Archeomagnetic Jerks & Abrupt Climate Change

[Saul]

http://sciences.blogs.liberation.fr/home/files/Courtillot07EPSL.pdf

I have been looking into puzzling cyclic changes the geomagnetic field which appear to be solar driven as they match the solar magnetic cycle timing. The sun is moved by the large planets about its barycenter. The change in direction of the sun and its acceleration at the time of the change in its direction appear to interrupt the solar tachocline which is the interface between the solar radiative zone and convection zone. The tachocline is the region where sun spots are produced. When the tachocline is disturbed sunspots cannot long build in the tachocline. A sunspot requires a field strength of around 2000 gauss to avoid being torn to pieces as it moves from the bottom of the convection zone (tachocline) to the solar surface.

The restart of the solar magnetic cycle appears to create massive coronal mass ejection CME which when they strike the Earth's ionosphere create very large electrical discharges from the ionosphere to the planet's surface. The timing of perihelion and the Earth's axis tilt at the time of the event controls which hemisphere the strike hits.

I would assume the polarity of the strike remains the same. Depending on the polarity of the Earth's magnetic field at the time of the event and the hemisphere the strike occurs in, determines whether the strike will reduce or increase the Earth's magnetic field. This explains why the strike does not always have a strong cooling effect on the climate. Prior to the strike the solar magnetic cycle is in a deep minimum which cools the planet. The geomagnetic field resists changes so will initially weaken in the region of the strike before the effect is integrated into the total geomagnetic field constructively or de-constructively.

The ice sheet insulate the planet and force the strike down to lower latitudes where it has less affect on creating the geomagnetic field. This explains why the geomagnetic field drops in intensity by 70% during the glacial phase of the glacial/interglacial cycle.

It has been known for sometime that cosmogenic isotopes changes track the abrupt climate changes on the planet.

Read this paper thinking about the above proposed mechanism.

Are there connections between the Earth's magnetic field and climate?

Understanding climate change is an active topic of research. Much of the observed increase in global surface temperature over the past 150 years occurred prior to the 1940s and after the 1980s. The main causes invoked are solar variability, changes in atmospheric greenhouse gas content or sulfur due to natural or anthropogenic action, or internal variability of the coupled ocean–atmosphere system. Magnetism has seldom been invoked, and evidence for connections between climate and magnetic field variations have received little attention. We review evidence for correlations which could suggest such (causal or non-causal) connections at various time scales (recent secular variation approx. 10–100 yr, historical and archeomagnetic change approx. 100–5000 yr, and excursions and reversals 10^3–10^6 yr), and attempt to suggest mechanisms.

Based on newly acquired archeo-intensity data from archeological and historically dated material recovered from western Europe and the Middle-East, Genevey and Gallet [55] and Gallet et al. [56] observed rather sharp maxima in time variations of the intensity of the ancient field, associated with sharp curvature changes in direction. These features, which are stronger and faster than previously realized [57,58,53] have been called
“archeomagnetic jerks” (Fig. 4). The name may be a bit misleading, as these are rapid, approx. 100-yr long increases in field intensity by 15–30%.

 

[Xnn]

Sorry Saul; When I look at historic arctic temperatures over the last 2000 years, there doesn't appear to be much of a solar magnetic cycle to it. Just a slow gradual decline related to the procession of the perihelion up until the late 1800's when industrial CO2 emissions took off.

http://www.ucar.edu/news/releases/2009/arctic2k.jsp

 

[Saul]

Sorry Saul; When I look at historic arctic temperatures over the last 2000 years, there doesn't appear to be much of a solar magnetic cycle to it. Just a slow gradual decline related to the procession of the perihelion up until the late 1800's when industrial CO2 emissions took off.

http://www.ucar.edu/news/releases/2009/arctic2k.jsp

The scientists reconstructed summer temperatures across the Arctic over the last 2,000 years by decade, extending a view of climate far beyond the 400 years of Arctic-wide records previously available at that level of detail. They found that thousands of years of gradual Arctic cooling, related to natural changes in Earth's orbit, would continue today if not for emissions of carbon dioxide and other greenhouse gases.

The problem is the reconstruction is mixing paleo data with instrumentation data. Depending on the calibration of paleo data it makes the cycle disappear.

Not the reconstruction is summer temperature. One would expect do to precession the summers would get cooler and the winters would get colder.

http://upload.wikimedia.org/wikipedia/commons/c/c2/Vostok-ice-core-petit.png

There are absolutely abrupt changes in the climatic record.

For example, the above graph shows all of the past interglacial periods ended abruptly.

 

[Saul]

http://www.pnas.org/content/97/4/1331.full

Abrupt climate change has in 1990's by examining the Greenland Ice Core.

Ice-core evidence of abrupt climate changes

Ice-core records show that climate changes in the past have been large, rapid, and synchronous over broad areas extending into low latitudes, with less variability over historical times. These ice-core records come from high mountain glaciers and the polar regions, including small ice caps and the large ice sheets of Greenland and Antarctica.
As the world slid into and out of the last ice age, the general cooling and warming trends were punctuated by abrupt changes. Climate shifts up to half as large as the entire difference between ice age and modern conditions occurred over hemispheric or broader regions in mere years to decades. Such abrupt changes have been absent during the few key millennia when agriculture and industry have arisen. The speed, size, and extent of these abrupt changes required a reappraisal of climate stability. Records of these changes are especially clear in high-resolution ice cores. Ice cores can preserve histories of local climate (snowfall, temperature), regional (wind-blown dust, sea salt, etc.), and broader (trace gases in the air) conditions, on a common time scale, demonstrating synchrony of climate changes over broad regions.

http://www.pnas.org/content/97/4/1331/F1.large.jpg

 

[BigFairy]

Hi, thanks for the info. Sounds promising

 

[Andre]

The problem with paleo proxy reconstruction is that it is always an "affirming the consequent" fallacy. When it rains, the streets are wet. The streets are wet, so it rains. It could be true but it could not be true as well.

