[gem (OP)]

Hi all,

Ok Halc it seems your getting a little frustrated and you seem to have a problem with the data.

These are length of solar day, which get shorter this time of every year due to our orbit not being perfectly circular. This is purely a visual effect, not an actual delta in the spin rate.

I was talking about the spin rate, the sidereal rate, the time it takes to revolve exactly 360°, which is the rate from which the angular momentum is computed. This is a thread about momentum, not about when the sun appears to rise.

I'm afraid your mistaken, for example, the earth rotation ( LOD ) was actually slowing down between the 5th to the 13 th of august,

and the published values I posted are from : LOD - FINALS.DAILY (IAU1980) from the IERS

What part of my comment is mistaken? I didn't contradict the numbers. I said that the LOD numbers are a visual effect, completely unrelated to the daily variations in the angular velocity of Earth. Do you have any reading comprehension skills at all???

why did the LOD get shorter yesterday will today and tomorrow ?

What part of my explanation cannot you comprehend?

Sorry, I cannot add more because you're just repeating things. The LOD variations as published on your site is due to our elliptical orbit and has nothing to do with changes in the time taken to go around 360°, which is about 23 hours 56 minutes with a lot less variation than the numbers you post, but variation nevertheless, and almost always increasing due to the perpetual negative torque continuously being applied from outside the planet.

Now the science that is behind the figures I posted is very comprehensive for the LOD,

derived from the EOP  (Earth Orientation Parameters) determined by combining the most recently available observed and modeled data (including VLBI 24-hour and intensive, GPS, and AAM). The combination process involves applying systematic corrections and slightly smoothing, in order to remove the high frequency noise.
finals.daily from where I sourced the values, contains for the last 90 days the values from IERS Bulletin A for x/y pole, UT1-UTC, LOD, dPsi, dEps

Celestial pole offsets (dPsi, dEps) are related to the IAU1980 nutation theory.

Now EOP are the parameters which provide the rotation of the ITRS  (The International Terrestrial Reference System) the ICRS (The International Celestial Reference System) as a function of time.

The ICRS is realized by VLBI estimates of equatorial coordinates of a set of extragalactic compact radio sources,
(the International Celestial Reference Frame)

Therefore I don't understand why you think the there should be a lot less variation than the numbers posted.
 

[Eternal Student]

Hi everyone.

Sidereal day     vs.    Solar day
   This video draws the usual diagrams and says the usual things to explain the difference.   You'll only need the first 2 minutes but the whole thing is only 3 minutes.

   Now imagine the orbit of the earth around the sun is elliptical and not circular.  The angle between the earth and the sun changes by a variable amount, it's not exactly 1 degree per day it just averages at about this amount.
   Halc was suggesting your (Gem) data measures the solar day not the sidereal day.

Best Wishes.

[Bored chemist]

The difference between the apparent (based on the Sun) and real rotations of the Earth is this
https://en.wikipedia.org/wiki/Equation_of_time

[gem (OP)]

Hi all,

Thanks for the input ES and BC,

Yes its absolutely fair enough, Halc was making that point, and I thought I had addressed it by pointing out the reverse affect to the data I posted was measured to be happening a few days earlier, which wouldn't tie in with the Solar day example/argument, indeed its reversed again since I posted the results.


Also in regards to the value of the numbers involved I believe the range of the Solar day effect, is somewhere in the range/vicinity of ;

± 4 seconds throughout the year,

Whereas the fluctuations I posted sit within range of about

± 1.5 x10^-3 seconds throughout the year.
 
It really is quite an achievement of science that there is monitoring to that degree.   
 

[gem (OP)]

Hi all,
So Halc,

These are length of solar day, which get shorter this time of every year due to our orbit not being perfectly circular. This is purely a visual effect, not an actual delta in the spin rate.

I was talking about the spin rate, the sidereal rate, the time it takes to revolve exactly 360°, which is the rate from which the angular momentum is computed. This is a thread about momentum, not about when the sun appears to rise.

I'm afraid your mistaken, for example, the earth rotation ( LOD ) was actually slowing down between the 5th to the 13 th of august,

and the published values I posted are from : LOD - FINALS.DAILY (IAU1980) from the IERS

What part of my comment is mistaken? I didn't contradict the numbers. I said that the LOD numbers are a visual effect, completely unrelated to the daily variations in the angular velocity of Earth. Do you have any reading comprehension skills at all???

why did the LOD get shorter yesterday will today and tomorrow ?

What part of my explanation cannot you comprehend?

