PhysOrg - 31 May 2010
Superrotation on Venus: Driven By Waves Generated By Dissipation of the Transterminator FlowOne 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 meters per second, takes only four Earth days to go all the way around. The only other place in the Solar System in which atmospheric superrotation is common is on Saturn’s moon Titan.
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. They ... are thought to be driven by interaction with the solar wind.
Durand-Manterola and his 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. They propose 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.
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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.
- arXiv.org > astro-ph > arXiv:1005.3488 > 19 May 2010
Context: The superrotation phenomenon in the atmosphere on Venus has been known since the late 60's. But until now no mechanism proposed has satisfactorily explained this phenomenon.
Objective: The aim of this research is to propose a mechanism, until now never considered, which could drive the atmosphere of Venus in its superrotation. This mechanism involves the transfer of the transterminator ionospheric flow momentum to the lower atmosphere via pressure waves generated in the cryosphere of Venus. The mechanism proposed presents a source of energy sufficiently strong to allow the transfer of energy despite dissipation.
Method: The energy flow which transports the transterminator flow and the energy lost by the viscosity in the superrotating atmosphere were calculated. Both results were compared to establish if there is sufficient energy in the transterminator flow to drive the superrotation. Finally, the amplitude that the waves should have to be able to obtain the momentum necessary to induce superrotation was calculated. Also an experimental model was made presenting some similarities with the process described.