We have just witnessed a tremendous exposure of proxies being misunderstood completely, here, within these threads in the last weeks, without a lot of people noticing.

It's between this https://www.physicsforums.com/showthread.php?t=333747

and this: https://www.physicsforums.com/showthread.php?t=335069&page=2

with this post

https://www.physicsforums.com/showpost.php?p=2334915&postcount=6

in which it is shown that the isotope proxy warming started around 15000 years ago


and this: https://www.physicsforums.com/showthread.php?t=335069&page=2

There's no conflict at all with warming starting at one time and accelerating briefly at another. Here's a very recent paper which gives considerable detail on timing of events and the possible roles of different sheets, and considering the regional variability involved.
Peter U. Clark, et al. (2009) The Last Glacial Maximum, in Science Vol 325, 710-714, doi:10.1126/science.1172873

in which it is suggested that widespread northern hemisphere warming started 3000-4000 years earlier.

That's huge.

I'll elaborate tomorrow.

 

[Saul]

I have been looking for evidence of a periodic solar forcing of the geomagnetic field.

Attached below is the evidence.

This paper discusses five volcanoes that erupted during a magnetic field excursion. The five volcanoes are geographically in the same area, but are not linked by the same magna chamber.

What it appears is the solar magnetic cycle is periodically interrupted. As part of the restart of the solar magnetic field, the sun produces massive coronal mass ejections. The CME create space charge imbalances in the ionosphere which in turn creates an electrical discharge from the ionosphere to the planet's surface.

The hemisphere where the strike occurs is controlled by the timing of perihelion (closest approach of the sun to earth) and the Earth's tilt at the time of event.

Ice is an insulator. The ice sheets push the strike to lower latitudes. At lower latitudes the strike has less effect on the geomagnetic field, which explains why the geomagnetic field drops in intensity by a factor of 5 to 6 during the glacial part of the glacial/interglacial cycle.

The strike reinforces the geomagnetic field if the polarity of the magnetic field induced matches the current polarity of the geomagnetic field. If it is opposite to the polarity of the geomagnetic field it will create a magnetic field anomaly in the region of the strike and will eventually reverse the geomagnetic field with subsequent strikes.

The position of the continents controls the effectiveness of the strike and its effect. This explains why there were periods when the geomagnetic field has cyclically reversing with a period of around 20 kyr and others where the field did not change for millions of years.

http://www.agu.org/pubs/crossref/2006/2006GL027284.shtml

Geomagnetic excursion captured by multiple volcanoes in a monogenetic field

Five monogenetic volcanoes within the Quaternary Auckland volcanic field are shown to have recorded a virtually identical but anomalous paleomagnetic direction (mean inclination and declination of 61.7° and 351.0°, respectively), consistent with the capture of a geomagnetic excursion. Based on documented rates of change of paleomagnetic field direction during excursions this implies that the volcanoes may have all formed within a period of only 50–100 years or less. These temporally linked volcanoes are widespread throughout the field and appear not to be structurally related. However, the general paradigm for the reawakening of monogenetic fields is that only a single new volcano or group of closely spaced vents is created, typically at intervals of several hundred years or more. Therefore, the results presented show that for any monogenetic field the impact of renewed eruptive activity may be significantly under-estimated, especially for potentially affected population centres and the siting of sensitive facilities.

 

[Saul]

This is the paper that shows the geomagnetic field drops by a factor of 5. The time constant for a core based change in the geomagnetic field is relatively long 2 to 5 kyrs. There is no explanation for how and why the geomagnetic field would change so rapidly.

The Archeomagnetic Jerks occur with a periodicity of 600 years. Besides the time constant issue it does not seem possible a core based mechanism could change cyclically every 600 years.

http://eprints.whiterose.ac.uk/416/1/gubbinsd4.pdf

Is the geodynamo process intrinsically unstable? K. Zhangand, David Gubbins

Recent studies suggest that the Earth's magnetic field has fallen dramatically in magnitude and changed direction repeatedly since the last reversal 700 kyr ago (Langereis et al. 1997; Lund et al. 1998). These important results paint a rather different picture of the long-term behaviour of the field from the conventional one of a steady dipole reversing at random intervals: instead, the field appears to spend up to 20 per cent of its time in a weak, non-dipole state (Lund et al. 1998).

One of us (Gubbins 1999) has suggested that this is evidence of a rapid natural timescale (500 yr) in the outer core, and that the magnetic field is usually prevented from reversing completely by the longer diffusion time of the inner core (2 to 5 kyr). This raises a number of important but difficult questions for geodynamo theory.

How can the geomagnetic field change so rapidly and dramatically? Can slight variations of the geomagnetic field affect the dynamics of core convection significantly? If so, is the geodynamo process intrinsically unstable?