Tallbloke's Talkshop

Richard says:

Hmm.

If you take a large, smooth, rotating plate at the bottom of a wide, air filled, cylinder then I suspect that, even with a very poor coupling between the plate and the air, the whole mass will assume a constant rotation throughout within a fairly short time period.

The exact profile will depend on the losses that oppose the rotation and where they occur.

Therefore the whole atmosphere will rotate with the planet (actually the surface directly below it) unless there are some losses to slow it in particular places/heights.

[Reply] The word ‘therefore’ is usually reserved until after the experiment. 😉

Bloke down the pub says:

My guess would be that the coriolis effect has a net effect that produces a westerly rotation of the atmosphere. The corotation is therefore likely to be driven by pressure differences caused by differential heating by the sun.

Bloke down the pub says:

That might be circuitous thinking, but that seems appropriate for a post on corotation.

Stephen Wilde says:

Any ideas how to relate this to climate phenomena ?

At first glance I would think it a contributor to background chaotic variability rather than the cause of any specific measurable observation.

Schrodinger's Cat says:

The viscosity is relevant if shear forces are applied, but where is the physical resistance to the motion of the atmosphere in space? Gravity comes into this as well, holding the atmosphere against the planet, which happens to be rotating. This stops the atmosphere from continuing its motion in a straight line or tangent. The same is true of the oceans.

I agree that there must be a motion gradient somewhere, but that may be academic if it lies at the edge of space.

pochas says:

tallbloke says:
January 22, 2013 at 7:20 pm

“Solar wind/magnetosphere?”

To these I would add tides, with two question marks. If anyone can quantize any of these, please speak up.

Brian H says:

“Bloke down the pub says:
January 22, 2013 at 11:39 am

That might be circuitous thinking, but that seems appropriate for a post on corotation.”

I don’t think circuitous means what you think it means. LOL Look it up for a good laugh.

Tim;
So, what’s the deal with planets with atmospheres but no magnetospheres, like Mars and Venus?

Tim Cullen says:

Stephen Wilde says: January 22, 2013 at 1:00 pm
Any ideas how to relate this to climate phenomena?

The concept of “viscosity” is associated with “friction” and that implies “heating”.
This topic is introduced in the final section of this posting… so it seems appropriate to delay this discussion for a couple of days…

Tim Cullen says:

suricat says: January 22, 2013 at 11:24 pm
Tim, the region of Earth’s atmosphere that ‘co-rotates’ most closely with Earth’s rotation is ‘The Boundary Layer’. Even here there are ‘discrepancies’ (fluctuations in wind direction).

There are definitely “discrepancies” that effect atmospheric corotation… most of these discrepancies are not fully understood [just like weather systems]… and there may be confounding electromagnetic factors that need to be addressed.

For example:
Excess [“super”] rotation has been observed at altitudes ranging from 200 to 300 kilometres where the atmosphere rotates up to 1.25 faster than the Earth.

http://malagabay.files.wordpress.com/2013/01/the-rotational-speed-of-the-upper-atmosphere.gif?w=640&h=476

However, the atmosphere corotates at the surface of the Earth… this is best experienced on a calm summers day in England… sometimes a sea breeze help on a really hot summers day. Yes there are winds and weather systems. BUT even the fiercest hurricane [or jet stream] pales into insignificance when compared to the Earth’s equatorial rotation speed of 1,674.4 kilometres per hour.

So: There is corotation at the surface, the boundary layer and up to the plasmapause.
There are discrepancies encountered with altitude… some of these discrepancies are transitory [just like weather system] and some of these discrepancies are very variable… so it is not a perfect corotation… but I think “corotating” is a very reasonable characterisation of the Earth’s atmosphere.

Tim Cullen says:

Tim Folkerts says: January 23, 2013 at 2:07 am

Perhaps you would like to confirm your views with a few experiments…
Perhaps experiment with something really viscous [like mixing a bucker of plaster] to see how easy it is to get the mixture “corotating”.

Tim Cullen says:

Sera says: January 23, 2013 at 7:36 am
Gravity holds everything in place…
there is nothing to prevent the atmosphere from co-rotating, so it does.

