How life could help atmospheric tides slow a planet’s rotation

Posted: November 6, 2018 by oldbrew in atmosphere, research, solar system dynamics, Tides
Tags: ,

Layers of Earth’s atmosphere


Some fairly advanced theorising here, but the possibilities look interesting. For example, could ‘resonant trapping’ exist?

Resonating oscillations of a planet’s atmosphere caused by gravitational tides and heating from its star could prevent a planet’s rotation from steadily slowing over time, according to new research by Caleb Scharf, who is the Director of Astrobiology at Columbia University.

His findings suggest that the effect is enhanced for a planet with an atmosphere that has been oxygenated by life, and the resulting ‘atmospheric tides’ could even act as a biosignature, reports Phys.org.

Tides can distort a planet’s mass, which in turn affects its rotation. We’re most familiar with gravitational tides, which on Earth we feel from the gravity of the Moon and the Sun. These gravitational tides create bulges as Earth spins, and the Moon and Sun tug on those bulges, slowing the spin.

By contrast, atmospheric tides, sometimes called thermal or solar tides, occur when sunlight heats the surface and air on Earth’s daytime side. That heating shifts the atmosphere’s mass from the hottest point to cooler points on the planet. As with gravitational tides, atmospheric tides cause bulges that are vulnerable to gravitational pulls. Those bulges subtly change the shape of Earth’s atmosphere, stretching it from a sphere to something slightly less symmetrical and more elliptical. Scharf suggests imagining a ‘handle’ on Earth, and that forces pulling on the atmospheric handle can then help speed up or slow down the planet’s rotation.

Resonant frequencies

Usually, the effects produced by these thermal tidal forces are relatively small, but the effects can be increased in certain circumstances, such as in resonances. These are natural vibrational frequencies that describe the undulating movement of bridges in the wind, or being pushed higher and higher on a swing. Atmospheric redistribution becomes amplified when the planet’s rotation rate matches the natural frequency of the atmosphere’s oscillation.

Scharf uses another metaphor to explain resonance: “It’s like playing a violin,” he tells Astrobiology Magazine. “The atmosphere is a violin string wrapped around the planet. If you draw the bow at the proper speed across the string, you get the right note and the loudest sound.”

Scientists believe resonance occurred with Earth when its days were about 21 hours long. That day length would have created a peak in the atmospheric movement, which means it would have felt the strongest tidal pulls from the Sun and the Moon, creating a particularly big ‘handle’ and maximum torque. At that resonance, the influence of a star over a planet’s atmosphere is at its largest, as are the effects on the planet’s rotation.

A phenomenon called ‘resonant trapping’ can occur when the opposing forces exerted on the atmospheric handle, and by the planet’s usual gravitational tides, reach equilibrium, locking in the planet’s rotation rate.

Breaking out of the trap

According to Scharf, research suggests that Earth may have been resonantly trapped at the 21-hour day length for “hundreds of millions of years,” perhaps in the Precambrian Era over 500 million years ago. The effects of resonant trapping are difficult to measure by themselves, but in general Scharf notes that planets with faster rotations have hotter equators and cooler poles. Being resonantly trapped may have affected Earth’s climate, but more important is the role of resonant trapping in climate evolution.

Resonance can be (and in the case of Earth would by necessity have been) broken by temperature fluctuations, such as a rapid warming after a deep freeze, which would re-initiate the increasing of the day length over millions of years as a planet’s rotation resumes slowing down.

For instance, it’s possible that 3 to 4 billion years ago, Earth had a 12-hour day, and that over time it lengthened to 24 hours. At some point in the distant future, an Earth day could be longer than 24 hours.

Continued here.

Comments
  1. ivan says:

    Did they consider the effect of all the renewable energy windmills? The fact they are pulling energy out of the wind must be changing the resonance of the atmosphere to a much larger extent in a shorter time than ever before. Or is that a subject that must not be considered?

