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A new theory to explain superrotation on Venus

One of the mysteries in our Solar System is superrotation, a phenomenon known since the late 1960s, in which the winds on Venus blow faster than the planet rotates. Scientists have proposed a number of theories, but none have been completely satisfactory. Now scientists in Mexico have for the first time suggested a viable mechanism by which a faster wind higher above the planet is driving the superrotation.

A complete rotation of the planet Venus takes 243 Earth days, but the atmosphere, traveling at speeds of around 200 m/s, takes only four Earth days to go all the way around. Scientists have been studying the supersonic-speed winds in the ionosphere 150-800 kilometers above the surface. The winds, known as the “transterminator” flow, travel at several kilometers per second and are thought to be driven by interaction with the solar wind.

The team propose that the transterminator flow in the cryosphere could transfer flow momentum to the atmosphere below in the form of pressure waves as they dissipate. The interaction on the night side between the flow on the dawn side and the flow on the dusk side generates waves because they flow at different speeds, with the dusk side flow being much faster.

The waves travel down from the ionosphere, and through the thermosphere and mesosphere to the troposphere depositing most of the momentum and dissipating in the cloud layer, moving the atmosphere in a retrograde direction and driving the superrotation. There is enough energy in the transterminator flow to overcome the viscosity and drive superrotation. The produce 84 dB on the night side, enough to maintain a roar in the clouds on the planet’s night side “similar to a symphony orchestra playing ‘fortissimo’.”

The Akatsuki extraterrestrial weather satellite, which was launched from Japan last Friday, should arrive at Venus in December, when it may shed some light on the issue.

Image: Global view of the surface of Venus. via. High-Res: 4096×4096 px (1.7 MB)

Source: PhysOrg.com