The question to be addressed is WHAT [and how] enables atmospheric corotation.
Gravity may constrain the vertical movement of the atmospheric gases but the horizontal [orbital] corotation of the atmospheric requires a little more explanation in my opinion.

Richard says:

I think a more relevant experiment would be to take a 33rpm disc player and surround the turntable with a cylinder to enclose the air above it.

Leave the truntable running for about an hour or two and see what the movement in the air above the plater looks like.

My guess is that it will be rotating at about the same velocity as the disc (with losses to the clyinder wall and the bulk air above).

Give a vertical profile through the atmosphere is very short compared to the width the above should be closer to the answer than using a coffee cup and water.

Tim Cullen says:

tallbloke says: January 23, 2013 at 9:32 am
Well, it was spinning along with the solids when the Earth was formed so initial inertia doesn’t need to be overcome.

That may well be a bit of mainstream “circular logic” because getting the “initial spin” into the mainstream formation theories takes a bit of “spinning” 🙂 but let’s assume we have some initial spin.

Newton says that in the absence of opposing forces, stuff keeps on keeping on.

So he does… but I doubt that he reached that conclusion after playing a game of snooker, billiards or pool. The basic problem with “keeping on” in the atmosphere [especially in the lower atmosphere] is that gas particles have a nasty habit of bumping into each other… and unfortunately these colliding gas particles have “six degrees of freedom” when they are playing “snooker” in the atmosphere.

Therefore, there is a need for a continuing input of energy [momentum] into the atmosphere if the atmosphere is to remain corotating. Unfortunately, for the mainstream, continually driving this momentum into the atmosphere from the surface of planet Earth is extremely difficult because air has an extremely low viscosity and a lot of freedom to randomly collide.

Additionally, there is no observational evidence that suggests the planet’s surface is transferring momentum into the atmosphere… there are no continuous “trailing edge” winds [or clouds] associated with hills [and mountains] on the equator as they rotate at 1,674.4 kilometres per hour…. there is no continuous air turbulence [wind speed gradient] near the planet’s surface to indicate the surface is transferring momentum into a very low viscosity gas…. as Wikipedia correctly states “if the viscosity is very high, such as in pitch, the fluid will seem to be a solid in the short term” but even then they use caveats like “seem” and “short term”.

Personally, the “bottom up” approach seems to be all “spin” an no “science”… whereas the “top down” approach presents some scientific possibilities [like Richard Holle’s earlier comment].

Schrodinger's Cat says:

The earth has been rotating since its creation, presumably because there is no opposing force to slow it down. Since space has neglible matter, there is no viscous drag (opposing force) on the top of the atmosphere so the atmosphere and the earth rotate as one.

The coffee cup experiment is different because the wall of the cup is static as is the fluid layer in contact with it, while the fluid in the centre of the cup is being rotated by a rotor (spoon). The body of the fluid is then torn apart to accomodate this situation. The cohesiveness of the fluid or its resistance to shear is what we call viscosity.

In the case of the spinning earth with its atmosphere, there is no static matter (coffee cup wall) to create a shear force, only empty space. Imagine the spoon exerted gravity on the coffee to hold it in place and the cup wall was no longer there, and there was no air to exert drag, the coffee would rotate with the spoon with no shear gradient.

None of this stops us from speculating about how the rotating fluid shell will interact with solar heating, plasma, magnetic fields, external gravity, etc. Certainly, some of the directional influences such as solar radiation and solar gravity might be expected to create an effect on the part of the shell facing the sun and as the shell rotates, a more complex and dynamic situation emerges.

Furthermore, individual components of the atmosphere may be affected differently, for example whether the molecules have a diplole, their absorption frequencies, whether the are easily ionised, etc. One could imagine physical and chemical changes taking place in the rotaing shell.

The possible electromagnetic effects are fascinating since we have a large magnet spinning in the solar magnetic field and solar wind.

In conclusion, I think the rotating shell of fluid is a useful way to think of the atmosphere, but I’m not convinced that the earth is pulling the atmosphere along with some sort of drag on the top of the atmosphere creating shear in between. The atmosphere has momentum so it will continue to move at contant velocity, gravity ensures that this is converted to angular momentum and there is no matter in space to exert friction or drag, i.e. no opposing force.

