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Giant Streak Structure Found in Venus’ Cloudtops



A team of researchers in Japan has discovered a giant striped structure in the tops of the clouds of Venus. The discovery is based on the observations of Venus from the Japanese spacecraft Akatsuki. The results were published on January 9 in the journal Nature Communications.

Venus is different from any other planet in the Solar System. The entire planet is enveloped by thick clouds of sulfuric acid between altitudes of 45 km to 70 km. This often shroud prevented scientists from studying in detail the so-called "twin planet" of the Earth. But Japanese researchers are making progress.

The discovery of these giant stripes began with the Japanese Akatsuki spacecraft. Akatsuki, also called Venus Climate Orbiter, is a mission of the Japan Aerospace Exploration Agency (JAXA). The spacecraft has been in orbit around Venus since December 201

5. He discovered the massive striped structure in the mid and low cloud images of the night side of Venus taken by the IR2 (Infrared 2) camera on the orbiter. The observational data of IR2 were not of high quality and unfortunately that camera no longer works, so it was not able to further examine the structure and make fun of the cause of the strip.

  Venus in the ultraviolet courtesy of the Akatsuki spacecraft of JAXA. The thick atmosphere of the planet makes observation difficult. Credit: JAXA / Akatsuki / ISAS / DART
Venus in the ultraviolet courtesy of the Akatsuki spacecraft of JAXA. The thick atmosphere of the planet makes observation difficult. Credit: JAXA / Akatsuki / ISAS / DARTS / Damia Bouic

The Japanese team, led by project professor Hiroki Kashimura, (Kobe University, Graduate School of Science), used a computer program called AFES-Venus to calculate the simulations of Venus & atmosphere. This is something commonly done on Earth to predict weather, storms and climate change. They hoped that Akatsuki's simulations and observations would reveal the nature of the planetary scale stripes.

(Left) The lower clouds of Venus observed with the Akatsuki IR2 camera. The bright parts show where the cloud cover is thin. You can see the striped structure of the planetary scale inside the yellow dotted lines. (Right) The planetary-scale structure reconstructed from the AFES-Venus simulations. The bright parts show a strong downward flow. (Partial modification of the image in the document Nature Communications CC BY 4.0?

When it comes to Venus, the simulations are an even more important tool to understand what happens in the atmosphere of that planet, because observing it is so The difficulty in observing Venus also makes it difficult to confirm the simulations.

But the AFES-Venus had already had some success. The program had been used successfully to reproduce the super rotational winds and the polar temperature structures in the atmosphere of Venus also used another simulator provided by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) to create numerical simulations at a higher resolution than Venus.

analyzed the simulations and discovered what they think causes these gigantic striations formed by the interaction of two atmospheric phenomena: the first cause of this structure is a phenomenon connected to the daily climate of the Earth: polar jet flows.

Polar jet flows are formed in the mid-high levels of the atmosphere here on Earth. The simulations in this study show that the same thing happens on Venus. Both are formed by the large-scale wind dynamics in the atmosphere of both planets. But on Venus, there's something else at work.

The formation mechanism for the planetary-scale strip structure. The giant vortexes caused by the Rossby waves (on the left) are inclined by high-latitude jet streams and extend (on the right). Within the stretched vortex, the convergence zone of the strip structure is formed, an outflow occurs and the lower clouds become thin. Venus rotates in a western direction, so even jet flows blow west.

At low latitudes, an atmospheric wave due to the distribution of large-scale flows and the effect of planetary rotation (Rossby wave) generates large vortexes across the equator at latitudes of 60 degrees in both directions. Venus is different from the Earth when it comes to rotation. It rotates in the opposite direction to the Earth and rotates slowly: the planet takes 243 Earth days to complete a rotation.

When the vortexes are added to the flows of polar jets over Venus, the vortices incline and elongate, and the convergence zone between the north and south winds appears as a strip. The north-south wind that is pushed out of the convergence zone becomes a strong downward flow, resulting in the planetary-scale structure.

Polar views of the atmospheric stripes in the atmosphere of Venus captured by the IR2 instrument on the Akatsuki spacecraft. C is the polar view south and D is the north polar view. Image: Kashimura et. to the. 2019.

The study is a successful combination of observational tests and simulations. The atmosphere of Venus is difficult to study and most of the studies have focused on two dimensions, from east to west. But this study begins to add a third dimension to our understanding of Venus.

The team behind the studio is confident of their findings, but warn that it is not a complete picture of the causes of the gigantic series. As they say in their article, "Although we discussed a possible mechanism of planetary-scale structure formation as above, we should note that the details of disturbances, instabilities and angular momentum balance in our simulation are not yet clear and remain from explore. "

They also state that further studies are needed to understand all the details behind the phenomena. "We need to understand these mechanisms to assess the robustness or sensitivity of the speculated training mechanism presented here, but we keep these further investigations for our future studies."

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