Sorry, I cannot add more because you're just repeating things. The LOD variations as published on your site is due to our elliptical orbit and has nothing to do with changes in the time taken to go around 360°, which is about 23 hours 56 minutes with a lot less variation than the numbers you post, but variation nevertheless, and almost always increasing due to the perpetual negative torque continuously being applied from outside the planet.

Ok, given the last few posts have hopefully given a bit more clarity to the relevance to momentum of the data posted, are we ready to move past the comments above, or do you require me to repeat some points 

As you will see the fluctuation range under discussion  demonstrated in the link also
https://commons.wikimedia.org/wiki/File:Deviation_of_day_length_from_SI_day.svg#/media/File:Deviation_of_day_length_from_SI_day.svg


What Halc was mistaken by is a totally separate effect, as it states at the Top of the page, link below :
 

For regular changes in the length of a solar day through the year due to the obliquity of the ecliptic and the eccentricity of the Earth's orbit around the Sun, see Equation of time.

https://en.wikipedia.org/wiki/Day_length_fluctuations

Comprendi ?

[Bored chemist]

Hi all,

Thanks for the input ES and BC,

Yes its absolutely fair enough, Halc was making that point, and I thought I had addressed it by pointing out the reverse affect to the data I posted was measured to be happening a few days earlier, which wouldn't tie in with the Solar day example/argument, indeed its reversed again since I posted the results.


Also in regards to the value of the numbers involved I believe the range of the Solar day effect, is somewhere in the range/vicinity of ;

± 4 seconds throughout the year,

Whereas the fluctuations I posted sit within range of about

± 1.5 x10^-3 seconds throughout the year.
 
It really is quite an achievement of science that there is monitoring to that degree.   
 

So, if you had stated the units properly, you could have avoided all that stuff.

[gem (OP)]

Hi all,

BC
Which units are not correct ?

[Bored chemist]

Hi all,

BC
Which units are not correct ?

Length of day variations/fluctuations in milli seconds as published today for the relevant dates.   ( - = minus )

15/08/2021  - 0.4058
16/08/2021  - 0.6633
17/08/2021  - 0.9998
18/08/2021  - 1.0715

You should have said "milliseconds per year" or whatever.

[gem (OP)]

Hi all,
Ok thanks,

The numbers are how much from zero each day value is. Plus/minus
(in milli seconds)

Therefore my predictions/calculations  were correct.
🌍🧐

[gem (OP)]

Hi all

Ok Halc

I have totally lost track of your point with this sidetrack. This new chart mostly illustrates the effects of external torque on Earth, but it does also suggest large scale sustained momentum transfer between air and ground.

What are you driving at with all these posts? Are you in denial of momentum conservation? Are you in denial that thermal energy from the sun can generate air currents on Earth? It is really unclear since the posts have no common thread and seem just haphazard.

Righto you now accept that there is a on going large scale transfer of momentum between the atmosphere and the solid Earth, measurable (daily) as changes in Earth rotation rate,
and polar motion

Yes, electromagnetic energy from the Sun generates wind in the Earths atmosphere
 
This from the go to guy;

The atmospheric angular momentum (AAM) is that due to the motion of the winds and to the changes in mass distribution

https://syrte.obspm.fr/astro/journees2019/FILES/salstein.pdf



Now I am repeating myself at your request,
So current theory needs to state, where the initial action reaction pairing, due to the spontaneous convection occurs in the earths uncoupled atmosphere.

Given the motion/momentum generated, impacts things like sail boats mountains trees. and oceans, with varying degrees of partially inelastic collisions, that would alter the vector total expected from a closed system.

Therefore it needs to be demonstrated if the solid earth can/cannot discriminate between these collision and a meteorite, in regards to the potential change of momentum. that is created in the atmosphere, current theory requires the solid earth to be able to discriminate.

You ask where I am going with this, you need to consider the implications of what I am suggesting and the subsequent questions that raises.
 
gem

However this is only a preamble that links to several other phenomena,

[Bored chemist]

Righto you now accept that there is a on going large scale transfer of momentum between the atmosphere and the solid Earth, measurable (daily) as changes in Earth rotation rate,
and polar motion

On average, that transfer is zero in the long term.

[gem (OP)]

Hi all,

Ok BC

On average, that transfer is zero in the long term.

Appearances can be deceptive, there are patterns in the data that suggest that may not be the case.