Richard says:

“Definitely worth a try… perhaps we need to add a bit of smoke into the enclosed atmosphere… and then get the turntable to rotate at one revolution per day….”

Hmm. Only if you let it rotate for a year or more to get to a stable state and then I suspect the answer will be the same.

The point is that there have to be losses to somewhere (Newton) to drain off any rotation that otherwise is drag input from the surface. Unless there are those losses the system will remain as a cohesive whole and rotate as a block.

Tim Cullen says:

Schrodinger’s Cat says: January 23, 2013 at 11:18 am

The earth has been rotating since its creation, presumably because there is no opposing force to slow it down.

That is a basic assumption… an alternative assumption is that there is some opposing force and the system needs an constant input of energy… given that no one has yet discovered the secrets of “frictionless” motion I would suggest your initial assumption is over optimistic.

Since space has neglible matter, there is no viscous drag (opposing force) on the top of the atmosphere so the atmosphere and the earth rotate as one.

I am not certain we have quite sorted out how things actually function at the “top of the atmosphere”… we have a corotating plasmasphere surrounded by a magnetosphere which somehow manages to deflect the main bulk of the supersonic solar wind through some form of mysterious “collision free” interaction [so I have been told]. Evidently there is at least one “opposing force” working its magic at the “top of the atmosphere”… we need to learn a lot more… and presume a lot less.

In the case of the spinning earth with its atmosphere, there is no static matter (coffee cup wall) to create a shear force, only empty space.

I am not sure the solar wind would agree with you on that one.

None of this stops us from speculating about how the rotating fluid shell will interact with solar heating, plasma, magnetic fields, external gravity, etc. Certainly, some of the directional influences such as solar radiation and solar gravity might be expected to create an effect on the part of the shell facing the sun and as the shell rotates, a more complex and dynamic situation emerges.

We definitely agree on that.

Furthermore, individual components of the atmosphere may be affected differently, for example whether the molecules have a diplole, their absorption frequencies, whether the are easily ionised, etc. One could imagine physical and chemical changes taking place in the rotaing shell.

We definitely agree on that

The possible electromagnetic effects are fascinating since we have a large magnet spinning in the solar magnetic field and solar wind.

We definitely agree on that

In conclusion, I think the rotating shell of fluid is a useful way to think of the atmosphere, but I’m not convinced that the earth is pulling the atmosphere along with some sort of drag on the top of the atmosphere creating shear in between. The atmosphere has momentum so it will continue to move at contant velocity, gravity ensures that this is converted to angular momentum and there is no matter in space to exert friction or drag, i.e. no opposing force.

And I am not convinced that the earth is pulling the atmosphere along with some sort of drag at the bottom of the atmosphere.

Tim Folkerts says:

“Perhaps experiment with something really viscous [like mixing a bucker of plaster] to see how easy it is to get the mixture “corotating”.
Except that the air has very little viscosity. And there is no “stationary bucket” around the earth. So you analogy fails.

Actually, the better analogy would be a (lightweight) bucket suspended from a rope on a (nearly) frictionless swivel. And I guarantee that the entire bucket and the plaster in it would almost immediately get co-rotating with a rotating stirrer. Even a bucket of water or air would pretty soon be rotating at the same angular velocity as whatever is stirring it.

Perhaps you would like to confirm your views with a few experiments…
So you don’t believe the atmosphere was created by out-gassing?
Or maybe you don’t believe in conservation of angular momentum?
Or maybe you don’t believe that a low viscosity gas stirred a few trillion times would eventually get spinning?
Or maybe you don’t believe in Newton’s 1st Law (you have already been arguing against this one with Tallbloke)?

** Which of these did you want experimental confirmation for?

“it’s a bit like the first “break” in snooker …
Except that the table and the snooker balls ALREADY had angular velocity when the balls were set out. And that over time there have already been 2 trillion previous breaks.

