Paleo reversals and the dynamo effect

[andycass]

Hi,

I am exploring a theory and would like your initial reaction to it. The latest research unfortunately I do not have access to however I think there may be an easier way to understand the magnetism created by the Earth dynamo by realising that it is simply the sum of all the dynamos. I assume that every part of the earth’s interior if moving relative to its neighbour has the potential to generate substantial magnetic fields. And while the current models are largely based on fluid mechanics, we could assume that the dynamos are capable of generating a field in any orientation, the sum of which would normally be close to zero as they mostly cancel the others out.

If we allow for the influence of the Earth's movement through the orbital plane, we are traveling through a weak field. But if one were to assume that any magnetic field that reached the near Earth region was acted upon by solar wind and electro-magnetic energy, and that he resulting geometry of the current magnetosphere with substantial electrical current from very high altitude is the result of the weak influence of an exciter circuit that allows the sum of the dynamos to stabilise in a particular orientation each little dynamo as its strength grew the magnetosphere grew and the influence grew.

Now let us assume that there is a significant solar event that distorted the magnetosphere such that the exciting field allowed the sum of the dynamos to stabilise in a different orientation, one might create a magnetic reversal without having to change the entire fluid dynamics of everything deeper than 400 KM.

I have not been able to understand the mechanics of the interplay between plasma, electrical energy and the magnetic lines of flux, other than to realize that all current models assume that the Earth is a dynamo, and do not account for the abundance of energy in all forms in the near Earth region other than as a result of the magnetic field. I think the physics would be made much easier if it were reduced from the formation of a dynamo within the Earth to allowing the Earth to have almost an infinite supply of little dynamos and studying the sum as the excited result of multiply reinforcing interactions in the near Earth region. This would also have the advantage not relying on a fixed type of movement within the earth, but as long as she was churning away down there we will get the field that se see today. All geo data point to random heat flux at inner core boundary and at the outer core boundary, but the evidence is weighted to huge convection currents driving plate tectonics. All this movement regardless of form or location could contribute to our understanding and the model becomes much easier to study, as we can assess the data from the near Earth environment.

 

[Andre]

I'm not sure if I understand what you're getting at. It was my impression that the geodynamo model was successfully mimicing paleo magnetic excursions and field reversals (Gary Glatzmayer et al). I think that we need the model. If the magnetic field was generated outside the Earth only to be fortified by induction then Venus should also have a magnetic field. But it hasn't.

There was also a impressive promotion last year on a mathematical model for chaotic thermo fluid behaviout in the Outer core, that was able to predict paleomagnetic excursions. Can't find it back on the moment.

 

[andycass]

Hi Andre, The Glatzmaier model has assisted the understanding of how the dynamo may function, but predicts a reversal period of 100,000y, also that the inner core rotates with twice the period as measured by seismic data. In addition, the basis is chaotic flow around the inner core, and evidence suggests even distribution of heat flux. To tell you the truth I don’t really understand how they derive this model as it is not my field, only that the model touted so loosely fits data.

My thinking is based on the idea that it is not necessary to create coherent field from a chaotic structure, that the existence of near Earth fields provides a structure with which to initiate the field if it is in harmony with it, and that it should be easier to look into the interactions of the Earth's field and the additional energy available to it through the sun.

I would love to see further stuff on the model if you can locate it, I would much appreciate it.

Re Venus, Don’t know if it has a core nor fluid or whatever, but the existence of the effect here would not necessarily mean that it would have to work else where, only that it was a factor.

 

[Andre]

Andy,

I'm afraid I don't quite get it. Anyway, I had a brief discussion with GC and it turned out for instance that he had not included precession in his model. While others think that precession may be the driving force of the magnetic field:

http://www.cosis.net/abstracts/EAE03/00778/EAE03-J-00778.pdf

Geophysical Research Abstracts, Vol. 5, 00778, 2003cEuropean Geophysical Society 2003

PRO/CON A PRECESSIONAL GEODYNAMO
J. Vanyo

Departments of Mechanical Engineering and of Geological Sciences, University of California,Santa Barbara, CA, 93106 USA
(vanyo@engineering.ucsb.edu)