Halc

You then have to stop mixing talk about the real Earth with its friction, mass transfer, momentum fluctuations and all, and work with an ideal case, say a frictionless solid ball with spinning atmosphere that is initially totally stationary relative to its rotating reference frame, and then heated on one side. That will generate air currents. The vertical reaction pair is with the surface which does not give with the altered pressure. The initial horizontal action-reaction pair would be atmosphere on either side of the heated region which would either move apart or together (probably the latter).  Either way, you now have wind (air no longer stationary in that rotating frame), but no sailboat since our ideal planet is frictionless, so nothing for the keel to dig into. Can't even fly a kite.

If the planet is not frictionless as you describe, then yes, the atmosphere ceases to be a closed system, but planet+atmosphere still can be, and conservation laws still apply. Are you asserting otherwise, or is you point something else? It's still unclear.

OK I don't quite agree with the vertical action reaction statement but putting that to one side and concentrate on the sideways component, being equal and opposite as per Newton, we end up with wind, interacting with the real surface, with one eye on the friction-less surface scenario, do we not end up with the situation in reality, where this new constantly generated movement of mass relative to the surface, then requires a perfectly balanced coefficient of friction in all directions over the globe.

Otherwise the status quo of the friction-less solid sphere is not replicated, and treating the earth and the atmosphere as a closed system fails.

https://en.wikipedia.org/wiki/Anemometer

[Bored chemist]

Appearances can be deceptive, there are patterns in the data that suggest that may not be the case.

There's one pattern- tidal drag- though it's not entirely obvious if the air pulls the ground or pushes it. (Does the tide mainly affect the sea and that affects the solid earth which affects the air, or does the pull of the tide on the air  have more effect?)

There are tiny effects due to radiation pressure and solar wind.

But the conservation of angular momentum means that the solid earth and the oceans and the atmosphere taken as a whole are an isolated system.
So, apart from the small external effects, the angular momentum of the system is fixed and, because it can't change shape or size much (Earthquakes and melting polar ice can change the shape slightly; weather changes the position of the water a bit), the period of rotation is nearly fixed.

[gem (OP)]

Hi all,

So BC,
Yes that is a very good description of the current understanding, treating the earth and atmosphere, as a combined closed system, as mainstream science absolutely does.

Halc

Those equal and opposite laws apply vertically just as much as horizontally. Air will not accelerate without a net force exerted on it by something else.

Yes but not initially involving the surface, as you stated, warm air is displaced by cooler/denser air

In regards to the point made with to many commas,,,,, then lets try the globe vessel suspended on a friction-less gimble
filled with water, with a fixed amount of angular momentum, lets set it at zero.

Lets then apply heat centrally, underneath it (as we are not in an inertial reference frame) so we get a central column of convection upwards and an equal flow downwards around the sides of the globe.
If the inside of the vessel surface coefficient of friction was designed to replicate an anemometer to favour more friction in one direction, what effect would this have on the momentum of the system ?   
https://en.wikipedia.org/wiki/Anemometer

[Halc]

Those equal and opposite laws apply vertically just as much as horizontally. Air will not accelerate without a net force exerted on it by something else.

Yes but not initially involving the surface, as you stated, warm air is displaced by cooler/denser air

You're mixing up cause and effect. This only happens after the air starts moving. Net motion cannot happen without the force exerted by an external object.
So initially, heat just changes the local pressure. In the absence of force from the ground, that air would expand equally in all six directions until a new equilibrium is found. This is why a balloon in orbit cannot get to a higher orbit just by heating it. So the ground resists the motion downward. Increased pressure at the ground pushes the warm air up.  One it moves (up and out at first) it becomes less dense and then buoyancy takes over, but even that requires reaction force from the ground.
Fluid dynamics is incredibly complicated and requires considerable prerequisite calculus courses that I'm not going into. I'm trying to keep it simple.

In regards to the point made with to many commas,,,,, then lets try the globe vessel suspended on a friction-less gimble

We all decided that it wouldn't work. The system is subject to external torque. The (spherical) vessel will not necessarily rotate in the opposite direction of the rotation of its contents.

Lets then apply heat centrally, underneath it (as we are not in an inertial reference frame)

We're not? You said it was all stationary at first. Sounds pretty inertial except for the gravity.

so we get a central column of convection upwards and an equal flow downwards around the sides of the globe.

Yes. I had tried applying the heat to the sides to get rotation to attempt to get the vessel to rotate the other way to preserve angular momentum, but it wasn't preserved because we didn't keep the system closed.

