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betzalel
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There has been a series of papers recently published that provide observational data that indicates that something is cyclically abruptly changing the geomagnetic field.
The rapidity of the observed geomagnetic field changes cannot be explained by a core based mechanism. There is no geological mechanism that can change the liquid core cyclically and quickly enough to cause the observed surface geomagnetic field changes.
As the mantel is conductive and liquid core is conductive, counter emfs are generated that resit rapid core based changes. For that reason geomagnetic field reversals and excursions where believed based on the assumed toy model to take roughly 2000 to 5000 years.
These rapid paradoxical geomagnetic excursions correlate with abrupt climate changes and with super volcano eruptions.
The geomagnetic field changes come in a small, medium, and large. The small and medium geomagnetic field changes have been shown to correlate with very large solar magnetic cycle changes.
http://www.sciencedaily.com/releases/2012/10/121016084936.htm
http://www.paleomag.net/members/qingsongliu/References/EPSL/Thouveny%20excursions%20since%20400%20ka%20EPSL%202004.pdf
The rapidity of the observed geomagnetic field changes cannot be explained by a core based mechanism. There is no geological mechanism that can change the liquid core cyclically and quickly enough to cause the observed surface geomagnetic field changes.
As the mantel is conductive and liquid core is conductive, counter emfs are generated that resit rapid core based changes. For that reason geomagnetic field reversals and excursions where believed based on the assumed toy model to take roughly 2000 to 5000 years.
These rapid paradoxical geomagnetic excursions correlate with abrupt climate changes and with super volcano eruptions.
The geomagnetic field changes come in a small, medium, and large. The small and medium geomagnetic field changes have been shown to correlate with very large solar magnetic cycle changes.
http://www.sciencedaily.com/releases/2012/10/121016084936.htm
http://www.paleomag.net/members/qingsongliu/References/EPSL/Thouveny%20excursions%20since%20400%20ka%20EPSL%202004.pdf
http://eprints.whiterose.ac.uk/416/1/gubbinsd4.pdfSome 41,000 years ago, a complete and rapid reversal of the geomagnetic field occured. Magnetic studies of the GFZ German Research Centre for Geosciences on sediment cores from the Black Sea show that during this period, during the last ice age, a compass at the Black Sea would have pointed to the south instead of north.
What is remarkable is the speed of the reversal: "The field geometry of reversed polarity, with field lines pointing into the opposite direction when compared to today's configuration, lasted for only about 440 years, and it was associated with a field strength that was only one quarter of today's field," explains Norbert Nowaczyk. "The actual polarity changes lasted only 250 years. In terms of geological time scales, that is very fast." During this period, the field was even weaker, with only 5% of today's field strength. As a consequence, Earth nearly completely lost its protection shield against hard cosmic rays,
The largest volcanic eruption on the Northern hemisphere in the past 100,000 years, namely the eruption of the super volcano 39,400 years ago in the area of today's Phlegraean Fields near Naples, Italy, is also documented within the studied sediments from the Black Sea. The ashes of this eruption, during which about 350 cubic kilometers of rock and lava were ejected, were distributed over the entire eastern Mediterranean and up to central Russia.
Is the geodynamo process intrinsically unstable?
Recent palaeomagnetic studies suggest that excursions of the geomagnetic field, during which the intensity drops suddenly by a factor of 5 to 10 and the local direction changes dramatically, are more common than previously expected. The `normal' state of the geomagnetic field, dominated by an axial dipole, seems to be interrupted every 30 to 100 kyr; it may not therefore be as stable as we thought. We have investigated a possible mechanism for the instability of the geodynamo by calculating the critical Rayleigh number (Rc) for the onset of convection in a rotating spherical shell permeated by an imposed magnetic field with both toroidal and poloidal components.
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 ¢eld 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?
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