Space Probe Spots Venus’ Equatorial Winds

A Japanese satellite has collected data on high-velocity winds at Venus’ equator that could help clarify theories about superrotation.

AsianScientist (Sep. 6, 2017) – Scientists in Japan and the US have observed unusually high wind velocities near the equator of Venus. They report their results in the journal Nature Geoscience.

Venus rotates westward with a very low angular speed; it takes 243 Earth days to rotate once. The planet’s atmosphere rotates in the same direction but at much higher angular speeds, which is called superrotation.

The planet is covered by thick clouds that extend from an altitude of about 45 kilometers to 70 kilometers. The superrotation reaches its maximum near the top of this cloud, where the rotational speed is about 60 times that of the planet itself. The cause of this phenomenon, however, is shrouded in mystery.

Previous observations of Venus’ atmosphere by the Venus Express orbiter of the European Space Agency and the Galileo spacecraft of the US National Aeronautics and Space Administration have suggested that the wind speeds at lower-to-middle cloud altitudes are horizontally uniform and have few temporal variations.

The Akatsuki was launched in 2010 by the Japan Aerospace Exploration Agency to unravel the atmospheric mysteries of Venus. Although lower-altitude clouds cannot be observed using visible light, the Akatsuki’s near-infrared camera IR2 can successfully track clouds—in particular, thicker clouds between 45 kilometers to 60 kilometers in altitude, based on their silhouettes.

In this study, the team of researchers from Japan and the US analyzed the data collected by Akatsuki between March and August 2016. The team employed a cloud-tracking method they recently developed to deduce horizontal distributions of winds based on data from the Akatsuki.

They discovered an equatorial jet in the wind velocities based on image data from July 2016 and that the jet persisted for two months. This was in stark contrast to earlier observations in March when the wind velocities in the same latitude zones were rather slow.

The findings showed for the first time that wind velocities in the atmosphere of Venus can be markedly high, forming a jet near the equator, which have never been observed before.

“Our study uncovered that wind velocities in the lower-to-middle cloud layer have temporal and spatial variabilities much greater than previously thought,” said Associate Professor Takeshi Horinouchi of Hokkaido University, Japan.

“Although it remains unclear why such an equatorial jet appears, the mechanisms that could cause it are limited and related to various theories about superrotation. Hence, further study of the Akatsuki data should help glean useful knowledge about local jets and help address superrotation theories,” he added.

The article can be found at: Horinouchi et al. (2017) Equatorial Jet in the Lower to Middle Cloud Layer of Venus Revealed by Akatsuki.


Source: Hokkaido University; Photo: Planet-C Project Team.
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