If the inside of the vessel surface coefficient of friction was designed to replicate an anemometer to favour more friction in one direction

An anemometer has equal friction in all directions, else equal magnitude wind from different directions would make it rotate at different speeds, which defeats the purpose of a speed measuring device. But I think you mean put up sails on the sides of the vessel that inhibit flow in one direction more than another. So all this fluid is going down the sides and up the middle. If we have asymmetrical friction on the sides, we can get the vessel to rotate, but not necessarily the system.

what effect would this have on the momentum of the system ?

Linear momentum: So long as the center of gravity doesn't go anywhere, the system does not move. If the center of gravity goes up or down, external force from the gimbal will counter it, leaving it with zero momentum.

Angular momentum: So long as the center of gravity remains over the gimbal axes, the system angular momentum must remain zero. You're introducing asymmetries with the variable friction along the vessel (similar to the asymmetries of applying the heat off-center), so I suspect that the center of gravity will move to one side, in which case the system will be subjected to an external torque applied through the gimbal and will acquire nonzero angular velocity.  The water will rotate and take the vessel with it since it has friction.

[Bored chemist]

what effect would this have on the momentum of the system ?   

Have you applied an external force or an external torque to the system?
If not, then nothing will happen to the momentum or angular momentum of the system.

[Bored chemist]

Is it my imagination or does this thread have parallels with this one
https://www.thenakedscientists.com/forum/index.php?topic=80717.0
where one of our esteemed members forgot about the conservation laws?

[gem (OP)]

Hi all,

Ok, Halc

gem; my bold

Therefore changing the density which triggers convection due to buoyancy spontaneously creating upthrust,  exerted as a result of the weight of the denser overlying fluid. "this can only occur in a non inertial frame of reference"

Halc

You can apply an inertial frame of reference on any system you like. Your assertion in quotes still suggests that convection currents cannot occur with say gas in a box in deep space, which is about as inertial as it gets. That assertion is dead wrong. You heat gas, it expands, and that expansion is motion (convection)

I don't believe you can apply an inertial reference frame if buoyancy is occurring, my statement of convection due to buoyancy is dead right, in your example of a box in deep space with energy added will not get convection due to buoyancy, unless you accelerate the box. (non inertial reference frame)
 
Halc

Not generated. Transferred. It has to come from somewhere, so an equal and opposite torque needs to be transferred to the ground or the air or somewhere. Despite the asymmetry, a continuously spinning anemometer in steady wind has no net torque on it. The net transfer is only needed to speed it up or slow it down.

I believe the torque is generated from the frictional forces of the velocity of the mass of air colliding with the cups and circular design of the apparatus.

A constant torque force is applied/transferred  to the earths surface when a continuously spinning anemometer in steady wind is anchored to it, given the frictional force that is occurring.

Therefore it still needs to be demonstrated  the solid earth can discriminate between these collision and a meteorite, in regards to the potential change of momentum of the solid earth. from the dynamical motion that is created in the atmosphere,independently of the solid earth through buoyancy/convection expansion and contraction, pressure differences and subsequent collisions/transfers between the atmosphere and the surface, .

 

[Bored chemist]

I believe the torque is generated from the frictional forces of the velocity of the mass of air colliding with the cups and circular design of the apparatus.

A counter-torque is generated on the air. - A straightforward application of Newton's 3rd law.
That, in turn exerts a torque on the  solid Earth.

But the angular momentum of the whole ( rock, air, anemometer, bloke holding it ) system remains unchanged.

[gem (OP)]

Hi all,

BC

But the angular momentum of the whole ( rock, air, anemometer, bloke holding it ) system remains unchanged.

Halc

Buoyancy is not a violation of momentum conservation.  It cannot generate new momentum, so to speak. The total remains constant for a closed system.

When the forces are not balanced, due to expansion of the atmosphere that's heated, the volume/droplet of air accelerates, due to the upthrust of the buoyancy effect.
This changes momentum due to the acceleration of bulk motion of fluids, the rate of change in momentum is equal to
   
Δmomentum = ρ.Δv/Δt
 
This is equal to the net force on the volume/droplet.

these forces that change the momentum of a volume/droplet of a fluid come from the gradient of the pressure and gravity.

This occurs due to energy input from outside the system under consideration doing work on the system to increase the volume occupied by mass, which then facilitates the separate spontaneous buoyancy/convection  action/reaction.
Which  happens independently of the solid surface, that it later interacts with via partially inelastic collisions/friction

Therefore the conditions of conservation of momentum are not met.

Halc

I don't know what you mean by 'discriminate'. It is an epistemological word

If you don't like the use of the word discriminate, I am happy to switch it to differentiate