The modest amount of research that exists on the ability, or lack of ability, of mantle precession to power a geodynamo developed mostly during the last half of the 1900s. Papers by Roberts and Stewartson (1965) and by Busse (1968) studied precession generally without a pro/con conclusion. Malkus in the late 1960s attempted to advance apositive role for precession through experiments and analysis. His experiments have survived criticism, but his analyses were discounted, especially by Rochester, Jacobs,Smylie, and Chong (1975) and by Loper (1975). Rochester, et al. critiqued existing analyses of precession, including those of Malkus, but did not reach a strong position either pro or con a precessional geodynamo. Loper argued emphatically that precession was not capable of powering the geodynamo. Explicit analyses that either critique or support LoperSs arguments have yet to appear in the literature. During the 1970s,Vanyo and associates studied energy dissipation during precession of satellite liquidfuels and its effect on satellite attitude stability. Engineers and scientists in every country that has launched satellites completed similar research. Some is published in theaerospace literature, more is available in company and government reports. Beginningin 1981, Vanyo and associates applied this knowledge to the very similar problem of energy dissipation and flow patterns in precessing mechanical models scaled geometrically and dynamically to the EarthSs liquid core. Energy experiments indicate massive amounts of mechanical energy are dissipated at the CMB, and flow experi-ments show complex motions within the boundary layer and axial flows with helicity throughout the interior. Analysis of Earth core precession also advanced, especially in several papers by Kerswell and by Tilgner in the late 1990s. Detail numerical models have yet to appear. Although progress in understanding the role of precession in Earth core motions has advanced, there remains a common belief, often expressed explicitly, that precession is incapable of energizing a geodynamo, a la Loper. We will present a critique of LoperSs 1975 paper and briefly discuss the common practice and belief that the geodynamo must be energized by thermal and/or compositional driven convection (motion). We note here that there is no observational evidence for existence of thermal or compositional convection within the liquid core or for growth of the solid core. Although there has been considerable success in adapting data in thermal/compositional models to yield near realistic solutions, that does not constitute a proof that those models apply to the Earth. There is absolute observational evidence for mantle precession, an Earth feature that is unique, along with the EarthSs magnetic field, among the terrestrial planets. We argue that great difficulty experienced in analysis and computation of precessional flow is a major explanation for its absence in current models of the geodynamo.

Unfortunately Prof Vanyo is retired.

You may find much useful material here:

http://mahi.ucsd.edu/cathy/SEDI2002/Sessions.html

Still looking for that promotion paper.

Andre

 

[andycass]

Hi Andre, Thanks for the material.

Since you state that you still don't get it, i can't be explaining myself very well, I don't dispute the models to date, as achieving part of the explination as to the existence of the dynamo, i am just thinking that maybe we don't have to think about how it started on its own if the existence of the interactions in the magnetosphere would help stabilise it N/S, would allow it to process, as any spinning thing does due to the conservation of angular momentum, and may help us understand why it reverses.

I also do not really believe that the magnetic variations in a sun storm would be enough to change the field, but what I was wondering, if I might draw on a memorable analogy, the force of the wind blowing on the Tacoma narrows bridge. The wind in no way could cause the bridge to fail, but there was a harmony in the structure that the slightest wind exerting only 10's of Newtons pressure on the structure caused... you will probably remember.

I assume that energy in the magnetosphere, almost irrespective of its form, whether as charged plasma, light, solar wind, magnetism and other forms, and flowing in patterns and being shaped as dictated by the magnetic field could have a similar effect, and that by measurably changing the structure of the magnetosphere by such storm the harmonics changed and reinforced different
If there is chaotic flow regimes in and around the core, then it stands to reason that a dynamo effect could take up any orientation, but those within a harmonised regime would generate far more field.

 

[Andre]

Okay understand it but actually the apparent absence of a visible relationship between paleo magnetic history and climate history has puzzled the paleo magnetists.

There is no correlation found between the climate proxies (ice cores, ocean sediment cores etc) and paleomagnetic sequencing and excursion, except for the puzzling dominant 100,000 year cycle, however totally out of phase.

 

[andycass]

Hi Andre,

Maybe there wouldn't need to be a correlation, because the changes in the near Earth conditions, may be enough to exite a polarity change, but not enough to drastically alter the climate.

I understand that the recent increased activity has distorted the magnetosphere so that the Bow shock wave between the solar energy nd the Earth's magnetosphere was shifted half the distance towards the earth. I do not have acess to such data but i have heard it reported. If that is the case, maybe that is evidence that the structure can me majorly distorted and but climate systems are for example, too volitile to be changed, or that the correlations are too weak etc.

My problem is not having the ability to put any numbers to my thoughts and not really understanding the near Earth energy flows and srtucture.

Regards

Andy

 

[Andre]

Okay, Andy

However if you look at the Earth magnetic field strenght in the current (Brunhes) Cron, there is a stroking resemblance with the climate indicators in the ice and ocean cores. Also spikes (Paleo Magnetic Excursions) rougly spaced with 20-40 and 100 Ky. But they are out of phase for 10,000-30,000 years, so a relation with climate is not that far fetched.

compare the graph of Magnetic field strength
http://www.geo.uu.nl/~forth/publications/Related_pubs/Guyodo99.pdf

and the Benthic stack for instance:

http://jlevine.lbl.gov/BenStackintro.html

 

[andycass]

Interesting,

i guess the question that i am asking is, is there a correlation with the suns activity, ie sun has an 11 year cycle of reversals, however this is too shorter time scale. Do you know of any other cycles? or could it be related to something such as impact affecting the fields regioanlly?

questions just keep on flooding on...

Andy

 

[Andre]

Well for more solar cycles, the solar cycle expert seems to be Dr Theodore Landscheidt:

http://sharpgary.org/landscheidt.html

with some links to papers.

Still, the Earth and solar magnetic field interaction is not very clear.