  2. cognog2 says:

    I understand, from something I read, that the Earth has slowed down by by a nano smidge or two during my lifetime and also the Moon has moved away by a bit of a centimetre. Can’t say I have noticed it!,

  3. erl happ says:

    Is it not electromagnetic forces that are responsible for the rotation of the Earth. The atmosphere spins in the same direction but at a faster speed than terra-firma and especially so in the winter hemisphere.If this is the case only a weakening of the electromagnetic influence could slow the Earth’s rotation.

  4. oldbrew says:

    If there’s a ‘gravitational’ effect from another body (Moon, Sun), does that count as electromagnetic?

  5. JB says:

    A planet’s rotational period is driven by the gravitational force of the sun. This was discussed in chapter 11 of Pari Spolter’s 1993 book, The Gravitational Force of the Sun. A planet’s gravitational force,which in turn establishes its strength of gravity is proportional to the mass of the planet to the mass of the sun, multiplied by the sun’s gravitational force. Pari established what the true gravitational force of the sun is, and why Newton’s equation is non-predictive.

    “The velocity at the equatorial surface, if not retarded by the weight of the body, would be: Vel_grav = (grav_planet * Radius_equator)^-½. The sidereal period of rotation of the body gives the actual velocity at the equatorial surface, V_equator.” p223

    A table of calculated rotational periods in seconds for the major solar system bodies is given on page 224.

    The phenomenon discussed in Scharf’s study is of secondary influence, if at all.

  6. erl happ says:

    Gravity causing rotation? Implausible.

  7. oldbrew says:

    Erl: not causing but affecting via tidal mechanics. Moon>Earth effect is just a weaker version of Earth>Moon, which as we know causes the same side of the Moon to face Earth = tidal locking (one orbit = one rotation).

  8. Curious George says:

    Do their data show that the Earth supports life?

  9. oldbrew says:

    George – good point.

  10. JB says:

    @ Erl Pari makes no effort in her book to define what the gravitational force of the sun is composed of. But the equations she published do work out without a single error. My take on it is the force which she ascribes to the sun is operational on all bodies of the solar system and the effects are proportional to mass. I lean toward current flow along the galactic arm as the source of the motive force. But I have no way of arguing the idea. The book is a very good read, highly stimulating. I learned a number of things from it, other than what she intended.

  11. erl happ says:

    Thanks JB. Here’s my take on the matter: One only needs to combine a magnetic field and an electric current and there will be movement. The atmosphere over the winter pole is highly ionised. There is a ‘magnetosphere’. The plasma component of the atmosphere responds to the magnetic field, forcing a rotation of the entire atmosphere in the same direction of rotation of the Earth itself, but faster.

    The rate of ionisation of the winter atmosphere is already high due to the seasonal peak in the partial pressure of ozone. Add the ionisation due to cosmic rays that varies with solar activity and you have one source of variation in the rate of spin of the atmosphere.

    Cosmic rays impinge most at jet stream altitudes where polar cyclones originate. Polar cyclones drive high latitude surface pressure and thereby the planetary winds……. driving climate everywhere. The phenomenon is described as ‘Annular modes’ of surface pressure variation……or in other words where the wind comes from.

    The time taken by the Earth to do a single rotation is affected by the rate of atmospheric drag.

    Across the globe, the degree of variation that one observes in surface temperature is several times as much in the winter than it is in the summer.

  12. JB says:

    Erl, beyond plasma currents interacting with magnetic fields, where those effects impact temperature and pressure I’m on a slippery slope. My education and career was confined to the relationship of magnetic fields that form with current flow. I have read somewhat about the current flow and charge distribution in cyclones (Influence of Cyclones on the Atmospheric Electric Field of Kamchatka, Kuznetsov/Cherneva/Druzhin). I don’t recall them covering temperature or pressure effects. Climate effects related to ionization and planetary magnetic fields is way over my head.

    Have you been following Don Scott’s investigations into the magnetic field effects of Birkeland current flow?

    I think you will be interested in the very last part on the topic of hurricanes.

