Venus has a fast-moving atmosphere and a "tsunami" in its deepest clouds. Now, an international team of scientists has led the first detailed study of the evolution of the discontinuity of Venus's clouds, which appears as a gigantic atmospheric wave. The tsunami in the planet's deepest clouds is believed to play a significant role in the acceleration of Venus's fast-moving atmosphere.
The team, which includes scientists from the University of Seville and University of the Basque Country, carried out observations of Venus's clouds and the tsunami in them continuously for more than 100 days.
The study describing the findings was recently published in the journal Astronomy & Astrophysics.
Tsunami in Venus’s clouds propagated to around 70 kilometres above the planet’s surface
According to a statement issued by the University of Seville, the team observed a truly unexpected event. The Ultraviolet Imaging (UVI) camera on board the Akatsuki mission, which allows astronomers to see the highest clouds in Venus, captured ultraviolet images in June which seem to reflect the fact that the discontinuity of Venus's clouds was capable of propagating for a few hours to around 70 kilometres above the surface of the planet.
In the statement, Javier Peralta, one of the authors on the paper, said the finding is surprising, because until now, the discontinuity appeared 'trapped' in the deepest clouds and researchers had never observed the discontinuity at such a high altitude.
In 2022, Peralta was responsible for designing the strategy for the observations of Venus made by the Wide-Field Imager for Parker Solar Probe (WISPR), an imaging instrument of the Parker Solar Probe, during the approach or departure manoeuvres of Parker's flybys near Venus. Peralta also contributed to the physical interpretation of these observations, and compared thermal emission images of the surface of Venus captured by WISPR, and the IR1 camera of JAXA's (Japanese Aerospace Exploration Agency) Akatsuki spacecraft.
Why did the discontinuity in Venus’s clouds propagate to such great heights?
The Akatsuki images not only highlight the fact that the discontinuity may have propagated to the upper clouds of Venus, but also help researchers understand the reasons behind this displacement.
It is a general rule that regions where winds have the same speed as a wave act as a physical barrier for the propagation of that wave. Since 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. However, it meets the winds, which serve as obstacles, on its way, and eventually dissipates.
According to the statement, the experts were surprised when they measured the winds in the high clouds with Akatsuki, because they observed that the winds there were unusually slow in the first half of 2022. These winds were several times slower than the discontinuity itself.
When the winds grow much more slowly with height, the discontinuity takes longer to find atmospheric regions as fast as itself. This allows the discontinuity to propagate to higher altitudes, and explains the reason behind the tsunami in Venus's deepest clouds occurring at such high altitudes.
Peralta explained that the phenomenon of Venus's atmosphere spinning 60 times faster than the surface is known as superrotation. This atmospheric phenomenon also occurs on Saturn's moon Titan and on many exoplanets, but after more than half a century of research, scientists still cannot satisfactorily explain it.