superrotation

Superrotation is a dynamical state in which a planet’s atmosphere or outer atmospheric layer rotates around the planet faster than the solid body itself. In this regime the atmospheric angular momentum corresponds to a rotation period shorter than the planet’s sidereal day. The term is commonly used to describe planetary atmospheres, especially cases where equatorial regions complete a circuit more rapidly than the planet’s rotation would suggest.

The best known example is Venus. Venus has a very slow, retrograde rotation with a sidereal day of about 243 Earth days. In contrast, the planet’s atmosphere at the equator completes a rotation roughly every 4 Earth days, amounting to a superrotation by a factor of about 60. Equatorial wind speeds can reach around 80–100 meters per second. This strong atmospheric circulation extends over a wide latitudinal range and strongly influences global climate patterns on Venus.

The mechanisms behind superrotation are an active area of research. Proposed explanations include the transport of angular momentum by planetary-scale waves—such as Rossby and Kelvin waves—coupled with thermal tides driven by solar heating, and strong Hadley-type circulations that redistribute momentum. The relative importance of these processes can vary with planetary parameters, including insolation, atmospheric composition, and vertical structure.

Beyond Venus, superrotation is discussed in the context of other atmospheres, including some exoplanets. For tidally influenced worlds such as hot Jupiters, strong eastward jet streams can also produce notable equatorial superrotation, affecting the distribution of heat and observable phase curves. Understanding superrotation helps explain wind patterns and climate dynamics across diverse planetary environments.

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