“The mainstream literature does not support this “first step” by reference to a paper….
Yes it does. You even cite it for us — “(see, for example, Hines [1960])” !
Have you read it? Or any of the other “mainstream literature” on the topic? If not, how can you make any claims about what the “mainstream literature” may or may not say?

Schrodinger's Cat says:

Thanks for your feedback.

The points I have been making relate to Newtonian mechanics where the bodies have atomic or molecular mass and force is defined as mass times acceleration.

The solar wind consists of electrons and protons and I doubt if Newtonian mechanics will apply. I’m not suggesting that the solar wind does not interact with our earth system – I’m sure it does.

I’m not sure that we can assume that subatomic partices will exert force in the classical sense. For example, an atom will appear as 99% empty space to an approaching electron.

Greg says:

“The objective of this experiment is to understand how easy [or difficult or impossible] it is to get the whole beverage to corotate using a plastic drinking straw”

Given about 4.3 bn years I’m sure you could get it to turn. But as TB pointed out the atmosphere was turning as the planet formed, the only question is why doesn’t it slow due to turbulence dispersing the energy. I think I covered some more realistic ideas on that.

The case of gas giants is more interesting but since we don’t know the composition it’s all rather arbitrary discussion.

Schrodinger's Cat says:

The idea of turbulence or other factors within the atmosphere affecting the rotation of the atmosphere seems unlikely to me. Man, like the surface of the earth and the shell of atmosphere is also travelling through space. Whether we jump up and down, fly through the air or try to blow each other up makes little difference to the angular momentum of the earth, its atmosphere or the laws of motion that govern our human endeavours.

oldbrew says:

Where does centripetal/centrifugal force fit in?

http://faculty.wwu.edu/vawter/PhysicsNet/Topics/RotationalKinematics/CentripetalForce.html

oldbrew says:

Tim Cullen says (11:55):
‘we have a corotating plasmasphere surrounded by a magnetosphere which somehow manages to deflect the main bulk of the supersonic solar wind through some form of mysterious “collision free” interaction [so I have been told].’

Magnetic repulsion?

oldbrew says:

The graphic at the start of this paper may be of interest.

http://milesmathis.com/pause.html

wayne says:

I think you are correct Ray to bring up the solar wind. Pure friction. I just did a lengthy calculation over a billion year scale to get a rough estimate of the momentum imparted by Venus’s 35,000 m/s revolution velocity rubbing against the approrx. 300,000 m/s solar wind, 2.5 protons/cm^3, and it seems it is adequate to cause the high speed winds in the upper atmosphere. The higher you go, the higher the velocity, implying the top-down angular momentum being fed in from above.

The specific angle of the helio sheath at Venu’s orbit was the only rather loose parameter I couldn’t seem to tie down.

Greg says:

I made similar suggestions to explain the r^4 relation I fitted in the other threads on this topic. If Wayne has a mechanism and numbers that makes it very interesting.

wayne says:

Sure Greg, here is a line-by-line display from my little physics calculator (for ease). If you have better numbers, change them at will and for sure let me know of any mistakes I might have made. By these it seems it would take somewhere between two and three billion years if all else stays constant. Also that is using Earth’s orbit density of the solar wind, not Venus’s; at Venus it seems it would be more dense so that estimate might be too long. I was just looking if it was even a possibility… not necessary a proof of cause. Also the solar wind is assumed radial from the sun without any magnetic curvature.

The ‘revolution velocity’ would have been better termed the ‘orbital speed’.