    A weakness in Pari’s book to me is the failure to recognize the fact that the “gravitational force”, being the same everywhere within the solar system, negates the idea that such force originates with the sun. Magnetic field strength in a wire disperses at the rate of 1/r; gravity, light, sound (without impediments), at 1/r^2; and the unrestricted Birkeland current’s field disperses at 1/r^-2. Now the only way I can conceive of a Birkeland current’s magnetic field as being the motive source for planetary orbital and axial rotation is for the area of the field to be extraordinarily large–in terms of what we’re conditioned to conceive them. Pari appeared to miss this obvious detail. When she discusses the “gravitational force of the sun” I take it to mean the force that induces gravitation. Gravity appears as a term in the equations that predict the velocity of orbit and rotation. But my suspicion is it is not gravity at all, but some phenomenon where matter is being displaced by the same force which produces gravity. Somehow the spiral rotation Anthony Peratt documented in his plasma current experiments is driving the rotation of matter.

    Dr Scott introduces his analysis of rotating fields in his 2014 presentation:

    the meat begins at 12:xx minutes.

    Well this fairly well exhausts what I’ve learned on the topic.

  13. erl happ says:

    JB, Thanks for the information. It underscores a reality that is unfortunate. Understanding the Earth’s climate….or the planetary winds that condition surface temperature, requires a multidisciplinary approach. So much of our education and experience is based on tight specialisation.
    Personally, I come from the observational end where I am familiar with the movement of the air and an asking ‘why is it so?’. Visually, we have this: https://earth.nullschool.net/#current/wind/isobaric/250hPa/orthographic=-245.88,-35.73,684/loc=115.282,-34.006
    We can see evidence of counter rotation, separated according to altitude. Compare the 250hPa level with the 10hPa level. At this altitude we are dealing with 75% of the atmosphere by weight, that part above the 250hPa level where ionisation is ubiquitous, in part due to the impact of cosmic rays, in fact much more so than any ionisation due to the impact of short wave radiation. This fast rotation is a winter hemisphere feature, fastest in the region affected by the polar night.

    This diagram https://spaceweatherarchive.com/ shows where free oxygen atoms are the result of ionisation of O2 by short wave radiation from the sun. It’s a feature of the mesosphere rather than the stratosphere. It starts at the D level of what is otherwise known as the ‘ionosphere’. The presence of O3 atoms in what we call the stratosphere is due to relative freedom from the pressures of ionisation and vigorous mixing processes. It’s the winter atmosphere, relatively free of the pressures of ionising radiation that exhibits the highest ozone content.

    Scott makes the common sense point that gravity is about collisions…..not spin. He says that the universe is filled with plasma. Intergalactic space is not empty. And that observation, incorporating a role for plasma, is true of 25-30% of the weight of the atmosphere of the Earth, at least the upper third in high latitudes So, Birkenland currents do play a role. In fact a major role, because Polar cyclones are the most vigorous and influential aspect of the movement of the atmosphere, and they originate at the 250hPa level. It’s observed that the tropopause below a low pressure system is several kilometres lower than average. The atmosphere above the tropopause where the polar cyclone is generated is ozone rich, warmer and rarefied, accounting for the lower surface pressure. The stratosphere is warmed by the absorption of long wave radiation from the Earth, not short wave radiation from the sun.

    Unfortunately, academic climate science is blinded by the general assumption that there is a correlation between the carbon dioxide concentration in the atmosphere and surface temperature. Obvious stuff can not be mentioned. It’s politically incorrect to state the obvious.

    Sydney Chapman, the Birkenland critic, is credited with working out, in 1930, the photochemical mechanisms that give rise to the ozone layer. Unfortunately he was just plain wrong.

    Chapman’s idea of the origins of the stratosphere is still the conventional wisdom. Birkenland’s time is yet to come.

    I will second Scott’s motion: You have to look.

    Thanks for educating me re Birkenland currents. I now know where Chapman fits in. Just another ‘observation free’ mathematical theorist. However, back in the 1930’s people were just coming to grips with the idea that the atmosphere could warm up with elevation rather than cool down all the way up to the thermosphere. So, you have to admire his enterprise.

    Climate scientists are slowly coming to grips with the notion that surface weather is determined top down rather than bottom up.

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