Why does atmosphere rotate w/ constant angular velocity?

[Dotini]

@slick_willy

@Drakkith

More data on Atmospheric Angular Momentum (AAM) and Length of Day (LOD)

http://onlinelibrary.wiley.com/doi/10.1029/2006RG000213/full

[2] Angular momentum characterizes the rotation of physical systems ranging from the atomic scale to galaxies. In particular, the global angular momentum M of the atmosphere reflects both the rotation tied to that of the Earth and rotation due to the winds. A wealth of data and theories is available to determine the distribution of angular momentum and to provide the reasons for its changes. Attention is restricted in this review to large-scale motions, although angular momentum is also of key importance, say, in hurricanes or tornadoes. The global atmospheric angular momentum is the integral

http://onlinelibrary.wiley.com/store/10.1029/2006RG000213/asset/equation/rog1654-math-0001.gif?v=1&t=ippj8s7t&s=2c2bab9f874ffdbedcaaf572f9d2096c39ec53ce
of the angular momentum

http://onlinelibrary.wiley.com/store/10.1029/2006RG000213/asset/equation/rog1654-math-0002.gif?v=1&t=ippj8s7t&s=518c5825d4839641914d971653bfaf4b0138cb78
per unit volume over the volume V of the Earth's atmosphere. In (2), r is the position vector pointing from the center of the Earth to the volume element dV of density ρ (see Figure 1). It is customary to assume a dry atmosphere because the contribution of the water substance to the total mass of the atmosphere is small. In principle, the density ρ in (2) also contains the water substance in all phases. The rotation of the Earth is represented by its angular velocity Ω with Ω = 2π/d. The relative velocity of the air with respect to this rotation is v and

http://onlinelibrary.wiley.com/store/10.1029/2006RG000213/asset/equation/rog1654-math-0003.gif?v=1&t=ippj8s7t&s=060425d355ced8d7b10839d0ee943b43171d0166
is the absolute velocity.

Figure 1.

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Rotating Earth and the components Miii of the global angular momentum M in the rotating coordinate system with basic vectors ii. The position vector r points to a volume element dV in space, where the unit vectors eλ, eϕ, and er of the local rotating spherical coordinate system are defined.

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Figure 2
Time and zonal mean of the (a) axial wind term [

w3] in 106 Had s and (b) south-north difference of the mass term [

m3] in 105 Had s as a function of height z (km) and latitude. The terms are integrated over zonal annuli of 5° width and 1000 m depth. Data basis is ERA-40 (1958–2001).-----------------------------------------------------------------------

[6] The laws of angular momentum emerged only slowly in fluid mechanics (see Truesdell [1968] for a lucid account). Bernoulli [1747] may have been first to apply angular momentum concepts correctly in a model of the equatorial easterlies. On the other hand, Hadley [1735] used inaccurate arguments concerning angular momentum in his celebrated treatise on trade winds. A historic account is, however, beyond the scope of this article. For our purpose it is sufficient to state that the axial angular momentum cycle of the atmosphere and its link to the rotating Earth via the torques have been a key topic of meteorology at least since the 1950s. Starr [1948], Starr and White [1951], Lorenz [1967], and others worked out the basic features of the atmosphere's axial angular momentum budget (see Oort [1989] and Rosen [1993] for introductions into historical aspects). The review by Oort and Peixoto [1983]describes the mean distribution of the axial angular momentum in the atmosphere, its transports, with particular emphasis on the role of eddies, and the contributions of latitude belts to friction and mountain torques. In general, good agreement is found between observed changes of M3 and those of LOD as predicted by (15) [Rosen, 1993].

Edit: Figure 2 (a) and (b) added. Enjoy.

 

[Designman]

Cwatters, I think you got it! There is no friction to a body spinning in space, solid or gas.

 

[Dotini]

For the curious, a smattering of additional sources cover super rotation of Earth's upper atmosphere, diurnal variations in Earth's rotation, and uncertainty in wind friction torque:

http://www.sciencedirect.com/science/article/pii/0032063371901760
http://oro.open.ac.uk/39811/
http://www.nature.com/nature/journal/v231/n5298/abs/231109b0.html
http://link.springer.com/article/10.1023/A:1014847319391

http://www.mdpi.com/1424-8220/15/2/2944/htm
Abstract
The Earth's rotation undergoes changes with the influence of geophysical factors, such as Earth's surface fluid mass redistribution of the atmosphere, ocean and hydrology. However, variations of Earth Rotation Parameters (ERP) are still not well understood, particularly the short-period variations (e.g., diurnal and semi-diurnal variations) and their causes.