//! radius of Venus
R.v = 6050 ‹km›
6.0500e+006
————————————————
//! orbit velocity of Venus
V.v = 35 ‹km/s›
3.5e+04
————————————————
//! area of Venus as a disk
A.v.disk = π * R.v² ‹m²›
1.1499e+014
————————————————
//! mean mass of venus's atmosphere
m.v.atm = 5E+20/2 ‹kg›
2.5000e+020
————————————————
//! velocity of the solar wind
V.sw = 300 ‹km/s›
3e+05
————————————————
//! proton density of the solar wind
ρ.protons = 2.5 ‹1/cm³›
2.5000e+006
————————————————
//! period being considered
t = 31.5E06 ‹s/yr› * 1e9 ‹yr›
3.1500e+016
————————————————
//! mass hitting Venus's disk every billion years
kg = ( ρ.protons * V.sw * A.v.disk * t ) / ‹NA› * 0.5 ‹kg/mol›
2.2555e+018
————————————————
//! momentum of friction at interface at angle of intersection
angle.ratio = atan(V.v / V.sw)
0.1161
————————————————
r2d(angle.ratio) //degrees
6.654
————————————————
Ns = ( kg * V.v * angle.ratio ) ‹kg•m/s›
9.1687e+021
————————————————
//! ratio of momentum to the mass of 1/2 of the atm
ratio = Ns / m.v.atm
36.67
————————————————
//! velocity in three billion years
v = ( ratio * 3 ) ‹m/s›
110
————————————————
//! as mi/hr
v / ‹mi/hr›
246.1
————————————————

wayne says:

Brother !! Wait a minute, excuse my missing right peripheral vision. 😉 I always doubt myself too much. That is seconds per one billion years and is correct.

Well, have some fun with that calculation!

suricat says:

wayne says: January 25, 2013 at 1:50 am

Correct, or not. Planetary mechanics is new to me and when it comes to astrophysics, this engineer is ‘blown away’! 🙂

“The specific angle of the helio sheath at Venu’s orbit was the only rather loose parameter I couldn’t seem to tie down.”

An introduction into 1st/2nd year engineering insight may help:

http://webphysics.iupui.edu/JITTworkshop/152Basics/vectors/vectors.html

I’ll explain this, if your need is such, but I think your understanding is above this level. Perhaps you needed a reminder (I did! It’s been so long since I learned this stuff). 😉

Best regards, Ray.

wayne says:

“Density is lower high up so although velocity is high, momentum isn’t.”

Momentum units do not have volume. You must be speaking of momentum per volume, like (kg.m/s)/m3 and stated that way you are exactly right there, it is extremely tiny and takes millions of years worth of seconds to even start to be even of any large effect.

The mass density is extremely diffuse, ~2.5 protons (thing H) per cubic centimeter, see NASA space weather real-time charts, but the velocities are huge. Momentum calculations such as above have nothing to do with volume unless you word the problem that way, I didn’t. There just the mass they are colliding against that is 1/2 the mass of Venus’s atmosphere.

You might say the collisions are occurring high in the atmosphere, true, but unless the majority of the atoms and molecules collided with are being accelerated past the escape velocity that momentum will eventually diffuse into all of the atmosphere and if consistently on one side of nadir will impart a rotation, that is the way I attacked it.

You should find that all of those factors are already in that stream of calculations.

wayne says:

Could it be that Venus’ atmosphere is too thick, and the top down propogated AM is lost in turbulence before it reaches the surface to assist the rotation? Someone was saying there doesn’t seem to be erosion on the surface consistent with high winds.

—

Absolutely. I was assuming zero (or near) wind velocity at the surface and maximum wind velocity near the ToA. That is why I cut the mass that had to absorb the momentum over a long geological time to one half. However, I haven’t checked to see if the real wind velocity profiles like that, linear with height. If it is just a very thin slice at those high velocities is would seem so say those calcs are way off or not even real. I left that open, just wanted others to play with the figures or even rearrange the logic, just wanted to say that was easily calculable, though roughly.

I did question how much the velocity would change over just a one year span… like 0.00000008 m/s or even less! That is assuming it could reach current velocity in one billion years. Now I’d call the solar wind quite weak. 😉

Tim Cullen says:

suricat says: January 29, 2013 at 3:10 am
Can we come up with something of a more ‘bottom up’ approach than a ‘top down’ approach?

Ray,
There appears to be a basic problem of physics because corotation can’t be achieved when the rotation is “driven” from the centre [“bottom up”]… the viscosity and the increasing circumference [as you move out from the centre] always results in rotational dissipation – as seen [below] in the image of plaster being mixed:

If you take the view that momentum [somehow] accumulates [over time] then the rotation will accelerate towards corotation and then continue to accumulate until super-rotation is achieved… then it would move towards disintegration…

However, the concept of momentum accumulation [from a “bottom up” or “top down” driver] is fictional [even in a closed system] because the rotating system must generate a “return” [or “back flow”] that continually feeds the “driver”… in other words… a vortex flow… this is very much like using an electric mixer in the kitchen when the spinning blades are positioned at the centre of the dish [or when mixing plaster].

