Does air in the atmosphere suffer friction in some way due solely to the planet's rotation?
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$\begingroup$ Cross-site duplicate: physics.stackexchange.com/q/772328/6319 $\endgroup$– gerrit ♦Commented Jul 17, 2023 at 6:52
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$\begingroup$ The ambiguous wording in this question invites ambiguous answers. There is no air in the atmosphere that is "solely" influenced by one effect; all effects are present at once and ultimate atmospheric behaviour is the result of an interaction between these effects. $\endgroup$– WillCommented Jul 17, 2023 at 10:46
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$\begingroup$ If it didn't... Why would we get "still" air and wind directions largely determined by pressure gradients. If the atmosphere didn't, on-average, rotate with the earth, we'd have a fairly constant 1000mph retrograde wind (obviously varying by lattitude) $\endgroup$– ScottishTapWaterCommented Jul 17, 2023 at 12:50
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2 Answers
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The short answer is yes.
Whenever a fluid moves against something else it will experience friction, it's a function of fluid dynamics.
The atmosphere is a weakly viscous fluid, but friction is important wherever the velocity gradient is very large. The frictional effect is therefore strong at least in a layer next to the surface of the Earth. Such a layer is called the boundary layer.
The amount of friction the atmosphere experiences depends on the roughness of the Earth. Over flat terrain it will experience less friction than over rough terrain such as mountains, forests or tall buildings.
The Planetary Boundary Layer (PBL) or Atmospheric Boundary Layer is the part of the atmosphere that makes contact with the Earth's surface.
As a result of surface friction, winds in the PBL are usually weaker than above and tend to blow toward areas of low pressure.
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2$\begingroup$ While I agree with what you have written, I don't see how it answers the question. How does the Earth's rotation come into play? $\endgroup$– f.thorpe ♦Commented Jul 17, 2023 at 5:11
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Since you say "due solely to the planet's rotation", the best answer might be "No." The atmosphere rotates as a body with the planet. The interplanetary medium is so diffuse there is essentially no friction between it and the atmosphere. Whenever there is a pressure difference between one location on the earth's surface and another nearby place, there is a force tending to cause wind from the higher pressure to the lower pressure location, and a friction force resisting that. But the planet's rotation does not apply any sideways force on the atmosphere, since the atmosphere is already rotating too. So there is no force for friction to resist, and therefore no friction caused solely by the earth's rotation.
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2$\begingroup$ I tend to agree with this answer, yes there is drag and the laminar flow is disrupted due to the surface. However, that is regardless of the Earth's rotation because the atmosphere can be moving in any direction, has momentum, etc. $\endgroup$– f.thorpe ♦Commented Jul 17, 2023 at 5:11
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$\begingroup$ @MarkFoskey I am not sure if I understand this answer. You first said that there would be no friction. But then you said that there would be friction between the atmosphere and the ground $\endgroup$– vengaqCommented Jul 17, 2023 at 13:05
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$\begingroup$ So, even if the atmosphere rotates at the same speed as Earth does, there would still be perturbations to its circulation due to defects in the surface? @f.thorpe $\endgroup$– vengaqCommented Jul 17, 2023 at 13:07
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$\begingroup$ @vengaq even though the whole atmosphere is moving at the same speed as the earth, locally, it's not (because "wind"). And wind (being moving gases, meaning a moving fluid) experiences friction at the boundary layer with the Earth. $\endgroup$– RonJohnCommented Jul 17, 2023 at 18:11
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$\begingroup$ @vengaq All atmospheric particles already have momentum due to Earth's rotation, but that is not wind. Wind is driven by solar heating and is dynamic depending on pressure gradients. The only direct effect on wind due to the rotation of the Earth that I can think of is the coriolis effect. $\endgroup$– f.thorpe ♦Commented Jul 17, 2023 at 23:38