Atmospheric super-rotation is a phenomenon where a

planet A planet is a large, Hydrostatic equilibrium, rounded Astronomical object, astronomical body that is generally required to be in orbit around a star, stellar remnant, or brown dwarf, and is not one itself. The Solar System has eight planets b ...

atmosphere An atmosphere () is a layer of gases that envelop an astronomical object, held in place by the gravity of the object. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A stellar atmosph ...

rotates faster than the planet itself. This behavior is observed in the atmospheres of

Venus Venus is the second planet from the Sun. It is often called Earth's "twin" or "sister" planet for having almost the same size and mass, and the closest orbit to Earth's. While both are rocky planets, Venus has an atmosphere much thicker ...

Titan Titan most often refers to: * Titan (moon), the largest moon of Saturn * Titans, a race of deities in Greek mythology Titan or Titans may also refer to: Arts and entertainment Fictional entities Fictional locations * Titan in fiction, fictiona ...

Jupiter Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a Jupiter mass, mass more than 2.5 times that of all the other planets in the Solar System combined a ...

, and Saturn. Venus exhibits the most extreme super-rotation, with its atmosphere circling the planet in four Earth days, much faster than the planet's own rotation of 243 Earth days. The phenomenon of atmospheric super-rotation can influence a planet's climate and atmospheric dynamics.

Dynamics of super-rotation

In understanding super-rotation, the role of atmospheric waves and instabilities is crucial. These dynamics, including Rossby waves and

Kelvin wave A Kelvin wave is a wave in the ocean, a large lake or the atmosphere that balances the Earth's Coriolis force against a topographic boundary such as a coastline, or a waveguide such as the equator. A feature of a Kelvin wave is that it is non-d ...

s, are integral in transferring momentum and energy within atmospheres, contributing to the maintenance of super-rotation. For instance, on Venus, the interaction of thermal tides with planetary-scale Rossby waves is thought to contribute significantly to its rapid super-rotational winds. Similarly, in Earth's atmosphere, Kelvin waves generate eastward along the equator, playing a vital role in phenomena like the El Niño-Southern Oscillation, demonstrating the broader implications of these dynamics in atmospheric scienc

https://doi.org/10.1007/s11214-020-00703-9]

Venus: Extreme super-rotation

The

atmosphere of Venus The atmosphere of Venus is the very dense layer of gases surrounding the planet Venus. Venus's atmosphere is composed of 96.5% carbon dioxide and 3.5% nitrogen, with other chemical compounds present only in trace amounts. It is much denser and ho ...

is a prominent case of extreme super-rotation; the Venusian atmosphere circles the planet in just four Earth days, much faster than Venus'

sidereal day Sidereal time ("sidereal" pronounced ) is a system of timekeeping used especially by astronomers. Using sidereal time and the celestial coordinate system, it is easy to locate the positions of celestial objects in the night sky. Sidereal t ...

of 243 Earth days. The initial observations of Venus' super rotation were Earth-based. Modern GCM models and observations are often enhanced by looking at past ancient climates. In a model where Venus is assumed to have an atmospheric mass similar to Earth, subsolar-antisolar circulation could have dominated over super-rotation in an ancient thinner atmosphere.

Titan

Super-rotation present in the stratosphere of Titan has been inferred by Voyager IRIS, Cassini CIRIS, stellar occultation and temperature observations, and Doppler shifts of the Huygens probe’s radio signal. Latitudinal pressure gradients established from measurements taken by Voyager IRIS were sufficient to produce super-rotation of the atmosphere. Stratospheric zonal winds on Titan were observed on the order of 100-200 m s⁻¹, faster than the highest zonal winds on Earth at ~60-70 m s⁻¹. Questions on the effect of obliquity in super-rotation on Titan is often compared to Venus, as they share similar centrifugal accelerations to achieve dynamic balance. Any seasonal variations effected by obliquity between Titan and Venus is much different, as the small obliquity of Venus at 2.7° negates any strong seasonal effects. Titans obliquity at 26.7° is high enough to cause seasonal variations within the stratospheric spin. Attempts to model super-rotation on the gas giants, including Titan, has been abundant. The first observations of Titan in the 1980's revealed little information about circulation within the atmosphere due to the low contrast photochemical haze covering the moon. The first

general circulation model A general circulation model (GCM) is a type of climate model. It employs a mathematical model of the general circulation of a planetary atmosphere or ocean. It uses the Navier–Stokes equations on a rotating sphere with thermodynamic terms for ...