Basically, as far as I can see, the ONLY way that corotation can be achieved is via a “top down” driver that effectively focuses the momentum towards the centre in a “forced” vortex… this “forced” vortex flow [incidentally] generate a centripetal flow [force] which I suspect is the mysterious “force at a distance” that is commonly called gravity… this is why I think corotation is such an important issue… that is why I encouraged a bit of experimentation [whilst preparing a cup of coffee] because gravity may be just a simple “kitchen sink” phenomenon.
Regards – Tim

Tim Cullen says:

suricat says: January 30, 2013 at 4:19 am
It’s all about (for an Earth scenario) Earth’s centrifuge and the Coriolis effect.

Ray,
If the corotation is driven form the surface then the atmospheric particles would tend towards a tangential trajectory: slowly rising at the curvature of the Earth falls away during rotation. The tangential velocity tends to reduce due to the viscosity of the atmosphere [friction/collisions]… therefore, the tangential velocity cannot remain corotating because a) velocity is being lost and 2) the rotational circumference increases with altitude. In other words any surface driven corotation dissipates.
Thus, my analogy was perfectly appropriate if you attempt to drive corotation from the centre.

Personally, I can’t imagine any situation where an optical illusion [the Coriolis Effect] has any effect on atmospheric corotation [or any other mechanical process]:

Inventions and Deceptions – Coriolis Effect

Regards Tim

Tim Cullen says:

Greg says: January 30, 2013 at 10:01 am
Coriolis “force” is nothing more than the moment of inertia. It is a convenience ‘fictitious force’ that allows the application of simple Newtonian mechanics in a rotating frame of reference. The frame is rotating which means everything tied to it is accelerating. If you explain this acceleration by a fictitious force you can pretend that Newtons laws apply within your earth bound coordinate frame.

The Coriolis Effect describes the visual illusion that can be created when an object [travelling in a straight line] is viewed [or tracked] in relation to another object that is rotating.

The Coriolis Effect does not describe the movement of two objects that are corotating [by definition].

Further analysis to required to discover why the mainstream needs to deploy a “fictitious force” so regularly… further analysis is required to discover why the mainstream wants to [as you say] “pretend that Newtons laws apply”…

Evidently something is going on… it just isn’t the Coriolis Effect.
It looks like a real theory is needed – not an optical illusion.

Tim Folkerts says:

“Further analysis to required to discover why the mainstream needs to deploy a “fictitious force” so regularly… ”

Because lots of reference frames (like the rotating earth) and not inertial reference frames. Object on a rotating earth do NOT go in straight lines (as viewed by observers in that reference frame). The do indeed curve (as viewed by observers in that reference frame). An observer who IS on an inertial reference frame watching the motion of objects would not need to invoke the “fictitious” Coriolis force.

Watch these for a good introduction:

Tim Cullen says:

Tim Folkerts says: January 30, 2013 at 5:19 pm

My original comment was [and still is]:

Personally, I can’t imagine any situation where an optical illusion [the Coriolis Effect] has any effect on atmospheric corotation [or any other mechanical process]:

The mathematics of the Coriolis Effect enables the observer on a rotating platform perform a “coordinate transformation” – no problem… but [as I stated] there is no Coriolis Force.

Greg says:

tallbloke says:
January 30, 2013 at 8:27 pm

I wonder if cyclonic weather systems miight get their spin from the Makarieva effect. I told Tim Cullen about noticing the way milk powder starts a spinning vortex as it dissolves in your coffee. Maybe the condensation of water vapour in the atmosphere has a similar effect, sucking wind in and starting a spinning weather system.
===

In a way that would seem to be along the lines of what she is proposing. Precipitation and Makarieva effect would explain the movement towards the centre. However, the air rushing towards the centre of such a system only starts spinning because of the Coriolis effect. Once a particular packet of air aquires a velocity it has momentum (additional to that of the rotation of the atmosphere in general, which can be dealt with separately and vector added later).

