower than the discontinuity itself. And if the winds grow much more slowly with height, the discontinuity takes longer to find atmospheric regions as fast as itself, allowing it to propagate to higher altitudes.

“Measuring the winds on Venus is essential to try to explain why Venus’s atmosphere spins 60 times faster than the surface. This atmospheric phenomenon is known as superrotation. It also happens on the Saturn moon Titan and on many exoplanets, but after more than half a century o research we still cannot satisfactorily explain it,” explains this researcher.

Venus cloud discontinuity in 2022. The first long-term study with uninterrupted observations, Astronomy and Astrophysics

Editor’s note: this is the preprint server entry for the research article reverend in this press release.

The Venus’ Cloud Discontinuity in 2022

J. Peralta, A. Cidadão, L. Morrone, C. Foster, M. Bullock, E. F. Young, I. Garate-Lopez, A. Sánchez-Lavega, T. Horinouchi, T. Imamura, E. Kardasis, A. Yamazaki, S. Watanabe

First identified in 2016 by JAXA’s Akatsuki mission, the discontinuity/disruption is a recurrent wave observed to propagate during decades at the deeper clouds of Venus (47–56 km above the surface), while its absence at the clouds’ top (∼70 km) suggests that it dissipates at the upper clouds and contributes in the maintenance of the puzzling atmospheric superrotation of Venus through wave-mean flow interaction. Taking advantage of the campaign of ground-based observations undertaken in coordination with the 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 with suitable filters acquired by Akatsuki/UVI, amateur observers and NASA’s IRTF/SpeX, respectively. Hundreds of images were inspected in search of manifestations of the discontinuity events and to measure key 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 91∘±8∘, length/width of 4100±800 / 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 hours as a result of an altitude change in the critical level for this wave due to slower zonal winds.

Comments: 8 pages, 4 figures, 2 animated figures, 1 table
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Atmospheric and Oceanic Physics (
Cite as: arXiv:2302.04689 [astro-ph.EP] (or arXiv:2302.04689v1 [astro-ph.EP] for this version)
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From: Javier Peralta
[v1] Thu, 9 Feb 2023 15:06:58 UTC (4,676 KB)

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