(GCMs) in the 1990s provided insight into the stratospheric properties that should be expected on Titan with further observation, and predicted super-rotation with winds up to 200 m/s. Super-rotation was supported by the first 3D Titan GCM created by the Laboratoire de Météorologie Dynamique (LMD), in which they used an atmosphere similar to the observations of Voyager and recently Cassini. The most recent GCM that is able to simulate super-rotation in the stratosphere successfully is TitanWRF. Modeled after the PlanetWRF, which was designed to be a global weather, research, and forecasting (WRF) model, TitanWRF added planetary physics and generalized parameters to produce a successful super-rotation model. Work done with TitanWRF v2 was able to simulate gradients in latitudinal temperature, zonal wind jets and super-rotation in the stratosphere. Comparing TitanWRF v2 simulations with constant solar forcing (seasonal cycle removed) models, showed that in the latter, a rapid buildup in rotation, attaining > 100m/s, happened in a few Titan years. The parameters in these older forcing models differ greatly in the mechanisms involved in generating the initial super-rotation compared to the more realistic TitanWRF models. After initial spin up, similarities evolve between the different models when a steady state is produced, but differ again in the final states of the model. The initial mechanism producing spin up to super-rotation is still an on going question, as correlations between models differ greatly within this regime.

Jupiter and Saturn: Gas Giant's atmospheres

The visible cloud tops of Jupiter and Saturn provides further evidence on its deep atmospheric circulation demonstrating the presence of atmospheric super-rotation. Jupiter's auroras, in particular, highlight the planet's rapid atmospheric movements through their ethereal glow and varying cloud depths.

Earth's super-rotation

On Earth, there is a phenomenon that its

thermosphere The thermosphere is the layer in the Earth's atmosphere directly above the mesosphere and below the exosphere. Within this layer of the atmosphere, ultraviolet radiation causes photoionization/photodissociation of molecules, creating ions; the ...

has a slight net super-rotation, exceeding the surface rotational velocity. The size of this phenomenon varies widely across different models. Some models suggest that

global warming Present-day climate change includes both global warming—the ongoing increase in global average temperature—and its wider effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes ...

is likely to cause an increase in super-rotation in the future, including possible change in surface winds patterns. In simplified GCM models, equatorial super-rotation emerges without obliquity and the addition of tropical heating anomalies. At present, a counter balance between the easterly Coriolis torque and the westerly torque maintains subrotation in the upper tropical troposphere. This leads to the prospect that with warmer and tropical wave sources in past ancient climates, Earth's atmosphere might have super-rotated.

Exoplanets and hot Jupiters

Super-rotation in planetary atmospheres extends to the study of exoplanets, particularly, hot Jupiters. These distant worlds, orbiting close to their stars, often exhibit extreme atmospheric conditions, including super-rotation, which influences their thermal structures and potential habitability. Observations from telescopes like the

Hubble Space Telescope The Hubble Space Telescope (HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the Orbiting Solar Observatory, first space telescope, but it is one of the largest and most ...

have unveiled super-rotational wind speeds of thousands of kilometers per hour on some hot Jupiters. Moreover, the phenomenon shows how hot Jupiters are tidally locked, where one side continuously faces the star. This suggests a mechanism for heat distribution in planets, a factor in understanding their climatic conditions and patterns.

References

{{reflist Planetary atmospheres