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Venus: computer simulated global view centered at 90 degrees east longitude. Credit: NASA / JPL
Images of the Akatsuki spacecraft reveal what it maintains VenusThe atmosphere rotates much faster than the planet itself.
An international research team led by Takeshi Horinouchi from Hokkaido University has revealed that this “super rotation” is held close to the equator by atmospheric tidal waves formed by solar heating on the day side of the planet and cooling on its night side. . However, closer to the poles, atmospheric turbulence and other types of waves have a more pronounced effect. The study was published online at Science April 23th.
Venus rotates very slowly, taking 243 Earth days to rotate once around its axis. Despite this very slow rotation, the atmosphere of Venus turns west 60 times faster than its planetary rotation. This super rotation increases with altitude, taking only four Earth days to circulate across the planet to the top of the cloud layer. The fast-moving atmosphere transports heat from the planet side to the night side, reducing temperature differences between the two hemispheres. “However, since super rotation was discovered in the 1960s, the mechanism behind its formation and maintenance has been a long-standing mystery,” says Horinouchi.
The proposed system that maintains the super (yellow) rotation of the atmosphere of Venus. The thermal tide (red) towards the equatorial summit imposes the super rotation towards the west. The atmosphere is controlled by a dual circulation system: the southern (vertical) (white) circulation that slowly transports heat to the poles and the super rotation that rapidly transports heat to the night side of the planet. Credit: Planet-C project team
Horinouchi and colleagues at the Institute for Space Science and Astronautics (ISAS, JAXA) and other institutes developed a highly accurate new method for tracking clouds and deriving wind speeds from images provided by ultraviolet and infrared cameras on the Akatsuki spacecraft, which began its orbit of Venus in December 2015. This allowed them to estimate the contributions from the atmosphere. waves and turbulence to the super rotation.
The group noted for the first time that atmospheric temperature differences between low and high latitudes are as small as cannot be explained without circulation through the latitudes. “Since such circulation should alter the wind distribution and weaken the superrotation peak, it also implies that there is another mechanism that reinforces and maintains the observed wind distribution,” Horinouchi explained. Other analyzes revealed that maintenance is sustained by the thermal tide, an atmospheric wave excited by the contrast of solar heating between the day and night sides, which provides acceleration at low latitudes. Previous studies proposed that atmospheric turbulence and waves other than the thermal tide can provide acceleration. However, the current study showed that they work in the opposite way to weakly slow super rotation at low latitudes, despite the fact that they play an important role in mid to high latitudes.
Their findings uncovered the factors that maintain super rotation while suggesting a double circulation system that effectively transports heat around the world: the southern circulation that slowly transports heat to the poles and the super rotation that rapidly transports heat to the poles. the night side of the planet.
“Our study could help to better understand atmospheric systems on tidal-blocked exoplanets whose side is always facing the central stars, which is similar to Venus having a very long solar day,” Horinouchi added.
Read Venus’ atmosphere rotates much faster than its surface due to thermal tides for more information on this research.
References
“Super rotation of the Venetian atmosphere”, by Sebastien Lebonnois at the Laboratoire de Météorologie Dynamique (LMD / IPSL) in Paris, France; S. Lebonnois at the Sorbonne Université in Paris, France; S. Lebonnois at ENS in Paris, France; S. Lebonnois at the PSL Research University in Paris, France; S. Lebonnois at the Ecole Polytechnique in Paris, France; S. Lebonnois at the Institut Polytechnique de Paris in Paris, France; S. Lebonnois at CNRS in Paris, France.
DOI: 10.1126 / science.abb2424
“How Waves and Turbulence Maintain the Super Rotation of Venus’ Atmosphere”, by Takeshi Horinouchi at Hokkaido University in Sapporo, Japan; Takeshi Horinouchi; Atsushi Yamazaki; Shin-ya Murakami; Javier Peralta; Masato Nakamura; Takehiko Satoh of the Japan Aerospace Exploration Agency in Sagamihara, Japan; Yoshi-Yuki Hayashi at Kobe University in Kobe, Japan; Shigeto Watanabe; Takao M. Sato at the Hokkaido Information University in Ebetsu, Japan; Manabu Yamada at the Chiba Institute of Technology in Narashino, Japan; Toru Kouyama at the National Institute of Advanced Industrial Science and Technology in Tokyo, Japan; Makoto Taguchi; Tetsuya Fukuhara at Rikkyo University in Tokyo, Japan; Masahiro Takagi at Kyoto Sangyo University in Kyoto, Japan; Kazunori Ogohara at the University of Shiga Prefecture in Hikone, Japan; Sanjay S. Limaye at the University of Wisconsin-Madison in Madison, WI; Takeshi Imamura at the University of Tokyo in Kashiwa, Japan; Masato Nakamura; Takehiko Satoh at the Graduate University for Advanced Studies (SOKENDAI) in Tokyo, Japan.
DOI: 10.1126 / science.aaz4439
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