Consider air moving northwards at about the latitude of Leeds, for example. Moving north also implies moving to a smaller radius. By conservation of angular momentum this implies a corresponding increase in angular velocity. As it is now rotating faster it will get a bit ahead of where Leeds is on the map as well as moving north. ie it has also moved (accelerated) to the east. The opposite applies to air moving south from Glasgow, which has reduced angular velocity and gets deflected to the west. Do the same all the way around and you see the anticlockwise cyclonic pattern starting to form.

The effect is that simple to understand and physically real. It is nothing more than the conservation of momentum. Cyclones are not ‘optical illusions’. You can either do all the maths on those vectors in a stationary frame of reference, (an inertial frame in the relativistic jargon), or you can see the acceleration to the east as being the result of a fictitious force called Coriolis. This is the non existant force that _would_ create the same movement as that caused by the interaction of the Earth’s rotation and the momentum vector of the moving air.

There’s no ‘magic’ or cheating going on here, it’s just a convenient short-cut. If you don’t like you are not forced to accept or use it. Just do it all long hand until you’ve convinced yourself you get the same results (or proved that you don’t 😉 ).

This does not have much to do with your cup of Yorkshire tea which is spinning because you stirred it. Though I suspect you will find that you do have the parabolic velocity profile that I meantioned in attempting an explanation for the r^4 relation I found fitting co-rotation data. Except with the outside being stationary in this case.

suricat says:

Tim Cullen says: January 30, 2013 at 8:01 am

“Ray,
If the corotation is driven form the surface then the atmospheric particles would tend towards a tangential trajectory: slowly rising at the curvature of the Earth falls away during rotation.”

Correct (odd inclusions permitted). The particle ~maintains its inertia, thus, ascends ‘retrograde’ WRT Earth’s surface. ~No inertia is gained/lost as the particle rises, so the particle can’t keep up with Earth’s rotational speed at this ‘greater radius/altitude’. Why does the particle ‘rise/gain altitude’ when it leaves the Boundary Layer? I think we need you to understand how to ‘map’ the Coriolis Effect before we can get into the ‘force’ that’s at work. 😦

“The tangential velocity tends to reduce due to the viscosity of the atmosphere [friction/collisions]… therefore, the tangential velocity cannot remain corotating because a) velocity is being lost and 2) the rotational circumference increases with altitude. In other words any surface driven corotation dissipates.”

There’s confusion here! The velocity of the particle remains ~unchanged!

An ‘ascending’ particle within an atmosphere shall ‘always’ display a ‘retrograde’ motion towards the ‘rotating’ planet it’s ‘ascending from’ because its vector is ‘~a straight line’ while ‘the planet’ continues to rotate beneath. Please look at your ‘graphic’ link and realise this. The ‘clue’ is in ‘angles’, as in ‘angular momentum/linear momentum’. 🙂

Think of the ‘whole thing’ as ‘current flow’ within a non viscous ‘fluid’, but ‘not’ an egg beater, or plaster mixer. They’re too viscous/thixotropic! 🙂

Best regards, Ray.

suricat says:

Greg says: January 31, 2013 at 12:04 am

Thanx Greg. I just hope this ‘turns on a light bulb’ for Tim Cullen. The ‘transmission’ of understanding can be ‘really’ frustrating at times. 🙂

Best regards, Ray.

Greg says:

Just thought I ought to correct my example of geostationary satellite. It anyone had followed my suggestion of looking at the coriolis force in this case they would have quickly pointed out that it is zero, since it is stationary in the earth reference frame. What stops the satellite from falling is another “optical illusion” called the centrifugal force.

Again this is totally fictitious and again is in reality just conservation of momentum.

Viewed from outside the earth gravity provides a force towards the centre which produces the circular motion of the satellite’s orbit. If we regard it with reference to the earth bound coordinates it ‘floats’ despite gravity pulling it towards Earth. Thus we need to introduce a ‘fictitious force’ called the centrifugal force.

There is no real force repusing an object from the centre in circular motion, it is just the tendance of the object to continue in a straight line: intetia.