http://science.sciencemag.org/content/264/5160/830.abstract
Abstract
Recent space-geodetic observations have revealed daily and subdaily variations in the Earth's rotation rate. Although spectral analysis suggests that the variations are primarily of tidal origin, comparisons to previous theoretical predictions based on various ocean models have been less than satisfactory. This disagreement is partly caused by deficiencies in physical modeling.

http://www.sciencedirect.com/science/article/pii/S1674984716300301
Abstract
The wind stress acquired from European Centre for Medium-Range Weather Forecasts (ECMWF), National Centers for Environmental Prediction (NCEP) climate models and QSCAT satellite observations are analyzed by using frequency-wavenumber spectrum method. The spectrum of two climate models, i.e., ECMWF and NCEP, is similar for both 10 m wind data and model output wind stress data, which indicates that both the climate models capture the key feature of wind stress. While the QSCAT wind stress data shows the similar characteristics with the two climate models in both spectrum domain and the spatial distribution, but with a factor of approximately 1.25 times larger than that of climate models in energy. These differences show the uncertainty in the different wind stress products, which inevitably cause the atmospheric friction torque uncertainties on solid Earth with a 60% departure in annual amplitude, and furtherly affect the precise estimation of the Earth's rotation.

 

[Dotini]

As if all that wasn't enough to wrap my mind around, there is this: "polar wind", particles jetting out from the poles, only to be trapped in the magnetotail and be recycled into the atmosphere and Van Allen belts!

https://en.wikipedia.org/wiki/Polar_wind
The Earth's plasma fountain, showing oxygen, helium, and hydrogen ions which gush into space from regions near the Earth's poles. The faint yellow area shown above the north pole represents gas lost from Earth into space; the green area is the aurora borealis-or plasma energy pouring back into the atmosphere.[1]

Plasma Fountain
This figure depicts the oxygen, helium, and hydrogen ions that gush into space from regions near the Earth's poles. The faint yellow gas shown above the north pole represents gas lost from Earth into space; the green gas is the aurora borealis-or plasma energy pouring back into the atmosphere. FIGURE CREDIT: NASA---------------------------------------------------------------------------------

Polar wind at Titan, Earth, Venus, even Mars
http://www.space.com/29700-saturn-moon-titan-earth-like-winds.html

Saturn's moon Titan was already known to have similarities with Earth: a thick atmosphere, a rocky surface, lakes and rivers. Now, new data show that it also shares a peculiar effect that draws gases out of the atmosphere and into space. This photograph of Titan's atmosphere was taken by the Cassini space probe.
Credit: NASA/JPL/Space Science Institute, Processed by Kevin M. Gill

In our solar system

, the objects with rainfall, rivers and oceans can be counted on two fingers: Earth, and Saturn's moon Titan. Both also share

a thick atmosphere, rocky ground and plate tectonics, and now, they have one more thing in common: polar wind that pulls gases from their atmospheres right out into space.

On Earth, the same effect charges particles in the atmosphere and draws them up along the planet's magnetic field, where they can escape at the poles. Although Titan is the only other object in the solar system known to share this property, the researchers suggested that these particle escapes likely are happening on Mars and Venus as well.

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And "electric wind",

Abstract
Understanding what processes govern atmospheric escape and the loss of planetary water is of paramount importance for understanding how life in the universe can exist. One mechanism thought to be important at all planets is an “ambipolar” electric field that helps ions overcome gravity. We report the discovery and first quantitative extraterrestrial measurements of such a field at the planet Venus. Unexpectedly, despite comparable gravity, we show the field to be five times stronger than in Earth's similar ionosphere. Contrary to our understanding, Venus would still lose heavy ions (including oxygen and all water-group species) to space, even if there were no stripping by the solar wind. We therefore find that it is possible for planets to lose heavy ions to space entirely through electric forces in their ionospheres and such an “electric wind” must be considered when studying the evolution and potential habitability of any planet in any star system.

http://onlinelibrary.wiley.com/doi/10.1002/2016GL068327/full

Figure 1.

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• http://api.onlinelibrary.wiley.com/asset/v1/doi/10.1002%2F2016GL068327/powerpoint/image_n%2Fgrl54302-fig-0001.png?l=SkaBT8QEx2pjprjJHz2CVSseSET6UD5ZV2ueMEywV0Z5hHx5UbQSQzexHwkhtQqTXsIaR2ARwe4%3D&s=%22b2b8e3938d874a21829220c56c8caf63%22&a=wol

The induced magnetosphere of Venus and formation of the electric wind.

 

[256bits]

http://www.msn.com/en-ca/weather/topstories/outrageously-strong-electric-winds-in-venus-destroyed-its-oceans/ar-AAhnoKR?ocid=ansmsnweather11
Picture of Venus.
And a video from a NASA representative.
Electric field proposed as being responsible for the loss of water on Venus.