If anyone wishes to reject Coriolis they need to reject centrifugal as well.

If you can understand and accept the latter, it should not be hard to understand the former.

suricat says:

*Tim Cullen says: January 31, 2013 at 9:59 am

Tim, that remark wasn’t aimed at you, but at myself. I’m not a tutor and often find it hard to find the best way to offer a universally understood ‘explication’. 🙂

*Greg says: January 31, 2013 at 10:25 am

I immediately took that as a ‘logic slip/typo’ Greg. 🙂

Are you an engineer like myself? Just curious.

*Tim Cullen says: January 31, 2013 at 10:38 am

“From my perspective conservation of momentum is a very different concept to the Coriolis Effect which describes an optical illusion [for the observer] and a coordinate transformation [for the mathematician].”

For Earth’s atmosphere, the two are the same. The Coriolis ‘Effect’ is a “coordinate transformation” for what an observer within an ‘Earth reference frame’ would see happening to the ‘mass flow’ in Earth’s atmosphere. Do we really need to get into Relativity here? 😦

“Overall, these are wonderful contributions [from my perspective] because they don’t stop at a mathematical explanation [like the Coriolis Effect] but actually advance into the realm of real world mechanics [like the spin of cyclones]… and it is real world mechanics that provides the most rewarding line of inquiry [from my perspective].”

Then you shouldn’t have posted on “Planetary Rotation – Atmospheric Corotation”, because you describe your main interest as ‘weather’.

*tchannon says: January 31, 2013 at 11:10 am

“Here we are, this will do”

Thanks TC. This is a good link to ‘weather’. 🙂

*oldbrew says: January 31, 2013 at 12:51 pm

“Greg says: ‘If anyone wishes to reject Coriolis they need to reject centrifugal as well.’

RP Singh says: ‘It is convenient but not necessary to invent pseudogravity (centrifugal force) to cancel the centripetal force in order to avoid radial motion. Centripetal force is real; centrifugal force is fictitious.’

R. P. Singh: A Constructive Model of Gravitation

[See para 13.3]”

On reading para 13.3 I’ve a problem with the first three statements there.

“A force normal to a body’s uniform velocity keeps the body in a circular orbit; that force is called centripetal force.
A satellite around the earth is under the centripetal force of the earth’s gravity. The centripetal force is being ‘used up’ in keeping the satellite in orbit; a body in it gets no reaction force and feels weightlessness.”

Mass ‘in a vacuum’ is uniformly acted upon by the force of gravity! That goes without saying, but how is the ‘centripetal force’ “used up” in keeping the satellite in orbit?

Its ‘rate of changing vector direction’, or controversially, its ‘centrifugal component’. The ‘centrifugal component’ is nothing more than its resistance to a changing directional vector and is summed as the ‘inertia force’ required to alter it’s directional vector to the ‘observed’ deviation.

IMHO, this guy ignores ‘reactionary’ forces, thus, ignores half of ‘the system’. 🙂

This seems to be an ‘old chestnut’ between mathematicians and engineers. As soon as ‘Pi’ enters an equation there are sides drawn for the better explanation. Do we use Pi*D, or 2Pi*r? 🙂

This is ‘so far away’ from what I wanted to contribute here, but that’s democracy for you.

Best regards, Ray.

oldbrew says:

TB 9:04 am – is the link wrong?

Another site (link below) discussing SSW refers to Coriolis. This seems even more tortured as they say the winds can reverse and ‘The stratospheric polar vortex can completely disintegrate.’

http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/fw/crls.rxml

I suggest references to Coriolis are thrown in as a makeweight to try and get a weak explanation to sound scientific 😉

Tim Cullen says:

Greg says: February 1, 2013 at 8:40 am
The ocean gyres of all the worlds oceans really do turn. Cyclones really do turn.
There is no optical illusions here.

Cyclones and gyres rotate.
What causes the spin?
Definitely not a “coordinate transformation”.
Definitely not an “optical illusion”.

tallbloke says: February 1, 2013 at 9:04 am
For what it’s worth, I think ‘coriolis force’ is a lazy answer to a complex set of issues.

Exactly to the point.